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Sample records for ofdm based cognitive

  1. A Blind OFDM Detection and Identification Method Based on Cyclostationarity for Cognitive Radio Application

    NASA Astrophysics Data System (ADS)

    Han, Ning; Sohn, Sung Hwan; Kim, Jae Moung

    The key issue in cognitive radio is to design a reliable spectrum sensing method that is able to detect the signal in the target channel as well as to recognize its type. In this paper, focusing on classifying different orthogonal frequency-division multiplexing (OFDM) signals, we propose a two-step detection and identification approach based on the analysis of the cyclic autocorrelation function. The key parameters to separate different OFDM signals are the subcarrier spacing and symbol duration. A symmetric peak detection method is adopted in the first step, while a pulse detection method is used to determine the symbol duration. Simulations validate the proposed method.

  2. Novel Spectrum Sensing Algorithms for OFDM Cognitive Radio Networks.

    PubMed

    Shi, Zhenguo; Wu, Zhilu; Yin, Zhendong; Cheng, Qingqing

    2015-01-01

    Spectrum sensing technology plays an increasingly important role in cognitive radio networks. Consequently, several spectrum sensing algorithms have been proposed in the literature. In this paper, we present a new spectrum sensing algorithm "Differential Characteristics-Based OFDM (DC-OFDM)" for detecting OFDM signal on account of differential characteristics. We put the primary value on channel gain θ around zero to detect the presence of primary user. Furthermore, utilizing the same method of differential operation, we improve two traditional OFDM sensing algorithms (cyclic prefix and pilot tones detecting algorithms), and propose a "Differential Characteristics-Based Cyclic Prefix (DC-CP)" detector and a "Differential Characteristics-Based Pilot Tones (DC-PT)" detector, respectively. DC-CP detector is based on auto-correlation vector to sense the spectrum, while the DC-PT detector takes the frequency-domain cross-correlation of PT as the test statistic to detect the primary user. Moreover, the distributions of the test statistics of the three proposed methods have been derived. Simulation results illustrate that all of the three proposed methods can achieve good performance under low signal to noise ratio (SNR) with the presence of timing delay. Specifically, the DC-OFDM detector gets the best performance among the presented detectors. Moreover, both of the DC-CP and DC-PT detector achieve significant improvements compared with their corresponding original detectors. PMID:26083226

  3. Novel Spectrum Sensing Algorithms for OFDM Cognitive Radio Networks

    PubMed Central

    Shi, Zhenguo; Wu, Zhilu; Yin, Zhendong; Cheng, Qingqing

    2015-01-01

    Spectrum sensing technology plays an increasingly important role in cognitive radio networks. Consequently, several spectrum sensing algorithms have been proposed in the literature. In this paper, we present a new spectrum sensing algorithm “Differential Characteristics-Based OFDM (DC-OFDM)” for detecting OFDM signal on account of differential characteristics. We put the primary value on channel gain θ around zero to detect the presence of primary user. Furthermore, utilizing the same method of differential operation, we improve two traditional OFDM sensing algorithms (cyclic prefix and pilot tones detecting algorithms), and propose a “Differential Characteristics-Based Cyclic Prefix (DC-CP)” detector and a “Differential Characteristics-Based Pilot Tones (DC-PT)” detector, respectively. DC-CP detector is based on auto-correlation vector to sense the spectrum, while the DC-PT detector takes the frequency-domain cross-correlation of PT as the test statistic to detect the primary user. Moreover, the distributions of the test statistics of the three proposed methods have been derived. Simulation results illustrate that all of the three proposed methods can achieve good performance under low signal to noise ratio (SNR) with the presence of timing delay. Specifically, the DC-OFDM detector gets the best performance among the presented detectors. Moreover, both of the DC-CP and DC-PT detector achieve significant improvements compared with their corresponding original detectors. PMID:26083226

  4. Derivation of GFDM Based on OFDM Principles

    SciTech Connect

    Hussein Moradi; Behrouz Farhang-Boroujeny

    2015-06-01

    This paper starts with discussing the principle based on which the celebrated orthogonal frequency division multiplexing (OFDM) signals are constructed. It then extends the same principle to construct the newly introduced generalized frequency division multiplexing (GFDM) signals. This novel derivation sheds light on some interesting properties of GFDM. In particular, our derivation seamlessly leads to an implementation of GFDM transmitter which has significantly lower complexity than what has been reported so far. Our derivation also facilitates a trivial understanding of how GFDM (similar to OFDM) can be applied in MIMO channels.

  5. Spectral Efficiency Comparison of OFDM/FBMC for Uplink Cognitive Radio Networks

    NASA Astrophysics Data System (ADS)

    Zhang, H.; Le Ruyet, D.; Roviras, D.; Medjahdi, Y.; Sun, H.

    2010-12-01

    Cognitive radio (CR) is proposed to automatically detect and exploit unused spectrum while avoiding harmful interference to the incumbent system. In this paper, we emphasize the channel capacity comparison of a CR network using two types of multicarrier communications: conventional Orthogonal Frequency Division Multiplexing (OFDM) with Cyclic Prefix (CP) and Filter Bank based MultiCarrier (FBMC) modulations. We use a resource allocation algorithm in which subcarrier assignment and power allocation are carried out sequentially. By taking the impact of Inter-Cell Interference (ICI) resulting from timing offset into account, the maximization of total information rates is formulated under an uplink scenario with pathloss and Rayleigh fading, subject to maximum power constraint as well as mutual interference constraint between primary user (PU) and secondary user (SU). Final simulation results show that FBMC can achieve higher channel capacity than OFDM because of the low spectral leakage of its prototype filter.

  6. An ICA based MIMO-OFDM VLC scheme

    NASA Astrophysics Data System (ADS)

    Jiang, Fangqing; Deng, Honggui; Xiao, Wei; Tao, Shaohua; Zhu, Kaicheng

    2015-07-01

    In this paper, we propose a novel ICA based MIMO-OFDM VLC scheme, where ICA is applied to convert the MIMO-OFDM channel into several SISO-OFDM channels to reduce computational complexity in channel estimation, without any spectral overhead. Besides, the FM is first investigated to further modulate the OFDM symbols to eliminate the correlation of the signals, so as to improve the separation performance of the ICA algorithm. In the 4×4MIMO-OFDM VLC simulation experiment, LOS path and NLOS paths are both considered, each transmitting signal at 100 Mb/s. Simulation results show that the BER of the proposed scheme reaches the 10-5 level at SNR=20 dB, which is a large improvement compared to the traditional schemes.

  7. Ellipse-based DCO-OFDM for visible light communications

    NASA Astrophysics Data System (ADS)

    Mao, Tianqi; Wang, Zhaocheng; Wang, Qi; Dai, Linglong

    2016-02-01

    Ellipse-based DC-biased optical orthogonal frequency division multiplexing (E-DCO-OFDM) is proposed for visible light communications (VLC), which achieves a significant peak-to-average power ratio (PAPR) reduction, thus enhancing the overall performance when light-emitting diode (LED) nonlinearity is considered. In E-DCO-OFDM, the real-valued output of OFDM is modulated onto an ellipse, whereby only the imaginary part of the complex point on the ellipse is transmitted. Although the PAPR of E-DCO-OFDM decreases as the ratio of major radius to minor radius becomes larger, it may be more vulnerable to the effect of noise, leading to the performance loss. Therefore, the relationship between the system performance and the critical parameters in E-DCO-OFDM, such as the ratio between the major and minor radius of the ellipse, is investigated. Meanwhile, simulations demonstrate that E-DCO-OFDM adopting the optimal parameters achieves a considerable signal-to-noise ratio (SNR) gain over the conventional DCO-OFDM.

  8. Out-of-band emission suppression techniques based on a generalized OFDM framework

    NASA Astrophysics Data System (ADS)

    You, Zihao; Fang, Juan; Lu, I.-Tai

    2014-12-01

    Orthogonal frequency division multiplexing (OFDM)-based cognitive radio (CR) systems suffer from the large out-of-band emission (OOBE) that may interfere with other users. Since most existing OFDM OOBE suppression schemes are derived on the base of an original OFDM system without any other scheme, we first propose a generalized OFDM framework that is capable of describing these schemes no matter whether any one or more of the schemes is applied. Then, according to the place where these schemes are implemented in our framework, they are classified into three groups, namely symbol mapping techniques, precoding techniques, and time-domain techniques. Finally, based on the proposed framework, we propose three new schemes by combining a precoding scheme named singular value decomposition (SVD) precoding with three other schemes from the three groups, namely spectral precoding, N-continuous symbol mapping, and filtering. Numerical results show the power spectral density (PSD), peak-to-average power ratio (PAPR), and bit error rate (BER) performances of the three proposed schemes. Since the individual schemes have complementary characteristics, the three proposed combined schemes are constructed to maintain the merits and avoid the drawbacks of the individual schemes involved. Thus, it is demonstrated that the proposed framework can be employed to develop other new combined OOBE suppression schemes tailoring to some specific practical needs.

  9. Companding transform based SPM compensation in coherent optical OFDM transmission.

    PubMed

    Chung, Hwan Seok; Chang, Sun Hyok; Kim, Kwangjoon

    2011-12-12

    We demonstrate a mitigation of fiber nonlinearity based on μ-law companding transform in coherent optical OFDM transmissions. High peak-to-average power ratio (PAPR) increases fiber nonlinear impairments caused by the Kerr effect in optical fiber. The μ-law companding modifies amplitude profile of OFDM signal with time domain signal processing, which reduces high PAPR of OFDM signal. The effects of companding parameter on noise enhancement and PAPR variation are presented. The impacts of companding transform on system performances are evaluated in a single polarization system as well as polarization multiplexed system. The resolution of analog-to-digital converter (ADC), dispersion map of transmission link, and launch power tolerance are also considered. The results of bit-error-rate (BER) measurements show that the μ-law companding improves OSNR margin over 5.5 dB after transmission of 1,040 km over SMF. PMID:22274091

  10. An OFDM-Based Speech Encryption System without Residual Intelligibility

    NASA Astrophysics Data System (ADS)

    Tseng, Der-Chang; Chiu, Jung-Hui

    Since an FFT-based speech encryption system retains a considerable residual intelligibility, such as talk spurts and the original intonation in the encrypted speech, this makes it easy for eavesdroppers to deduce the information contents from the encrypted speech. In this letter, we propose a new technique based on the combination of an orthogonal frequency division multiplexing (OFDM) scheme and an appropriate QAM mapping method to remove the residual intelligibility from the encrypted speech by permuting several frequency components. In addition, the proposed OFDM-based speech encryption system needs only two FFT operations instead of the four required by the FFT-based speech encryption system. Simulation results are presented to show the effectiveness of this proposed technique.

  11. Image-based target detection with multispectral UWB OFDM radar

    NASA Astrophysics Data System (ADS)

    Bufler, Travis D.; Garmatyuk, Dmitriy S.

    2012-06-01

    This paper proposes an image-based automatic target detection algorithm to be used in clutter and sparse target environments. We intend to apply the algorithm to an ultra-wideband multispectral radar concept by means of employing multi-carrier waveforms based upon Orthogonal Frequency Division Multiplexing (OFDM) modulation. Individual sub-bands of an OFDM waveform can be processed separately to yield range and cross-range reconstruction of a target scene containing both targets and clutter. Target detection in resulting images will be performed and contrasted with the detection performance of a traditional fixed-waveform Synthetic Aperture Radar system. The target detection algorithm is implemented through the use of scalar and vector field operations performed on the images from the reconstructed target scene. We hypothesize that the use of vector operations and field analysis will allow for an adaptive approach to the detection of targets within clutter.

  12. Next generation 3-D OFDM based optical access networks using FEC under various system impairments

    NASA Astrophysics Data System (ADS)

    Kumar, Pravindra; Srivastava, Anand

    2013-12-01

    Passive optical network based on orthogonal frequency division multiplexing (OFDM-PON) exhibits excellent performance in optical access networks due to its greater resistance to fiber dispersion, high spectral efficiency and exibility on both multiple services and dynamic bandwidth allocation. The major elements of conventional OFDM communication system are two-dimensional (2-D) signal mapper and one-dimensional (1-D) inverse fast fourier transform (IFFT). Three dimensional (3-D) OFDM use the concept of 3-D signal mapper and 2-D IFFT. With 3-D OFDM, minimum Euclidean distance (MED) is increased which results in BER performance improvement. As bit error rate (BER) depends on minimum Euclidean distance (MED) which is 15.46 % more in case of 3-D OFDM as compared to 2-D OFDM. Forward error correction (FEC) coding is a technique where redundancy is added to original bit sequence to increase the reliability of communication system. In this paper, we propose and analytically analyze a new PON architecture based on 3-D OFDM with convolutional coding and Viterbi decoding and is compared with conventional 2-D OFDM under various system impairments for coherent optical orthogonal frequency division multiplexing (CO-OFDM) without using any optical dispersion compensation. Analytical result show that at BER of 10-9, there is 2.7 dB, 3.8 dB and 9.3 dB signal-to-noise ratio (SNR) gain with 3-D OFDM, 3-D OFDM combined with convolutional coding and Viterbi hard decision decoding (CC-HDD) and 3-D OFDM combined with convolutional coding and Viterbi soft decision decoding (CC-SDD) respectively as compared to 2-D OFDM-PON. At BER of 10-9, 3-D OFDM-PON with CC-HDD gives 2.8 dB improvement in optical budget for both upstream and downstream path and gives 5.7 dB improvement in optical budget using 3-D OFDM-PON combined with CC-SDD as compared to conventional OFDM-PON system.

  13. Performance Enhancement of Multi-Cyclic Detector for Cognitive Radios with an OFDM Primary System

    NASA Astrophysics Data System (ADS)

    Kim, Minseok; Po, Kimtho; Takada, Jun-Ichi

    Spectrum sensing, a key technical challenge in cognitive radios (CR) technology, is a technique that enables the spectrum of licensed systems to be accessed without causing undue interference. It is well known that cyclostationarity detectors have great advantages over energy detectors in terms of the robustness to noise uncertainty that significantly degrades the performance as well as the capability to distinguish the signal of interest from the other interferences and noise. The generalized likelihood ratio test (GLRT) is a recognized sensing technique that utilizes the inherent cyclostationarity of the signal and has been intensively studied. However, no comprehensive evaluation on its performance enhancement has been published to date. Moreover high computational complexity is still a significant problem for its realization. This paper proposes a maximum ratio combining multi-cyclic detector which uses multiple cyclic frequencies for performance enhancement with reduced computational complexity. An orthogonal frequency-division multiplexing (OFDM) signal based on the ISDB-T (integrated services digital broadcasting terrestrial), a Japanese digital television broadcasting standard, was used in the evaluation assuming this as a primary system in WRAN (wireless regional area network) applications like IEEE 802.22.

  14. High Data Rate OFDM-Based Radio over FSO Communication System Using M-QAM Modulation

    NASA Astrophysics Data System (ADS)

    Kumar, Naresh; Teixeira, Antonio Luis Jesus

    2015-12-01

    In this paper, we have presented analysis of OFDM-based Radio over FSO Communication System using M-QAM Modulation under different data rate and attenuation. A distance of 1,000 m was achieved at 10 Gbit/s data rate in OFDM-based Radio over FSO Communication System.

  15. Precoding techniques for PAPR reduction in asymmetrically clipped OFDM based optical wireless system

    NASA Astrophysics Data System (ADS)

    Ranjha, Bilal; Kavehrad, Mohsen

    2013-01-01

    In this paper, we have analyzed different precoding based Peak-to-Average-Power (PAPR) reduction techniques for asymmetrically-clipped Orthogonal Frequency Division Multiplexing (OFDM) optical wireless communication systems. Intensity Modulated Direct Detection (IM/DD) technique is among the popular techniques for optical wireless communication systems. OFDM cannot be directly applied to IM systems because of the bipolar nature of the output signal. Therefore some variants of OFDM systems have been proposed for (IM/DD) optical wireless systems. Among them are DC-biased-OFDM, Asymmetrically-Clipped Optical OFDM (ACO-OFDM) [2] and Pulse Amplitude Modulated Discrete Multitone (PAM-DMT) [3]. Both ACO-OFDM and PAM-DMT require low average power and thus are very attractive for optical wireless systems. OFDM systems suffer from high PAPR problem that can limit its performance due to non-linear characteristics of LED. Therefore PAPR reduction techniques have to be employed. This paper analyzes precoding based PAPR reduction methods for ACO-OFDM and PAM-DMT. We have used Discrete Fourier Transform (DFT) coding, Zadoff-Chu Transform (ZCT) [8] and Discrete Cosine Transform (DCT) for ACOOFDM and only DCT for PAM-DMT since the modulating symbols are real. We have compared the performance of these precoding techniques using different QAM modulation schemes. Simulation results have shown that both DFT and ZCT offer more PAPR reduction than DCT in ACO-OFDM. For PAM-DMT, DCT precoding yields significant PAPR reduction compared to conventional PAM-DMT signal. These precoding schemes also offer the advantage of zero signaling overhead.

  16. Channel estimation in DFT-based offset-QAM OFDM systems.

    PubMed

    Zhao, Jian

    2014-10-20

    Offset quadrature amplitude modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) exhibits enhanced net data rates compared to conventional OFDM, and reduced complexity compared to Nyquist FDM (N-FDM). However, channel estimation in discrete-Fourier-transform (DFT) based offset-QAM OFDM is different from that in conventional OFDM and requires particular study. In this paper, we derive a closed-form expression for the demultiplexed signal in DFT-based offset-QAM systems and show that although the residual crosstalk is orthogonal to the decoded signal, its existence degrades the channel estimation performance when the conventional least-square method is applied. We propose and investigate four channel estimation algorithms for offset-QAM OFDM that vary in terms of performance, complexity, and tolerance to system parameters. It is theoretically and experimentally shown that simple channel estimation can be realized in offset-QAM OFDM with the achieved performance close to the theoretical limit. This, together with the existing advantages over conventional OFDM and N-FDM, makes this technology very promising for optical communication systems. PMID:25401598

  17. A novel optical transmission link with DHT-based constant envelope optical OFDM signal

    NASA Astrophysics Data System (ADS)

    Ma, Jianxin; Liang, Hao

    2013-07-01

    In this paper, we have proposed a novel optical OFDM transmission link that takes advantages of discrete Hartley Transform (DHT) and constant envelope (CE) modulation, obtaining DHT-based constant envelope optical OFDM. The numerical results show that this design achieves better performance when compared with conventional O-OFDM in terms of bit error rate (BER) and peak-to-average power ratio (PAPR). The impact of phase modulation index (PMI) on both PAPR and noise tolerance is investigated. Since the scheme has simplified design, it is believed to be a cost-effective in the practical implement.

  18. EAM-based multiband OFDM systems incorporating PAPR reduction and SSII cancellation

    NASA Astrophysics Data System (ADS)

    Yang, Pengfei; Shi, Hu; Chen, Xue

    2016-04-01

    Multiband orthogonal frequency division multiplexing (OFDM) subcarrier allocation is a good scheme to fully utilize the available bandwidth under the restriction of dispersion- and chirp-induced power fading in electro-absorption modulator (EAM)-based intensity-modulation-direct-detection (IMDD) OFDM system. In this paper, a modified Tone Reservation (TR) technique combined with subcarrier interleaving is proposed to reduce high peak to average power ratio (PAPR) while minimizing the penalty of subcarrier-to-subcarrier intermixing interference. In the experiment, by incorporating of these two techniques, the receiver sensitivity is improved by about 1.8 dB when a 20 Gbps OFDM signal transmitted along 100 km long single mode fiber in an EAM-based multiband IMDD-OFDM system.

  19. Reducing PAPR of optical OFDM system based on PTS and companding joint algorithm

    NASA Astrophysics Data System (ADS)

    Jia, Yangjing; Li, Ping; Lei, Dongming; Chen, Ailin; Wang, Jinpeng; Zou, Nianyu

    2015-10-01

    Optical orthogonal frequency division multiplexing (OFDM) system combines the advantages of both wireless OFDM and optical fiber technology, thus has high spectral efficiency and can effectively resist polarization mode dispersion and chromatic dispersion in fiber link. However, high peak-to-average power ratio (PAPR) is one of the important shortcomings of optical OFDM system, which requires not only amplifiers with a greater dynamic range, but also leads to serious fiber nonlinear effect. So how to reduce PAPR of optical OFDM system is a crucial issue. This work, aiming to reduce PAPR and improving system BER, analyzes suppression technology of PAPR based on optical OFDM system. Firstly, to improve BER, we utilize Partial Transmit Sequence (PTS) algorithm which introduces phase factors b(v) multiplying IFFT converted signals and searches a b(v) which will make PAPR minimum. But this method needs much calculation. Then we exploit companding which can compress amplitude of big OFDM signals and expand small signals. Secondly, simulating the two algorithms respectively and finding two algorithms can suppress PAPR, but the effect has room for improvement. Therefore, an implementation of PTS and companding joint algorithm is proposed, then simulating this method and adding it into optical OFDM system. A system was set up, fiber length setting as 10km, utilizing a MZM modulator and a distributed feedback laser, taking 4QAM and 512points IFFT. The results show that, joint algorithm can reduce PAPR from about 12dB to 8dB, improving the problem of high PAPR, constellation convergence, enhances optical OFDM system transmission performance.

  20. Energy-efficient optical network units for OFDM PON based on time-domain interleaved OFDM technique.

    PubMed

    Hu, Xiaofeng; Cao, Pan; Zhang, Liang; Jiang, Lipeng; Su, Yikai

    2014-06-01

    We propose and experimentally demonstrate a new scheme to reduce the energy consumption of optical network units (ONUs) in orthogonal frequency division multiplexing passive optical networks (OFDM PONs) by using time-domain interleaved OFDM (TI-OFDM) technique. In a conventional OFDM PON, each ONU has to process the complete downstream broadcast OFDM signal with a high sampling rate and a large FFT size to retrieve its required data, even if it employs a portion of OFDM subcarriers. However, in our scheme, the ONU only needs to sample and process one data group from the downlink TI-OFDM signal, effectively reducing the sampling rate and the FFT size of the ONU. Thus, the energy efficiency of ONUs in OFDM PONs can be greatly improved. A proof-of-concept experiment is conducted to verify the feasibility of the proposed scheme. Compared to the conventional OFDM PON, our proposal can save 17.1% and 26.7% energy consumption of ONUs by halving and quartering the sampling rate and the FFT size of ONUs with the use of the TI-OFDM technology. PMID:24921501

  1. Ultrawideband imaging radar based on OFDM: system simulation analysis

    NASA Astrophysics Data System (ADS)

    Garmatyuk, Dmitriy

    2006-05-01

    Orthogonal frequency division-multiplexing (OFDM) is rapidly emerging as a preferred method of UWB signaling in commercial applications aimed mainly at low-power, high data-rate communications. This paper explores the possibility of applying OFDM to use in imaging radar technology. Ultra-wideband nature of the signal provides for high resolution of the radar, whereas usage of multi-sub-carrier method of modulation allows for dynamic spectrum allocation. Robust multi-path performance of OFDM signals and heavy reliance of transceiver design on digital processors easily implemented in modern VLSI technology make a number of possible applications viable, e.g.: portable high-resolution indoor radar/movement monitoring system; through-the-wall/foliage synthetic aperture imaging radar with a capability of image transmission/broadcasting, etc. Our work is aimed to provide a proof-of-concept simulation scenario to explore numerous aspects of UWB-OFDM radar imaging through evaluating range and cross-range imaging performance of such a system with an eventual goal of software-defined radio (SDR) implementation. Stripmap SAR topology was chosen for modeling purposes. Range/cross-range profiles were obtained along with full 2-D images for multi-target in noise scenarios. Model set-up and results of UWB-OFDM radar imaging simulation study using Matlab/Simulink modeling are presented and discussed in this paper.

  2. IRCI free colocated mimo radar based on sufficient cyclic prefix OFDM waveforms

    NASA Astrophysics Data System (ADS)

    Cao, Yun-he; Xia, Xiang-gen; Wang, Sheng-hua

    2015-07-01

    In this paper, we propose a cyclic prefix (CP) based MIMO-OFDM range reconstruction method and its corresponding MIMO-OFDM waveform design for co-located MIMO radar systems. Our proposed MIMO-OFDM waveform design achieves the maximum signal-to-noise ratio (SNR) gain after the range reconstruction and its peak-to-average power ratio (PAPR) in the discrete time domain is also optimal, i.e., 0dB, when Zadoff-Chu sequences are used in the discrete frequency domain as the weighting coefficients for the subcarriers. We also investigate the performance when there are transmit and receive digital beamforming (DBF) pointing errors. It is shown that our proposed CP based MIMO-OFDM range reconstruction is inter-range-cell interference (IRCI) free no matter whether there are transmit and receive DBF pointing errors or not. Simulation results are presented to verify the theory and compare it with the conventional OFDM and LFM co-located MIMO radars.

  3. Pilot-based blind phase estimation for coherent optical OFDM system.

    PubMed

    Zhang, Xuebing; Li, Jianping; Li, Chao; Luo, Ming; Li, Haibo; He, Zhixue; Yang, Qi; Lu, Chao; Li, Zhaohui

    2014-09-22

    A pilot-based blind (PBB) phase estimation method for the coherent optical orthogonal frequency-division multiplexing (CO-OFDM) system is demonstrated in this paper. Instead of inserting the pilot-subcarriers that are loaded with the already known information in the OFDM signal, the unknown and specially designed signal is used to replace the signal on the pilot subcarriers to decrease the waste of spectrum and has demonstrated good performance in the phase noise compensation. Therefore, the spectral efficiency (SE) is further improved compared with the conventional pilot-aided (PA) phase noise estimation method. Both the proposed PBB and conventional PA estimation methods are compared in a CO-OFDM transmission experiment, which is modulated by 4 quadrature amplitude modulation (4-QAM) formats and transmitted over 1760-km standard single-mode fiber (SSMF) without optical dispersion compensation. The experimental results show that the proposed PBB method can achieve the similar performance as the conventional PA method. PMID:25321759

  4. Per-symbol-based digital back-propagation approach for PDM-CO-OFDM transmission systems.

    PubMed

    Peng, Wei-Ren; Takahashi, Hidenori; Morita, Itsuro; Tsuritani, Takehiro

    2013-01-28

    For polarization-division-multiplexing coherent optical orthogonal frequency division multiplexing (PDM-CO-OFDM) systems, we propose a per-symbol-based digital back-propagation (DBP) approach which, after cyclic prefix removal, conducts DBP for each OFDM symbol. Compared with previous DBP, this new proposal avoids the use of inefficient overlap-and-add operation and saves one fast Fourier transform (FFT) module, therefore simplifying the hardware implementation. Transmitting a 16-QAM, 42.8-Gb/s PDM-CO-OFDM signal over 960-km standard single mode fiber (SSMF), we compare the previous and the proposed DBP approaches with different receiver's sampling rates and different step lengths in each DBP iteration, and found that the proposed DBP can achieve a similar performance as that of the previous DBP while enjoying a simpler implementation. We have also specifically introduced a small self-phase modulation (SPM) model for DBP and demonstrated its feasibility with the same experimental setup. PMID:23389137

  5. Adaptive reconfigurable V-BLAST type equalizer for cognitive MIMO-OFDM radios

    NASA Astrophysics Data System (ADS)

    Ozden, Mehmet Tahir

    2015-12-01

    An adaptive channel shortening equalizer design for multiple input multiple output-orthogonal frequency division multiplexing (MIMO-OFDM) radio receivers is considered in this presentation. The proposed receiver has desirable features for cognitive and software defined radio implementations. It consists of two sections: MIMO decision feedback equalizer (MIMO-DFE) and adaptive multiple Viterbi detection. In MIMO-DFE section, a complete modified Gram-Schmidt orthogonalization of multichannel input data is accomplished using sequential processing multichannel Givens lattice stages, so that a Vertical Bell Laboratories Layered Space Time (V-BLAST) type MIMO-DFE is realized at the front-end section of the channel shortening equalizer. Matrix operations, a major bottleneck for receiver operations, are accordingly avoided, and only scalar operations are used. A highly modular and regular radio receiver architecture that has a suitable structure for digital signal processing (DSP) chip and field programable gate array (FPGA) implementations, which are important for software defined radio realizations, is achieved. The MIMO-DFE section of the proposed receiver can also be reconfigured for spectrum sensing and positioning functions, which are important tasks for cognitive radio applications. In connection with adaptive multiple Viterbi detection section, a systolic array implementation for each channel is performed so that a receiver architecture with high computational concurrency is attained. The total computational complexity is given in terms of equalizer and desired response filter lengths, alphabet size, and number of antennas. The performance of the proposed receiver is presented for two-channel case by means of mean squared error (MSE) and probability of error evaluations, which are conducted for time-invariant and time-variant channel conditions, orthogonal and nonorthogonal transmissions, and two different modulation schemes.

  6. Hybrid time-frequency domain equalization for LED nonlinearity mitigation in OFDM-based VLC systems.

    PubMed

    Li, Jianfeng; Huang, Zhitong; Liu, Xiaoshuang; Ji, Yuefeng

    2015-01-12

    A novel hybrid time-frequency domain equalization scheme is proposed and experimentally demonstrated to mitigate the white light emitting diode (LED) nonlinearity in visible light communication (VLC) systems based on orthogonal frequency division multiplexing (OFDM). We handle the linear and nonlinear distortion separately in a nonlinear OFDM system. The linear part is equalized in frequency domain and the nonlinear part is compensated by an adaptive nonlinear time domain equalizer (N-TDE). The experimental results show that with only a small number of parameters the nonlinear equalizer can efficiently mitigate the LED nonlinearity. With the N-TDE the modulation index (MI) and BER performance can be significantly enhanced. PMID:25835706

  7. Evaluation of multiple-channel OFDM based airborne ultrasonic communications.

    PubMed

    Jiang, Wentao; Wright, William M D

    2016-09-01

    Orthogonal frequency division multiplexing (OFDM) modulation has been extensively used in both wired and wireless communication systems. The use of OFDM technology allows very high spectral efficiency data transmission without using complex equalizers to correct the effect of a frequency-selective channel. This work investigated OFDM methods in an airborne ultrasonic communication system, using commercially available capacitive ultrasonic transducers operating at 50kHz to transmit information through the air. Conventional modulation schemes such as binary phase shift keying (BPSK) and quadrature amplitude modulation (QAM) were used to modulate sub-carrier signals, and the performances were evaluated in an indoor laboratory environment. Line-of-sight (LOS) transmission range up to 11m with no measurable errors was achieved using BPSK at a data rate of 45kb/s and a spectral efficiency of 1b/s/Hz. By implementing a higher order modulation scheme (16-QAM), the system data transfer rate was increased to 180kb/s with a spectral efficiency of 4b/s/Hz at attainable transmission distances up to 6m. Diffraction effects were incorporated into a model of the ultrasonic channel that also accounted for beam spread and attenuation in air. The simulations were a good match to the measured signals and non-LOS signals could be demodulated successfully. The effects of multipath interference were also studied in this work. By adding cyclic prefix (CP) to the OFDM symbols, the bit error rate (BER) performance was significantly improved in a multipath environment. PMID:27365316

  8. Parallel and interlaced bandwidth allocation based on all-optical sub-banding WDM-OFDM PON network

    NASA Astrophysics Data System (ADS)

    Zou, Shumin; Zheng, Xi; Fang, Wuliang; Li, Xinying; Zhang, Junwen; Shao, Yufeng; Chi, Nan

    2010-12-01

    For the first time, we propose and demonstrate a novel three-level Signal allocation scheme OFDM PON architecture which makes the best use of OFDM characteristics. In the architecture, we produce five-carrier signal optically by MZM, use odd carriers modulating downlink data and retain even carriers for uplink data. Multiple signal distribution methods can be switched flexibly. By simulation, a small PON systems with four ONU based on this architecture was realized. Both the downlink and uplink transmission adopt 4-QAM-OFDM signal. The transmission rate will be demonstrated to exceed 10Gbit/s.

  9. Toward user mobility for OFDM-based visible light communications.

    PubMed

    Hong, Yang; Chen, Lian-Kuan

    2016-08-15

    We propose and experimentally demonstrate a mobile visible light communications (mobi-VLC) transmission system. The impact of user mobility on the performance of the mobi-VLC system is characterized, and we propose the use of the channel-independent orthogonal circulant matrix transform (OCT) precoding to combat the packet loss performance degradation induced by mobility. A mobile user terminal is used to detect the signal from a blue laser placed at 1 m away from the moving track. Various moving speeds (20, 40, 60, and 80  cm/s) and lateral moving distances (30, 40, and 50 cm) of the user terminal are investigated. The effectiveness of the OCT precoding is evaluated by the comparison with the conventional orthogonal frequency division multiplexing (OFDM) scheme and the adaptive-loaded discrete multi-tone (DMT) scheme. Experimental results show that the system performance degrades with the increase in user mobility speed and in moving distance. Furthermore, the OCT precoding provides performance improvement that is superior over that of conventional OFDM schemes, and it exhibits lower packet loss rate than that of adaptive-loaded DMT. No packet loss for 300  Mb/s transmission is achieved with a 30 cm lateral moving distance at 20  cm/s. PMID:27519083

  10. A novel transform domain processing based channel estimation method for OFDM radio-over-fiber systems.

    PubMed

    Tao, Li; Yu, Jianjun; Yang, Qi; Shao, Yufeng; Zhang, Junwen; Chi, Nan

    2013-03-25

    In this paper, a transform domain processing (TDP) based channel estimation method for orthogonal frequency-division multiplexing (OFDM) Radio-over-Fiber (RoF) systems is proposed. Theoretically investigation shows that TDP can greatly reduce the number of required training symbols. An 8 x 4.65 Gb/s multi-user OFDM RoF system over 40 km fiber link and 60 GHz wireless link is experimentally demonstrated utilizing TDP scheme. Compared with conventional time domain averaging (TDA) scheme, the overhead can be reduced from several tens of training symbols to merely one symbol and the receiver sensitivity has been improved by 1.8 dB at BER of 3.8 x 10(-3). The calculated BER performance for 8 wireless users clearly validates the feasibility of this TDP-based channel estimation method. PMID:23546130

  11. The optimization of FHT-based ACO-OFDM atmospheric laser communication system in terms of PAPR reduction

    NASA Astrophysics Data System (ADS)

    Guo, Qiwen; Wei, Yiran; Duan, Yuning

    2013-08-01

    The application of orthogonal frequency division multiplexing (OFDM) in atmospheric laser communication is not as wildly as expected. This is should be owing to several problems rooted in OFDM system and the incompatibility between IM and OFDM. Aiming to analyze the major problems and propose optimized solutions, in the first part of this paper, we introduce the application of fast Hartley transform (FHT), as a suitable alternative to FFT, in asymmetrically clipped (AC) OFDM Atmospheric laser communication system. Then we demonstrate the problem of high PAPR embedded in such system. In the following part of this paper, we firstly review and analyze the performance of some standard methods, namely, Clipping, Companding, Selective Mapping (SLM), Partial Transmit Sequence (PTS), used to reduce the high peak to average power ratio (PAPR) caused by OFDM. And then we make some modifications on those methods so that they could be applied on DHT based AC-OFDM atmospheric laser communication system with more effectiveness. Finally, we propose and compare four different PAPR reduction techniques obtained by serialization of those modified methods. And by using Matlab simulation we demonstrate the feasibility of the proposed methods.

  12. All-optical virtual private network and ONUs communication in optical OFDM-based PON system.

    PubMed

    Zhang, Chongfu; Huang, Jian; Chen, Chen; Qiu, Kun

    2011-11-21

    We propose and demonstrate a novel scheme, which enables all-optical virtual private network (VPN) and all-optical optical network units (ONUs) inter-communications in optical orthogonal frequency-division multiplexing-based passive optical network (OFDM-PON) system using the subcarrier bands allocation for the first time (to our knowledge). We consider the intra-VPN and inter-VPN communications which correspond to two different cases: VPN communication among ONUs in one group and in different groups. The proposed scheme can provide the enhanced security and a more flexible configuration for VPN users compared to the VPN in WDM-PON or TDM-PON systems. The all-optical VPN and inter-ONU communications at 10-Gbit/s with 16 quadrature amplitude modulation (16 QAM) for the proposed optical OFDM-PON system are demonstrated. These results verify that the proposed scheme is feasible. PMID:22109510

  13. Detection of code spread OFDM based on 0-1 integer quadratic programming

    NASA Astrophysics Data System (ADS)

    Elghariani, Ali; Zoltowski, Michael D.

    2012-05-01

    In this paper we introduce Integer Quadratic Programming (MIQP) approach to optimally detect QPSK Code Spread OFDM (CS-OFDM) by formulating the problem as a combinatorial optimization problem. The Branch and Bound (BB) algorithm is utilized to solve this integer quadratic programming problem. Furthermore, we propose combined preprocessing steps that can be applied prior to BB so that the computational complexity of the optimum receiver is reduced. The first step in this combination is to detect as much as possible symbols using procedures presented in [9], which is basically based on the gradient of quadratic function. The second step detects the undetected symbols from the first step using MMSE estimator. The result of the latter step will be used to predict the initial upper bound of the BB algorithm. Simulation results show that the proposed preprocessing combination when applied prior to BB provides optimal performance with a significantly reduced computational complexity.

  14. Transmission analysis of CPolM-based OFDM FSO system in atmospheric turbulence

    NASA Astrophysics Data System (ADS)

    Su, Yuwei; Bai, Fan; Sato, Takuro

    2016-06-01

    In this paper, we propose to implement a consecutive polarization modulation (CPolM) scheme to transmit orthogonal frequency division multiplexing (OFDM) signal over the turbulent free-space optical (FSO) links. We analyze the fluctuation of polarization states of an optical wave while propagating through the turbulence channel of which the refractive-index property is described by Kolmogorov spectrum. The transmission performance in terms of signal-to-noise-ratio (SNR), symbol-error-ratio (SER) and outage probability of the proposed system are evaluated. The proposed system provides a more efficient way to compensate scintillation effects in a comparison with the intensity modulation (IM) based OFDM FSO system under a varying degrees of turbulence strength regimes.

  15. Nonlinear multi-agent path search method based on OFDM communication

    NASA Astrophysics Data System (ADS)

    Sato, Masatoshi; Igarashi, Yusuke; Tanaka, Mamoru

    This paper presents novel shortest paths searching system based on analog circuit analysis which is called sequential local current comparison method on alternating-current (AC) circuit (AC-SLCC). Local current comparison (LCC) method is a path searching method where path is selected in the direction of the maximum current in a direct-current (DC) resistive circuit. Since a plurality of shortest paths searching by LCC method can be done by solving the current distribution on the resistive circuit analysis, the shortest path problem can be solved at supersonic speed. AC-SLCC method is a novel LCC method with orthogonal frequency division multiplexing (OFDM) communication on AC circuit. It is able to send data with the shortest path and without major data loss, and this suggest the possibility of application to various things (especially OFDM communication techniques).

  16. Channel estimation for OFDM system in atmospheric optical communication based on compressive sensing

    NASA Astrophysics Data System (ADS)

    Zhao, Qingsong; Hao, Shiqi; Geng, Hongjian; Sun, Han

    2015-10-01

    Orthogonal frequency division multiplexing (OFDM) technique applied to the atmospheric optical communication can improve data transmission rate, restrain pulse interference, and reduce effect of multipath caused by atmospheric scattering. Channel estimation, as one of the important modules in OFDM, has been investigated thoroughly and widely with great progress. In atmospheric optical communication system, channel estimation methods based on pilot are common approaches, such as traditional least-squares (LS) algorithm and minimum mean square error (MMSE) algorithm. However, sensitivity of the noise effects and high complexity of computation are shortcomings of LS algorithm and MMSE algorithm, respectively. Here, a new method based on compressive sensing is proposed to estimate the channel state information of atmospheric optical communication OFDM system, especially when the condition is closely associated with turbulence. Firstly, time-varying channel model is established under the condition of turbulence. Then, in consideration of multipath effect, sparse channel model is available for compressive sensing. And, the pilot signal is reconstructed with orthogonal matching tracking (OMP) algorithm, which is used for reconstruction. By contrast, the work of channel estimation is completed by LS algorithm as well. After that, simulations are conducted respectively in two different indexes -signal error rate (SER) and mean square error (MSE). Finally, result shows that compared with LS algorithm, the application of compressive sensing can improve the performance of SER and MSE. Theoretical analysis and simulation results show that the proposed method is reasonable and efficient.

  17. Link Correlation Based Transmit Sector Antenna Selection for Alamouti Coded OFDM

    NASA Astrophysics Data System (ADS)

    Ahn, Chang-Jun

    In MIMO systems, the deployment of a multiple antenna technique can enhance the system performance. However, since the cost of RF transmitters is much higher than that of antennas, there is growing interest in techniques that use a larger number of antennas than the number of RF transmitters. These methods rely on selecting the optimal transmitter antennas and connecting them to the respective. In this case, feedback information (FBI) is required to select the optimal transmitter antenna elements. Since FBI is control overhead, the rate of the feedback is limited. This motivates the study of limited feedback techniques where only partial or quantized information from the receiver is conveyed back to the transmitter. However, in MIMO/OFDM systems, it is difficult to develop an effective FBI quantization method for choosing the space-time, space-frequency, or space-time-frequency processing due to the numerous subchannels. Moreover, MIMO/OFDM systems require antenna separation of 5 ∼ 10 wavelengths to keep the correlation coefficient below 0.7 to achieve a diversity gain. In this case, the base station requires a large space to set up multiple antennas. To reduce these problems, in this paper, we propose the link correlation based transmit sector antenna selection for Alamouti coded OFDM without FBI.

  18. Sparsity-Based Space-Time Adaptive Processing Using OFDM Radar

    SciTech Connect

    Sen, Satyabrata

    2012-01-01

    We propose a sparsity-based space-time adaptive processing (STAP) algorithm to detect a slowly-moving target using an orthogonal frequency division multiplexing (OFDM) radar. We observe that the target and interference spectra are inherently sparse in the spatio-temporal domain, and hence we exploit that sparsity to develop an efficient STAP technique. In addition, the use of an OFDM signal increases the frequency diversity of our system, as different scattering centers of a target resonate at different frequencies, and thus improves the target detectability. First, we formulate a realistic sparse-measurement model for an OFDM radar considering both the clutter and jammer as the interfering sources. Then, we show that the optimal STAP-filter weight-vector is equal to the generalized eigenvector corresponding to the minimum generalized eigenvalue of the interference and target covariance matrices. To estimate the target and interference covariance matrices, we apply a residual sparse-recovery technique that enables us to incorporate the partially known support of the sparse vector. Our numerical results demonstrate that the sparsity-based STAP algorithm, with considerably lesser number of secondary data, produces an equivalent performance as the other existing STAP techniques.

  19. Performance study of an OFDM visible light communication system based on white LED array

    NASA Astrophysics Data System (ADS)

    Tian, Chong-Wen; Li, Yan-Ting; Ye, Wei-Lin; Quan, Xiang-Yin; Song, Zhanwei; Zheng, Chuan-Tao

    2011-11-01

    By introducing orthogonal frequency division multiplexing (OFDM) technology, a visible light communication (VLC) system using a 5×5 white LED array is studied in this paper. The OFDM transmitter and receiver are modeled through MATLAB/Simulink tool. The electrical-optical-electrical (EOE) response of the VLC channel, which is also the response of the detector, is derived based on Lambert's lighting model. Then the modeling on the overall OFDM/VLC system is established by combining the above three models together. The effects of the factors which include the digital modulation, Reed-Solomon (RS) coding, pilot form, pilot ratio (PR) and communication distance on the bit error rate (BER) of the system are discussed. The results show that through the use of RS coding, block pilot, quadrate phase shift keying (QPSK) modulation and a suitable pilot ratio about 1/3, under the communication rate about 550 kbit/s, the BER can be dropped to below 10-5, and the communication distance can reach 0.9 m.

  20. Design and performance evaluation of an OpenFlow-based control plane for software-defined elastic optical networks with direct-detection optical OFDM (DDO-OFDM) transmission.

    PubMed

    Liu, Lei; Peng, Wei-Ren; Casellas, Ramon; Tsuritani, Takehiro; Morita, Itsuro; Martínez, Ricardo; Muñoz, Raül; Yoo, S J B

    2014-01-13

    Optical Orthogonal Frequency Division Multiplexing (O-OFDM), which transmits high speed optical signals using multiple spectrally overlapped lower-speed subcarriers, is a promising candidate for supporting future elastic optical networks. In contrast to previous works which focus on Coherent Optical OFDM (CO-OFDM), in this paper, we consider the direct-detection optical OFDM (DDO-OFDM) as the transport technique, which leads to simpler hardware and software realizations, potentially offering a low-cost solution for elastic optical networks, especially in metro networks, and short or medium distance core networks. Based on this network scenario, we design and deploy a software-defined networking (SDN) control plane enabled by extending OpenFlow, detailing the network architecture, the routing and spectrum assignment algorithm, OpenFlow protocol extensions and the experimental validation. To the best of our knowledge, it is the first time that an OpenFlow-based control plane is reported and its performance is quantitatively measured in an elastic optical network with DDO-OFDM transmission. PMID:24514962

  1. Electrical Spreading Code-Based OFDM Optical Access Networks for Budget Enhancement and Reduced System Bandwidth Requirement

    NASA Astrophysics Data System (ADS)

    Kumar, Pravindra; Srivastava, Anand

    2015-12-01

    Passive optical networks based on orthogonal frequency division multiplexing (OFDM-PON) give better performance in high-speed optical access networks. For further improvement in performance, a new architecture of OFDM-PON based on spreading code in electrical domain is proposed and analytically analyzed in this paper. This approach is referred as hybrid multi-carrier code division multiple access-passive optical network (MC-CDMA-PON). Analytical results show that at bit error rate (BER) of 10-3, there is 9.4 dB and 14.2 dB improvement in optical power budget for downstream and upstream, respectively, with MC-CDMA-PON system as compared to conventional OFDM-PON system for the same number of optical network units (ONUs).

  2. ICA-based compensation for IQ imbalance in OFDM optical fiber communication

    NASA Astrophysics Data System (ADS)

    Jiang, Shan; Hu, Guijun; Li, Zhaoxi; Mu, Liping; Zhang, Jingdong

    2014-01-01

    A method based on the independent component analysis (ICA) is proposed to compensate the in-phase and quadrature-phase the (IQ) imbalance in orthogonal frequency division multiplexing (OFDM) optical fiber communication systems. The mathematical model of IQ imbalance system has been analyzed. Then, ICA algorithm is applied in the system to combat the mirror interference introduced by IQ imbalance. This algorithm can realize the joint compensation of both transmitter and receiver IQ imbalance with the optical channel that contains noise, attenuation and chromatic dispersion. The simulation shows that the performance degradation caused by IQ imbalance can be compensated by ICA algorithm effectively.

  3. Coherent optical OFDM: theory and design.

    PubMed

    Shieh, W; Bao, H; Tang, Y

    2008-01-21

    Coherent optical OFDM (CO-OFDM) has recently been proposed and the proof-of-concept transmission experiments have shown its extreme robustness against chromatic dispersion and polarization mode dispersion. In this paper, we first review the theoretical fundamentals for CO-OFDM and its channel model in a 2x2 MIMO-OFDM representation. We then present various design choices for CO-OFDM systems and perform the nonlinearity analysis for RF-to-optical up-converter. We also show the receiver-based digital signal processing to mitigate self-phase-modulation (SPM) and Gordon-Mollenauer phase noise, which is equivalent to the midspan phase conjugation. PMID:18542158

  4. OFDM-PON optical fiber access technologies

    NASA Astrophysics Data System (ADS)

    Qiu, Kun; Yi, Xinwen; Zhang, Jing; Zhang, Hongbo; Deng, Mingliang; Zhang, Chongfu

    2011-12-01

    The introduction of OFDM into PON networks is to leverage the merits of OFDM to provide the flexibility and reduce the cost. In this paper, we present our latest works on OFDM-PON. Firstly, we propose and demonstrate a novel OFDMPON upstream transmission architecture with traffic aggregation by orthogonal band multiplexing. The multiplexed 10- Gb/s OFDM signal is collectively received. We also conduct a proof-of-concept experiment to verify the architecture. Secondly, we propose and experimentally demonstrate wavelet packet transform based OFDM (WPT-OFDM) using real-valued transforms, which enables the cost-effective intensity modulation/direct detection (IM/DD). Unlike conventional FFT-based OFDM, the need for cyclic prefix is eliminated due to the time-frequency localization properties of the wavelet.

  5. All optical OFDM transmission systems

    NASA Astrophysics Data System (ADS)

    Rhee, June-Koo K.; Lim, Seong-Jin; Kserawi, Malaz

    2011-12-01

    All-optical OFDM data transmission opens up a new realm of advanced optical transmission at extreme data rates, as subcarriers are multiplexed and demultiplexed by all optical discrete Fourier transforms (DFT). This paper reviews the principles of all optical OFDM transmission and its system application techniques, providing the generic ideas and the practical implementation issues to achieve 100Gbps or higher data rates with a spectral efficiency of 1 bps/Hz or better. This paper also include discussions on all-optical OFDM implementation variants such as an AWG-based OFDM multiplexer and demultiplexer, a receiver design without optical sampling, a transmitter design with frequency-locked cw lasers, an OFDM cyclic prefix designs, and a chromatic dispersion mitigation technique.

  6. OFDM and compressive sensing based GPR imaging using SAR focusing algorithm

    NASA Astrophysics Data System (ADS)

    Zhang, Yu; Xia, Tian

    2015-04-01

    This paper presents a new ground penetrating radar (GPR) design approach using orthogonal frequency division multiplexing (OFDM) and compressive sensing (CS) algorithms. OFDM technique is applied to leverage GPR operating speed with multiple frequency tones transmission and receiving concurrently, and CS technique allows utilizing reduced frequency tones without compromising data reconstruction accuracy. Combination of OFDM and CS boosts the radar operating efficiency. For GPR image reconstruction, a synthetic aperture radar (SAR) technique is implemented.

  7. Demonstration of 2.97-Gb/s video signal transmissions in DML-based IM-DDO-OFDM systems

    NASA Astrophysics Data System (ADS)

    Chen, Ming; He, Jing; Deng, Rui; Chen, Qinghui; Zhang, Jinlong; Chen, Lin

    2016-05-01

    To further investigate the feasibility of the digital signal processing (DSP) algorithms (e.g., symbol timing synchronization, channel estimation and equalization, and sampling clock frequency offset (SCFO) estimation and compensation) for real-time optical orthogonal frequency-division multiplexing (OFDM) system, 2.97-Gb/s real-time high-definition video signal parallel transmission is experimentally demonstrated in OFDM-based short-reach intensity-modulated direct-detection (IM-DD) systems. The experimental results show that, in the presence of ∼12 ppm SCFO between transmitter and receiver, the adaptively modulated OFDM signal transmission over 20 km standard single-mode fiber with an error bit rate less than 1 × 10-9 can be achieved by using only DSP-based small SCFO estimation and compensation method without utilizing forward error correction technique. To the best of our knowledge, for the first time, we successfully demonstrate that the video signal at a bit rate in excess of 1-Gb/s transmission in a simple real-valued inverse fast Fourier transform and fast Fourier transform based IM-DD optical OFDM system employing a directly modulated laser.

  8. Non-line-of-sight ultraviolet communication based on DHT ACO-OFDM

    NASA Astrophysics Data System (ADS)

    Gao, Qian; Chen, Gang

    2012-10-01

    Free space optical (FSO) communication has attracted tremendous research interest in the recent year. Most existing works focus only on the line-of-sight (LOS) transmission by infrared (IR) or visible light lasers/LEDs, while this article suggested a framework of non-line-of-sight (NLOS) FSO, motivated by our recent experimental results on the successful transmission of NLOS ultraviolet (UV) beams for up to kilometers, which is comparable to the typical distance a LOS FSO transmission. The NLOS provides an alternate path when the LOS path is shadowed or is highly attenuated. In order to mitigate the multipath dispersion of the NLOS FSO, a baseband orthogonal frequency division multiplexing (OFDM) modulation scheme was proposed, based on Discrete Hartley Transform (DHT) and asymmetric clipping to guarantee the positive-realness of the transmitted optical intensity. The proposed system could reduce the hardware complexity of transmitter and receiver. Minimum mean square error (MMSE) precoder was applied before the DHT to remove the crosstalk between subcarriers, i.e. the frequency domain orthogonality of OFDM was preserved. Performance of the BPSK modulated communication system was given under lognormal atmospheric turbulence for demonstration of the feasibility of the proposed method.

  9. VLSI Design of a Variable-Length FFT/IFFT Processor for OFDM-Based Communication Systems

    NASA Astrophysics Data System (ADS)

    Kuo, Jen-Chih; Wen, Ching-Hua; Lin, Chih-Hsiu; Wu, An-Yeu (Andy)

    2003-12-01

    The technique of orthogonal frequency division multiplexing (OFDM) is famous for its robustness against frequency-selective fading channel. This technique has been widely used in many wired and wireless communication systems. In general, the fast Fourier transform (FFT) and inverse FFT (IFFT) operations are used as the modulation/demodulation kernel in the OFDM systems, and the sizes of FFT/IFFT operations are varied in different applications of OFDM systems. In this paper, we design and implement a variable-length prototype FFT/IFFT processor to cover different specifications of OFDM applications. The cached-memory FFT architecture is our suggested VLSI system architecture to design the prototype FFT/IFFT processor for the consideration of low-power consumption. We also implement the twiddle factor butterfly processing element (PE) based on the coordinate rotation digital computer (CORDIC) algorithm, which avoids the use of conventional multiplication-and-accumulation unit, but evaluates the trigonometric functions using only add-and-shift operations. Finally, we implement a variable-length prototype FFT/IFFT processor with TSMC[InlineEquation not available: see fulltext.]m 1P4M CMOS technology. The simulations results show that the chip can perform ([InlineEquation not available: see fulltext.]-[InlineEquation not available: see fulltext.])-point FFT/IFFT operations up to[InlineEquation not available: see fulltext.] operating frequency which can meet the speed requirement of most OFDM standards such as WLAN, ADSL, VDSL ([InlineEquation not available: see fulltext.]), DAB, and[InlineEquation not available: see fulltext.]-mode DVB.

  10. A performance investigation of correlation-based and pilot-tone-assisted frequency offset compensation method for CO-OFDM.

    PubMed

    Cao, Shengjiao; Yu, Changyuan; Kam, Pooi-Yuen

    2013-09-23

    We carry out a comprehensive analysis to examine the performance of our recently proposed correlation-based and pilot-tone-assisted frequency offset compensation method in coherent optical OFDM system. The frequency offset is divided into two parts: fraction part and integer part relative to the channel spacing. Our frequency offset scheme includes the correlation-based Schmidl algorithm for fraction part estimation as well as pilot-tone-assisted method for integer part estimation. In this paper, we analytically derive the error variance of fraction part estimation methods in the presence of laser phase noise using different correlation-based algorithms: Schmidl, Cox and Cyclic Prefix based. This analytical expression is given for the first time in the literature. Furthermore, we give a full derivation for the pilot-tone-assisted integer part estimation method using the OFDM model. PMID:24104171

  11. Study of S-G filter based real-time OFDM-PON system

    NASA Astrophysics Data System (ADS)

    Deng, Conghui; Zhang, Qi; Wang, Yongjun; Xin, Xiangjun

    2013-12-01

    Real-time Orthogonal Frequency Division Multiplexing Passive Optical Network (OFDM-PON) has been extensively studied at home and abroad in recent years. In this paper, we realize a real-time OFDM transmitter system and introduce Savitzky-Golay filter to smooth the transmitted signal into the communication system. Firstly, the architecture of the real-time OFDM-PON was proposed in which a Xilinx V5 FPGA is used to generate the OFDM signal and a S-G filter is used to smooth the signal and weaken the noise. At the receiver, we use MATLAB to recover the signal and simulate the constellation diagram and bit error rate. What's more, this paper introduces the basic principle of S-G filter and analysis the performance of the filter when it is used in an OFDM system. In conclusion, the simulation results show that the S-G filter implemented in the real-time OFDM-PON system is easy to realize that it can reduce the complexity of the system and bit error rate at the same time. As a result, it is proofed to be suitable for the real-time OFDM-PON system.

  12. On-the-field performance of quintuple-play long-reach OFDM-based WDM-PON optical access networks.

    PubMed

    Llorente, Roberto; Morant, Maria; Pellicer, Eloy; Herman, Milan; Nagy, Zsolt; Alves, Tiago; Cartaxo, Adolfo; Herrera, Javier; Correcher, Jose; Quinlan, Terence; Walker, Stuart; Rodrigues, Cláudio; Cluzeaud, Pierre; Schmidt, Axel; Piesiewicz, Radoslaw; Sambaraju, Rakesh

    2014-03-24

    In this paper the on-the-field performance of a WDM-PON optical access providing quintuple-play services using orthogonal frequency division multiplexing (OFDM) modulation is evaluated in a real fiber-to-the-home (FTTH) network deployed by Towercom operator in Bratislava (Slovakia). A bundle of quintuple-play services comprising full-standard OFDM-based signals (LTE, WiMAX, UWB and DVB-T) and an ad-hoc OFDM-GbE signal is transmitted in coexistence per single user. Both downstream and upstream transmission performances are evaluated in different on-the-field long-reach optical link distance configurations. Four wavelength multi-user transmission of quintuple-play OFDM services is demonstrated exceeding 60.8 km reach in standard single mode fiber. PMID:24663968

  13. Extended Cyclostationary Signatures for OFDM in the Presence of Hardware Imperfections

    NASA Astrophysics Data System (ADS)

    Schmitz, Johannes; Zivkovic, Milan; Mathar, Rudolf

    2012-09-01

    Cyclostationary signatures have been shown to be an effective method for OFDM network synchronization and Cognitive Radio coordination. In this article, an extended method that utilizes cyclostationary signatures for signal parameter identification of OFDM-based Cognitive Radio nodes is presented. The scenario, implemented on a GNU Radio based evaluation platform, shows how different signal parameters, e.g. carrier frequency, occupied bandwidth and the used modulation scheme can be identified at the receiver side using the described approach. A major drawback of cyclostationary detection in OFDM systems is its sensitivity to frequency offset and sampling rate mismatches between oscillators at the transmitter and the receiver. An analytical model that characterizes this impairments is derived, followed by a discussion of implementation issues and the performance evaluation of proposed cyclostationary signature detection, both in a simulation environment and through RF experiments.

  14. PAPR Reduction in All-optical OFDM Systems Based on Phase Pre-emphasis

    NASA Astrophysics Data System (ADS)

    He, Zhou; Li, Wei; Tao, Zhiyong; Shao, Ji ng; Liang, Xiaojun; Deng, Zhuanhua; Huang, Dexiu

    2011-02-01

    This paper investigates the peak-to-average power ratio (PAPR) theory in all-optical orthogonal frequency division multiplexing (OFDM) optical fibre communication systems. We find out that phase pre-emphasis could effectively reduce PAPR in all-optical OFDM communication systems which employ intensity modulation-direct detection (IM-DD) method. An equation is developed and proposed to calculate suitable phasing values for pre-emphasis. Furthermore, we find out that phase pre-emphasis cannot reduce PAPR effectively in all-optical OFDM systems that employ Phase Shift Keying (PSK) or Quadracture Amplitude Modulation (QAM) method.

  15. Optical single-sideband OFDM transmission based on a two-segment EAM.

    PubMed

    Cheng, Hsuan-Lin; Chen, Wei-Hung; Wei, Chia-Chien; Chiu, Yi-Jen

    2015-01-26

    This paper presents a novel optical single-sideband (SSB) OFDM modulation scheme using a two-segment electro-absorption modulator (EAM). Differences in the chirp characteristics of two segments of the EAM make it possible to design driving signals capable of suppressing one of the optical sidebands, such that the optical OFDM signal does not suffer from frequency-selective power fading following dispersive fiber transmission. Our experiment results demonstrate optical OFDM transmissions at 13.5-Gbps over a 0 ∼ 200-km IM/DD system without the need for dispersion compensation and distance-dependent bit- and power-loading. PMID:25835857

  16. PAPR reduction based on chaos combined with SLM technique in optical OFDM IM/DD system

    NASA Astrophysics Data System (ADS)

    Xiao, Yaoqiang; Chen, Ming; Li, Fan; Tang, Jin; Liu, Yi; Chen, Lin

    2015-01-01

    This paper proposes a method to decrease the PAPR of 16-quadrature-amplitude-modulation (16QAM) orthogonal-frequency-division-multiplexing (OFDM) signal. The method is to combine chaos with selected mapping (CSLM) technique so that the chaotic sequences are able to control generation of phase rotation factors. The research has utilized this method to transmit OFDM signal along 100 km long single-mode fiber in an IM/DD system to test OFDM signal performance. Our experimental results show that the receiver sensitivity is improved by about 1.4 dB when a 3.28 GB/s OFDM signal at a bit error rate of 1 × 10-3 is launched by transmission power at 2, 6, 8 and 10 dBm, respectively. Moreover, comparison with traditional SLM technique, the CSLM technique can improve the BER of the system.

  17. PAPR reduction based on improved Nyquist pulse shaping technology in OFDM-RoF systems

    NASA Astrophysics Data System (ADS)

    Liu, Jian-fei; Li, Ning; Lu, Jia; Zeng, Xiang-ye; Li, Jie; Wang, Meng-jun

    2013-01-01

    High peak-to-average power ratio (PAPR) is the main disadvantage in orthogonal frequency-division multiplexing (OFDM) communication systems, which also exists in OFDM-radio over fiber (RoF) systems. In this paper, we firstly analyze the impact of high PAPR on a 40 GHz OFDM-RoF system, and then describe the theory of Nyquist pulse shaping technology for reducing PAPR. To suppress PAPR further, an improved Nyquist pulse shaping technology is proposed, in which the distribution of original-data amplitude is changed by properly selecting the time-limited waveforms of the different subcarriers. We firstly apply the improved Nyquist pulse shaping technology to an OFDM-RoF system. The simulation results show that PAPR is effectively reduced by more than 2 dB with the bit error rate (BER) declining by about 0.125%.

  18. Joint timing and frequency synchronization based on weighted CAZAC sequences for reduced-guard-interval CO-OFDM systems.

    PubMed

    Omomukuyo, Oluyemi; Chang, Deyuan; Zhu, Jingwen; Dobre, Octavia; Venkatesan, Ramachandran; Ngatched, Telex; Rumbolt, Chuck

    2015-03-01

    A novel joint symbol timing and carrier frequency offset (CFO) estimation algorithm is proposed for reduced-guard-interval coherent optical orthogonal frequency-division multiplexing (RGI-CO-OFDM) systems. The proposed algorithm is based on a constant amplitude zero autocorrelation (CAZAC) sequence weighted by a pseudo-random noise (PN) sequence. The symbol timing is accomplished by using only one training symbol of two identical halves, with the weighting applied to the second half. The special structure of the training symbol is also utilized in estimating the CFO. The performance of the proposed algorithm is demonstrated by means of numerical simulations in a 115.8-Gb/s 16-QAM RGI-CO-OFDM system. PMID:25836807

  19. Mitigation of phase noise in all-optical OFDM systems based on minimizing interaction time between subcarriers

    NASA Astrophysics Data System (ADS)

    Hmood, Jassim K.; Noordin, Kamarul A.; Harun, Sulaiman W.; Shalaby, Hossam M. H.

    2015-11-01

    A new approach to mitigate the phase noise in all-optical OFDM systems is analytically modeled and numerically demonstrated. The interaction time between subcarriers is minimized by shaping the envelopes of QAM subcarriers and making a delay time between even and odd subcarriers. Return-to-zero (RZ) coding is adopted for shaping the envelopes of subcarriers. In addition, the subcarriers are alternately delayed (AD) by optical time delayers. The performance of an all-optical OFDM system, that implements the proposed technique, is analyzed and simulated. This system has 29 subcarriers with symbol rate of 25 Gsymbol/s and is composed of coupler-based inverse fast Fourier transform (IFFT)/fast Fourier transform (FFT) schemes. Each subcarrier is modulated with QAM format before shaping with RZ coding. Due to RZ being more affected by dispersion; a full periodic dispersion map is adopted to keep the total accumulated dispersion low. The results reveal that the nonlinear phase noise (NPN) due to fiber nonlinearity is significantly mitigated when the time delay between the odd and even subcarriers is equal to half the symbol period. The total phase noise variance is reduced from 9.3×10-3 to 6.1×10-3 rad2 when employing AD RZ-QAM for a transmission distance of 550 km. Furthermore, both the transmission distance and optical signal to noise ratio (OSNR) are improved when compared to all-optical OFDM systems that adopt traditional QAM modulation formats.

  20. A Study of Dispersion Compensation of Polarization Multiplexing-Based OFDM-OCDMA for Radio-over-Fiber Transmissions.

    PubMed

    Yen, Chih-Ta; Chen, Wen-Bin

    2016-01-01

    Chromatic dispersion from optical fiber is the most important problem that produces temporal skews and destroys the rectangular structure of code patterns in the spectra-amplitude-coding-based optical code-division multiple-access (SAC-OCDMA) system. Thus, the balance detection scheme does not work perfectly to cancel multiple access interference (MAI) and the system performance will be degraded. Orthogonal frequency-division multiplexing (OFDM) is the fastest developing technology in the academic and industrial fields of wireless transmission. In this study, the radio-over-fiber system is realized by integrating OFDM and OCDMA via polarization multiplexing scheme. The electronic dispersion compensation (EDC) equalizer element of OFDM integrated with the dispersion compensation fiber (DCF) is used in the proposed radio-over-fiber (RoF) system, which can efficiently suppress the chromatic dispersion influence in long-haul transmitted distance. A set of length differences for 10 km-long single-mode fiber (SMF) and 4 km-long DCF is to verify the compensation scheme by relative equalizer algorithms and constellation diagrams. In the simulation result, the proposed dispersion mechanism successfully compensates the dispersion from SMF and the system performance with dispersion equalizer is highly improved. PMID:27618042

  1. Compressive sensing based Bayesian sparse channel estimation for OFDM communication systems: high performance and low complexity.

    PubMed

    Gui, Guan; Xu, Li; Shan, Lin; Adachi, Fumiyuki

    2014-01-01

    In orthogonal frequency division modulation (OFDM) communication systems, channel state information (CSI) is required at receiver due to the fact that frequency-selective fading channel leads to disgusting intersymbol interference (ISI) over data transmission. Broadband channel model is often described by very few dominant channel taps and they can be probed by compressive sensing based sparse channel estimation (SCE) methods, for example, orthogonal matching pursuit algorithm, which can take the advantage of sparse structure effectively in the channel as for prior information. However, these developed methods are vulnerable to both noise interference and column coherence of training signal matrix. In other words, the primary objective of these conventional methods is to catch the dominant channel taps without a report of posterior channel uncertainty. To improve the estimation performance, we proposed a compressive sensing based Bayesian sparse channel estimation (BSCE) method which cannot only exploit the channel sparsity but also mitigate the unexpected channel uncertainty without scarifying any computational complexity. The proposed method can reveal potential ambiguity among multiple channel estimators that are ambiguous due to observation noise or correlation interference among columns in the training matrix. Computer simulations show that proposed method can improve the estimation performance when comparing with conventional SCE methods. PMID:24983012

  2. Low-bit rate feedback strategies for iterative IA-precoded MIMO-OFDM-based systems.

    PubMed

    Teodoro, Sara; Silva, Adão; Dinis, Rui; Gameiro, Atílio

    2014-01-01

    Interference alignment (IA) is a promising technique that allows high-capacity gains in interference channels, but which requires the knowledge of the channel state information (CSI) for all the system links. We design low-complexity and low-bit rate feedback strategies where a quantized version of some CSI parameters is fed back from the user terminal (UT) to the base station (BS), which shares it with the other BSs through a limited-capacity backhaul network. This information is then used by BSs to perform the overall IA design. With the proposed strategies, we only need to send part of the CSI information, and this can even be sent only once for a set of data blocks transmitted over time-varying channels. These strategies are applied to iterative MMSE-based IA techniques for the downlink of broadband wireless OFDM systems with limited feedback. A new robust iterative IA technique, where channel quantization errors are taken into account in IA design, is also proposed and evaluated. With our proposed strategies, we need a small number of quantization bits to transmit and share the CSI, when comparing with the techniques used in previous works, while allowing performance close to the one obtained with perfect channel knowledge. PMID:24678274

  3. Low-Bit Rate Feedback Strategies for Iterative IA-Precoded MIMO-OFDM-Based Systems

    PubMed Central

    Teodoro, Sara; Silva, Adão; Dinis, Rui; Gameiro, Atílio

    2014-01-01

    Interference alignment (IA) is a promising technique that allows high-capacity gains in interference channels, but which requires the knowledge of the channel state information (CSI) for all the system links. We design low-complexity and low-bit rate feedback strategies where a quantized version of some CSI parameters is fed back from the user terminal (UT) to the base station (BS), which shares it with the other BSs through a limited-capacity backhaul network. This information is then used by BSs to perform the overall IA design. With the proposed strategies, we only need to send part of the CSI information, and this can even be sent only once for a set of data blocks transmitted over time-varying channels. These strategies are applied to iterative MMSE-based IA techniques for the downlink of broadband wireless OFDM systems with limited feedback. A new robust iterative IA technique, where channel quantization errors are taken into account in IA design, is also proposed and evaluated. With our proposed strategies, we need a small number of quantization bits to transmit and share the CSI, when comparing with the techniques used in previous works, while allowing performance close to the one obtained with perfect channel knowledge. PMID:24678274

  4. Independent component analysis based channel equalization for 6 × 6 MIMO-OFDM transmission over few-mode fiber.

    PubMed

    He, Zhixue; Li, Xiang; Luo, Ming; Hu, Rong; Li, Cai; Qiu, Ying; Fu, Songnian; Yang, Qi; Yu, Shaohua

    2016-05-01

    We propose and experimentally demonstrate two independent component analysis (ICA) based channel equalizers (CEs) for 6 × 6 MIMO-OFDM transmission over few-mode fiber. Compared with the conventional channel equalizer based on training symbols (TSs-CE), the proposed two ICA-based channel equalizers (ICA-CE-I and ICA-CE-II) can achieve comparable performances, while requiring much less training symbols. Consequently, the overheads for channel equalization can be substantially reduced from 13.7% to 0.4% and 2.6%, respectively. Meanwhile, we also experimentally investigate the convergence speed of the proposed ICA-based CEs. PMID:27137537

  5. OFDM-based broadband underwater wireless optical communication system using a compact blue LED

    NASA Astrophysics Data System (ADS)

    Xu, Jing; Kong, Meiwei; Lin, Aobo; Song, Yuhang; Yu, Xiangyu; Qu, Fengzhong; Han, Jun; Deng, Ning

    2016-06-01

    We propose and experimentally demonstrate an IM/DD-OFDM-based underwater wireless optical communication system. We investigate the dependence of its BER performance on the training symbol number as well as LED's bias voltage and driving voltage. With single compact blue LED and a low-cost PIN photodiode, we achieve net bit rates of 225.90 Mb/s at a BER of 1.54×10-3 using 16-QAM and 231.95 Mb/s at a BER of 3.28×10-3 using 32-QAM, respectively, over a 2-m air channel. Over a 2-m underwater channel, we achieve net bit rates of 161.36 Mb/s using 16-QAM, 156.31 Mb/s using 32-QAM, and 127.07 Mb/s using 64-QAM, respectively. The corresponding BERs are 2.5×10-3, 7.42×10-4, and 3.17×10-3, respectively, which are all below the FEC threshold.

  6. Measurement-Based Performance Evaluation of Coded MIMO-OFDM Spatial Multiplexing with MMSE Spatial Filtering in an Indoor Line-of-Sight Environment

    NASA Astrophysics Data System (ADS)

    Nishimoto, Hiroshi; Nishimura, Toshihiko; Ohgane, Takeo; Ogawa, Yasutaka

    The MIMO system can meet the growing demand for higher capacity in wireless communication fields. So far, the authors have reported that, based on channel measurements, uncoded performance of narrowband MIMO spatial multiplexing in indoor line-of-sight (LOS) environments generally outperforms that in non-LOS (NLOS) ones under the same transmit power condition. In space-frequency coded MIMO-OFDM spatial multiplexing, however, we cannot expect high space-frequency diversity gain in LOS environments because of high fading correlations and low frequency selectivity of channels so that the performance may degrade unlike uncoiled cases. In this letter, we present the practical performance of coded MIMO-OFDM spatial multiplexing based on indoor channel measurements. The results show that an LOS environment tends to provide lower space-frequency diversity effect whereas the MIMO-OFDM spatial multiplexing performance is still better in the environment compared with an NLOS environment.

  7. A new MIMO SAR system based on Alamouti space-time coding scheme and OFDM-LFM waveform design

    NASA Astrophysics Data System (ADS)

    Shi, Xiaojin; Zhang, Yunhua

    2015-10-01

    In recent years, multi-input and multi-output (MIMO) radar has attracted much attention of many researchers and institutions. MIMO radar transmits multiple signals, and receives the backscattered signals reflected from the targets. In contrast with conventional phased array radar and SAR system, MIMO radar system has significant potential advantages for achieving higher system SNR, more accurate parameter estimation, or high resolution of radar image. In this paper, we propose a new MIMO SAR system based on Alamouti space-time coding scheme and orthogonal frequency division multiplexing linearly frequency modulated (OFDM-LFM) for obtaining higher system signal-to-noise ratio (SNR) and better range resolution of SAR image.

  8. Adaptation of AMO-FBMC-OQAM in optical access network for accommodating asynchronous multiple access in OFDM-based uplink transmission

    NASA Astrophysics Data System (ADS)

    Jung, Sun-Young; Jung, Sang-Min; Han, Sang-Kook

    2015-01-01

    Exponentially expanding various applications in company with proliferation of mobile devices make mobile traffic exploded annually. For future access network, bandwidth efficient and asynchronous signals converged transmission technique is required in optical network to meet a huge bandwidth demand, while integrating various services and satisfying multiple access in perceived network resource. Orthogonal frequency division multiplexing (OFDM) is highly bandwidth efficient parallel transmission technique based on orthogonal subcarriers. OFDM has been widely studied in wired-/wireless communication and became a Long term evolution (LTE) standard. Consequently, OFDM also has been actively researched in optical network. However, OFDM is vulnerable frequency and phase offset essentially because of its sinc-shaped side lobes, therefore tight synchronism is necessary to maintain orthogonality. Moreover, redundant cyclic prefix (CP) is required in dispersive channel. Additionally, side lobes act as interference among users in multiple access. Thus, it practically hinders from supporting integration of various services and multiple access based on OFDM optical transmission In this paper, adaptively modulated optical filter bank multicarrier system with offset QAM (AMO-FBMC-OQAM) is introduced and experimentally investigated in uplink optical transmission to relax multiple access interference (MAI), while improving bandwidth efficiency. Side lobes are effectively suppressed by using FBMC, therefore the system becomes robust to path difference and imbalance among optical network units (ONUs), which increase bandwidth efficiency by reducing redundancy. In comparison with OFDM, a signal performance and an efficiency of frequency utilization are improved in the same experimental condition. It enables optical network to effectively support heterogeneous services and multiple access.

  9. Adaptive Zero-Padding OFDM over Frequency-Selective Multipath Channels

    NASA Astrophysics Data System (ADS)

    Wang, Neng; Blostein, Steven D.

    2004-12-01

    We present a novel bandwidth (BW) efficient orthogonal frequency division multiplexing (OFDM) scheme with adaptive zero-padding (AZP-OFDM) for wireless transmission. Redundancy issues in OFDM based on cyclic prefix (CP), zero-padding (ZP), as well as no guard interval (NGI) systems are analyzed. A novel system design criterion based on the channel matrix condition is studied and applied to the design of an AZP-OFDM system. Simulation results have shown that the proposed AZP-OFDM offers performance similar to that of CP-OFDM, complexity similar to that of ZP-OFDM, with BW efficiency higher than that of both CP- and ZP-OFDM in channels with small to moderate delay spread. In channels with large delay spread, AZP scheme adaptively maintains high performance at the expense of BW efficiency. Essentially, AZP-OFDM offers a more flexible tradeoff between symbol recovery, BW efficiency, and complexity.

  10. Performance comparison of a fiber optic communication system based on optical OFDM and an optical OFDM-MIMO with Alamouti code by using numerical simulations

    NASA Astrophysics Data System (ADS)

    Serpa-Imbett, C. M.; Marín-Alfonso, J.; Gómez-Santamaría, C.; Betancur-Agudelo, L.; Amaya-Fernández, F.

    2013-12-01

    Space division multiplexing in multicore fibers is one of the most promise technologies in order to support transmissions of next-generation peta-to-exaflop-scale supercomputers and mega data centers, owing to advantages in terms of costs and space saving of the new optical fibers with multiple cores. Additionally, multicore fibers allow photonic signal processing in optical communication systems, taking advantage of the mode coupling phenomena. In this work, we numerically have simulated an optical MIMO-OFDM (multiple-input multiple-output orthogonal frequency division multiplexing) by using the coded Alamouti to be transmitted through a twin-core fiber with low coupling. Furthermore, an optical OFDM is transmitted through a core of a singlemode fiber, using pilot-aided channel estimation. We compare the transmission performance in the twin-core fiber and in the singlemode fiber taking into account numerical results of the bit-error rate, considering linear propagation, and Gaussian noise through an optical fiber link. We carry out an optical fiber transmission of OFDM frames using 8 PSK and 16 QAM, with bit rates values of 130 Gb/s and 170 Gb/s, respectively. We obtain a penalty around 4 dB for the 8 PSK transmissions, after 100 km of linear fiber optic propagation for both singlemode and twin core fiber. We obtain a penalty around 6 dB for the 16 QAM transmissions, with linear propagation after 100 km of optical fiber. The transmission in a two-core fiber by using Alamouti coded OFDM-MIMO exhibits a better performance, offering a good alternative in the mitigation of fiber impairments, allowing to expand Alamouti coded in multichannel systems spatially multiplexed in multicore fibers.

  11. Comparison of DSP-based nonlinear equalizers for intra-channel nonlinearity compensation in coherent optical OFDM.

    PubMed

    Giacoumidis, Elias; Mhatli, Sofien; Nguyen, Tu; Le, Son T; Aldaya, Ivan; McCarthy, Mary E; Ellis, Andrew D; Eggleton, Benjamin J

    2016-06-01

    A novel versatile digital signal processing (DSP)-based equalizer using support vector machine regression (SVR) is proposed for 16-quadrature amplitude modulated (16-QAM) coherent optical orthogonal frequency-division multiplexing (CO-OFDM) and experimentally compared to traditional DSP-based deterministic fiber-induced nonlinearity equalizers (NLEs), namely the full-field digital back-propagation (DBP) and the inverse Volterra series transfer function-based NLE (V-NLE). For a 40 Gb/s 16-QAM CO-OFDM at 2000 km, SVR-NLE extends the optimum launched optical power (LOP) by 4 dB compared to V-NLE by means of reduction of fiber nonlinearity. In comparison to full-field DBP at a LOP of 6 dBm, SVR-NLE outperforms by ∼1  dB in Q-factor. In addition, SVR-NLE is the most computational efficient DSP-NLE. PMID:27244401

  12. Investigation of PMD in direct-detection optical OFDM with zero padding.

    PubMed

    Li, Xiang; Alphones, Arokiaswami; Zhong, Wen-De; Yu, Changyuan

    2013-09-01

    We investigate the polarization-mode dispersion (PMD) effect of zero padding OFDM (ZP-OFDM) in direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) systems. We first study the conventional equalization method for ZP-OFDM. Then an equalization method based on sorted QR decomposition is proposed to further improve the performance. It is found that the performance improvement of ZP-OFDM is due to the frequency domain oversampling (FDO) induced inter-carrier interference (ICI). Numerical simulation results show that compared with cyclic prefix OFDM (CP-OFDM), ZP-OFDM has a significantly higher tolerance to PMD in DDO-OFDM systems when the channel spectral nulls occur at certain differential group delay (DGD) values. PMID:24103957

  13. All-optical virtual private network system in OFDM based long-reach PON using RSOA re-modulation technique

    NASA Astrophysics Data System (ADS)

    Kim, Chang-Hun; Jung, Sang-Min; Kang, Su-Min; Han, Sang-Kook

    2015-01-01

    We propose an all-optical virtual private network (VPN) system in an orthogonal frequency division multiplexing (OFDM) based long reach PON (LR-PON). In the optical access network field, technologies based on fundamental upstream (U/S) and downstream (D/S) have been actively researched to accommodate explosion of data capacity. However, data transmission among the end users which is arisen from cloud computing, file-sharing and interactive game takes a large weight inside of internet traffic. Moreover, this traffic is predicted to increase more if Internet of Things (IoT) services are activated. In a conventional PON, VPN data is transmitted through ONU-OLT-ONU via U/S and D/S carriers. It leads to waste of bandwidth and energy due to O-E-O conversion in the OLT and round-trip propagation between OLT and remote node (RN). Also, it causes inevitable load to the OLT for electrical buffer, scheduling and routing. The network inefficiency becomes more critical in a LR-PON which has been researched as an effort to reduce CAPEX and OPEX through metro-access consolidation. In the proposed system, the VPN data is separated from conventional U/S and re-modulated on the D/S carrier by using RSOA in the ONUs to avoid bandwidth consumption of U/S and D/S unlike in previously reported system. Moreover, the transmitted VPN data is re-directed to the ONUs by wavelength selective reflector device in the RN without passing through the OLT. Experimental demonstration for the VPN communication system in an OFDM based LR-PON has been verified.

  14. Variable length adjacent partitioning for PTS based PAPR reduction of OFDM signal

    NASA Astrophysics Data System (ADS)

    Ibraheem, Zeyid T.; Rahman, Md. Mijanur; Yaakob, S. N.; Razalli, Mohammad Shahrazel; Kadhim, Rasim A.

    2015-05-01

    Peak-to-Average power ratio (PAPR) is a major drawback in OFDM communication. It leads the power amplifier into nonlinear region operation resulting into loss of data integrity. As such, there is a strong motivation to find techniques to reduce PAPR. Partial Transmit Sequence (PTS) is an attractive scheme for this purpose. Judicious partitioning the OFDM data frame into disjoint subsets is a pivotal component of any PTS scheme. Out of the existing partitioning techniques, adjacent partitioning is characterized by an attractive trade-off between cost and performance. With an aim of determining effects of length variability of adjacent partitions, we performed an investigation into the performances of a variable length adjacent partitioning (VL-AP) and fixed length adjacent partitioning in comparison with other partitioning schemes such as pseudorandom partitioning. Simulation results with different modulation and partitioning scenarios showed that fixed length adjacent partition had better performance compared to variable length adjacent partitioning. As expected, simulation results showed a slightly better performance of pseudorandom partitioning technique compared to fixed and variable adjacent partitioning schemes. However, as the pseudorandom technique incurs high computational complexities, adjacent partitioning schemes were still seen as favorable candidates for PAPR reduction.

  15. An optimal scaling scheme for DCO-OFDM based visible light communications

    NASA Astrophysics Data System (ADS)

    Jiang, Rui; Wang, Qi; Wang, Fang; Dai, Linglong; Wang, Zhaocheng

    2015-12-01

    DC-biased optical orthogonal frequency-division multiplexing (DCO-OFDM) is widely used in visible light communication (VLC) systems to provide high data rate transmission. As intensity modulation with direct detection (IM/DD) is employed to modulate the OFDM signal, scale up the amplitude of the signal can increase the effective transmitted electrical power whereas more signals are likely to be clipped due to the limited dynamic range of LEDs, resulting in severe clipping distortion. Thus, it is crucial to scale the signal to find a tradeoff between the effective electrical power and the clipping distortion. In this paper, an optimal scaling scheme is proposed to maximize the received signal-to-noise-plus-distortion ratio (SNDR) with the constraint of the radiated optical power in a practical scenario where DC bias is fixed for a desired dimming level. Simulation results show that the system with the optimal scaling factor outperforms that with fixed scaling factor under different equivalent noise power in terms of the bit error ratio (BER) performance.

  16. Variable length adjacent partitioning for PTS based PAPR reduction of OFDM signal

    SciTech Connect

    Ibraheem, Zeyid T.; Rahman, Md. Mijanur; Yaakob, S. N.; Razalli, Mohammad Shahrazel; Kadhim, Rasim A.

    2015-05-15

    Peak-to-Average power ratio (PAPR) is a major drawback in OFDM communication. It leads the power amplifier into nonlinear region operation resulting into loss of data integrity. As such, there is a strong motivation to find techniques to reduce PAPR. Partial Transmit Sequence (PTS) is an attractive scheme for this purpose. Judicious partitioning the OFDM data frame into disjoint subsets is a pivotal component of any PTS scheme. Out of the existing partitioning techniques, adjacent partitioning is characterized by an attractive trade-off between cost and performance. With an aim of determining effects of length variability of adjacent partitions, we performed an investigation into the performances of a variable length adjacent partitioning (VL-AP) and fixed length adjacent partitioning in comparison with other partitioning schemes such as pseudorandom partitioning. Simulation results with different modulation and partitioning scenarios showed that fixed length adjacent partition had better performance compared to variable length adjacent partitioning. As expected, simulation results showed a slightly better performance of pseudorandom partitioning technique compared to fixed and variable adjacent partitioning schemes. However, as the pseudorandom technique incurs high computational complexities, adjacent partitioning schemes were still seen as favorable candidates for PAPR reduction.

  17. A PAPR reduction technique using Hadamard transform combined with clipping and filtering based on DCT/IDCT for IM/DD optical OFDM systems

    NASA Astrophysics Data System (ADS)

    Mangone, Fall; He, Jing; Tang, Jin; Xiao, Jiangnan; Chen, Ming; Li, Fan; Chen, Lin

    2014-08-01

    In Intensity Modulator/Direct Detection (IM/DD) optical OFDM systems, the high peak-to-power average ratio (PAPR) will cause signal impairments through the nonlinearity of modulator and fiber. In this paper, a joint PAPR reduction technique based on Hadamard transformation and clipping and filtering using DCT/IDCT transform has been proposed for mitigating the impairments in IM/DD optical OFDM system. We then experimentally evaluated the effect of PAPR reduction on the bit error rate (BER) performance and the results show the effectiveness of the proposed technique. At a bit error rate (BER) of 1 × 10-3, the receiver sensitivity of the proposed 2.5 Gb/s IM/DD optical OFDM system after 100-km standard single-mode fiber transmission has been improved by 0.8 dB, 1.3 dB and 3.1 dB for a launch power of 6.4 dBm, 8 dBm and 10 dBm respectively when compared with the classical system.

  18. Using specific and adaptive arrangement of grid-type pilot in channel estimation for white-lightLED-based OFDM visible light communication system

    NASA Astrophysics Data System (ADS)

    Lin, Wan-Feng; Chow, Chi-Wai; Yeh, Chien-Hung

    2015-03-01

    Orthogonal frequency division multiplexing (OFDM) is a promising candidate for light emitting diode (LED)-based optical wireless communication (OWC); however, precise channel estimation is required for synchronization and equalization. In this work, we study and discover that the channel response of the white-lightLED-based OWC was smooth and stable. Hence we propose and demonstrate using a specific and adaptive arrangement of grid-type pilot scheme to estimate the LED OWC channel response. Experimental results show that our scheme can achieve better transmission performance and with some transmission capacity enhancement when compared with the method using training-symbol scheme (also called block-type pilot scheme).

  19. Fast adaptive OFDM-PON over single fiber loopback transmission using dynamic rate adaptation-based algorithm for channel performance improvement

    NASA Astrophysics Data System (ADS)

    Kartiwa, Iwa; Jung, Sang-Min; Hong, Moon-Ki; Han, Sang-Kook

    2014-03-01

    In this paper, we propose a novel fast adaptive approach that was applied to an OFDM-PON 20-km single fiber loopback transmission system to improve channel performance in term of stabilized BER below 2 × 10-3 and higher throughput beyond 10 Gb/s. The upstream transmission is performed through light source-seeded modulation using 1-GHz RSOA at the ONU. Experimental results indicated that the dynamic rate adaptation algorithm based on greedy Levin-Campello could be an effective solution to mitigate channel instability and data rate degradation caused by the Rayleigh back scattering effect and inefficient resource subcarrier allocation.

  20. Experimental demonstration of low-complexity fiber chromatic dispersion mitigation for reduced guard-interval OFDM coherent optical communication systems based on digital spectrum sub-band multiplexing.

    PubMed

    Malekiha, Mahdi; Tselniker, Igor; Nazarathy, Moshe; Tolmachev, Alex; Plant, David V

    2015-10-01

    We experimentally demonstrate a novel digital signal processing (DSP) structure for reduced guard-interval (RGI) OFDM coherent optical systems. The proposed concept is based on digitally slicing optical channel bandwidth into multiple spectrally disjoint sub-bands which are then processed in parallel. Each low bandwidth sub-band has a smaller delay-spread compared to a full-band signal. This enables compensation of both chromatic dispersion (CD) and polarization mode dispersion using a simple timing and one-tap-per-symbol frequency domain equalizer with a small cyclic prefix overhead. In terms of the DSP architecture, this allows for a highly efficient parallelization of DSP tasks performed over the received signal samples by deploying multiple processors running at a lower clock rate. It should be noted that this parallelization is performed in the frequency domain and it allows for flexible optical transceiver schemes. In addition, the resulting optical receiver is simplified due to the removal of the CD compensation equalizer compared to conventional RGI-OFDM systems. In this paper we experimentally demonstrate digital sub-banding of optical bandwidth. We test the system performance for different modulation formats (QPSK, 16QAM and 32QAM) over various transmission distances and optical launch powers using a 1.5% CP overhead in all scenarios. We also compare the proposed RGI-OFDM architecture performance against common single carrier modulation formats. At the same total data rate and signal bandwidth both systems have similar performance and transmission reach whereas the proposed method allows for a significant reduction of computational complexity due to removal of CD pre/post compensation equalizer. PMID:26480077

  1. Partial spread OFDM

    NASA Astrophysics Data System (ADS)

    Elghariani, Ali; Zoltowski, Michael D.

    2012-05-01

    In this paper, partial spread OFDM system has been presented and its performance has been studied when different detection techniques are employed, such as minimum mean square error (MMSE), grouped Maximum Likelihood (ML) and approximated integer quadratic programming (IQP) techniques . The performance study also includes applying two different spreading matrices, Hadamard and Vandermonde. Extensive computer simulation have been implemented and important results show that partial spread OFDM system improves the BER performance and the frequency diversity of OFDM compared to both non spread and full spread systems. The results from this paper also show that partial spreading technique combined with suboptimal detector could be a better solution for applications that require low receiver complexity and high information detectability.

  2. MIMO OFDM radar IRCI free range reconstruction with sufficient cyclic prefix

    NASA Astrophysics Data System (ADS)

    Xia, Xiang-gen; Zhang, Tianxian; Kong, Lingjiang

    2015-07-01

    In this paper, we propose MIMO OFDM radar with sufficient cyclic prefix (CP), where all OFDM pulses transmitted from different transmitters share the same frequency band and are orthogonal to each other for every subcarrier in the discrete frequency domain. The orthogonality is not affected by time delays from transmitters. Thus, our proposed MIMO OFDM radar has the same range resolution as single transmitter radar and achieves full spatial diversity. Orthogonal designs are used to achieve this orthogonality across the transmitters, with which it is only needed to design OFDM pulses for the first transmitter. We also propose a joint pulse compression and pulse coherent integration for range reconstruction. In order to achieve the optimal SNR for the range reconstruction, we apply the paraunitary filterbank theory to design the OFDM pulses. We then propose a modified iterative clipping and filtering (MICF) algorithm for the designs of OFDM pulses jointly, when other important factors, such as peak-to-average power ratio (PAPR) in time domain, are also considered. With our proposed MIMO OFDM radar, there is no interference for the range reconstruction not only across the transmitters but also across the range cells in a swath called inter-range-cell interference (IRCI) free that is similar to our previously proposed CP based OFDM radar for single transmitter. Simulations are presented to illustrate our proposed theory and show that the CP based MIMO OFDM radar outperforms the existing frequency-band shared MIMO radar with polyphase codes and also frequency division MIMO radar.

  3. Reverse polarity optical-OFDM (RPO-OFDM): dimming compatible OFDM for gigabit VLC links.

    PubMed

    Elgala, Hany; Little, Thomas D C

    2013-10-01

    Visible light communications (VLC) technology permits the exploitation of light-emitting diode (LED) luminaries for simultaneous illumination and broadband wireless communication. Optical orthogonal frequency-division multiplexing (O-OFDM) is a promising modulation technique for VLC systems, in which the real-valued O-OFDM baseband signal is used to modulate the instantaneous power of the optical carrier to achieve gigabit data rates. However, a major design challenge that limits the commercialization of VLC is how to incorporate the industry-preferred pulse-width modulation (PWM) light dimming technique while maintaining a broadband and reliable communication link. In this work, a novel signal format, reverse polarity O-OFDM (RPO-OFDM), is proposed to combine the fast O-OFDM communication signal with the relatively slow PWM dimming signal, where both signals contribute to the effective LED brightness. The advantages of using RPO-OFDM include, (1) the data rate is not limited by the frequency of the PWM signal, (2) the LED dynamic range is fully utilized to minimize the nonlinear distortion of the O-OFDM communication signal, and (3) the bit-error performance is sustained over a large fraction of the luminaire dimming range. In addition, RPO-OFDM offers a practical approach to utilize off-the-shelf LED drivers. We show results of numerical simulations to study the trade-offs between the PWM duty cycle, average electrical O-OFDM signal power, radiated optical flux as well as human perceived light. PMID:24104338

  4. Multifrequency OFDM SAR in Presence of Deception Jamming

    NASA Astrophysics Data System (ADS)

    Schuerger, Jonathan; Garmatyuk, Dmitriy

    2010-12-01

    Orthogonal frequency division multiplexing (OFDM) is considered in this paper from the perspective of usage in imaging radar scenarios with deception jamming. OFDM radar signals are inherently multifrequency waveforms, composed of a number of subbands which are orthogonal to each other. While being employed extensively in communications, OFDM has not found comparatively wide use in radar, and, particularly, in synthetic aperture radar (SAR) applications. In this paper, we aim to show the advantages of OFDM-coded radar signals with random subband composition when used in deception jamming scenarios. Two approaches to create a radar signal by the jammer are considered: instantaneous frequency (IF) estimator and digital-RF-memory- (DRFM-) based reproducer. In both cases, the jammer aims to create a copy of a valid target image via resending the radar signal at prescribed time intervals. Jammer signals are derived and used in SAR simulations with three types of signal models: OFDM, linear frequency modulated (LFM), and frequency-hopped (FH). Presented results include simulated peak side lobe (PSL) and peak cross-correlation values for random OFDM signals, as well as simulated SAR imagery with IF and DRFM jammers'-induced false targets.

  5. Robust and tunable 16.375Gb/s dual-band optical OFDM transmissions over directly modulated VCSEL-based 200m OM2 MMFs.

    PubMed

    Deng, M L; Jiang, N; Duan, X; Giddings, R P; Yi, X W; Cao, B Y; Mansoor, S; Qiu, K; Tang, J M

    2015-01-12

    Utilizing low-cost, 2.2GHz modulation bandwidth, uncooled and standalone directly modulated VCSEL (DM-VCSEL)-based real-time dual-band optical OFDM (OOFDM) transmitters, aggregated 16.375Gb/s transmissions of OOFDM signals having bandwidths approximately 3.8 times higher than the VCSEL manufacturer-specified modulation bandwidths, are experimentally demonstrated, for the first time, over 200m OM2 MMF links based on intensity modulation and direct detection. The aggregated signal transmission capacities of the aforementioned links vary by just 8% for various OM2 MMFs ranging from 100m to 500m, and by just 10% over a 1GHz passband carrier frequency detuning range. Such dual-band OOFDM adaptability-induced excellent performance robustness and large passband frequency tunability can significantly relax the requirements on VCSEL modulation bandwidth for achieving specific transmission performances for cost-sensitive application scenarios such as data centers. PMID:25835683

  6. Flexible OFDM-based access systems with intrinsic function of chromatic dispersion compensation

    NASA Astrophysics Data System (ADS)

    Konishi, Tsuyoshi; Murakawa, Takuya; Nagashima, Tomotaka; Hasegawa, Makoto; Shimizu, Satoshi; Hattori, Kuninori; Okuno, Masayuki; Mino, Shinji; Himeno, Akira; Uenohara, Hiroyuki; Wada, Naoya; Cincotti, Gabriella

    2015-12-01

    Cost-effective and tunable chromatic dispersion compensation in a fiber link are still an open issue in metro and access networks to cope with increasing costs and power consumption. Intrinsic chromatic dispersion compensation functionality of optical fractional orthogonal frequency division multiplexing is discussed and experimentally demonstrated using dispersion-tunable transmitter and receiver based on wavelength selective switching devices.

  7. Symmetric 10 Gb/s wavelength reused bidirectional RSOA based WDM-PON with DPSK modulated downstream and OFDM modulated upstream signals

    NASA Astrophysics Data System (ADS)

    Choudhury, Pallab K.; Khan, Tanvir Zaman

    2016-08-01

    A 10 Gb/s bidirectional wavelength division multiplexing passive optical network (WDM-PON) with reflective semiconductor optical amplifier (RSOA) based colorless optical network unit (ONU) is proposed and analyzed for next generation gigabit class optical access network. Differential phase shift keying (DPSK) modulated signal is used in downstream and further reused as a seeding wavelength for upstream data modulation. By exploiting the constant envelope property of DPSK seed signal, the re-modulation noise in upstream receiver is effectively minimized without employing any constraint on extinction ratio of downstream signal. Orthogonal frequency division multiplexing (OFDM) signal is used in upstream transmission to overcome the limited bandwidth (∼1 GHz) response of RSOA remodulation. The results show that the proposed 10 Gb/s symmetric WDM-PON can achieve good performance over 25 km fiber transmission with error free operation in downstream and bit error rate (BER) lower than forward error correction (FEC) limit in upstream.

  8. Improved transmission performance of adaptively modulated optical OFDM signals over directly modulated DFB laser-based IMDD links using adaptive cyclic prefix.

    PubMed

    Giacoumidis, E; Wei, J L; Jin, X Q; Tang, J M

    2008-06-23

    The impact of Adaptive Cyclic Prefix (ACP) on the transmission performance of Adaptively Modulated Optical OFDM (AMOOFDM) is explored thoroughly in directly modulated DFB laser-based, IMDD links involving Multimode Fibres (MMFs)/Single-Mode Fibres (SMFs). Three ACP mechanisms are identified, each of which can, depending upon the link properties, affect significantly the AMOOFDM transmission performance. In comparison with AMOOFDM having a fixed cyclic prefix duration of 25%, AMOOFDM with ACP can not only improve the transmission capacity by a factor of >2 (>1.3) for >1000 m MMFs (<80 km SMFs) with 1 dB link loss margin enhancement, but also relax considerably the requirement on the DFB bandwidth. PMID:18575513

  9. Nonlinear effect mitigation based on PAPR reduction using electronic pre-distortion technique in direct-detection optical OFDM system

    NASA Astrophysics Data System (ADS)

    Chen, Hongxian; Yu, Jianjun; Xiao, Jiangnan; Cao, Zizheng; Li, Fan; Chen, Lin

    2013-10-01

    The nonlinear effect induced by the Mach-Zehnder modulator (MZM) and optical self-phase modulation (SPM) in the presence of high peak-to-average power ratio (PAPR) is investigated theoretically. We theoretically and experimentally investigate the direct-detection optical orthogonal frequency-division multiplexing (DD-OOFDM) system with an electronic pre-distortion technique of companding transform (CT) to reduce the peak-to-average power ratio (PAPR) of OFDM signals and improve the receiver sensitivity. Experimental results show that the PAPR reduction can reach about 3 dB when the complementary cumulative distribution function is 1 × 10-4, which means the number of random OFDM signals is 1 × 104, and the receiver sensitivity is improved by 0.7, 1.7, and 2.4 dB for the launch power of 2, 6 and 10 dB m, respectively, at the BER of 1 × 10-4 after transmission over 100-km single-mode fiber with the μ of 2. It shows that the PAPR reduction can mitigate not only the nonlinearity of MZM, but also the nonlinear phase noise in the fiber link when the optical power into fiber is high.

  10. Study of the all-optical high-speed OFDM transmission system based on MAMSK modulation

    NASA Astrophysics Data System (ADS)

    Shang, Tao; Sun, Jinkui; Li, Yang; Wang, Xin

    2012-12-01

    In this paper, an all-optical orthogonal frequency division multiplexing (OOFDM) system based on the multi-amplitude minimum shift keying (MAMSK) modulation is proposed. A scheme to realize MAMSK is designed, and the influence of modulation index on the performance of MAMSK is discussed. Numerical simulations and analysis are performed, and the comparison between the MAMSK-OOFDM and the MAMSK-WDM system is made. The lowest value of the BER of MAMSK-OOFDM is 3.98 × 10-6, while that of MAMSK-WDM is 7.94 × 10-4 when the input power is 0.8 mw and dispersion is completely compensated. The results show that, for its multi-level amplitude and excellent spectrum efficiency, MAMSK-OOFDM can greatly mitigate the effects caused by dispersive and nonlinear phenomena, and it can also effectively improve the capacity of the system.

  11. Fiber nonlinearity-induced penalty reduction in CO-OFDM by ANN-based nonlinear equalization.

    PubMed

    Giacoumidis, Elias; Le, Son T; Ghanbarisabagh, Mohammad; McCarthy, Mary; Aldaya, Ivan; Mhatli, Sofien; Jarajreh, Mutsam A; Haigh, Paul A; Doran, Nick J; Ellis, Andrew D; Eggleton, Benjamin J

    2015-11-01

    We experimentally demonstrate ∼2  dB quality (Q)-factor enhancement in terms of fiber nonlinearity compensation of 40  Gb/s 16 quadrature amplitude modulation coherent optical orthogonal frequency-division multiplexing at 2000 km, using a nonlinear equalizer (NLE) based on artificial neural networks (ANN). Nonlinearity alleviation depends on escalation of the ANN training overhead and the signal bit rate, reporting ∼4  dBQ-factor enhancement at 70  Gb/s, whereas a reduction of the number of ANN neurons annihilates the NLE performance. An enhanced performance by up to ∼2  dB in Q-factor compared to the inverse Volterra-series transfer function NLE leads to a breakthrough in the efficiency of ANN. PMID:26512532

  12. Plant Based Extracts and Cognition

    ClinicalTrials.gov

    2014-07-28

    Change in Cognitive Function and Fatigue During Extended Performance of the Cognitive Demand Battery (CDB) at 1, 3 and 6 Hours Post Consumption; Change in Long Term Declarative Memory at 1, 3 and 6 Hours Post-intervention.

  13. On Multiple-Input Multiple-Output OFDM with Index Modulation for Next Generation Wireless Networks

    NASA Astrophysics Data System (ADS)

    Basar, Ertugrul

    2016-08-01

    Multiple-input multiple-output orthogonal frequency division multiplexing with index modulation (MIMO-OFDM-IM) is a novel multicarrier transmission technique which has been proposed recently as an alternative to classical MIMO-OFDM. In this scheme, OFDM with index modulation (OFDM-IM) concept is combined with MIMO transmission to take advantage of the benefits of these two techniques. In this paper, we shed light on the implementation and error performance analysis of the MIMO-OFDM-IM scheme for next generation 5G wireless networks. Maximum likelihood (ML), near-ML, simple minimum mean square error (MMSE) and ordered successive interference cancellation (OSIC) based MMSE detectors of MIMO-OFDM-IM are proposed and their theoretical performance is investigated. It has been shown via extensive computer simulations that MIMO-OFDM-IM scheme provides an interesting trade-off between error performance and spectral efficiency as well as it achieves considerably better error performance than classical MIMO-OFDM using different type detectors and under realistic conditions.

  14. Identifying and individuating cognitive systems: a task-based distributed cognition alternative to agent-based extended cognition.

    PubMed

    Davies, Jim; Michaelian, Kourken

    2016-08-01

    This article argues for a task-based approach to identifying and individuating cognitive systems. The agent-based extended cognition approach faces a problem of cognitive bloat and has difficulty accommodating both sub-individual cognitive systems ("scaling down") and some supra-individual cognitive systems ("scaling up"). The standard distributed cognition approach can accommodate a wider variety of supra-individual systems but likewise has difficulties with sub-individual systems and faces the problem of cognitive bloat. We develop a task-based variant of distributed cognition designed to scale up and down smoothly while providing a principled means of avoiding cognitive bloat. The advantages of the task-based approach are illustrated by means of two parallel case studies: re-representation in the human visual system and in a biomedical engineering laboratory. PMID:27033708

  15. Banded all-optical OFDM super-channels with low-bandwidth receivers.

    PubMed

    Song, Binhuang; Zhu, Chen; Corcoran, Bill; Zhuang, Leimeng; Lowery, Arthur James

    2016-08-01

    We propose a banded all-optical orthogonal frequency division multiplexing (AO-OFDM) transmission system based on synthesising a number of truncated sinc-shaped subcarriers for each sub-band. This approach enables sub-band by sub-band reception and therefore each receiver's electrical bandwidth can be significantly reduced compared with a conventional AO-OFDM system. As a proof-of-concept experiment, we synthesise 6 × 10-Gbaud subcarriers in both conventional and banded AO-OFDM systems. With a limited receiver electrical bandwidth, the experimental banded AO-OFDM system shows 2-dB optical signal to noise ratio (OSNR) benefit over conventional AO-OFDM at the 7%-overhead forward error correction (FEC) threshold. After transmission over 800-km of single-mode fiber, ≈3-dB improvement in Q-factor can be achieved at the optimal launch power at a cost of increasing the spectral width by 14%. PMID:27505764

  16. Hadamard precoding for PAPR reduction in optical direct detection OFDM systems

    NASA Astrophysics Data System (ADS)

    Wang, Zhong-Peng; Xiao, Jiang-Nan; Li, Fan; Chen, Lin

    2011-09-01

    The high peak-to-average power ration (PAPR) values of optical orthogond frequency division multiplexing (OFDM) signal limit the system nonlinear tolerance (NLT). In this paper, a novel method based on Hadamard precoding is proposed to reduce the peak-to-average power ratio in optical direct detection OFDM system. The proposed scheme is successfully applied to an experimental system of optical direct-detection OFDM signal transmission through fiber. In this experiment, the 2.5 Gbit/s binary phase shift keying (BPSK) optical OFDM signals with Hadamard precoding are generated and transmitted though a single mode fiber. The experimental results show that the proposed scheme can reduce PAPR by almost 1.5 dB. Meantime the received sensitivity is improved by 2 dB with 100 km fiber transmission compared with that of an ordinary optical direct detection OFDM system.

  17. Object-Based Attention and Cognitive Tunneling

    ERIC Educational Resources Information Center

    Jarmasz, Jerzy; Herdman, Chris M.; Johannsdottir, Kamilla Run

    2005-01-01

    Simulator-based research has shown that pilots cognitively tunnel their attention on head-up displays (HUDs). Cognitive tunneling has been linked to object-based visual attention on the assumption that HUD symbology is perceptually grouped into an object that is perceived and attended separately from the external scene. The present research…

  18. Cognitive Bases of Human Creativity

    ERIC Educational Resources Information Center

    Sweller, John

    2009-01-01

    Cognitive load theory has been concerned primarily with techniques that will facilitate the acquisition by students of knowledge previously generated by others and deemed to be important by society. The initial generation of that knowledge, a creative process, has been largely ignored. The recent expansion of cognitive load theory's cognitive…

  19. Real-time experimental demonstrations of software reconfigurable optical OFDM transceivers utilizing DSP-based digital orthogonal filters for SDN PONs.

    PubMed

    Duan, X; Giddings, R P; Bolea, M; Ling, Y; Cao, B; Mansoor, S; Tang, J M

    2014-08-11

    Real-time optical OFDM (OOFDM) transceivers with on-line software-controllable channel reconfigurability and transmission performance adaptability are experimentally demonstrated, for the first time, utilizing Hilbert-pair-based 32-tap digital orthogonal filters implemented in FPGAs. By making use of an 8-bit DAC/ADC operating at 2GS/s, an oversampling factor of 2 and an EML intensity modulator, the demonstrated RF conversion-free transceiver supports end-to-end real-time simultaneous adaptive transmissions, within a 1GHz signal spectrum region, of a 2.03Gb/s in-phase OOFDM channel and a 1.41Gb/s quadrature-phase OOFDM channel over a 25km SSMF IMDD system. In addition, detailed experimental explorations are also undertaken of key physical mechanisms limiting the maximum achievable transmission performance, impacts of transceiver's channel multiplexing/demultiplexing operations on the system BER performance, and the feasibility of utilizing adaptive modulation to combat impairments associated with low-complexity digital filter designs. Furthermore, experimental results indicate that the transceiver incorporating a fixed digital orthogonal filter DSP architecture can be made transparent to various signal modulation formats up to 64-QAM. PMID:25321051

  20. Study of IQ imbalance in a single-side band radio-over-fiber system based on OFDM-MSK modulation

    NASA Astrophysics Data System (ADS)

    Li, Xinying; Shao, Yufeng; Fang, Wuliang; Huang, Bo; Zhang, Junwen; Zou, Shumin; Hou, Chunning; Fang, Yuan; Liu, Xiao; Zheng, Xi; Chi, Nan

    2010-12-01

    We propose and simulate a single-side band (SSB) Radio-over-Fiber ( RoF ) system based on OFDM-MSK modulation. In-phase/quadrature-phase (IQ) imbalance effect can significantly degrade the system performance. In order to obtain a better system performance, at the transmitter, the phase departure tolerance should be within 1 degree and the amplitude departure tolerance should be within 5% in the electrical domain, the phase departure tolerance should be within 10 degrees and the amplitude departure tolerance should be within 40% in the optical domain, the departure tolerance of splitting ratio should be within +/-12%, and at the same time, time misalignment should be within +/-32ps. At the receiver, the phase departure tolerance should be within 2 degrees and the amplitude departure tolerance should be within 10%. Furthermore, it's further found that the electrical part of the transmitter presents a stricter requirement on the IQ balance than the receiver, while the receiver presents a stricter requirement on the IQ balance than the optical part of the transmitter.

  1. Polarization demultiplexing in stokes space for coherent optical PDM-OFDM.

    PubMed

    Yu, Zhenming; Yi, Xingwen; Yang, Qi; Luo, Ming; Zhang, Jing; Chen, Lei; Qiu, Kun

    2013-02-11

    We propose a polarization demultiplexing method for coherent optical PDM-OFDM based on Stokes space, without inserting training symbols. The proposed approach performs well for different modulation formats of OFDM subcarrier, and shows comparable performances with that of conventional methods, but with a fast convergence speed and reduced overhead. The OFDM signal in the time domain cannot satisfy the conditions of SS-PDM accurately. Therefore, we first digitally convert the received OFDM signals to the frequency domain using fast Fourier transform (FFT). Each subcarrier of the OFDM signal has a much lower speed and narrower bandwidth, the polarization effects that it experiences can be treated as flat. Consequently, we can apply the polarization demultiplexing in Stokes space (SS-PDM) on per subcarrier basis. We verify this method in experiment by transmitting 66.6-Gb/s PDM-OFDM signal with 4QAM subcarrier modulation over 5440km SSMF and 133.3-Gb/s PDM-OFDM signal with 16QAM subcarrier modulation over 960km SSMF respectively. We also compare the results with those of training symbols. Finally, we analyze of the convergence speed of this method. PMID:23481844

  2. PAPR Reduction for PCC-OFDM Systems Using Neural Phase Rotator

    NASA Astrophysics Data System (ADS)

    Ohta, Masaya; Yamada, Hideyuki; Yamashita, Katsumi

    This paper proposes a novel Orthogonal frequency-division multiplexing (OFDM) system based on polynomial cancellation coded OFDM (PCC-OFDM). This proposed system can reduce peak-to-average power ratio (PAPR) by our neural phase rotator and it does not need any side information to transmit phase rotation factors. Moreover, this system can compensate the common phase error (CPE) by a proposed technique which allows estimating frequency offset at receiver. From numerical experiments, it is shown that our system can reduce PAPR and ICI at the same time and improve BER performance effectively.

  3. Power-efficient method for IM-DD optical transmission of multiple OFDM signals.

    PubMed

    Effenberger, Frank; Liu, Xiang

    2015-05-18

    We propose a power-efficient method for transmitting multiple frequency-division multiplexed (FDM) orthogonal frequency-division multiplexing (OFDM) signals in intensity-modulation direct-detection (IM-DD) optical systems. This method is based on quadratic soft clipping in combination with odd-only channel mapping. We show, both analytically and experimentally, that the proposed approach is capable of improving the power efficiency by about 3 dB as compared to conventional FDM OFDM signals under practical bias conditions, making it a viable solution in applications such as optical fiber-wireless integrated systems where both IM-DD optical transmission and OFDM signaling are important. PMID:26074605

  4. Reconfigurable cognitive transceiver for opportunistic networks

    NASA Astrophysics Data System (ADS)

    Maso, Marco; Baştuğ, Ejder; Cardoso, Leonardo S.; Debbah, Mérouane; Özdemir, Özgür

    2014-12-01

    In this work, we provide the implementation and analysis of a cognitive transceiver for opportunistic networks. We focus on a previously introduced dynamic spectrum access (DSA) - cognitive radio (CR) solution for primary-secondary coexistence in opportunistic orthogonal frequency division multiplexing (OFDM) networks, called cognitive interference alignment (CIA). The implementation is based on software-defined radio (SDR) and uses GNU Radio and the universal software radio peripheral (USRP) as the implementation toolkit. The proposed flexible transceiver architecture allows efficient on-the-fly reconfigurations of the physical layer into OFDM, CIA or a combination of both. Remarkably, its responsiveness is such that the uplink and downlink channel reciprocity from the medium perspective, inherent to time division duplex (TDD) communications, can be effectively verified and exploited. We show that CIA provides approximately 10 dB of interference isolation towards the OFDM receiver with respect to a fully random precoder. This result is obtained under suboptimal conditions, which indicates that further gains are possible with a better optimization of the system. Our findings point towards the usefulness of a practical CIA implementation, as it yields a non-negligible performance for the secondary system, while providing interference shielding to the primary receiver.

  5. Remote heterodyne millimeter-wave over fiber based OFDM-PON with master-to-slave injected dual-mode colorless FPLD pair.

    PubMed

    Chen, Hsiang-Yu; Chi, Yu-Chieh; Lin, Gong-Ru

    2015-08-24

    A remote heterodyne millimeter-wave (MMW) carrier at 47.7 GHz over fiber synthesized with the master-to-slave injected dual-mode colorless FPLD pair is proposed, which enables the future connection between the wired fiber-optic 64-QAM OFDM-PON at 24 Gb/s with the MMW 4-QAM OFDM wireless network at 2 Gb/s. Both the single- and dual-mode master-to-slave injection-locked colorless FPLD pairs are compared to optimize the proposed 64-QAM OFDM-PON. For the unamplified single-mode master, the slave colorless FPLD successfully performs the 64-QAM OFDM data at 24 Gb/s with EVM, SNR and BER of 8.5%, 21.5 dB and 2.9 × 10(-3), respectively. In contrast, the dual-mode master-to-slave injection-locked colorless FPLD pair with amplified and unfiltered master can transmit 64-QAM OFDM data at 18 Gb/s over 25-km SMF to provide EVM, SNR and BER of 8.2%, 21.8 dB and 2.2 × 10(-3), respectively. For the dual-mode master-to-slave injection-locked colorless FPLD pair, even though the modal dispersion occurred during 25-km SMF transmission makes it sacrifice the usable OFDM bandwidth by only 1 GHz, which guarantees the sufficient encoding bitrate for the optically generated MMW carrier to implement the fusion of MMW wireless LAN and DWDM-PON with cost-effective and compact architecture. As a result, the 47.7-GHz MMW carrier remotely beat from the dual-mode master-to-slave injection-locked colorless FPLD pair exhibits an extremely narrow bandwidth of only 0.48 MHz. After frequency down-conversion operation, the 47.7-GHz MMW carrier successfully delivers 4-QAM OFDM data up to 2 Gb/s with EVM, SNR and BER of 33.5%, 9.51 dB and 1.4 × 10(-3), respectively. PMID:26368237

  6. Software defined radio based multi-carrier multi-function waveform for cognitive radio

    NASA Astrophysics Data System (ADS)

    Zhou, Ruolin; Li, Xue; Chakravarthy, Vasu; Wu, Zhiqiang

    2010-04-01

    In this paper, we demonstrate an adaptive multicarrier multi-function waveform generator for cognitive radio via software defined radio. Using a USRP (universal software radio peripheral) software defined radio boards and GNU radio software, we implement a multi-carrier waveform generator which can generate multi-function waveforms such as OFDM, NC-OFDM, MC-CDMA, NC-MC-CDMA, CI/MC-CDMA, NCCI/ MC-CDMA, TDCS for cognitive radio. Additionally, we demonstrate a portable overlay cognitive radio using this multicarrier multi-function waveform generator. This cognitive radio is capable of detecting primary users in real time and adaptively adjusting its transmission parameters to avoid interference to primary users. More importantly, this cognitive radio can take advantage of multiple spectrum holes by employing non-contiguous multi-carrier transmission technologies. Additionally, we demonstrate that when the primary user transmission changes, the cognitive radio dynamically adjusts its transmission accordingly. We also demonstrate seamless real time video transmission between two cognitive radio nodes, while avoiding interference from primary users and interference to primary users operating in the same spectrum.

  7. Experimental Evaluation of Time Diversity Effect in Hybrid ARQ Considering Space and Path Diversity for Downlink OFDM-Based Broadband Radio Access

    NASA Astrophysics Data System (ADS)

    Miki, Nobuhiko; Atarashi, Hiroyuki; Higuchi, Kenichi; Sawahashi, Mamoru; Nakagawa, Masao

    This paper presents experimental evaluations of the effect of time diversity obtained by hybrid automatic repeat request (HARQ) with soft combining in space and path diversity schemes on orthogonal frequency division multiplexing (OFDM)-based packet radio access in a downlink broadband multipath fading channel. The effect of HARQ is analyzed through laboratory experiments employing fading simulators and field experiments conducted in downtown Yokosuka near Tokyo. After confirming the validity of experimental results based on numerical analysis of the time diversity gain in HARQ, we show by the experimental results that, for a fixed modulation and channel coding scheme (MCS), time diversity obtained by HARQ is effective in reducing the required received signal-to-interference plus noise power ratio (SINR) according to an increase in the number of transmissions, K, up to 10, even when the diversity effects are obtained through two-branch antenna diversity reception and path diversity using a number of multipaths greater than 12 observed in a real fading channel. Meanwhile, in combined use with the adaptive modulation and channel coding (AMC) scheme associated with space and path diversity, we clarify that the gain obtained by time diversity is almost saturated at the maximum number of transmissions in HARQ, K' = 4 in Chase combining and K' = 2 in Incremental redundancy, since the improvement in the residual packet error rate (PER) obtained through time diversity becomes small owing to the low PER in the initial packet transmission arising from appropriately selecting the optimum MCS in AMC. However, the experimental results elucidate that the time diversity in HARQ with soft combining associated with antenna diversity reception is effective in improving the throughput even in a broadband multipath channel with sufficient path diversity.

  8. Performance improvement of OFDM-FSO multi-user communication system with combined transmit frequency diversity and receive space diversity

    NASA Astrophysics Data System (ADS)

    Kumar, Pravindra; Srivastava, Anand

    2016-05-01

    Orthogonal frequency division multiplexed (OFDM) based free space optical (FSO) communication link gives improved performance because of narrow-band interference, improved robustness against fading and high bandwidth efficiency. It is further improved using transmit frequency diversity and space diversity at the receiver. In this paper, we propose to use OFDM architecture combined with spreading code in electrical domain, referred as code division multiplexed-orthogonal frequency division multiplexing (CDM-OFDM) which provides frequency diversity at the transmitter and using more than one receiver to get receive diversity. Analytical model of CDM-OFDM-FSO communication system with photo-detector space diversity using maximal ratio combining (MRC) is analyzed in the presence of turbulent atmosphere, multi-user-interference (MUI) and timing jitter. The error performance is computed in terms of receiver sensitivity and bit-error-rate (BER). In the analysis, Gamma-Gamma distribution is considered for atmospheric turbulence. The performance of OFDM-FSO link and CDM-OFDM-FSO link is compared. It is seen that for multiple users, CDM-OFDM-FSO link with transmit and receive diversity gives improved performance as compared to OFDM-FSO link.

  9. W-band OFDM photonic vector signal generation employing a single Mach-Zehnder modulator and precoding.

    PubMed

    Xiao, Jiangnan; Li, Xinying; Xu, Yuming; Zhang, Ziran; Chen, Long; Yu, Jianjun

    2015-09-01

    We present a simple radio-over-fiber (RoF) link architecture for millimeter-wave orthogonal frequency division multiplexing (OFDM) transmission using only one Mach-Zehnder modulator (MZM) and precoding technique. In the transmission system, the amplitudes and the phase of the driving radio-frequency (RF) OFDM signal on each sub-carrier are precoded, to ensure that the OFDM signal after photodetector (PD) can be restored to original OFDM signal. The experimental results show that the bit-error ratios (BERs) of the transmission system are less than the forward-error-correction (FEC) threshold of 3.8 × 10(-3), which demonstrates that the generation of OFDM vector signal based on our proposed scheme can be employed in our system architecture. PMID:26368494

  10. OFDM and PAM comparison using a high baudrate low resolution IM/DD interface for 400G Ethernet access.

    PubMed

    André, Nuno Sequeira; Louchet, Hadrien; Filsinger, Volker; Hansen, Erik; Richter, André

    2016-05-30

    We compare OFDM and PAM for 400G Ethernet based on a 3-bit high baudrate IM/DD interface at 1550nm. We demonstrate 27Gb/s and 32Gb/s transmission over 10km SSMF using OFDM and PAM respectively. We show that capacity can be improved through adaptation/equalization to achieve 42Gb/s and 64Gb/s for OFDM and PAM respectively. Experimental results are used to create realistic simulations to extrapolate the performance of both modulation formats under varied conditions. For the considered interface we found that PAM has the best performance, OFDM is impaired by quantization noise. When the resolution limitation is relaxed, OFDM shows better performance. PMID:27410115

  11. Fast dispersion estimation in coherent optical 16QAM fast OFDM systems.

    PubMed

    Zhao, J; Shams, H

    2013-01-28

    Fast channel estimation is crucial to increase the payload efficiency which is of particular importance for optical packet networks. In this paper, we propose a novel least-square based dispersion estimation method in coherent optical fast OFDM (F-OFDM) systems. Additionally, we experimentally demonstrate for the first time a 37.5 Gb/s 16QAM coherent F-OFDM system with 480 km transmission using the proposed scheme. The results show that this method outperforms the conventional channel estimation methods in minimizing the overhead load. A single training symbol can achieve near-optimum channel estimation without any prior information of the transmission distance. This makes optical F-OFDM a very promising scheme for the future burst-mode applications. PMID:23389231

  12. Behavioral, Cognitive, or Brain-Based Training?

    ERIC Educational Resources Information Center

    Whitmore, Paul G.

    2004-01-01

    Most trainers believe there are just two scientific approaches on which to base a training technology: behavioral psychology and cognitive psychology. There is a third scientific approach currently emerging that does deal with every kind of skill, and it comes from biology rather than psychology. This new approach is based on findings from…

  13. 4.8 Gbit/s 16-QAM-OFDM transmission based on compact 450-nm laser for underwater wireless optical communication.

    PubMed

    Oubei, Hassan M; Duran, Jose R; Janjua, Bilal; Wang, Huai-Yung; Tsai, Cheng-Ting; Chi, Yu-Cheih; Ng, Tien Khee; Kuo, Hao-Chung; He, Jr-Hau; Alouini, Mohamed-Slim; Lin, Gong-Ru; Ooi, Boon S

    2015-09-01

    We experimentally demonstrate an underwater wireless optical communications (UWOC) employing 450-nm TO-9 packaged and fiber-pigtailed laser diode (LD) directly encoded with an orthogonal frequency division multiplexed quadrature amplitude modulation (QAM-OFDM) data. A record data rate of up to 4.8 Gbit/s over 5.4-m transmission distance is achieved. By encoding the full 1.2-GHz bandwidth of the 450-nm LD with a 16-QAM-OFDM data, an error vector magnitude (EVM) of 16.5%, a signal-to-noise ratio (SNR) of 15.63 dB and a bit error rate (BER) of 2.6 × 10(-3), well pass the forward error correction (FEC) criterion, were obtained. PMID:26368431

  14. Web-Based Programs Assess Cognitive Fitness

    NASA Technical Reports Server (NTRS)

    2009-01-01

    The National Space Biomedical Research Institute, based in Houston and funded by NASA, began funding research for Harvard University researchers to design Palm software to help astronauts monitor and assess their cognitive functioning. The MiniCog Rapid Assessment Battery (MRAB) was licensed by the Criteria Corporation in Los Angeles and adapted for Web-based employment testing. The test battery assesses nine different cognitive functions and can gauge the effect of stress-related deficits, such as fatigue, on various tasks. The MRAB can be used not only for pre-employment testing but also for repeat administrations to measure day-to-day job readiness in professions where alertness is critical.

  15. Frequency interleaving towards spectrally efficient directly detected optical OFDM for next-generation optical access networks.

    PubMed

    Mehedy, Lenin; Bakaul, Masuduzzaman; Nirmalathas, Ampalavanapillai

    2010-10-25

    In this paper, we theoretically analyze and demonstrate that spectral efficiency of a conventional direct detection based optical OFDM system (DDO-OFDM) can be improved significantly using frequency interleaving of adjacent DDO-OFDM channels where OFDM signal band of one channel occupies the spectral gap of other channel and vice versa. We show that, at optimum operating condition, the proposed technique can effectively improve the spectral efficiency of the conventional DDO-OFDM system as much as 50%. We also show that such a frequency interleaved DDO-OFDM system, with a bit rate of 48 Gb/s within 25 GHz bandwidth, achieves sufficient power budget after transmission over 25 km single mode fiber to be used in next-generation time-division-multiplexed passive optical networks (TDM-PON). Moreover, by applying 64- quadrature amplitude modulation (QAM), the system can be further scaled up to 96 Gb/s with a power budget sufficient for 1:16 split TDM-PON. PMID:21164657

  16. Performance analysis of a finite radon transform in OFDM system under different channel models

    SciTech Connect

    Dawood, Sameer A.; Anuar, M. S.; Fayadh, Rashid A.; Malek, F.; Abdullah, Farrah Salwani

    2015-05-15

    In this paper, a class of discrete Radon transforms namely Finite Radon Transform (FRAT) was proposed as a modulation technique in the realization of Orthogonal Frequency Division Multiplexing (OFDM). The proposed FRAT operates as a data mapper in the OFDM transceiver instead of the conventional phase shift mapping and quadrature amplitude mapping that are usually used with the standard OFDM based on Fast Fourier Transform (FFT), by the way that ensure increasing the orthogonality of the system. The Fourier domain approach was found here to be the more suitable way for obtaining the forward and inverse FRAT. This structure resulted in a more suitable realization of conventional FFT- OFDM. It was shown that this application increases the orthogonality significantly in this case due to the use of Inverse Fast Fourier Transform (IFFT) twice, namely, in the data mapping and in the sub-carrier modulation also due to the use of an efficient algorithm in determining the FRAT coefficients called the optimal ordering method. The proposed approach was tested and compared with conventional OFDM, for additive white Gaussian noise (AWGN) channel, flat fading channel, and multi-path frequency selective fading channel. The obtained results showed that the proposed system has improved the bit error rate (BER) performance by reducing inter-symbol interference (ISI) and inter-carrier interference (ICI), comparing with conventional OFDM system.

  17. A P300-based cognitive assessment battery

    PubMed Central

    Kirschner, Aaron; Cruse, Damian; Chennu, Srivas; Owen, Adrian M; Hampshire, Adam

    2015-01-01

    Background It is well established that some patients who are diagnosed as being in a vegetative state or a minimally conscious state show reliable signs of volition that may only be detected by measuring neural responses. A pertinent question is whether these patients are capable of higher cognitive processes. Methods Here, we develop a series of EEG paradigms that probe several core aspects of cognition at the bedside without the need for motor responses and explore the sensitivity of this approach in a group of healthy controls. Results Using analysis of ERPs alone, this method can determine with high reliability whether individual participants are able to attend a stimulus stream, maintain items in working memory, or solve complex grammatical reasoning problems. Conclusion We suggest that this approach could form the basis of a brain-based battery for assessing higher cognition in patients with severe motor impairments or disorders of consciousness. PMID:26085962

  18. PAPR Reduction with Low Computational Complexity for OFDM Systems

    NASA Astrophysics Data System (ADS)

    gao, Jing; Wang, Jinkuan; Song, Xin; Wang, Bin

    The partial transmit sequence (PTS) technique has received much attention in reducing the high peak to average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals, but its exhaustive search of phase factors causes high computational complexity. To solve this problem, a novel method based on optimization algorithm is proposed to reduce the complexity by searching the weighting factors suboptimally. The simulation results show that the proposed algorithm can not only reduces the PAPR significantly, but also decreases the computational complexity.

  19. A collaborative knowledge base for cognitive phenomics

    PubMed Central

    Sabb, FW; Bearden, CE; Glahn, DC; Parker, DS; Freimer, N; Bilder, RM

    2014-01-01

    The human genome project has stimulated development of impressive repositories of biological knowledge at the genomic level and new knowledge bases are rapidly being developed in a ‘bottom-up’ fashion. In contrast, higher-level phenomics knowledge bases are underdeveloped, particularly with respect to the complex neuropsychiatric syndrome, symptom, cognitive, and neural systems phenotypes widely acknowledged as critical to advance molecular psychiatry research. This gap limits informatics strategies that could improve both the mining and representation of relevant knowledge, and help prioritize phenotypes for new research. Most existing structured knowledge bases also engage a limited set of contributors, and thus fail to leverage recent developments in social collaborative knowledge-building. We developed a collaborative annotation database to enable representation and sharing of empirical information about phenotypes important to neuropsychiatric research (www.Phenowiki.org). As a proof of concept, we focused on findings relevant to ‘cognitive control’, a neurocognitive construct considered important to multiple neuropsychiatric syndromes. Currently this knowledge base tabulates empirical findings about heritabilities and measurement properties of specific cognitive task and rating scale indicators (n = 449 observations). It is hoped that this new open resource can serve as a starting point that enables broadly collaborative knowledge-building, and help investigators select and prioritize endophenotypes for translational research. PMID:18180765

  20. [MINDFULNESS-BASED COGNITIVE THERAPY (MBCT) AND THE "THIRD WAVE" OF COGNITIVE-BEHAVIORAL THERAPIES (CBT)].

    PubMed

    Garay, Cristian Javier; Korman, Guido Pablo; Keegan, Eduardo Gustavo

    2015-01-01

    The paper presents the reasons that led to the incorporation of mindfulness as part of a cognitive therapy approach to the prevention of relapse of recurrent depressive disorders. It describes the context in which models focused on the contents of cognition gave way to models focused on cognitive processes. We highlight the problems encountered by the standard cognitive model when trying to account for the cognitive vulnerability of individuals who, having experienced a depressive episode, are in remission. We briefly describe the theoretical foundations of Mindfulness-Based Cognitive Therapy and its therapeutic approach. PMID:26323114

  1. Energy-efficient WDM-OFDM-PON employing shared OFDM modulation modules in optical line terminal.

    PubMed

    Hu, Xiaofeng; Zhang, Liang; Cao, Pan; Wang, Kongtao; Su, Yikai

    2012-03-26

    We propose and experimentally demonstrate a scheme to improve the energy efficiency of wavelength division multiplexing - orthogonal frequency division multiplexing - passive optical networks (WDM-OFDM-PONs). By using an N × M opto-mechanic switch in optical line terminal (OLT), an OFDM modulation module is shared by several channels to deliver data to multiple users with low traffic demands during non-peak hours of the day, thus greatly reducing the number of operating devices and minimizing the energy consumption of the OLT. An experiment utilizing one OFDM modulation module to serve three optical network units (ONUs) in a WDM-OFDM-PON is performed to verify the feasibility of our proposal. Theoretical analysis and numerical calculation show that the proposed scheme can achieve a saving of 23.6% in the energy consumption of the OFDM modulation modules compared to conventional WDM-OFDM-PON. PMID:22453478

  2. On-chip all-optical wavelength conversion of multicarrier, multilevel modulation (OFDM m-QAM) signals using a silicon waveguide.

    PubMed

    Li, Chao; Gui, Chengcheng; Xiao, Xi; Yang, Qi; Yu, Shaohua; Wang, Jian

    2014-08-01

    We report on-chip all-optical wavelength conversion of multicarrier multilevel modulation signals in a silicon waveguide. Using orthogonal frequency-division multiplexing (OFDM) combined with advanced multilevel quadrature amplitude modulation (QAM) signals (i.e., OFDM m-QAM), we experimentally demonstrate all-optical wavelength conversions of 3.2 Gbaud/s OFDM 16/32/64/128-QAM signals based on the degenerate four-wave mixing (FWM) nonlinear effect in a silicon waveguide. The measured optical signal-to-noise ratio (OSNR) penalties of wavelength conversion are ∼3  dB for OFDM 16-QAM and ∼4  dB for OFDM 32-QAM at 7% forward error correction (FEC) threshold and ∼3.5  dB for OFDM 64-QAM and ∼4.5  dB for OFDM 128-QAM at 20% FEC threshold. The observed clear constellations of converted idlers imply favorable performance obtained for silicon-waveguide-based OFDM 16/32/64/128-QAM wavelength conversions. PMID:25078234

  3. OFDM Radar Space-Time Adaptive Processing by Exploiting Spatio-Temporal Sparsity

    SciTech Connect

    Sen, Satyabrata

    2013-01-01

    We propose a sparsity-based space-time adaptive processing (STAP) algorithm to detect a slowly-moving target using an orthogonal frequency division multiplexing (OFDM) radar. We observe that the target and interference spectra are inherently sparse in the spatio-temporal domain. Hence, we exploit that sparsity to develop an efficient STAP technique that utilizes considerably lesser number of secondary data and produces an equivalent performance as the other existing STAP techniques. In addition, the use of an OFDM signal increases the frequency diversity of our system, as different scattering centers of a target resonate at different frequencies, and thus improves the target detectability. First, we formulate a realistic sparse-measurement model for an OFDM radar considering both the clutter and jammer as the interfering sources. Then, we apply a residual sparse-recovery technique based on the LASSO estimator to estimate the target and interference covariance matrices, and subsequently compute the optimal STAP-filter weights. Our numerical results demonstrate a comparative performance analysis of the proposed sparse-STAP algorithm with four other existing STAP methods. Furthermore, we discover that the OFDM-STAP filter-weights are adaptable to the frequency-variabilities of the target and interference responses, in addition to the spatio-temporal variabilities. Hence, by better utilizing the frequency variabilities, we propose an adaptive OFDM-waveform design technique, and consequently gain a significant amount of STAP-performance improvement.

  4. Direct-detection optical OFDM superchannel for long-reach PON using pilot regeneration.

    PubMed

    Hu, Rong; Yang, Qi; Xiao, Xiao; Gui, Tao; Li, Zhaohui; Luo, Ming; Yu, Shaohua; You, Shanhong

    2013-11-01

    We demonstrate a novel long-reach PON downstream scheme based on the regenerated pilot assisted direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) superchannel transmission. We use the optical comb source to form DDO-OFDM superchannel, and reserve the center carrier as a seed pilot. The seed pilot is further tracked and reused to generate multiple optical carriers at the local exchange. Each regenerated pilot carrier is selected to beat with an adjacent OFDM sub-band at ONU, so that the electrical bandwidth limitation can be much released compared to the conventional DDO-OFDM superchannel detection. With the proposed proof-of-concept architecture, we experimentally demonstrated a 116.7 Gb/s superchannel OFDM-PON system with transmission reach of 100 km, and 1:64 splitting ratio. We analyze the impact of carrier-to-sideband power ratio (CSPR) on system performance. The experiment result shows that, 5 dB power margin is still remained at ONU using such technique. PMID:24216872

  5. Channel Equalization and Phase Estimation for Reduced-Guard-Interval CO-OFDM Systems

    NASA Astrophysics Data System (ADS)

    Zhuge, Qunbi

    Reduced-guard-interval (RGI) coherent optical (CO) orthogonal frequency-division multiplexing (OFDM) is a potential candidate for next generation 100G beyond optical transports, attributed to its advantages such as high spectral efficiency and high tolerance to optical channel impairments. First of all, we review the coherent optical systems with an emphasis on CO-OFDM systems as well as the optical channel impairments and the general digital signal processing techniques to combat them. This work focuses on the channel equalization and phase estimation of RGI CO-OFDM systems. We first propose a novel equalization scheme based on the equalization structure of RGI CO-OFDM to reduce the cyclic prefix overhead to zero. Then we show that intra-channel nonlinearities should be considered when designing the training symbols for channel estimation. Afterwards, we propose and analyze the phenomenon of dispersion-enhanced phase noise (DEPN) caused by the interaction between the laser phase noise and the chromatic dispersion in RGI CO-OFDM transmissions. DEPN induces a non-negligible performance degradation and limits the tolerant laser linewidth. However, it can be compensated by the grouped maximum-likelihood phase estimation proposed in this work.

  6. Dispersion tolerance enhancement using an improved offset-QAM OFDM scheme.

    PubMed

    Zhao, Jian; Townsend, Paul D

    2015-06-29

    Discrete-Fourier transform (DFT) based offset quadrature amplitude modulation (offset-QAM) orthogonal frequency division multiplexing (OFDM) without cyclic prefix (CP) was shown to offer a dispersion tolerance the same as that of conventional OFDM with ~20% CP overhead. In this paper, we analytically study the fundamental mechanism limiting the dispersion tolerance of this conventional scheme. It is found that the signal and the crosstalk from adjacent subcarriers, which are orthogonal with π/2 phase difference at back to back, can be in-phase when the dispersion increases to a certain value. We propose a novel scheme to overcome this limitation and significantly improve the dispersion tolerance to that of one subcarrier. Simulations show that the proposed scheme can support a 224-Gb/s polarization-division-multiplexed offset-4QAM OFDM signal over 160,000 ps/nm without any CP under 128 subcarriers, and this tolerance scales with the square of the number of subcarriers. It is also shown that this scheme exhibits advantages of greatly enhanced spectral efficiency, larger dispersion tolerance, and/or reduced complexity compared to the conventional CP-OFDM and reduced-guard-interval OFDM using frequency domain equalization. PMID:26191771

  7. Dual-drive LiNbO3 interferometric Mach-Zehnder architecture with extended linear regime for high peak-to-average OFDM-based communication systems.

    PubMed

    Morant, Maria; Llorente, Roberto; Hauden, Jerome; Quinlan, Terence; Mottet, Alexandre; Walker, Stuart

    2011-12-12

    A dual-drive LiNbO(3) architecture modulator with chirp management is proposed and developed offering SFDR > 25 dB in a 1.4 V bias excursion compared to only 0.5 V bias excursion in a conventional Mach-Zehnder electro-optical modulator (MZ-EOM). The architecture effectively extends the linear regime and enables the optical transmission of wireless systems employing orthogonal division multiplexing (OFDM) modulation such as ultra-wide band (UWB) which require high linearity over a broad frequency range due to their high peak-to-average power ratio (PARP). Radio-over-fiber UWB transmission in a passive optical network is experimentally demonstrated employing this technique, exhibiting an enhancement of 2.2 dB in EVM after 57 km SSMF when the dual-drive developed modulator is employed. PMID:22274055

  8. Physical-layer network coding in coherent optical OFDM systems.

    PubMed

    Guan, Xun; Chan, Chun-Kit

    2015-04-20

    We present the first experimental demonstration and characterization of the application of optical physical-layer network coding in coherent optical OFDM systems. It combines two optical OFDM frames to share the same link so as to enhance system throughput, while individual OFDM frames can be recovered with digital signal processing at the destined node. PMID:25969046

  9. Low PMEPR OFDM Radar Waveform Design Using the Iterative Least Squares Algorithm

    NASA Astrophysics Data System (ADS)

    Huang, Tianyao; Zhao, Tong

    2015-11-01

    This letter considers waveform design of orthogonal frequency division multiplexing (OFDM) signal for radar applications, and aims at mitigating the envelope fluctuation in OFDM. A novel method is proposed to reduce the peak-to-mean envelope power ratio (PMEPR), which is commonly used to evaluate the fluctuation. The proposed method is based on the tone reservation approach, in which some bits or subcarriers of OFDM are allocated for decreasing PMEPR. We introduce the coefficient of variation of envelopes (CVE) as the cost function for waveform optimization, and develop an iterative least squares algorithm. Minimizing CVE leads to distinct PMEPR reduction, and it is guaranteed that the cost function monotonically decreases by applying the iterative algorithm. Simulations demonstrate that the envelope is significantly smoothed by the proposed method.

  10. Grouped DCT precoding for PAPR reduction in optical direct detection OFDM systems

    NASA Astrophysics Data System (ADS)

    Wang, Zhong-peng; Zhang, Shao-zhong

    2013-05-01

    A new grouped precoding technique based on discrete cosine transform (DCT) is presented for peak to average power ratio (PAPR) reduction of optical intensity modulated/direct detection (IM/DD) orthogonal frequency division multiplexing (OFDM) system. The computational complexity of the scheme is reduced by at least about 15% compared with that of the ordinary DCT precoding scheme when the number of groups is 2. The PAPR with this method can be reduced by about 0.8 dB. Meantime, compared with original OFDM, the bit error rate (BER) performance of system is improved. So the proposed scheme for reducing PAPR is very effective in optical IM/DD OFDM systems.

  11. Adaptive OFDM waveform design for spatio-temporal-sparsity exploited STAP radar

    NASA Astrophysics Data System (ADS)

    Sen, Satyabrata; Barhen, Jacob

    2015-05-01

    We propose a sparsity-based space-time adaptive processing (STAP) algorithm to detect a slowly-moving target using an orthogonal frequency division multiplexing (OFDM) radar. The motivation of employing an OFDM signal is that it improves the target-detectability from the interfering signals by increasing the frequency diversity of the system. However, due to the addition of one extra dimension in terms of frequency, the adaptive degrees-of- freedom in an OFDM-STAP also increases. Therefore, to avoid the construction a fully-adaptive OFDM-STAP, we propose a sparsity-based STAP algorithm. We observe that the interference spectrum is inherently sparse in the spatio-temporal domain, as the clutter responses occupy only a diagonal ridge on the spatio-temporal plane and the jammer signals interfere only from a few spatial directions. Hence, we exploit that sparsity to develop an efficient STAP technique that utilizes considerably lesser number of secondary data compared to the other existing STAP techniques, and produces nearly optimum STAP performance. In addition to designing the STAP filter, we propose to optimally design the transmit OFDM signals by maximizing the output signal- to-interference-plus-noise ratio (SINR) in order to improve the STAP-performance. The computation of output SINR depends on the estimated value of the interference covariance matrix, which we obtain by applying the sparse recovery algorithm. Therefore, we analytically assess the effects of the synthesized OFDM coefficients on the sparse recovery of the interference covariance matrix by computing the coherence measure of the sparse measurement matrix. Our numerical examples demonstrate the achieved STAP-performance due to sparsity- based technique and adaptive waveform design.

  12. Proposal of DCS-OFDM-PON upstream transmission with intensity modulator and collective self-coherent detection

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Yang, Heming; Zhao, Difu; Qiu, Kun

    2016-07-01

    We introduce digital coherent superposition (DCS) into optical access network and propose a DCS-OFDM-PON upstream transmission scheme using intensity modulator and collective self-coherent detection. The generated OFDM signal is real based on Hermitian symmetry, which can be used to estimate the common phase error (CPE) by complex conjugate subcarrier pairs without any pilots. In simulation, we transmit an aggregated 40 Gb/s optical OFDM signal from two ONUs. The transmission performance with DCS is slightly better after 25 km transmission without relative transmission time delay. The fiber distance for different ONUs to RN are not same in general and there is relative transmission time delay between ONUs, which causes inter-carrier-interference (ICI) power increasing and degrades the transmission performance. The DCS can mitigate the ICI power and the DCS-OFDM-PON upstream transmission outperforms the conventional OFDM-PON. The CPE estimation is by using two pairs of complex conjugate subcarriers without redundancy. The power variation can be 9 dB in DCS-OFDM-PON, which is enough to tolerate several kilometers fiber length difference between the ONUs.

  13. Cognitive fusion analysis based on context

    NASA Astrophysics Data System (ADS)

    Blasch, Erik P.; Plano, Susan

    2004-04-01

    The standard fusion model includes active and passive user interaction in level 5 - "User Refinement". User refinement is more than just details of passive automation partitioning - it is the active management of information. While a fusion system can explore many operational conditions over myopic changes, the user has the ability to reason about the hyperopic "big picture." Blasch and Plano developed cognitive-fusion models that address user constraints including: intent, attention, trust, workload, and throughput to facilitate hyperopic analysis. To enhance user-fusion performance modeling (i.e. confidence, timeliness, and accuracy); we seek to explore the nature of context. Context, the interrelated conditions of which something exists, can be modeled in many ways including geographic, sensor, object, and environmental conditioning. This paper highlights user refinement actions based on context to constrain the fusion analysis for accurately representing the trade space in the real world. As an example, we explore a target identification task in which contextual information from the user"s cognitive model is imparted to a fusion belief filter.

  14. Physical layer security in CO-OFDM transmission system using chaotic scrambling

    NASA Astrophysics Data System (ADS)

    Liu, Bo; Zhang, Lijia; Xin, Xiangjun; Yu, Jianjun

    2013-03-01

    This paper proposes a novel method for the optical OFDM system to improve the physical layer security based on chaotic scrambling. The 1-D Logistic map is adopted for chaos mapping. The chaotic scrambling algorithm can dynamically change the scrambling matrices according to the secure key, which further enhances the confidentiality of the physical layer. The experiment with Logistic mapped chaos scrambling is also given to demonstrate the efficiency of security algorithm. Meanwhile, the benchmark performance of the optical OFDM system is experimentally investigated in terms of the bit error rate (BER). The analysis indicates that the system can be robust against eavesdropping.

  15. Channel estimation algorithm for interference suppression in IMDD-OQAM-OFDM transmission systems

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Xiao, Shilin; Bi, Meihua; Liu, Ling; Zhou, Zhao

    2016-04-01

    In this paper, we investigate the intrinsic interference caused by intra-symbol data and channel noise in the intensity-modulation direct-detection OQAM-OFDM (IMDD-OQAM-OFDM) system by theoretical derivation. Based on the analysis, we proposed and experimentally demonstrated a channel estimation algorithm with the combination of IAM-C and frequency-averaging method to combat the effect of these noises. Experimental results show that compared to the common channel estimation algorithms, our algorithm can greatly reduce the error vector magnitude (EVM) and achieve ~1.5 dB sensitivity improvement.

  16. First demonstration of OFDM ECDMA for low cost optical access networks.

    PubMed

    Guo, X; Wang, Q; Li, X; Zhou, L; Fang, L; Wonfor, A; Wei, J L; von Lindeiner, J; Penty, R V; White, I H

    2015-05-15

    We demonstrate for the first time to the best of our knowledge an analogue orthogonal frequency division multiplexing (OFDM) based electrical code division multiplexing access (ECDMA) passive optical network (PON) for next generation access applications. Advantages of the system include low cost, high capacity, and enhanced spectral efficiency. A proof-of-principle 16 QAM OFDM ECDMA PON downlink experiment is used to show the transmission of an aggregate data rate of 24.8  Gb/s within an eight-user system. Transmission is achieved over 25 km of single-mode telecommunications fiber (SMF) with negligible dispersion and crosstalk penalties. PMID:26393737

  17. Faith-based cognitive behavioral therapy: easing depression in the elderly with cognitive decline.

    PubMed

    Ceramidas, Dagmar M

    2012-01-01

    Minimizing depression in residential aged care facilities is a formidable challenge but doing so may improve quality of life and protect against dementia. A pilot project with residents with cognitive decline and concurrent depression tested the suitability of a faith-based cognitive behavioral therapy (CBT) intervention in reducing participant levels of depression, offering promising results. PMID:22359836

  18. Improved Peak Cancellation for PAPR Reduction in OFDM Systems

    NASA Astrophysics Data System (ADS)

    Dan, Lilin; Xiao, Yue; Ni, Wei; Li, Shaoqian

    This letter presents an improved peak cancellation (PC) scheme for peak-to-average power ratio (PAPR) reduction in orthogonal frequency division multiplexing (OFDM) systems. The main idea is based on a serial peak cancellation (SPC) mode for alleviating the peak regrowth of the conventional schemes. Based on the SPC mode, two particular algorithms are developed with different tradeoff between PAPR and computational complexity. Simulation shows that the proposed scheme has a better tradeoff among PAPR, complexity and signal distortion than the conventional schemes.

  19. Photonic layer security in fiber-optic networks and optical OFDM transmission

    NASA Astrophysics Data System (ADS)

    Wang, Zhenxing

    Currently the Internet is experiencing an explosive growth in the world. Such growth leads to an increased data transmission rate demand in fiber-optical networks. Optical orthogonal frequency multiplexing (OFDM) is considered as a promising solution to achieve data rate beyond 100Gb/s per wavelength channel. In the meanwhile, because of extensive data transmission and sharing, data security has become an important problem and receives considerable attention in current research literature. This thesis focuses on data security issues at the physical layer of optical networks involving code-division multiple access (CDMA) systems and steganography methods. The thesis also covers several implementation issues in optical OFDM transmission. Optical CDMA is regarded as a good candidate to provide photonic layer security in multi-access channels. In this thesis we provide a systematic analysis of the security performance of incoherent optical CDMA codes. Based on the analysis, we proposed and experimentally demonstrated several methods to improve the security performance of the optical CDMA systems, such as applying all-optical encryption, and code hopping using nonlinear wavelength conversion. Moreover, we demonstrate that the use of wireless CDMA codes in optical systems can enhance the security in one single-user end-to-end optical channel. Optical steganography is another method to provide photonic data security and involves hiding the existence of data transmissions. In the thesis, we demonstrate that an optical steganography channel can exist in phase modulated public channels as well as traditional on-off-keying (OOK) modulated channels, without data synchronization. We also demonstrate an optical steganography system with enhanced security by utilizing temporal phase modulation techniques. Additionally, as one type of an overlay channel, the optical steganography technology can carry the sensor data collected by wireless sensor network on top of public optical

  20. Adaptive Cognitive-Based Selection of Learning Objects

    ERIC Educational Resources Information Center

    Karampiperis, Pythagoras; Lin, Taiyu; Sampson, Demetrios G.; Kinshuk

    2006-01-01

    Adaptive cognitive-based selection is recognized as among the most significant open issues in adaptive web-based learning systems. In order to adaptively select learning resources, the definition of adaptation rules according to the cognitive style or learning preferences of the learners is required. Although some efforts have been reported in…

  1. Computer-Based Cognitive Tools: Description and Design.

    ERIC Educational Resources Information Center

    Kennedy, David; McNaught, Carmel

    With computers, tangible tools are represented by the hardware (e.g., the central processing unit, scanners, and video display unit), while intangible tools are represented by the software. There is a special category of computer-based software tools (CBSTs) that have the potential to mediate cognitive processes--computer-based cognitive tools…

  2. Construct Definition Using Cognitively Based Evidence: A Framework for Practice

    ERIC Educational Resources Information Center

    Ketterlin-Geller, Leanne R.; Yovanoff, Paul; Jung, EunJu; Liu, Kimy; Geller, Josh

    2013-01-01

    In this article, we highlight the need for a precisely defined construct in score-based validation and discuss the contribution of cognitive theories to accurately and comprehensively defining the construct. We propose a framework for integrating cognitively based theoretical and empirical evidence to specify and evaluate the construct. We apply…

  3. Cognition for robot scanner based remote welding

    NASA Astrophysics Data System (ADS)

    Thombansen, U.; Ungers, Michael

    2014-02-01

    The effort for reduced cycle times in manufacturing has supported the development of remote welding systems which use a combination of scanners for beam delivery and robots for scanner positioning. Herein, close coupling of both motions requires a precise command of the robot trajectory and the scanner positioning to end up with a combined beam delivery. Especially the path precision of the robot plays a vital role in this kinematic chain. In this paper, a sensor system is being presented which allows tracking the motion of the laser beam against the work piece. It is based on a camera system which is coaxially connected to the scanner thus observing the relative motion of the laser beam relative to the work piece. The acquired images are processed with computer vision algorithms from the field of motion detection. The suitability of the algorithms is being demonstrated with a motion tracking tool which visualizes the homogeneity of the tracking result. The reported solution adds cognitive capabilities to manufacturing systems for robot scanner based materials processing. It allows evaluation of the relative motion between work piece and the laser beam. Moreover, the system can be used to adapt system programming during set-up of a manufacturing task or to evaluate the functionality of a manufacturing system during production. The presented sensor system will assist in optimizing manufacturing processes.

  4. A novel ECDM-OFDM-PON architecture for next-generation optical access network.

    PubMed

    Zhang, Lijia; Xin, Xiangjun; Liu, Bo; Yu, Jianjun; Zhang, Qi

    2010-08-16

    This paper proposes a novel architecture for next-generation passive optical network (PON) based on electrical code division multiplexing orthogonal frequency division multiplexing (ECDM-OFDM) access. The feasibility of bidirectional transmission with the same wavelength has been experimentally demonstrated under this architecture. An error-free transmission of two PON channels has been successfully demonstrated in the experiment. PMID:20721227

  5. Cognitive mapping based on synthetic vision?

    NASA Astrophysics Data System (ADS)

    Helmetag, Arnd; Halbig, Christian; Kubbat, Wolfgang; Schmidt, Rainer

    1999-07-01

    The analysis of accidents focused our work on the avoidance of 'Controlled Flight Into Terrain' caused by insufficient situation awareness. Analysis of safety concepts led us to the design of the proposed synthetic vision system that will be described. Since most information on these 3D-Displays is shown in a graphical way, it can intuitively be understood by the pilot. What are the new possibilities using SVS enhancing situation awareness? First, detection of ground collision hazard is possible by monitoring a perspective Primary Flight Display. Under the psychological point of view it is based on the perception of expanding objects in the visual flow field. Supported by a Navigation Display a local conflict resolution can be mentally worked out very fast. Secondly, it is possible to follow a 3D flight path visualized as a 'Tunnel in the sky.' This can further be improved by using a flight path prediction. These are the prerequisites for a safe and adequate movement in any kind of spatial environment. However situation awareness requires the ability of navigation and spatial problem solving. Both abilities are based on higher cognitive functions in real as well as in a synthetic environment. In this paper the current training concept will be analyzed. Advantages resulting from the integration of a SVS concerning pilot training will be discussed and necessary requirements in terrain depiction will be pinpointed. Finally a modified Computer Based Training for the familiarization with Salzburg Airport for a SVS equipped aircraft will be presented. It is developed by Darmstadt University of Technology in co-operation with Lufthansa Flight Training.

  6. Cognitive Content Engagement in Content-Based Language Teaching

    ERIC Educational Resources Information Center

    Kong, Stella; Hoare, Philip

    2011-01-01

    This article reports a study of aspects of pedagogy that can bring about students' cognitive engagement with academic content and, thus, use of the academic language in content-based language lessons in three middle schools in Xi'an, China. Two criteria--academic content level and depth of processing--were used to determine cognitive content…

  7. Implementation of orthogonal frequency division multiplexing (OFDM) and advanced signal processing for elastic optical networking in accordance with networking and transmission constraints

    NASA Astrophysics Data System (ADS)

    Johnson, Stanley

    An increasing adoption of digital signal processing (DSP) in optical fiber telecommunication has brought to the fore several interesting DSP enabled modulation formats. One such format is orthogonal frequency division multiplexing (OFDM), which has seen great success in wireless and wired RF applications, and is being actively investigated by several research groups for use in optical fiber telecom. In this dissertation, I present three implementations of OFDM for elastic optical networking and distributed network control. The first is a field programmable gate array (FPGA) based real-time implementation of a version of OFDM conventionally known as intensity modulation and direct detection (IMDD) OFDM. I experimentally demonstrate the ability of this transmission system to dynamically adjust bandwidth and modulation format to meet networking constraints in an automated manner. To the best of my knowledge, this is the first real-time software defined networking (SDN) based control of an OFDM system. In the second OFDM implementation, I experimentally demonstrate a novel OFDM transmission scheme that supports both direct detection and coherent detection receivers simultaneously using the same OFDM transmitter. This interchangeable receiver solution enables a trade-off between bit rate and equipment cost in network deployment and upgrades. I show that the proposed transmission scheme can provide a receiver sensitivity improvement of up to 1.73 dB as compared to IMDD OFDM. I also present two novel polarization analyzer based detection schemes, and study their performance using experiment and simulation. In the third implementation, I present an OFDM pilot-tone based scheme for distributed network control. The first instance of an SDN-based OFDM elastic optical network with pilot-tone assisted distributed control is demonstrated. An improvement in spectral efficiency and a fast reconfiguration time of 30 ms have been achieved in this experiment. Finally, I

  8. PAPR reduction in optical OFDM systems using asymmetrically clipping and signal scrambling technique

    NASA Astrophysics Data System (ADS)

    Chen, Lin; Fang, Yong; Huang, Qinghua; Sun, Yanzan

    2015-08-01

    Optical orthogonal frequency division multiplexing (OOFDM) is a promising technology in the next generation of high-speed and long-haul optical transmission, due to its high spectral efficiency, high speed of data transmission and strong ability of anti-dispersion. But optical OFDM system has a very high peak-to-average power ratio (PAPR). High PAPR will bring instantaneous high optical power to the optical OFDM system. Asymmetrically clipping and signal scrambling based on fast Hartley transform for PAPR reduction is proposed in optical OFDM system. Firstly, IFFT/FFT module in each sub-block of traditional signal scrambling technique is replaced with inverse fast Hartley transform (IFHT) and fast Hartley transform (FHT) module, which yield to the real signal in OOFDM system. Then, asymmetrically clipping technique is applied to turn it into a positive and real signal. Finally, the signal with the minimum PAPR is selected for transmission in the fiber channel. The PAPR of the optical OFDM signal can be reduced effectively. And without the Hermitian symmetry, the space and computational complexity are reduced accordingly.

  9. Optical wireless transmission of 405 nm, 1.45 Gbit/s optical IM/DD-OFDM signals through a 4.8 m underwater channel.

    PubMed

    Nakamura, Kazuhiko; Mizukoshi, Izumi; Hanawa, Masanori

    2015-01-26

    In this paper, we experimentally demonstrate wireless transmission of optical intensity modulation/direct detection-orthogonal frequency division multiplexing (IM/DD-OFDM) signals in an underwater channel using a field programmable gate array based real-time transmitter. The real-time transmission of a 405 nm 1.45 Gbit/s optical OFDM signal through a 4.8 m underwater channel with an error vector magnitude of approximately 10% was successfully achieved. PMID:25835913

  10. Investigation of receiver contraints on the transmission performance of 1 Tbps WDM-Nyquist and CO-OFDM signals

    NASA Astrophysics Data System (ADS)

    Hraghi, Abir; Menif, Mourad

    2015-01-01

    In this paper, we implement an Optical Flat Comb Source generating a coherent super-channel operating at 1 Tbps using Wavelength Division Multiplexing-Nyquist (WDM-Nyquist) and Coherent Optical-Orthogonal Frequency Division Multiplexing (CO-OFDM) approaches with 12.5 GHz channel spacing. We evaluate through simulation the performance of the two techniques for generating Dual Polarization Quadrature-Amplitude Modulation based on 16 (DP-16QAM). We first study the robustness of CO-OFDM system to the receiver constraints such as Analog-to-Digital Converters (ADCs) speed and the receiver bandwidth in Back-to-Back link (Optical Signal-to- Noise Ratio (OSNR)) and over longhaul dispersion compensated links using Standard Single Mode Fiber (SSMF). We find that CO-OFDM requires 6 Samples per Symbol (SpS) with a large receiver bandwidth (2.25× Baud rate) to achieve the same performance of WDM-Nyquist system in terms of SNR. However, the CO-OFDM system needs more than 6 SpS to achieve the same distances as WDM-Nyquist. We also study the impact of the input power level in terms of OSNR for CO-OFDM and WDM-Nyquist systems in order to evaluate the robustness of both systems to the nonlinear effects.

  11. PAPR reduction techniques for asymmetrically clipped optical OFDM communication system

    NASA Astrophysics Data System (ADS)

    Wang, Yong; Zhang, Zhaojun; Sun, Lu

    2014-07-01

    In the ultraviolet communication system, ACO-OFDM technology can effectively suppress inter-symbol interference on the system performance, and further improve the transmission rate of the system. However, ACO-OFDM has a high peak to average power ratio (PAPR), and high PAPR not only reduces the power efficiency of the optical modulator, but also bring damage to the human eye or skin. In order to solve the above problem, according to ACO-OFDM signal characteristics, two clipping and filtering algorithms are used, and its performance is simulated, the simulations show that the two algorithms are able to inhibit well the PAPR of ACO-OFDM system.

  12. Phased-array cancellation of nonlinear FWM in coherent OFDM dispersive multi-span links.

    PubMed

    Nazarathy, Moshe; Khurgin, Jacob; Weidenfeld, Rakefet; Meiman, Yehuda; Cho, Pak; Noe, Reinhold; Shpantzer, Isaac; Karagodsky, Vadim

    2008-09-29

    We develop an analytic model of Coherent Optical Orthogonal Frequency Division Multiplexing (OFDM) propagation and detection over multi-span long-haul fiber links, comprehensively and rigorously analyzing the impairments due the combined effects of FWM, Dispersion and ASE noise. Consistent with prior work of Innoe and Schadt in the WDM context, our new closed-form expressions for the total FWM received power fluctuations in the wake of dispersive phase mismatch in OFDM transmission, indicate that the FWM contributions of the multitude of spans build-up on a phased-array basis. For particular ultra-long haul link designs, the effectiveness of dispersion in reducing FWM is far greater than previously assumed in OFDM system analysis. The key is having the dominant FWM intermodulation products due to the multiple spans, destructively interfere, mutually cancelling their FWM intermodulation products, analogous to operating at the null of a phased-array antenna system. By applying the new analysis tools, this mode of effectively mitigating the FWM impairment, is shown under specific dispersion and spectral management conditions, to substantially suppress the FWM power fluctuations. Accounting for the phased-array concept and applying the compact OFDM design formulas developed here, we analyzed system performance of a 40 Gbps coherent OFDM system, over standard G.652 fiber, with cyclic prefix based electronic dispersion compensation but no optical compensation along the link. The transmission range for 10-3 target BER is almost tripled from 2560 km to 6960 km, relative to a reference system performing optical dispersion compensation in every span (ideally accounting for FWM and ASE noise and the cyclic prefix overhead, but excluding additional impairments). PMID:18825217

  13. Power optimized OSSB modulation to support multi-band OFDM services along hybrid long-reach WDM-PONs

    NASA Astrophysics Data System (ADS)

    Almeida, Paulo; Silva, Henrique

    2015-06-01

    In this paper, optical single sideband (OSSB) transmission of multi-services based on orthogonal frequency division multiplexing (OFDM) with different signal constellations is investigated through numerical simulation, when the modulation efficiency obtained with a dual-electrode Mach-Zehnder modulator (DE-MZM) is optimized by biasing it below its quadrature point. Furthermore, in order to overcome the intermodulation distortion resulting from modulation efficiency optimization, it is demonstrated that driving each electrical signal with a different electrical power is an effective solution for the signals considered. As result of the optimization, successful delivery after 130 km of a hybrid OSSB signal composed by a custom 16-quadrature amplitude modulation (QAM) OFDM gigabit Ethernet (GbE) signal, a 20 MHz 64-QAM LTE signal and three independent OFDM-UWB channels of the first group of ECMA-386 is demonstrated, with negligible power penalty.

  14. Experimental demonstration of novel source-free ONUs in bidirectional RF up-converted optical OFDM-PON utilizing polarization multiplexing.

    PubMed

    Zhang, Chongfu; Chen, Chen; Feng, Yuan; Qiu, Kun

    2012-03-12

    We propose and experimentally demonstrate a novel cost-effective optical orthogonal frequency-division multiplexing-based passive optical network (OFDM-PON) system, wherein all optical network units (ONUs) are source-free not only in the optical domain but also in the electric domain, by utilizing polarization multiplexing (PolMUX) in the downlink transmission. Two pure optical bands with a frequency interval of 10 GHz and downlink up-converted 10 GHz OFDM signal are carried in two orthogonal states of polarization (SOPs), respectively. 10 GHz radio frequency (RF) source can be generated by a heterodyne of two pure optical bands after polarization beam splitting in each ONU, therefore it can be used to down-convert the downlink OFDM signal and up-convert the uplink OFDM signal. In the whole bidirectional up-converted OFDM-PON system, only one single RF source is employed in the optical line terminal (OLT). Experimental results successfully verify the feasibility of our proposed cost-effective optical OFDM-PON system. PMID:22418506

  15. Science Teaching Based on Cognitive Load Theory: Engaged Students, but Cognitive Deficiencies

    ERIC Educational Resources Information Center

    Meissner, Barbara; Bogner, Franz X.

    2012-01-01

    To improve science learning under demanding conditions, we designed an out-of-school lesson in compliance with cognitive load theory (CLT). We extracted student clusters based on individual effectiveness, and compared instructional efficiency, mental effort, and persistence of learning. The present study analyses students' engagement. 50.0% of our…

  16. Iteration SSII cancellation in DD-OFDM PON upstream scheme

    NASA Astrophysics Data System (ADS)

    Ju, Cheng; Liu, Na; Chen, Xue

    2016-04-01

    Iteration interference cancellation algorithm is proposed in direct detection OFDM PON upstream scheme to mitigate subcarrier to subcarrier intermixing interference (SSII) caused by dispersion and square-law photo-detection. The receiver sensitivity is improved by 1 dB in 20-Gbps, 16-QAM OFDM PON upstream experiment after 100-km standard single mode fiber (SSMF) transmission.

  17. Comparisons of spectrally-enhanced asymmetrically-clipped optical OFDM systems.

    PubMed

    Lowery, Arthur James

    2016-02-22

    Asymmetrically clipped optical orthogonal frequency-division multiplexing (ACO-OFDM) is a technique that sacrifices spectral efficiency in order to transmit an orthogonally frequency-division multiplexed signal over a unipolar channel, such as a directly modulated direct-detection fiber or free-space channel. Several methods have been proposed to regain this spectral efficiency, including: asymmetrically clipped DC-biased optical OFDM (ADO-OFDM), enhanced U-OFDM (EU-OFDM), spectral and energy efficient OFDM (SEE-OFDM), Hybrid-ACO-OFDM and Layered-ACO-OFDM. This paper presents simulations up to high-order constellation sizes to show that Layered-ACO-OFDM offers the highest receiver sensitivity for a given optical power at spectral efficiencies above 3 bit/s/Hz. For comparison purposes, white Gaussian noise is added at the receiver, component nonlinearities are not considered, and the fiber is considered to be linear and dispersion-less. The simulations show that LACO-OFDM has a 7-dB sensitivity advantage over DC-biased OFDM (DCO-OFDM) for 1024-QAM at 87.5% of DCO-OFDM's spectral efficiency, at the same bit rate and optical power. This is approximately equivalent to a 4.4-dB advantage at the same spectral efficiency of 87.7% if 896-QAM were to be used for DCO-OFDM. PMID:26907048

  18. Security management based on trust determination in cognitive radio networks

    NASA Astrophysics Data System (ADS)

    Li, Jianwu; Feng, Zebing; Wei, Zhiqing; Feng, Zhiyong; Zhang, Ping

    2014-12-01

    Security has played a major role in cognitive radio networks. Numerous researches have mainly focused on attacking detection based on source localization and detection probability. However, few of them took the penalty of attackers into consideration and neglected how to implement effective punitive measures against attackers. To address this issue, this article proposes a novel penalty mechanism based on cognitive trust value. The main feature of this mechanism has been realized by six functions: authentication, interactive, configuration, trust value collection, storage and update, and punishment. Data fusion center (FC) and cluster heads (CHs) have been put forward as a hierarchical architecture to manage trust value of cognitive users. Misbehaving users would be punished by FC by declining their trust value; thus, guaranteeing network security via distinguishing attack users is of great necessity. Simulation results verify the rationality and effectiveness of our proposed mechanism.

  19. MAGELLAN: A cognitive map-based model of human wayfinding

    PubMed Central

    Manning, Jeremy R.; Lew, Timothy F.; Li, Ningcheng; Sekuler, Robert; Kahana, Michael J.

    2014-01-01

    In an unfamiliar environment, searching for and navigating to a target requires that spatial information be acquired, stored, processed, and retrieved. In a study encompassing all of these processes, participants acted as taxicab drivers who learned to pick up and deliver passengers in a series of small virtual towns. We used data from these experiments to refine and validate MAGELLAN, a cognitive map-based model of spatial learning and wayfinding. MAGELLAN accounts for the shapes of participants’ spatial learning curves, which measure their experience-based improvement in navigational efficiency in unfamiliar environments. The model also predicts the ease (or difficulty) with which different environments are learned and, within a given environment, which landmarks will be easy (or difficult) to localize from memory. Using just two free parameters, MAGELLAN provides a useful account of how participants’ cognitive maps evolve over time with experience, and how participants use the information stored in their cognitive maps to navigate and explore efficiently. PMID:24490847

  20. MAGELLAN: a cognitive map-based model of human wayfinding.

    PubMed

    Manning, Jeremy R; Lew, Timothy F; Li, Ningcheng; Sekuler, Robert; Kahana, Michael J

    2014-06-01

    In an unfamiliar environment, searching for and navigating to a target requires that spatial information be acquired, stored, processed, and retrieved. In a study encompassing all of these processes, participants acted as taxicab drivers who learned to pick up and deliver passengers in a series of small virtual towns. We used data from these experiments to refine and validate MAGELLAN, a cognitive map-based model of spatial learning and wayfinding. MAGELLAN accounts for the shapes of participants' spatial learning curves, which measure their experience-based improvement in navigational efficiency in unfamiliar environments. The model also predicts the ease (or difficulty) with which different environments are learned and, within a given environment, which landmarks will be easy (or difficult) to localize from memory. Using just 2 free parameters, MAGELLAN provides a useful account of how participants' cognitive maps evolve over time with experience, and how participants use the information stored in their cognitive maps to navigate and explore efficiently. PMID:24490847

  1. Power efficient and colorless PON upstream system using asymmetric clipping optical OFDM and TDMA technologies

    NASA Astrophysics Data System (ADS)

    Zhao, Yuan; Qiao, Yaojun; Ji, Yuefeng

    2012-04-01

    Asymmetric clipping optical orthogonal frequency division multiplexing (ACO-OFDM) based time division multiple access (TDMA) Passive Optical Network (PON) upstream transmission architecture is proposed. The system features low power consumption, colorless, and cost effectiveness. Performance and validity of 10 Gb/s upstream transmission are studied and confirmed by simulation. Performance degradation due to interference from rogue Optical Network Unit (ONU) is also studied.

  2. Cognitively automated assembly processes: a simulation based evaluation of performance.

    PubMed

    Mayer, Marcel Ph; Odenthal, Barbara; Faber, Marco; Schlick, Christopher M

    2012-01-01

    The numerical control of an experimental assembly cell with two robots--termed a cognitive control unit (CCU)--is able to simulate human information processing at a rule-based level of cognitive control. To enable the CCU to work on a large range of assembly tasks expected of a human operator, the cognitive architecture SOAR is used. The CCU can plan assembly processes autonomously and react to ad-hoc changes in assembly sequences effectively. Extensive simulation studies have shown that cognitive automation based on SOAR is especially suitable for random parts supply, which reduces planning effort in logistics. Conversely, a disproportional increase in processing time was observed for deterministic parts supply, especially for assemblies containing large numbers of identical parts. In this contribution, the effect of phase-shifts in deterministic part supply is investigated for assemblies containing maximal different parts. It can be shown that the concept of cognitive automation is as well suitable for these planning problems. PMID:22317246

  3. The Effects of Metaphorical Interface on Germane Cognitive Load in Web-Based Instruction

    ERIC Educational Resources Information Center

    Cheon, Jongpil; Grant, Michael M.

    2012-01-01

    The purpose of this study was to examine the effects of a metaphorical interface on germane cognitive load in Web-based instruction. Based on cognitive load theory, germane cognitive load is a cognitive investment for schema construction and automation. A new instrument developed in a previous study was used to measure students' mental activities…

  4. Coherent optical DFT-spread OFDM transmission using orthogonal band multiplexing.

    PubMed

    Yang, Qi; He, Zhixue; Yang, Zhu; Yu, Shaohua; Yi, Xingwen; Shieh, William

    2012-01-30

    Coherent optical OFDM (CO-OFDM) combined with orthogonal band multiplexing provides a scalable and flexible solution for achieving ultra high-speed rate. Among many CO-OFDM implementations, digital Fourier transform spread (DFT-S) CO-OFDM is proposed to mitigate fiber nonlinearity in long-haul transmission. In this paper, we first illustrate the principle of DFT-S OFDM. We then experimentally evaluate the performance of coherent optical DFT-S OFDM in a band-multiplexed transmission system. Compared with conventional clipping methods, DFT-S OFDM can reduce the OFDM peak-to-average power ratio (PAPR) value without suffering from the interference of the neighboring bands. With the benefit of much reduced PAPR, we successfully demonstrate 1.45 Tb/s DFT-S OFDM over 480 km SSMF transmission. PMID:22330476

  5. Proportional Data Rate Fairness Resource Allocation for MIMO-OFDM Multiple Access Channel by Considering the Correlation Effect of Line of Sight and Non Line of Sight Channel Conditions

    NASA Astrophysics Data System (ADS)

    Maung, Sann Maw; Sasase, Iwao

    In the MIMO-OFDM multiple access channel (MIMO-OFDM-MAC) uplink scenario, the base station decides the uplink parameters for multiple users based on channel state information (CSI) from each user in the system. The performance of MIMO-OFDM-MAC systems can be significantly improved by using an adaptive transmission and resource allocation schemes which consider the correlation effect of line of sight (LOS) and non line of sight (NLOS) channel conditions for different users in the system. A lot of papers have been published on resource allocation schemes for MIMO-OFDM systems. However, most of these resource allocation schemes have been considered for MIMO-OFDMA systems, where users are separated in the frequency domain and each user uses the same uplink and downlink channels in the same channel conditions. On the other hand, in the mulituser MIMO-OFDM systems, more than one user can be assigned the same frequency and channel conditions for the MIMO-OFDM broadcast channel (downlink) and MIMO-OFDM-MAC channel (uplink) are not the same. Therefore, the same resource allocation schemes for the conventional MIMO-OFDM systems can not be applied to multiuser MIMO-OFDM systems with different uplink and downlink channel conditions. Until now, most of the resource allocation schemes have been considered only for downlink MIMO-OFDM broadcast (MIMO-OFDM-BC) channel and very few papers tackle the fairness among users. Moreover, no paper considers a scheme to realize proportional data rate fairness among users in the MIMO-OFDM-MAC condition. In this paper, we propose a proportional data rate fairness resource allocation scheme with adaptive bit loading for MIMO-ODFM-MAC systems by considering the correlation effects of LOS and NLOS channel conditions in both spatial and frequency domains. Computer simulation results show that the proposed scheme can give larger system capacity while maintaining the proportional data rate fairness requirements among users in the system under the

  6. Zero-guard-interval coherent optical OFDM with overlapped frequency-domain CD and PMD equalization.

    PubMed

    Chen, Chen; Zhuge, Qunbi; Plant, David V

    2011-04-11

    This paper presents a new channel estimation/equalization algorithm for coherent OFDM (CO-OFDM) digital receivers, which enables the elimination of the cyclic prefix (CP) for OFDM transmission. We term this new system as the zero-guard-interval (ZGI)-CO-OFDM. ZGI-CO-OFDM employs an overlapped frequency-domain equalizer (OFDE) to compensate both chromatic dispersion (CD) and polarization mode dispersion (PMD) before the OFDM demodulation. Despite the zero CP overhead, ZGI-CO-OFDM demonstrates a superior PMD tolerance than the previous reduced-GI (RGI)-CO-OFDM, which is verified under several different PMD conditions. Additionally, ZGI-CO-OFDM can improve the channel estimation accuracy under high PMD conditions by using a larger intra-symbol frequency-averaging (ISFA) length as compared to RGI-CO-OFDM. ZGI-CO-OFDM also enables the use of ever smaller fast Fourier transform (FFT) sizes (i.e. <128), while maintaining the zero CP overhead. Finally, we provide an analytical comparison of the computation complexity between the conventional, RGI- and ZGI- CO-OFDM. We show that ZGI-CO-OFDM requires reasonably small additional computation effort (~13.6%) compared to RGI-CO-OFDM for 112-Gb/s transmission over a 1600-km dispersion-uncompensated optical link. PMID:21503054

  7. Transmission of OFDM wired-wireless quintuple-play services along WDM LR-PONs using centralized broadband impairment compensation.

    PubMed

    Alves, Tiago M F; Morant, Maria; Cartaxo, Adolfo V T; Llorente, Roberto

    2012-06-18

    The simultaneous transmission of four orthogonal frequency-division multiplexing (OFDM)-based signals used to provide quintuple-play services along wavelength division multiplexing (WDM) long-reach passive optical networks (LR-PONs) is demonstrated experimentally. Particularly, the transmission performance of custom signal bearing Gigabit Ethernet data, Worldwide Interoperability for Microwave Access, Long Term Evolution and Ultra Wideband (sub-bands 2 and 3) signals is evaluated for different LR-PONs reaches, considering single-wavelength and WDM transmission, and using a centralized impairment compensation technique at the central office that is transparent to the services provided.It is shown that error vector magnitude-compliant levels are obtained for all the OFDM-based signals in WDM LR-PONs reaching 100 km and that negligible inter-channel crosstalk is obtained for a channel spacing of 100 GHz regardless the OFDM-based signal considered. The successful multi-format OFDM transmission along the 100 km-long WDM LR-PON is achieved in the absence of optical dispersion compensation or single sideband modulation, and it is enabled by the performance improvement provided by the centralized impairment compensation realized. PMID:22714440

  8. Adaptive coded spreading OFDM signal for dynamic-λ optical access network

    NASA Astrophysics Data System (ADS)

    Liu, Bo; Zhang, Lijia; Xin, Xiangjun

    2015-12-01

    This paper proposes and experimentally demonstrates a novel adaptive coded spreading (ACS) orthogonal frequency division multiplexing (OFDM) signal for dynamic distributed optical ring-based access network. The wavelength can be assigned to different remote nodes (RNs) according to the traffic demand of optical network unit (ONU). The ACS can provide dynamic spreading gain to different signals according to the split ratio or transmission length, which offers flexible power budget for the network. A 10×13.12 Gb/s OFDM access with ACS is successfully demonstrated over two RNs and 120 km transmission in the experiment. The demonstrated method may be viewed as one promising for future optical metro access network.

  9. SFO compensation by pilot-aided channel estimation for real-time DDO-OFDM system

    NASA Astrophysics Data System (ADS)

    Deng, Rui; He, Jing; Chen, Ming; Chen, Lin

    2015-11-01

    In this paper, we experimentally demonstrated a pilot-aided and linear interpolated channel estimation technique in the real-time direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM) system using a cost-effective directly modulated laser (DML). It has been verified that the pilot-aided and linear interpolated channel estimation technique can help to compensate the sampling frequency offset (SFO) effect. The experimental results show that, based on the pilot-aided and linear interpolated channel estimation technique, even at a SFO of 170 ppm, a 16-QAM-OFDM signal can be successfully transmitted over 100-km SSMF under the hard-decision forward-error-correction (HD-FEC) threshold with a bit error rate of 3.8×10-3. And the effect of up to ~25 ppm SFO can be negligible.

  10. Demodulation Algorithms for the Ofdm Signals in the Time- and Frequency-Scattering Channels

    NASA Astrophysics Data System (ADS)

    Bochkov, G. N.; Gorokhov, K. V.; Kolobkov, A. V.

    2016-06-01

    We consider a method based on the generalized maximum-likelihood rule for solving the problem of reception of the signals with orthogonal frequency division multiplexing of their harmonic components (OFDM signals) in the time- and frequency-scattering channels. The coherent and incoherent demodulators effectively using the time scattering due to the fast fading of the signal are developed. Using computer simulation, we performed comparative analysis of the proposed algorithms and well-known signal-reception algorithms with equalizers. The proposed symbolby-symbol detector with decision feedback and restriction of the number of searched variants is shown to have the best bit-error-rate performance. It is shown that under conditions of the limited accuracy of estimating the communication-channel parameters, the incoherent OFDMsignal detectors with differential phase-shift keying can ensure a better bit-error-rate performance compared with the coherent OFDM-signal detectors with absolute phase-shift keying.

  11. Joint robustness security in optical OFDM access system with Turbo-coded subcarrier rotation.

    PubMed

    Zhang, Lijia; Liu, Bo; Xin, Xiangjun; Wang, Yongjun

    2015-01-12

    This paper proposes a novel robust physical secure method for optical orthogonal frequency division multiplexing (OFDM) access system based on Turbo-coded subcarrier rotation. It can realize a secure communication while keep robustness to channel noise. The subcarrier rotation is controlled by the interleaver module of Turbo coding, which is under the charge of Logistic map. The random puncturing can further enhance the security. The channel feedback can ensure the puncturing module working at a suitable coding rate. A 72.28 Gb/s encrypted 16QAM-OFDM signal is successfully demonstrated in the experiment. The results show robust performance under different channel noise conditions and good resistance to illegal optical network unit (ONU). PMID:25835649

  12. Compensation of IQ mismatch in optical PDM-OFDM coherent receivers

    NASA Astrophysics Data System (ADS)

    Chung, Hwan Seok; Chang, Sun Hyok; Kim, Kwangjoon

    2010-10-01

    The performance enhancements based on Gram-Schmidt orthogonalization procedure (GSOP) for compensating IQ mismatch in coherent optical orthogonal frequency division multiplexing (CO-OFDM) systems are investigated. We analytically explore IQ mismatch in optical OFDM systems and investigate the impacts of phase and amplitude IQ mismatch on required optical signal-to-noise ratio (OSNR) for the different values of data mapping and polarization multiplexing. The impacts of analog-to-digital converter (ADC) resolution and the number of samples in GSOP are also evaluated. The results show that the GSOP operation efficiently compensate IQ mismatch induced performance degradations regardless of the amount of IQ phase mismatch, density of data mapping, and polarization multiplexing.

  13. A joint swarm intelligence algorithm for multi-user detection in MIMO-OFDM system

    NASA Astrophysics Data System (ADS)

    Hu, Fengye; Du, Dakun; Zhang, Peng; Wang, Zhijun

    2014-11-01

    In the multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) system, traditional multi-user detection (MUD) algorithms that usually used to suppress multiple access interference are difficult to balance system detection performance and the complexity of the algorithm. To solve this problem, this paper proposes a joint swarm intelligence algorithm called Ant Colony and Particle Swarm Optimisation (AC-PSO) by integrating particle swarm optimisation (PSO) and ant colony optimisation (ACO) algorithms. According to simulation results, it has been shown that, with low computational complexity, the MUD for the MIMO-OFDM system based on AC-PSO algorithm gains comparable MUD performance with maximum likelihood algorithm. Thus, the proposed AC-PSO algorithm provides a satisfactory trade-off between computational complexity and detection performance.

  14. Cognitive Effects from Process Learning with Computer-Based Simulations.

    ERIC Educational Resources Information Center

    Breuer, Klaus; Kummer, Ruediger

    1990-01-01

    Discusses content learning versus process learning, describes process learning with computer-based simulations, and highlights an empirical study on the effects of process learning with problem-oriented, computer-managed simulations in technical vocational education classes in West Germany. Process learning within a model of the cognitive system…

  15. Cognitive control predicts use of model-based reinforcement learning.

    PubMed

    Otto, A Ross; Skatova, Anya; Madlon-Kay, Seth; Daw, Nathaniel D

    2015-02-01

    Accounts of decision-making and its neural substrates have long posited the operation of separate, competing valuation systems in the control of choice behavior. Recent theoretical and experimental work suggest that this classic distinction between behaviorally and neurally dissociable systems for habitual and goal-directed (or more generally, automatic and controlled) choice may arise from two computational strategies for reinforcement learning (RL), called model-free and model-based RL, but the cognitive or computational processes by which one system may dominate over the other in the control of behavior is a matter of ongoing investigation. To elucidate this question, we leverage the theoretical framework of cognitive control, demonstrating that individual differences in utilization of goal-related contextual information--in the service of overcoming habitual, stimulus-driven responses--in established cognitive control paradigms predict model-based behavior in a separate, sequential choice task. The behavioral correspondence between cognitive control and model-based RL compellingly suggests that a common set of processes may underpin the two behaviors. In particular, computational mechanisms originally proposed to underlie controlled behavior may be applicable to understanding the interactions between model-based and model-free choice behavior. PMID:25170791

  16. A Memory-Based Theory of Verbal Cognition

    ERIC Educational Resources Information Center

    Dennis, Simon

    2005-01-01

    The syntagmatic paradigmatic model is a distributed, memory-based account of verbal processing. Built on a Bayesian interpretation of string edit theory, it characterizes the control of verbal cognition as the retrieval of sets of syntagmatic and paradigmatic constraints from sequential and relational long-term memory and the resolution of these…

  17. A Case-Based Pharmacy Environment: Cognitive Flexibility + Social Constructivism.

    ERIC Educational Resources Information Center

    Oliver, Kevin M.

    The Internet Web Site on Virtual Clinical Applications and Disease Management is a hypermedia, case-based open learning environment that was designed to promote cognitive flexibility in college students at The University of Georgia College of Pharmacy. With a key objective of pharmacy education being patient problem-solving skills, this…

  18. The Effectiveness of Computer-Based Cognitive Training Programs

    ERIC Educational Resources Information Center

    Walcott, Christy M.; Phillips, Miranda E.

    2013-01-01

    The purpose of this article is to summarize empirical findings for school-age computer-based cognitive training (CCT) programs and to provide specific guidelines to practitioners who may be consulting with parents and schools about the utility of such programs. CCT programs vary in nature and in their targeted functions, but they share similar…

  19. Interdisciplinary Project-Based Learning: Technology for Improving Student Cognition

    ERIC Educational Resources Information Center

    Stozhko, Natalia; Bortnik, Boris; Mironova, Ludmila; Tchernysheva, Albina; Podshivalova, Ekaterina

    2015-01-01

    The article studies a way of enhancing student cognition by using interdisciplinary project-based learning (IPBL) in a higher education institution. IPBL is a creative pedagogic approach allowing students of one area of specialisation to develop projects for students with different academic profiles. The application of this approach in the Ural…

  20. Effects of a computer-based cognitive exercise program on age-related cognitive decline.

    PubMed

    Bozoki, Andrea; Radovanovic, Mirjana; Winn, Brian; Heeter, Carrie; Anthony, James C

    2013-01-01

    We developed a 'senior friendly' suite of online 'games for learning' with interactive calibration for increasing difficulty, and evaluated the feasibility of a randomized clinical trial to test the hypothesis that seniors aged 60-80 can improve key aspects of cognitive ability with the aid of such games. Sixty community-dwelling senior volunteers were randomized to either an online game suite designed to train multiple cognitive abilities, or to a control arm with online activities that simulated the look and feel of the games but with low level interactivity and no calibration of difficulty. Study assessment included measures of recruitment, retention and play-time. Cognitive change was measured with a computerized assessment battery administered just before and within two weeks after completion of the six-week intervention. Impediments to feasibility included: limited access to in-home high-speed internet, large variations in the amount of time devoted to game play, and a reluctance to pursue more challenging levels. Overall analysis was negative for assessed performance (transference effects) even though subjects improved on the games themselves. Post hoc analyses suggest that some types of games may have more value than others, but these effects would need to be replicated in a study designed for that purpose. We conclude that a six-week, moderate-intensity computer game-based cognitive intervention can be implemented with high-functioning seniors, but the effect size is relatively small. Our findings are consistent with Owen et al. (2010), but there are open questions about whether more structured, longer duration or more intensive 'games for learning' interventions might yield more substantial cognitive improvement in seniors. PMID:23542053

  1. Novel SLM Scheme with Low-Complexity for PAPR Reduction in OFDM System

    NASA Astrophysics Data System (ADS)

    Hsu, Chua-Yun; Chao, Hsin-Chieh

    Orthogonal frequency-division multiplexing (OFDM) is an attractive transmission technique for high-bit-rate communication systems. One major drawback of OFDM is the high peak-to-average power ratio (PAPR) of the transmitted signal. This study introduces a low-complexity selected mapping (SLM) OFDM scheme based on discrete Fourier transform (DFT) constellation-shaping. The DFT-based constellation-shaping algorithm applied with conventional SLM scheme usually requires a bank of DFT-shaping matrices to generate low-correlation constellation sequences and a bank of inverse fast Fourier transforms (IFFTs) to generate a set of candidate transmission signals, and this process usually results in high computational complexity. Therefore, a sparse matrix algorithm with low-complexity is proposed to replace the IFFT blocks and the DFT-shaping blocks in the proposed DFT constellation-shaping SLM scheme. By using the proposed sparse matrix, the candidate transmission signal with the lowest PAPR can be achieved with lower complexity than that of the conventional SLM scheme. The complexity analysis of the proposed algorithm shows great an improvement in the reduction of the number of multiplications. Moreover, this new low-complexity technique offers a PAPR that is significantly lower than that of the conventional SLM without any loss in terms of energy and spectral efficiency.

  2. Channel Acquisition for Massive MIMO-OFDM With Adjustable Phase Shift Pilots

    NASA Astrophysics Data System (ADS)

    You, Li; Gao, Xiqi; Swindlehurst, A. Lee; Zhong, Wen

    2016-03-01

    We propose adjustable phase shift pilots (APSPs) for channel acquisition in wideband massive multiple-input multiple-output (MIMO) systems employing orthogonal frequency division multiplexing (OFDM) to reduce the pilot overhead. Based on a physically motivated channel model, we first establish a relationship between channel space-frequency correlations and the channel power angle-delay spectrum in the massive antenna array regime, which reveals the channel sparsity in massive MIMO-OFDM. With this channel model, we then investigate channel acquisition, including channel estimation and channel prediction, for massive MIMO-OFDM with APSPs. We show that channel acquisition performance in terms of sum mean square error can be minimized if the user terminals' channel power distributions in the angle-delay domain can be made non-overlapping with proper phase shift scheduling. A simplified pilot phase shift scheduling algorithm is developed based on this optimal channel acquisition condition. The performance of APSPs is investigated for both one symbol and multiple symbol data models. Simulations demonstrate that the proposed APSP approach can provide substantial performance gains in terms of achievable spectral efficiency over the conventional phase shift orthogonal pilot approach in typical mobility scenarios.

  3. Adaptive modulation and intra-symbol frequency-domain averaging scheme for multiband OFDM UWB over fiber system

    NASA Astrophysics Data System (ADS)

    He, Jing; Li, Teng; Wen, Xuejie; Deng, Rui; Chen, Ming; Chen, Lin

    2016-01-01

    To overcome the unbalanced error bit distribution among subcarriers caused by inter-subcarriers mixing interference (ISMI) and frequency selective fading (FSF), an adaptive modulation scheme based on 64/16/4QAM modulation is proposed and experimentally investigated in the intensity-modulation direct-detection (IM/DD) multiband orthogonal frequency division multiplexing (MB-OFDM) ultra-wideband (UWB) over fiber system. After 50 km standard single mode fiber (SSMF) transmission, at the bit error ratio (BER) of 1×10-3, the experimental results show that the power penalty of the IM/DD MB-OFDM UWBoF system with 64/16/4QAM adaptive modulation scheme is about 3.6 dB, compared to that with the 64QAM modulation scheme. Moreover, the receiver sensitivity has been improved about 0.52 dB when the intra-symbol frequency-domain averaging (ISFA) algorithm is employed in the IM/DD MB-OFDM UWBoF system based on the 64/16/4QAM adaptive modulation scheme. Meanwhile, after 50 km SSMF transmission, there is a negligible power penalty in the adaptively modulated IM/DD MB-OFDM UWBoF system, compared to the optical back-to-back case.

  4. OBI reduction and optical power budget enhancement in OFDM-PON system using spreading code in electrical domain

    NASA Astrophysics Data System (ADS)

    Kumar, Pravindra; Srivastava, Anand

    2016-02-01

    Orthogonal frequency division multiplexing based passive optical network (OFDM-PON) gives better performance in high speed optical access networks because of its greater resistance to optical fiber dispersion and high bandwidth efficiency. Optical beating interference (OBI) is one of the main source of impairment which occurs in upstream direction. This paper proposes to use CDM/OFDM based PON architecture to reduce OBI in upstream and also improves optical power budget. In the analysis, no optical dispersion compensation has been used and all system related impairments have been considered for amplitude modulation/direct detection (AM/DD) optical communication system. Results depict that with BER value of 10-3, there is 8.1 dB gain in signal-to-noise ratio (SNR) and 5 dB, 9.5 dB improvement in optical power budget in downstream and upstream respectively. There is also 4.5 dB reduction in OBI in upstream direction with CDM/OFDM-PON system as compared to OFDM-PON system.

  5. Assessing Text Readability Using Cognitively Based Indices

    ERIC Educational Resources Information Center

    Crossley, Scott A.; Greenfield, Jerry; McNamara, Danielle S.

    2008-01-01

    Many programs designed to compute the readability of texts are narrowly based on surface-level linguistic features and take too little account of the processes which a reader brings to the text. This study is an exploratory examination of the use of Coh-Metrix, a computational tool that measures cohesion and text difficulty at various levels of…

  6. Factors Influencing the Use of Cognitive Tools in Web-Based Learning Environments: A Case Study

    ERIC Educational Resources Information Center

    Ozcelik, Erol; Yildirim, Soner

    2005-01-01

    High demands on learners in Web-based learning environments and constraints of the human cognitive system cause disorientation and cognitive overload. These problems could be inhibited if appropriate cognitive tools are provided to support learners' cognitive processes. The purpose of this study was to explore the factors influencing the use of…

  7. Decreasing Cognitive Load for Learners: Strategy of Web-Based Foreign Language Learning

    ERIC Educational Resources Information Center

    Zhang, Jianfeng

    2013-01-01

    Cognitive load is one of the important factors that influence the effectiveness and efficiency of web-based foreign language learning. Cognitive load theory assumes that human's cognitive capacity in working memory is limited and if it overloads, learning will be hampered, so that high level of cognitive load can affect the performance of learning…

  8. Channel Estimation and ISI/ICI Cancellation for MIMO-OFDM Systems with Insufficient Cyclic Prefix

    NASA Astrophysics Data System (ADS)

    Chiu, Yi-Jen; Chen, Chien-Sheng; Chang, Ting-Wei

    In multi-input multi-output orthogonal frequency division multiplexing (MIMO-OFDM) systems, the multipath components whose delays exceed cyclic prefix (CP) cause inter-symbol interference (ISI) and inter-carrier interference (ICI), which may degrade system performance severely. In this paper, we propose a joint channel estimation and ISI/ICI cancellation scheme in which a limited CP is used in a trade-off against high-rate performance in MIMO-OFDM systems. A channel estimation scheme based on the criterion of Expectation-Maximization (EM) algorithm can be proposed through the use of a training symbol. The EM algorithm uses an iterative procedure to estimate channel parameters and can estimate channel impulse response (CIR) accurately enough to mitigate ISI/ICI influences. Through the accurate CIR estimation, an efficient method has been developed to counteract ISI/ICI influences in signal detection in the case where the inserted CP length is less than the CIR length. Simulation results show that the proposed method can significantly enhance the overall MIMO-OFDM system performance after only a few iterations.

  9. Blind symbol synchronization for direct detection optical OFDM using a reduced number of virtual subcarriers.

    PubMed

    Bouziane, R; Killey, R I

    2015-03-01

    Symbol synchronization constitutes a major component in optical OFDM transceivers. In this paper, we propose reducing the complexity of a blind symbol synchronization technique for direct detection OFDM receivers based on virtual subcarriers by optimizing the number and location of the virtual subcarriers. Compared to the system design in our previous study, this new technique offers a reduction of 92% in the number of virtual subcarriers (from 26 to 2 in a system with 50 data carrying subchannels) resulting in significant savings in complexity with a minimal penalty. Moreover, it offers an increase in the system capacity as more subcarriers can be used to transmit data. The technique was assessed experimentally using a transmission system of direct detection 16-QAM optical OFDM operating at a data rate of 30.65 Gb/s over 23.3 km SSMF with BER of 10(-3). Negligible penalty was observed at high received powers. However, at low received powers, the number of averaging symbols had to be increased in order to improve the robustness of the method. PMID:25836864

  10. Power amplifier linearization technique with IQ imbalance and crosstalk compensation for broadband MIMO-OFDM transmitters

    NASA Astrophysics Data System (ADS)

    Gregorio, Fernando; Cousseau, Juan; Werner, Stefan; Riihonen, Taneli; Wichman, Risto

    2011-12-01

    The design of predistortion techniques for broadband multiple input multiple output-OFDM (MIMO-OFDM) systems raises several implementation challenges. First, the large bandwidth of the OFDM signal requires the introduction of memory effects in the PD model. In addition, it is usual to consider an imbalanced in-phase and quadrature (IQ) modulator to translate the predistorted baseband signal to RF. Furthermore, the coupling effects, which occur when the MIMO paths are implemented in the same reduced size chipset, cannot be avoided in MIMO transceivers structures. This study proposes a MIMO-PD system that linearizes the power amplifier response and compensates nonlinear crosstalk and IQ imbalance effects for each branch of the multiantenna system. Efficient recursive algorithms are presented to estimate the complete MIMO-PD coefficients. The algorithms avoid the high computational complexity in previous solutions based on least squares estimation. The performance of the proposed MIMO-PD structure is validated by simulations using a two-transmitter antenna MIMO system. Error vector magnitude and adjacent channel power ratio are evaluated showing significant improvement compared with conventional MIMO-PD systems.

  11. Effectiveness of phase-conjugated twin waves on fiber nonlinearity in spatially multiplexed all-optical OFDM system

    NASA Astrophysics Data System (ADS)

    Hmood, Jassim K.; Noordin, Kamarul A.; Harun, Sulaiman W.

    2016-07-01

    In this paper, we investigate the effectiveness of using phase-conjugated twin waves (PCTWs) technique to mitigate fiber nonlinear impairments in spatially multiplexed all-optical orthogonal frequency division multiplexing (AO-OFDM) systems. In this technique, AO-OFDM signal and its phase-conjugated copy are directly transmitted through two identical fiber links. At the receiver, the two signals are coherently superimposed to cancel the phase noise and to enhance signal-to-noise ratio (SNR). To show the effectiveness of proposed technique, a spatially multiplexed AO-OFDM system is demonstrated by numerical simulation. AO-OFDM signal and its phase conjugated copy are optically generated by using optical coupler-based inverse fast Fourier transform (OIFFT)/fast Fourier transform (OFFT). The generated signal includes 29 subcarriers where each subcarrier is modulated by 4-quadrature amplitude modulation (4QAM) format at a symbol rate of 25 Gsymbol/s. The results reveal that transmission performance is considerably improved where the transmission distance of the proposed system is increased by ∼45% as compared to that of original system without PCTWs technique.

  12. Performance analysis of an all-optical OFDM system in presence of non-linear phase noise.

    PubMed

    Hmood, Jassim K; Harun, Sulaiman W; Emami, Siamak D; Khodaei, Amin; Noordin, Kamarul A; Ahmad, Harith; Shalaby, Hossam M H

    2015-02-23

    The potential for higher spectral efficiency has increased the interest in all-optical orthogonal frequency division multiplexing (OFDM) systems. However, the sensitivity of all-optical OFDM to fiber non-linearity, which causes nonlinear phase noise, is still a major concern. In this paper, an analytical model for estimating the phase noise due to self-phase modulation (SPM), cross-phase modulation (XPM), and four-wave mixing (FWM) in an all-optical OFDM system is presented. The phase noise versus power, distance, and number of subcarriers is evaluated by implementing the mathematical model using Matlab. In order to verify the results, an all-optical OFDM system, that uses coupler-based inverse fast Fourier transform/fast Fourier transform without any nonlinear compensation, is demonstrated by numerical simulation. The system employs 29 subcarriers; each subcarrier is modulated by a 4-QAM or 16-QAM format with a symbol rate of 25 Gsymbol/s. The results indicate that the phase variance due to FWM is dominant over those induced by either SPM or XPM. It is also shown that the minimum phase noise occurs at -3 dBm and -1 dBm for 4-QAM and 16-QAM, respectively. Finally, the error vector magnitude (EVM) versus subcarrier power and symbol rate is quantified using both simulation and the analytical model. It turns out that both EVM results are in good agreement with each other. PMID:25836428

  13. Positive Effects of Computer-Based Cognitive Training in Adults with Mild Cognitive Impairment

    ERIC Educational Resources Information Center

    Herrera, C.; Chambon, C.; Michel, B. F.; Paban, V.; Alescio-Lautier, B.

    2012-01-01

    Considering the high risk for individuals with amnestic Mild Cognitive Impairment (A-MCI) to progress towards Alzheimer's disease (AD), we investigated the efficacy of a non-pharmacological intervention, that is, cognitive training that could reduce cognitive difficulties and delay the cognitive decline. For this, we evaluated the efficacy of a…

  14. Designing an Adaptive Web-Based Learning System Based on Students' Cognitive Styles Identified Online

    ERIC Educational Resources Information Center

    Lo, Jia-Jiunn; Chan, Ya-Chen; Yeh, Shiou-Wen

    2012-01-01

    This study developed an adaptive web-based learning system focusing on students' cognitive styles. The system is composed of a student model and an adaptation model. It collected students' browsing behaviors to update the student model for unobtrusively identifying student cognitive styles through a multi-layer feed-forward neural network (MLFF).…

  15. Building simplification algorithms based on user cognition in mobile environment

    NASA Astrophysics Data System (ADS)

    Shen, Jie; Shi, Junfei; Wang, Meizhen; Wu, Chenyan

    2008-10-01

    With the development of LBS, mobile map should adaptively satisfy the cognitive requirement of user. User cognition in mobile environment is much more objective oriented and also seem to be a heavier burden than the user in static environment. The holistic idea and methods of map generalization can not fully suitable for the mobile map. This paper took the building simplification in habitation generalization as example, analyzed the characteristic of user cognition in mobile environment and the basic rules of building simplification, collected and studied the state-of-the-art of algorithms of building simplification in the static and mobile environment, put forward the idea of hierarchical building simplification based on user cognition. This paper took Hunan road business district of Nanjing as test area and took the building data with shapfile format of ESRI as test data and realized the simplification algorithm. The method took user as center, calculated the distance between user and the building which will be simplified and took the distance as the basis for choosing different simplification algorithm for different spaces. This contribution aimed to hierarchically present the building in different level of detail by real-time simplification.

  16. A linear receiver for visible light communication systems with phase modulated OFDM

    NASA Astrophysics Data System (ADS)

    Xie, Gui-Teng; Yu, Hong-Yi; Zhu, Yi-Jun; Ji, Xin-Sheng

    2016-07-01

    In the orthogonal frequency-division multiplexing (OFDM) systems for visible light communication (VLC), the peak-to-average power ratio (PAPR) of OFDM signals is the primary concern of high-speed data transmission. In order to get low PAPR signals and reduce the influence of nonlinearity of the light-emitting diode (LED), a phase modulated OFDM (PM-OFDM) system is developed and a linear receiver is presented. Unlike the conventional angle detection receiver implemented by arctangent calculator, the linear receiver has lower computation complexity and is immune to the threshold effect. Simulation results indicate that the proposed PM-OFDM obtains significant performance gains over DC-biased optical OFDM (DCO-OFDM) and precoded OFDM.

  17. Generation and transmission of 85.4 Gb/s real-time 16QAM coherent optical OFDM signals over 400 km SSMF with preamble-less reception.

    PubMed

    Bouziane, Rachid; Schmogrow, Rene; Hillerkuss, D; Milder, P A; Koos, C; Freude, W; Leuthold, J; Bayvel, P; Killey, R I

    2012-09-10

    This paper presents a real-time, coherent optical OFDM transmitter based on a field programmable gate array implementation. The transmitter uses 16QAM mapping and runs at 28 GSa/s achieving a data rate of 85.4 Gb/s on a single polarization. A cyclic prefix of 25% of the symbol duration is added enabling dispersion-tolerant transmission over up to 400 km of SSMF. This is the first transmission experiment performed with a real-time OFDM transmitter running at data rates higher than 40 Gb/s. A key aspect of the paper is the introduction of a novel method for OFDM symbol synchronization without relying on training symbols. Unlike conventional preamble-based synchronization methods which perform cross-correlations at regular time intervals and let the system run freely in between, the proposed method performs synchronization in a continuous manner ensuring correct symbol alignment at all times. PMID:23037279

  18. Cognitive Modeling for Agent-Based Simulation of Child Maltreatment

    NASA Astrophysics Data System (ADS)

    Hu, Xiaolin; Puddy, Richard

    This paper extends previous work to develop cognitive modeling for agent-based simulation of child maltreatment (CM). The developed model is inspired from parental efficacy, parenting stress, and the theory of planned behavior. It provides an explanatory, process-oriented model of CM and incorporates causality relationship and feedback loops from different factors in the social ecology in order for simulating the dynamics of CM. We describe the model and present simulation results to demonstrate the features of this model.

  19. 450-nm GaN laser diode enables high-speed visible light communication with 9-Gbps QAM-OFDM.

    PubMed

    Chi, Yu-Chieh; Hsieh, Dan-Hua; Tsai, Cheng-Ting; Chen, Hsiang-Yu; Kuo, Hao-Chung; Lin, Gong-Ru

    2015-05-18

    A TO-38-can packaged Gallium nitride (GaN) blue laser diode (LD) based free-space visible light communication (VLC) with 64-quadrature amplitude modulation (QAM) and 32-subcarrier orthogonal frequency division multiplexing (OFDM) transmission at 9 Gbps is preliminarily demonstrated over a 5-m free-space link. The 3-dB analog modulation bandwidth of the TO-38-can packaged GaN blue LD biased at 65 mA and controlled at 25°C is only 900 MHz, which can be extended to 1.5 GHz for OFDM encoding after throughput intensity optimization. When delivering the 4-Gbps 16-QAM OFDM data within 1-GHz bandwidth, the error vector magnitude (EVM), signal-to-noise ratio (SNR) and bit-error-rate (BER) of the received data are observed as 8.4%, 22.4 dB and 3.5 × 10(-8), respectively. By increasing the encoded bandwidth to 1.5 GHz, the TO-38-can packaged GaN blue LD enlarges its transmission capacity to 6 Gbps but degrades its transmitted BER to 1.7 × 10(-3). The same transmission capacity of 6 Gbps can also be achieved with a BER of 1 × 10(-6) by encoding 64-QAM OFDM data within 1-GHz bandwidth. Using the 1.5-GHz full bandwidth of the TO-38-can packaged GaN blue LD provides the 64-QAM OFDM transmission up to 9 Gbps, which successfully delivers data with an EVM of 5.1%, an SNR of 22 dB and a BER of 3.6 × 10(-3) passed the forward error correction (FEC) criterion. PMID:26074558

  20. Sprint-based exercise and cognitive function in adolescents.

    PubMed

    Cooper, Simon B; Bandelow, Stephan; Nute, Maria L; Dring, Karah J; Stannard, Rebecca L; Morris, John G; Nevill, Mary E

    2016-12-01

    Moderate intensity exercise has been shown to enhance cognition in an adolescent population, yet the effect of high-intensity sprint-based exercise remains unknown and was therefore examined in the present study. Following ethical approval and familiarisation, 44 adolescents (12.6 ± 0.6 y) completed an exercise (E) and resting (R) trial in a counter-balanced, randomised crossover design. The exercise trial comprised of 10 × 10 s running sprints, interspersed by 50 s active recovery (walking). A battery of cognitive function tests (Stroop, Digit Symbol Substitution (DSST) and Corsi blocks tests) were completed 30 min pre-exercise, immediately post-exercise and 45 min post-exercise. Data were analysed using mixed effect models with repeated measures. Response times on the simple level of the Stroop test were significantly quicker 45 min following sprint-based exercise (R: 818 ± 33 ms, E: 772 ± 26 ms; p = 0.027) and response times on the complex level of the Stroop test were quicker immediately following the sprint-based exercise (R: 1095 ± 36 ms, E: 1043 ± 37 ms; p = 0.038), while accuracy was maintained. Sprint-based exercise had no immediate or delayed effects on the number of items recalled on the Corsi blocks test (p = 0.289) or substitutions made during the DSST (p = 0.689). The effect of high intensity sprint-based exercise on adolescents' cognitive function was dependant on the component of cognitive function examined. Executive function was enhanced following exercise, demonstrated by improved response times on the Stroop test, whilst visuo-spatial memory and general psycho-motor speed were unaffected. These data support the inclusion of high-intensity sprint-based exercise for adolescents during the school day to enhance cognition. PMID:27413677

  1. Simple signal-to-signal beat interference cancellation receiver based on balanced detection for a single-sideband optical OFDM signal with a reduced guard band.

    PubMed

    Ma, Jianxin

    2013-11-01

    A simple signal-to-signal beat interference cancellation receiver based on balanced detection (ICRBD) with an interleaver, a 2×2 three-decibel optical coupler, and a balanced photodiode pair is proposed for a single-sideband optical orthogonal frequency division multiplexing (SSB-OOFDM) signal with a reduced guard band (GB). Simulation demonstration of the ICRBD for a 40 Gbit/s 16-QAM SSB-OOFDM signal with a reduced GB was achieved successfully. PMID:24177087

  2. Transmission performance of the single-sideband optical OFDM signal with reduced guard-band based on beat interference cancellation receiver

    NASA Astrophysics Data System (ADS)

    Ma, Jianxin; Zheng, Guoli; Zhou, Wei

    2015-12-01

    We have investigated the fiber transmission performance of the single-sideband optical orthogonal frequency division multiplexing (SSB-OOFDM) signal with reduced guard band (GB) received by the beat interference cancellation receiver based on balanced detection (ICRBD). The simulation results show that the error vector magnitude (EVM) of the 40 Gb/s 16-QAM SSB-OOFDM with 2 GHz GB remains below the forward error correction (FEC) limit even after 5×100 km standard single-mode fiber (SSMF) transmission. The link has stable tolerance of both the laser linewidth and the linear channel imperfections.

  3. Mindfulness-based cognitive therapy: theory and practice.

    PubMed

    Sipe, Walter E B; Eisendrath, Stuart J

    2012-02-01

    Mindfulness-based cognitive therapy (MBCT) incorporates elements of cognitive-behavioural therapy with mindfulness-based stress reduction into an 8-session group program. Initially conceived as an intervention for relapse prevention in people with recurrent depression, it has since been applied to various psychiatric conditions. Our paper aims to briefly describe MBCT and its putative mechanisms of action, and to review the current findings about the use of MBCT in people with mood and anxiety disorders. The therapeutic stance of MBCT focuses on encouraging patients to adopt a new way of being and relating to their thoughts and feelings, while placing little emphasis on altering or challenging specific cognitions. Preliminary functional neuroimaging studies are consistent with an account of mindfulness improving emotional regulation by enhancing cortical regulation of limbic circuits and attentional control. Research findings from several randomized controlled trials suggest that MBCT is a useful intervention for relapse prevention in patients with recurrent depression, with efficacy that may be similar to maintenance antidepressants. Preliminary studies indicate MBCT also shows promise in the treatment of active depression, including treatment-resistant depression. Pilot studies have also evaluated MBCT in bipolar disorder and anxiety disorders. Patient and clinician resources for further information on mindfulness and MBCT are provided. PMID:22340145

  4. Evidence-based Assessment of Cognitive Functioning in Pediatric Psychology

    PubMed Central

    Brown, Ronald T.; Cavanagh, Sarah E.; Vess, Sarah F.; Segall, Mathew J.

    2008-01-01

    Objective To review the evidence base for measures of cognitive functioning frequently used within the field of pediatric psychology. Methods From a list of 47 measures identified by the Society of Pediatric Psychology (Division 54) Evidence-Based Assessment Task Force Workgroup, 27 measures were included in the review. Measures were organized, reviewed, and evaluated according to general domains of functioning (e.g., attention/executive functioning, memory). Results Twenty-two of 27 measures reviewed demonstrated psychometric properties that met “Well-established” criteria as set forth by the Assessment Task Force. Psychometric properties were strongest for measures of general cognitive ability and weakest for measures of visual-motor functioning and attention. Conclusions We report use of “Well-established” measures of overall cognitive functioning, nonverbal intelligence, academic achievement, language, and memory and learning. For several specific tests in the domains of visual-motor functioning and attention, additional psychometric data are needed for measures to meet criteria as “Well established.” PMID:18194973

  5. Combining discrete cosine transform with clipping for PAPR reduction in intensity-modulated OFDM systems

    NASA Astrophysics Data System (ADS)

    Wang, Zhong-peng; Chen, Shou-fa; Zhou, Yang; Chen, Ming; Tang, Jin; Chen, Lin

    2014-09-01

    In this paper, the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signal is reduced by combining the discrete cosine transform (DCT) with clipping in optical intensity-modulated direct-detection (IM/DD) OFDM systems. First, the data are transformed into new modified data by DCT. Second, the proposed scheme utilizes the clipping technique to further reduce the PAPR of OFDM signal. We experimentally demonstrate that the optical OFDM transmission system with this proposed scheme can achieve significant performance improvement in terms of PAPR and bit error rate (BER) compared with the original optical OFDM systems.

  6. Experimental characterization of an all-optical wavelength converter of OFDM signals using two-mode injection-locking in a Fabry-Pérot laser.

    PubMed

    Dang, Juntao; Yi, Xingwen; Zhang, Jing; Ye, Taiping; Xu, Bo; Qiu, Kun

    2016-07-25

    While optical OFDM has been demonstrated for superior transmission performance, its analogue waveform in the time domain challenges many conventional all-optical wavelength converters (AOWC) that are needed for future flexible optical networks. There only exist a few reports on AOWC of OFDM signals, which are mainly based on the low-efficient four-wave mixing. In this paper, we propose an AOWC for OFDM signals by using two-mode injection-locking in a low-cost Fabry-Pérot laser. The control signal and the probe signal at a milliwatt power level are combined and injected into the FP laser. By a proper control, they can be injection-locked to two longitudinal modes in the FP laser and subsequently, the transmission of the probe signal is conditioned by the control signal. We conduct an experimental study on various aspects of this AOWC. Despite a vendor-specified electrical-to-optical (E/O) modulation bandwidth of 2.5 GHz, we find that the optical-to-optical (O/O) modulation bandwidth of AOWC is free from this limit and can be much wider. We examine the linear transfer curve of the AOWC by simply using the OFDM waveforms as the stimulus. The performance tolerance to the wavelength detuning and injected power ratio is also measured. The proposed AOWC can provide a linear transfer function from the control signal to the probe signal to support the random-fluctuated OFDM waveform. We also investigate the maximum capacity of the AOWC by using the adaptive bit-loading OFDM. Finally, we measure the power penalty after the AOWC at two different bit rates to show the tradeoff between the penalty and capacity. PMID:27464125

  7. Internet-based cognitive behaviour therapy for depression and anxiety.

    PubMed

    2013-11-01

    Internet-based, or computerised, cognitive behaviour therapy (CBT) can be used to treat patients with depression or anxiety. Patients are engaged in structured programs of care, with several programs available either at no cost or moderate cost. Internet CBT (iCBT) may be particularly suited to patients with mobility issues or living in rural or remote areas. Although there are no adverse effects, clinicians should assess patients for risk issues and the need for more immediate assistance before recommending iCBT. Monitoring effectiveness of any intervention for the patient is important. iCBT has National Health and Medical Research Council (NHMRC) Level I evidence of efficacy. PMID:24217103

  8. Mindfulness-based cognitive therapy for depression: trends and developments

    PubMed Central

    MacKenzie, Meagan B; Kocovski, Nancy L

    2016-01-01

    Mindfulness-based cognitive therapy (MBCT) was developed as a psychological intervention for individuals at risk of depressive relapse. Possible mechanisms of change for this intervention are in line with its theoretical underpinnings, and include increases in mindfulness and/or decreases in negative repetitive thoughts. This review provides an overview of current trends in MBCT research, including efficacy and questions regarding the specific effects of MBCT in light of recent comparisons with structurally equivalent control conditions, mechanisms of change, and moderators of treatment outcome. In addition, future directions are discussed, such as challenges with training an adequate number of therapists and disseminating this therapy. PMID:27274325

  9. The effects of cognitive rehabilitation on Alzheimer’s dementia patients’ cognitive assessment reference diagnosis system performance based on level of cognitive functioning

    PubMed Central

    Hwang, Jung-Ha; Cha, Hyun-Gyu; Cho, Hyuk-Shin

    2015-01-01

    [Purpose] The purpose of this study is to apply cognitive rehabilitation according to Alzheimer’s disease (AD) patients’ level of cognitive functioning to compare changes in Cognitive Assessment Reference Diagnosis System performance and present standards for effective intervention. [Subjects] Subjects were 30 inpatients diagnosed with AD. Subjects were grouped by Clinical Dementia Rating (CDR) class (CDR-0.5, CDR-1, or CDR-2, n = 10 per group), which is based on level of cognitive functioning, and cognitive rehabilitation was applied for 50 minutes per day, five days per week, for four weeks. [Methods] After cognitive rehabilitation intervention, CARDS tests were conducted to evaluate memory. [Results] Bonferroni tests comparing the three groups revealed that the CDR-0.5 and CDR-1 groups showed significant increases in Delayed 10 word-list, Delayed 10 object-list, Recognition 10 object, and Recent memory performance compared to the CDR-2 group. In addition, the CDR-0.5 group showed significant decreases in Recognition 10 word performance compared to the CDR-1 group. [Conclusion] Cognitive rehabilitation, CDR-0.5 or CDR-1 subjects showed significantly greater memory improvements than CDR-2 subjects. Moreover, was not effective for CDR-2 subjects. PMID:26504315

  10. System design for OFDM systems with high-density constellations

    NASA Astrophysics Data System (ADS)

    Gu, Jian

    2001-10-01

    This paper addresses issues in designing OFDM systems with high-density constellations. To achieve high data throughput, many high-speed OFDM systems such as HiperLAN2 and IEEE 802.11a use high-density constellations such as 64QAM to reach up to 54Mbits/s over a 20 MHz frequency bandwidth. Compared with low-density constellation modulations, OFDM systems using M-QAM (M>=64) are very sensitive to analog circuits/components variations causing so-called I-Q imbalances. Moreover, for the purpose of high integration level and low cost, simple front-end radio/analog architectures such as direct conversion and low-IF are desirable but such architectures are even more sensitive to circuitry and component variation. We have developed a patent-pending technology called IQ-Balancing, which removes the adverse effect of I-Q imbalance and enables OFDM systems to have high tolerance to circuitry and component variations. With IQ-Balancing technology, direct conversion and low-IF architectures become very attractive for high-speed OFDM systems. Exploring further with IQ- balancing technology leads to a simple implementation of software Defined Radio (SDR).

  11. PAPR mitigation algorithms for OFDM WiMAX link

    NASA Astrophysics Data System (ADS)

    Rashwan, Gasem; Kenshil, Salih; Matin, Mohammad

    2013-09-01

    OFDM has been adopted in many high systems due to its high data rates and to its robust performance in fading channel. OFDM distributes the data among number of carriers which are called subcarriers. The subcarriers must be orthogonal to prevent the carrier from interfering to each other. Features such overcoming ISI (inter-symbol interference) and the complexity of Designing both receiver and transmitter made it ideal technique for both wired and wireless communication as long as optical communications. However, OFDM suffers from a defect called Peak Average power ratio (PAPR). APARP is crucial drawback that limits the way that OFDM functions and reducing or mitigating this factor in wireless and optical environment will help overcome and enhance the OFDM date rate. PAPR is the main cause of inter-carrier interference and high out-of-band power, and consequently Bit error rate BER. We investigate some of the techniques that mitigate the effect of PAPR. These techniques are merged together to provide a better PAPR reduction with the existing techniques. In this paper, we are proposing a new reduction algorithm to minimize the effect of the PAPR. The results and simulation are done in Optisystem V-11 and Matlab environment. These approaches will be applied on WiMAX application and the performances between the different techniques are examined.

  12. Understanding the Effects of Databases as Cognitive Tools in a Problem-Based Multimedia Learning Environment

    ERIC Educational Resources Information Center

    Li, Rui; Liu, Min

    2007-01-01

    The purpose of this study is to examine the potential of using computer databases as cognitive tools to share learners' cognitive load and facilitate learning in a multimedia problem-based learning (PBL) environment designed for sixth graders. Two research questions were: (a) can the computer database tool share sixth-graders' cognitive load? and…

  13. Improved Processing Speed: Online Computer-Based Cognitive Training in Older Adults

    ERIC Educational Resources Information Center

    Simpson, Tamara; Camfield, David; Pipingas, Andrew; Macpherson, Helen; Stough, Con

    2012-01-01

    In an increasingly aging population, a number of adults are concerned about declines in their cognitive abilities. Online computer-based cognitive training programs have been proposed as an accessible means by which the elderly may improve their cognitive abilities; yet, more research is needed in order to assess the efficacy of these programs. In…

  14. Responsible Adult Culture (RAC): Cognitive and Behavioral Changes at a Community-Based Correctional Facility

    ERIC Educational Resources Information Center

    Devlin, Renee S.; Gibbs, John C.

    2010-01-01

    This article examined cognitive and behavioral changes among participants in Responsible Adult Culture (RAC), a cognitive-behavioral (especially, cognitive restructuring) treatment program in use at the Franklin County Community-Based Correctional Facility (CBCF). Participants were adult felony offenders (approximately three-fourths male). A…

  15. Novel television-based cognitive training improves working memory and executive function.

    PubMed

    Shatil, Evelyn; Mikulecká, Jaroslava; Bellotti, Francesco; Bureš, Vladimír

    2014-01-01

    The main study objective was to investigate the effect of interactive television-based cognitive training on cognitive performance of 119 healthy older adults, aged 60-87 years. Participants were randomly allocated to a cognitive training group or to an active control group in a single-blind controlled two-group design. Before and after training interactive television cognitive performance was assessed on well validated tests of fluid, higher-order ability, and system usability was evaluated. The participants in the cognitive training group completed a television-based cognitive training programme, while the participants in the active control group completed a TV-based programme of personally benefiting activities. Significant improvements were observed in well validated working memory and executive function tasks in the cognitive training but not in the control group. None of the groups showed statistically significant improvement in life satisfaction score. Participants' reports of "adequate" to "high" system usability testify to the successful development and implementation of the interactive television-based system and compliant cognitive training contents. The study demonstrates that cognitive training delivered by means of an interactive television system can generate genuine cognitive benefits in users and these are measurable using well-validated cognitive tests. Thus, older adults who cannot use or afford a computer can easily use digital interactive television to benefit from advanced software applications designed to train cognition. PMID:24992187

  16. Precise SER Analysis and Performance Results of OSTBC MIMO-OFDM Systems over Uncorrelated Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Ahmad Ansari, Ejaz; Rajatheva, Nandana

    Although the topic of multiple-input multiple-output (MIMO) based orthogonal frequency division multiplexing (OFDM) over different fading channels is well investigated, its closed form symbol error rate (SER) expressions and performance results employing orthogonal space time block codes (OSTBCs) over uncorrelated frequency-selective Nakagami-m fading channels are still not available. The closed form expressions are extremely useful for evaluating system's performance without carrying out time consuming simulations. Similarly, the performance results are also quite beneficial for determining the system's performance in the sense that many practical wireless standards extensively employ MIMO-OFDM systems in conjunction with M-ary quadrature amplitude modulation (M-QAM) constellation. This paper thus, derives exact closed form expressions for the SER of M-ary Gray-coded one and two dimensional constellations when an OSTBC is employed and Nt transmit antennas are selected for transmission over frequency-selective Nakagami-m fading channels. For this purpose, first an exact closed-form of average SER expression of OSTBC based MIMO-OFDM system for M-ary phase shift keying (M-PSK) using traditional probability density function (PDF) approach is derived. We then compute exact closed form average SER expressions for M-ary pulse amplitude modulation (M-PAM) and M-QAM schemes by utilizing this generalized result. These expressions are valid over both frequency-flat and frequency-selective Nakagami-m fading MIMO channels and can easily be evaluated without using any numerical integration methods. We also show that average SER of MIMO-OFDM system using OSTBC in case of frequency-selective Rayleigh fading channels remains independent to the number of taps, L of that fading channel and the performance of the same system for two-tap un-correlated Rayleigh and Nakagami-m fading channels is better than that of the correlated one. Moreover, Monte Carlo simulation of MIMO-OFDM system

  17. Sex-based memory advantages and cognitive aging: a challenge to the cognitive reserve construct?

    PubMed

    Caselli, Richard J; Dueck, Amylou C; Locke, Dona E C; Baxter, Leslie C; Woodruff, Bryan K; Geda, Yonas E

    2015-02-01

    Education and related proxies for cognitive reserve (CR) are confounded by associations with environmental factors that correlate with cerebrovascular disease possibly explaining discrepancies between studies examining their relationships to cognitive aging and dementia. In contrast, sex-related memory differences may be a better proxy. Since they arise developmentally, they are less likely to reflect environmental confounds. Women outperform men on verbal and men generally outperform women on visuospatial memory tasks. Furthermore, memory declines during the preclinical stage of AD, when it is clinically indistinguishable from normal aging. To determine whether CR mitigates age-related memory decline, we examined the effects of gender and APOE genotype on longitudinal memory performances. Memory decline was assessed in a cohort of healthy men and women enriched for APOE ɛ4 who completed two verbal [Rey Auditory Verbal Learning Test (AVLT), Buschke Selective Reminding Test (SRT)] and two visuospatial [Rey-Osterrieth Complex Figure Test (CFT), and Benton Visual Retention Test (VRT)] memory tests, as well as in a separate larger and older cohort [National Alzheimer's Coordinating Center (NACC)] who completed a verbal memory test (Logical Memory). Age-related memory decline was accelerated in APOE ɛ4 carriers on all verbal memory measures (AVLT, p=.03; SRT p<.001; logical memory p<.001) and on the VRT p=.006. Baseline sex associated differences were retained over time, but no sex differences in rate of decline were found for any measure in either cohort. Sex-based memory advantage does not mitigate age-related memory decline in either APOE ɛ4 carriers or non-carriers. PMID:25665170

  18. Sex-Based Memory Advantages and Cognitive Aging: A Challenge to the Cognitive Reserve Construct?

    PubMed Central

    Caselli, Richard J.; Dueck, Amylou C.; Locke, Dona E.C.; Baxter, Leslie C.; Woodruff, Bryan K.; Geda, Yonas E.

    2016-01-01

    Education and related proxies for cognitive reserve (CR) are confounded by associations with environmental factors that correlate with cerebrovascular disease possibly explaining discrepancies between studies examining their relationships to cognitive aging and dementia. In contrast, sex-related memory differences may be a better proxy. Since they arise developmentally, they are less likely to reflect environmental confounds. Women outperform men on verbal and men generally outperform women on visuospatial memory tasks. Furthermore, memory declines during the preclinical stage of AD, when it is clinically indistinguishable from normal aging. To determine whether CR mitigates age-related memory decline, we examined the effects of gender and APOE genotype on longitudinal memory performances. Memory decline was assessed in a cohort of healthy men and women enriched for APOE ε4 who completed two verbal [Rey Auditory Verbal Learning Test (AVLT), Buschke Selective Reminding Test (SRT)] and two visuospatial [Rey-Osterrieth Complex Figure Test (CFT), and Benton Visual Retention Test (VRT)] memory tests, as well as in a separate larger and older cohort [National Alzheimer’s Coordinating Center (NACC)] who completed a verbal memory test (Logical Memory). Age-related memory decline was accelerated in APOE ε4 carriers on all verbal memory measures (AVLT, p = .03; SRT p<.001; logical memory p<.001) and on the VRT p = .006. Baseline sex associated differences were retained over time, but no sex differences in rate of decline were found for any measure in either cohort. Sex-based memory advantage does not mitigate age-related memory decline in either APOE ε4 carriers or non-carriers. PMID:25665170

  19. Uplink User Signal Separation for OFDMA-Based Cognitive Radios

    NASA Astrophysics Data System (ADS)

    Şahin, MustafaE; Guvenc, Ismail; Arslan, Hüseyin

    2009-12-01

    Spectrum awareness of orthogonal frequency division multiple access- (OFDMA-) based cognitive radios (CRs) can be improved by enabling them to separate the primary user signals in the uplink (UL). Assuming availability of information about the basic parameters of the primary system as well as time synchronization to the first arriving user signal, two algorithms are proposed in this paper. The first one targets estimating the size of the frequency allocation block of the primary system. The performance of this algorithm is compared with the results of a Gaussian approximation-based approach that aims to determine the probability of correct block size estimation theoretically. The second one is a semiblind user separation algorithm, which estimates the carrier frequency offsets and time delays of each block by exploiting the cross-correlations over pilot subcarriers. A two-dimensional clustering method is then employed to group the estimates, where each group belongs to a different user. It is shown that the proposed algorithms can improve the spectrum opportunity detection of cognitive radios. Feasibility of the algorithms is proved through practical simulations.

  20. On the Properties of Cubic Metric for OFDM Signals

    NASA Astrophysics Data System (ADS)

    Kim, Kee-Hoon; No, Jong-Seon; Shin, Dong-Joon

    2016-01-01

    As a metric for amplitude fluctuation of orthogonal frequency division multiplexing (OFDM) signal, cubic metric (CM) has received an increasing attention because it is more closely related to the distortion induced by nonlinear devices than the well-known peak-to-average power ratio (PAPR). In this paper, the properties of CM of OFDM signal is investigated. First, asymptotic distribution of CM is derived. Second, it is verified that 1.7 times oversampling rate is good enough to capture the CM of continuous OFDM signals in terms of mean square error, which is also practically meaningful because the fast Fourier transform size is typically 1.7 times larger than the nominal bandwidth in the long-term evolution (LTE) of cellular communication systems.

  1. Heritability in Cognitive Performance: Evidence Using Computer-Based Testing

    ERIC Educational Resources Information Center

    Hervey, Aaron S.; Greenfield, Kathryn; Gualtieri, C. Thomas

    2012-01-01

    There is overwhelming evidence of genetic influence on cognition. The effect is seen in general cognitive ability, as well as in specific cognitive domains. A conventional assessment approach using face-to-face paper and pencil testing is difficult for large-scale studies. Computerized neurocognitive testing is a suitable alternative. A total of…

  2. An introduction to digital modulation and OFDM techniques

    NASA Astrophysics Data System (ADS)

    Maddocks, M. C. D.

    This report differs from most BBC Research Department reports in that it does not contain details of a specific project undertaken at Kingswood Warren. While there has been a continuing development of aspects of digital modulation systems by BBC research engineers over many years, the purpose of this report is to be tutorial. That is, digital transmission techniques need to be explained in a general way if full advantage is to be obtained from other reports concerning digital broadcasting transmission systems. There are, however, references to other specialized publications if particular details are required. The text of this report is based on a paper which was prepared for an Institution of Electrical Engineers' vacation school on new broadcast standards and systems. It discusses, at a general level, the various issues and trade-offs that must be considered in the design of a digital modulation system for broadcast use. It particularly concentrates on giving a simple description of the use and benefits of OFDM systems. The particular issues can be applied to various future broadcast systems which are under development at the BBC and as part of collaborative work in international projects.

  3. [Mindfulness-based cognitive therapy : current status and future applications].

    PubMed

    Irving, Julie A; Segal, Zindel V

    2013-01-01

    Against the backdrop of dauntingly high prevalence rates of clinical depression and subsequent relapse, Segal, Teasdale and Williams (2002) sought to develop an intervention that would address the long-term sequence of depression. In the past decade, Mindfulness-Based Cognitive Therapy has been supported with a robust evidence base, highlighting its efficacy in the short, and long-term follow-up studies. Currently, novel adaptations of this intervention are being developed and piloted with a wide range of clinical issues that share amplified ruminative processes as a core feature of pathology. This review aims to summarize current and past research on MBCT, and to practically illuminate how this intervention can aid individuals in stepping out of the ruminative spirals that are part-and-parcel with major depressive episode. PMID:24719003

  4. A Companding Technique for PAPR Reduction of OFDM Systems

    NASA Astrophysics Data System (ADS)

    Hao, Miin-Jong; Liaw, Chung-Ping

    A companding technique using the hyperbolic tangent transform is proposed for reducing the peak-to-average-power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. This technique is practical and can be implemented easily in integrated circuit design. The PAPR value of an OFDM system and the optimal companding coefficient to attain the minimum quantization error are derived. Error probability performance of the system after the companding is evaluated. Our simulation results exhibits that the system with the suggested scheme has nearly the same performance as the systems with the μ-law or A-law companding techniques.

  5. Cognitive process-based subtypes of developmental coordination disorder (DCD).

    PubMed

    Asonitou, Katerina; Koutsouki, Dimitra

    2016-06-01

    The purpose of the study was to identify the cognitive subtypes demonstrated by children with developmental coordination disorder (DCD) using the Planning-Attention-Simultaneous-Successive Processing (PASS) theory and the Cognitive Assessment System (D-N CAS). Participants were 108 children aged 5- and 6-years old, 54 with DCD and 54 without DCD, all attending typical kindergartens. They were examined on 31 cognitive-motor variables. Hierarchical-agglomerative and iterative partitioning cluster analyses including 9 motor and 7 cognitive variables revealed the following six subtypes: It is well known that DCD is a heterogeneous condition. However, whenever cognitive processes were lower than average, cognitive-motor relationship was evident in subgroups C1, C4, C5 and C6. Early identification of task-specific cognitive-motor difficulties may be essential for early educational intervention practices in order to anticipate and improve learning, academic and performing difficulties. PMID:26991728

  6. A Peak Power Reduction Method with Adaptive Inversion of Clustered Parity-Carriers in BCH-Coded OFDM Systems

    NASA Astrophysics Data System (ADS)

    Muta, Osamu; Akaiwa, Yoshihiko

    In this paper, we propose a simple peak power reduction (PPR) method based on adaptive inversion of parity-check block of codeword in BCH-coded OFDM system. In the proposed method, the entire parity-check block of the codeword is adaptively inversed by multiplying weighting factors (WFs) so as to minimize PAPR of the OFDM signal, symbol-by-symbol. At the receiver, these WFs are estimated based on the property of BCH decoding. When the primitive BCH code with single error correction such as (31,26) code is used, to estimate the WFs, the proposed method employs a significant bit protection method which assigns a significant bit to the best subcarrier selected among all possible subcarriers. With computer simulation, when (31,26), (31,21) and (32,21) BCH codes are employed, PAPR of the OFDM signal at the CCDF (Complementary Cumulative Distribution Function) of 10-4 is reduced by about 1.9, 2.5 and 2.5dB by applying the PPR method, while achieving the BER performance comparable to the case with the perfect WF estimation in exponentially decaying 12-path Rayleigh fading condition.

  7. Clinical diagnosis support system based on case based fuzzy cognitive maps and semantic web.

    PubMed

    Douali, Nassim; De Roo, Jos; Jaulent, Marie-Christine

    2012-01-01

    Incorrect or improper diagnostic tests uses have important implications for health outcomes and costs. Clinical Decision Support Systems purports to optimize the use of diagnostic tests in clinical practice. The computerized medical reasoning should not only focus on existing medical knowledge but also on physician's previous experiences and new knowledge. Such medical knowledge is vague and defines uncertain relationships between facts and diagnosis, in this paper, Case Based Fuzzy Cognitive Maps (CBFCM) are proposed as an evolution of Fuzzy Cognitive Maps. They allow more complete representation of knowledge since case-based fuzzy rules are introduced to improve diagnosis decision. We have developed a framework for interacting with patient's data and formalizing knowledge from Guidelines in the domain of Urinary Tract Infection. The conducted study allowed us to test cognitive approaches for implementing Guidelines with Semantic Web tools. The advantage of this approach is to enable the sharing and reuse of knowledge from Guidelines, physicians experiences and simplify maintenance. PMID:22874199

  8. Requirements of older adults for a daily use of an internet-based cognitive training platform.

    PubMed

    Haesner, Marten; O'Sullivan, Julie L; Gövercin, Mehmet; Steinhagen-Thiessen, Elisabeth

    2015-03-01

    A decline of cognitive abilities is a part of normal human ageing. However, recent research has demonstrated that an enriched environment can have a beneficial impact on cognitive function in old age. Accordingly, mentally and socially active lifestyles are associated with less cognitive decline in old age. Specific interventions such as computerized cognitive training programs for older adults are also known to have a positive effect on the level of cognitive functioning. Therefore, online platforms combining cognitive training with web 2.0 features may yield multiple benefits for older users. However, to date only little research exists on technological acceptance and media use in this age-group especially for cognitively-impaired seniors. Therefore, in order to assess specific preferences and potential barriers of older adults regarding a web-based platform for cognitive training, we conducted qualitative interviews with 12 older adults. Half of the participants were diagnosed with mild cognitive impairment (MCI). Most importantly, our results show that cognitive exercises should incorporate themes and topics older adults are interested in. Additional communication features could serve as ideal methods for increasing user motivation. Furthermore, we derived eight critical requirements of older adults concerning daily use of a web-based cognitive training platform. Implications for future research and development are discussed. PMID:24725153

  9. Using single side-band modulation for colorless OFDM-WDM access network to alleviate Rayleigh backscattering effects.

    PubMed

    Yeh, Chien-Hung; Chow, Chi-Wai

    2016-05-16

    In this investigation, we demonstrate a new colorless orthogonal-frequency-division-multiplexing (OFDM) wavelength-division-multiplexing passive optical network (WDM-PON) system with Rayleigh backscattering (RB) noise mitigation. Here, only a single laser source at the central office (CO) is needed to produce the downstream signal and distributed continuous-wave (CW) carrier, which will then be modulated at the optical networking unit (ONU) to produce the upstream signal. Single side-band (SSB) modulation is used to wavelength-shift the distributed CW carrier, which will be launched into a reflective semiconductor optical amplifier (RSOA) based ONU for directly modulation of 5.15 Gbps OFDM upstream signal. To avoid the radio-frequency (RF) power fading and chromatic fiber dispersion, the four-band OFDM modulation is proposed to generate a 40 Gbps downstream when a Mach-Zehnder modulator (MZM) with -0.7 chirp parameter is used. Hence, the RB circumvention can be centralized in the CO. Moreover, the signal performances of downstream and upstream are also studied and discussed in this measurement. PMID:27409910

  10. New PAPR Reduction in an OFDM System Using Hybrid of PTS-CAPPR Methods with GA Coded Side Information Technique

    NASA Astrophysics Data System (ADS)

    Pradabpet, Chusit; Yoshizawa, Shingo; Miyanaga, Yoshikazu; Dejhan, Kobchai

    In this paper, we propose a new PAPR reduction by using the hybrid of partial transmit sequences (PTS) and cascade adaptive peak power reduction (CAPPR) methods with side information (SI) technique coded by genetic algorithm (GA). These methods are used in an Orthogonal Frequency Division Multiplexing (OFDM) system. The OFDM employs orthogonal sub-carriers for data modulation. These sub-carriers unexpectedly present a large peak to average power ratio (PAPR) in some cases. A proposed reduction method realizes both the advantages of PTS and CAPPR at the same time. In order to obtain the optimum condition on PTS for PAPR reduction, a quite large calculation cost is demanded and thus it is impossible to obtain the optimum PTS in a short time. In the proposed method, by using the pseudo-optimum condition based on a GA coded SI technique, the total calculation cost becomes drastically reduced. In simulation results, the proposed method shows the improvement on PAPR and also reveals the high performance on bit error rate (BER) of an OFDM system.

  11. 622-Mbps Orthogonal Frequency Division Multiplexing (OFDM) Digital Modem Implemented

    NASA Technical Reports Server (NTRS)

    Kifle, Muli; Bizon, Thomas P.; Nguyen, Nam T.; Tran, Quang K.; Mortensen, Dale J.

    2002-01-01

    Future generation space communications systems feature significantly higher data rates and relatively smaller frequency spectrum allocations than systems currently deployed. This requires the application of bandwidth- and power-efficient signal transmission techniques. There are a number of approaches to implementing such techniques, including analog, digital, mixed-signal, single-channel, or multichannel systems. In general, the digital implementations offer more advantages; however, a fully digital implementation is very difficult because of the very high clock speeds required. Multichannel techniques are used to reduce the sampling rate. One such technique, multicarrier modulation, divides the data into a number of low-rate channels that are stacked in frequency. Orthogonal frequency division multiplexing (OFDM), a form of multicarrier modulation, is being proposed for numerous systems, including mobile wireless and digital subscriber link communication systems. In response to this challenge, NASA Glenn Research Center's Communication Technology Division has developed an OFDM digital modem (modulator and demodulator) with an aggregate information throughput of 622 Mbps. The basic OFDM waveform is constructed by dividing an incoming data stream into four channels, each using either 16- ary quadrature amplitude modulation (16-QAM) or 8-phase shift keying (8-PSK). An efficient implementation for an OFDM architecture is being achieved using the combination of a discrete Fourier transform (DFT) at the transmitter to digitally stack the individual carriers, inverse DFT at the receiver to perform the frequency translations, and a polyphase filter to facilitate the pulse shaping.

  12. Physical-enhanced secure strategy in an OFDM-PON.

    PubMed

    Zhang, Lijia; Xin, Xiangjun; Liu, Bo; Yu, Jianjun

    2012-01-30

    The physical layer of optical access network is vulnerable to various attacks. As the dramatic increase of users and network capacity, the issue of physical-layer security becomes more and more important. This paper proposes a physical-enhanced secure strategy for orthogonal frequency division multiplexing passive optical network (OFDM-PON) by employing frequency domain chaos scrambling. The Logistic map is adopted for the chaos mapping. The chaos scrambling strategy can dynamically allocate the scrambling matrices for different OFDM frames according to the initial condition, which enhance the confidentiality of the physical layer. A mathematical model of this secure system is derived firstly, which achieves a secure transmission at physical layer in OFDM-PON. The results from experimental implementation using Logistic mapped chaos scrambling are also given to further demonstrate the efficiency of this secure strategy. An 10.125 Gb/s 64QAM-OFDM data with Logistic mapped chaos scrambling are successfully transmitted over 25-km single mode fiber (SMF), and the experimental results show that proposed security scheme can protect the system from eavesdropper and attacker, while keep a good performance for the legal ONU. PMID:22330465

  13. Equation-Method for correcting clipping errors in OFDM signals.

    PubMed

    Bibi, Nargis; Kleerekoper, Anthony; Muhammad, Nazeer; Cheetham, Barry

    2016-01-01

    Orthogonal frequency division multiplexing (OFDM) is the digital modulation technique used by 4G and many other wireless communication systems. OFDM signals have significant amplitude fluctuations resulting in high peak to average power ratios which can make an OFDM transmitter susceptible to non-linear distortion produced by its high power amplifiers (HPA). A simple and popular solution to this problem is to clip the peaks before an OFDM signal is applied to the HPA but this causes in-band distortion and introduces bit-errors at the receiver. In this paper we discuss a novel technique, which we call the Equation-Method, for correcting these errors. The Equation-Method uses the Fast Fourier Transform to create a set of simultaneous equations which, when solved, return the amplitudes of the peaks before they were clipped. We show analytically and through simulations that this method can, correct all clipping errors over a wide range of clipping thresholds. We show that numerical instability can be avoided and new techniques are needed to enable the receiver to differentiate between correctly and incorrectly received frequency-domain constellation symbols. PMID:27386375

  14. A Summarization on PAPR Techniques for OFDM Systems

    NASA Astrophysics Data System (ADS)

    Elavarasan, Parthasarathy; Nagarajan, G.

    2015-12-01

    Communication is one of the main aspects of life. With the advancement in age and its growing demands, there has been rapid growth in the field of communications. Signals, which were initially sent in the analog domain, are being sent in the digital domain. For better transmission, still the single carrier waves are being replaced by multi carriers. Multi carrier systems like CDMA and OFDM are now a day being implemented normally. In the OFDM system, orthogonally placed sub carriers are used to carry the data from the transmitter end to the receiver end. Presence of guard band in this system deals with the problem of ISI and noise is minimized by larger number of sub carriers. But the large peak to average power ratio (PAPR) of these signal have some undesirable effects on the system. This paper focuses on presenting the basics of an OFDM system and various methods to reduce the PAPR. High peak to average power ratio of the transmit signal is a major drawback of multicarrier transmission in OFDM. This article describes some of the important PAPR reduction techniques for multicarrier transmission including amplitude clipping and filtering, coding, partial transmit sequence, selected mapping, interleaving, tone reservation, tone injection and active constellation extension. Finally the criterion for PAPR reduction technique selection has been discussed.

  15. Manual-based cognitive behavioral and cognitive rehabilitation therapy for young-onset dementia: a case report.

    PubMed

    Tonga, Johanne Bjoernstad; Arnevik, Espen Ajo; Werheid, Katja; Ulstein, Ingun Dina

    2016-03-01

    There is a growing attention worldwide to young-onset dementia (YOD) and this group's special challenges and needs. The literature on psychosocial interventions for this population is scarce, and little is known about the specific challenges and benefits of working therapeutically with this group of patients. The aim of this study was to explore if a manual-based structured cognitive behavioral/cognitive rehabilitation program would be beneficial for these patients. One case, a 63-year-old woman with YOD, is presented to illustrate how this intervention can be applied to individual patients to manage depressive symptoms in YOD. PMID:26552831

  16. Biogeography-based optimisation of Cognitive Radio system

    NASA Astrophysics Data System (ADS)

    Kaur, Kiranjot; Rattan, Munish; Singh Patterh, Manjeet

    2014-01-01

    Biogeography-based optimisation (BBO) is a novel population-based global optimisation algorithm that is stimulated by the science of biogeography. The mathematical models of biogeography describe how a species arises, migrates from one habitat (Island) to another or gets extinct. BBO searches for the global optimum mainly through two steps: migration and mutation. These steps are controlled by immigration and emigration rates of the species in the habitat which are also used to share information between the habitats. In this paper, BBO has been applied to Cognitive Radio (CR) system for optimising its various transmission parameters to meet the quality of service (QoS) that is defined by the user in terms of minimum transmit power, minimum bit error rate (BER), maximum throughput, minimum interference and maximum spectral efficiency. To confirm the capability of biogeography-based optimisation algorithm, the results obtained by BBO are compared with that obtained by using genetic algorithm (GA) for the various QoS parameters, and it has been observed that BBO outperforms GA in system optimisation.

  17. System for Processing Coded OFDM Under Doppler and Fading

    NASA Technical Reports Server (NTRS)

    Tsou, Haiping; Darden, Scott; Lee, Dennis; Yan, Tsun-Yee

    2005-01-01

    An advanced communication system has been proposed for transmitting and receiving coded digital data conveyed as a form of quadrature amplitude modulation (QAM) on orthogonal frequency-division multiplexing (OFDM) signals in the presence of such adverse propagation-channel effects as large dynamic Doppler shifts and frequency-selective multipath fading. Such adverse channel effects are typical of data communications between mobile units or between mobile and stationary units (e.g., telemetric transmissions from aircraft to ground stations). The proposed system incorporates novel signal processing techniques intended to reduce the losses associated with adverse channel effects while maintaining compatibility with the high-speed physical layer specifications defined for wireless local area networks (LANs) as the standard 802.11a of the Institute of Electrical and Electronics Engineers (IEEE 802.11a). OFDM is a multi-carrier modulation technique that is widely used for wireless transmission of data in LANs and in metropolitan area networks (MANs). OFDM has been adopted in IEEE 802.11a and some other industry standards because it affords robust performance under frequency-selective fading. However, its intrinsic frequency-diversity feature is highly sensitive to synchronization errors; this sensitivity poses a challenge to preserve coherence between the component subcarriers of an OFDM system in order to avoid intercarrier interference in the presence of large dynamic Doppler shifts as well as frequency-selective fading. As a result, heretofore, the use of OFDM has been limited primarily to applications involving small or zero Doppler shifts. The proposed system includes a digital coherent OFDM communication system that would utilize enhanced 802.1la-compatible signal-processing algorithms to overcome effects of frequency-selective fading and large dynamic Doppler shifts. The overall transceiver design would implement a two-frequency-channel architecture (see figure

  18. Optical OFDM transmission for long-haul, metro/access, and data center applications

    NASA Astrophysics Data System (ADS)

    Srivastava, Anand

    2013-12-01

    Orthogonal frequency division multiplexing (OFDM) is a modulation technique which is now used in most new and emerging broadband wired and wireless communication systems because it is an effective solution to inter-symbol interference caused by a dispersive channel. Very recently a number of researchers have shown that OFDM is also a promising technology for optical communications. This paper gives a overview of OFDM for long-haul, metro/access and data center highlighting the aspects that are likely to be important in optical applications. To achieve good performance in optical systems OFDM must be adapted in various ways. The constraints imposed by optical channel are discussed and the new forms of optical OFDM which have been developed are outlined. The main drawbacks of OFDM are its high peak to average power ratio and its sensitivity to phase noise and frequency offset. The impairments that these cause are described and their implications for optical systems discussed.

  19. Blood Glucose, Diet-Based Glycemic Load and Cognitive Aging Among Dementia-Free Older Adults

    PubMed Central

    Andel, Ross; McEvoy, Cathy; Dahl Aslan, Anna K.; Finkel, Deborah; Pedersen, Nancy L.

    2015-01-01

    Background. Although evidence indicates that Type II Diabetes is related to abnormal brain aging, the influence of elevated blood glucose on long-term cognitive change is unclear. In addition, the relationship between diet-based glycemic load and cognitive aging has not been extensively studied. The focus of this study was to investigate the influence of diet-based glycemic load and blood glucose on cognitive aging in older adults followed for up to 16 years. Methods. Eight-hundred and thirty-eight cognitively healthy adults aged ≥50 years (M = 63.1, SD = 8.3) from the Swedish Adoption/Twin Study of Aging were studied. Mixed effects growth models were utilized to assess overall performance and change in general cognitive functioning, perceptual speed, memory, verbal ability, and spatial ability as a function of baseline blood glucose and diet-based glycemic load. Results. High blood glucose was related to poorer overall performance on perceptual speed as well as greater rates of decline in general cognitive ability, perceptual speed, verbal ability, and spatial ability. Diet-based glycemic load was related to poorer overall performance in perceptual speed and spatial ability. Conclusion. Diet-based glycemic load and, in particular, elevated blood glucose appear important for cognitive performance/cognitive aging. Blood glucose control (perhaps through low glycemic load diets) may be an important target in the detection and prevention of age-related cognitive decline. PMID:25149688

  20. Design of cognitive engine for cognitive radio based on the rough sets and radial basis function neural network

    NASA Astrophysics Data System (ADS)

    Yang, Yanchao; Jiang, Hong; Liu, Congbin; Lan, Zhongli

    2013-03-01

    Cognitive radio (CR) is an intelligent wireless communication system which can dynamically adjust the parameters to improve system performance depending on the environmental change and quality of service. The core technology for CR is the design of cognitive engine, which introduces reasoning and learning methods in the field of artificial intelligence, to achieve the perception, adaptation and learning capability. Considering the dynamical wireless environment and demands, this paper proposes a design of cognitive engine based on the rough sets (RS) and radial basis function neural network (RBF_NN). The method uses experienced knowledge and environment information processed by RS module to train the RBF_NN, and then the learning model is used to reconfigure communication parameters to allocate resources rationally and improve system performance. After training learning model, the performance is evaluated according to two benchmark functions. The simulation results demonstrate the effectiveness of the model and the proposed cognitive engine can effectively achieve the goal of learning and reconfiguration in cognitive radio.

  1. Prevalence of Dementia and Cognitive Complaints in the Context of High Cognitive Reserve: A Population-Based Study

    PubMed Central

    Perquin, Magali; Diederich, Nico; Pastore, Jessica; Lair, Marie-Lise; Stranges, Saverio; Vaillant, Michel

    2015-01-01

    Objectives This study aimed to assess the prevalence of dementia and cognitive complaints in a cross-sectional sample of Luxembourg seniors, and to discuss the results in the societal context of high cognitive reserve resulting from multilingualism. Methods A population sample of 1,377 people representative of Luxembourg residents aged over 64 years was initially identified via the national social insurance register. There were three different levels of contribution: full participation in the study, partial participation, and non-participation. We examined the profiles of these three different samples so that we could infer the prevalence estimates in the Luxembourgish senior population as a whole using the prevalence estimates obtained in this study. Results After careful attention to the potential bias and of the possibility of underestimation, we considered the obtained prevalence estimates of 3.8% for dementia (with corresponding 95% confidence limits (CL) of 2.8% and 4.8%) and 26.1% for cognitive complaints (CL = [17.8–34.3]) as trustworthy. Conclusion Based on these findings, we postulate that high cognitive reserve may result in surprisingly low prevalence estimates of cognitive complaints and dementia in adults over the age of 64 years, which thereby corroborates the longer disability-free life expectancy observed in the Luxembourg population. To the best of our knowledge, this study is the first to report such Luxembourgish public health data. PMID:26390288

  2. Spectrally Efficient Underwater Acoustic Communications: Channel Characterization and Design Aspects for OFDM

    NASA Astrophysics Data System (ADS)

    Radosevic, Andreja

    In this dissertation, we consider design aspects of spectrally efficient underwater acoustic (UWA) communications. In particular, we first focus on statistical characterization and capacity evaluation of shallow water acoustic communications channels. Wideband single-carrier and multi-carrier probe signals are employed during the Kauai Acoustic Communications MURI 2008 (KAM08) and 2011 (KAM11) experiments, to measure the time-varying channel response, and to estimate its statistical properties and capacity that play an important role in the design of spectrally efficient communication systems. Besides the capacity analysis for unconstrained inputs, we determine new bounds on the achievable information rate for discrete-time Gaussian channels with inter-symbol interference and independent and uniformly distributed channel input symbols drawn from finite-order modulation alphabets. Specifically, we derived new bounds on the achievable rates for sparse channels with long memory. Furthermore, we explore design aspects of adaptive modulation based on orthogonal frequency division multiplexing (OFDM) for UWA communications, and study its performance using real-time at-sea experiments. Lastly, we investigate a channel estimation (CE) method for improving the spectral efficiency of UWA communications. Specifically, we determine the performance of a selective decision directed (DD) CE method for UWA OFDM-based communications.

  3. Achievable information rates calculation for optical OFDM few-mode fiber long-haul transmission systems.

    PubMed

    Lin, Changyu; Djordjevic, Ivan B; Zou, Ding

    2015-06-29

    We propose a method to estimate the lower bound of achievable information rates (AIRs) of high speed orthogonal frequency-division multiplexing (OFDM) in spatial division multiplexing (SDM) optical long-haul transmission systems. The estimation of AIR is based on the forward recursion of multidimensional super-symbol efficient sliding-window Bahl-Cocke-Jelinek-Raviv (BCJR) algorithm. We consider most of the degradations of fiber links including nonlinear effects in few-mode fiber (FMF). This method does not consider the SDM as a simple multiplexer of independent data streams, but provides a super-symbol version for AIR calculation over spatial channels. This super-symbol version of AIR calculation algorithm, in principle, can be used for arbitrary multiple-input-multiple-output (MIMO)-SDM system with channel memory consideration. We illustrate this method by performing Monte Carlo simulations in a complete FMF model. Both channel model and algorithm for calculation of the AIRs are described in details. We also compare the AIRs results for QPSK/16QAM in both single mode fiber (SMF)- and FMF-based optical OFDM transmission. PMID:26191696

  4. Digital Game-Based Learning Supports Student Motivation, Cognitive Success, and Performance Outcomes

    ERIC Educational Resources Information Center

    Woo, Jeng-Chung

    2014-01-01

    Traditional multimedia learning is primarily based on the cognitive load concept of information processing theory. Recent digital game-based learning (DGBL) studies have focused on exploring content support for learning motivation and related game characteristics. Motivation, volition, and performance (MVP) theory indicates that cognitive load and…

  5. Effectiveness of Cognitive Skills-Based Computer-Assisted Instruction for Students with Disabilities: A Synthesis

    ERIC Educational Resources Information Center

    Weng, Pei-Lin; Maeda, Yukiko; Bouck, Emily C.

    2014-01-01

    Computer-assisted instruction (CAI) for students with disabilities can be categorized into the following categories: visual, auditory, mobile, and cognitive skills-based CAI. Cognitive-skills based CAI differs from other types of CAI largely in terms of an emphasis on instructional design features. We conducted both systematic review of…

  6. Web-Based Learning Programs: Use by Learners with Various Cognitive Styles

    ERIC Educational Resources Information Center

    Chen, Ling-Hsiu

    2010-01-01

    To consider how Web-based learning program is utilized by learners with different cognitive styles, this study presents a Web-based learning system (WBLS) and analyzes learners' browsing data recorded in the log file to identify how learners' cognitive styles and learning behavior are related. In order to develop an adapted WBLS, this study also…

  7. Dispersion and nonlinear effects in OFDM-RoF system

    NASA Astrophysics Data System (ADS)

    Alhasson, Bader H.; Bloul, Albe M.; Matin, M.

    2010-08-01

    The radio-over-fiber (RoF) network has been a proven technology to be the best candidate for the wireless-access technology, and the orthogonal frequency division multiplexing (OFDM) technique has been established as the core technology in the physical layer of next generation wireless communication system, as a result OFDM-RoF has drawn attentions worldwide and raised many new research topics recently. At the present time, the trend of information industry is towards mobile, wireless, digital and broadband. The next generation network (NGN) has motivated researchers to study higher-speed wider-band multimedia communication to transmit (voice, data, and all sorts of media such as video) at a higher speed. The NGN would offer services that would necessitate broadband networks with bandwidth higher than 2Mbit/s per radio channel. Many new services emerged, such as Internet Protocol TV (IPTV), High Definition TV (HDTV), mobile multimedia and video stream media. Both speed and capacity have been the key objectives in transmission. In the meantime, the demand for transmission bandwidth increased at a very quick pace. The coming of 4G and 5G era will provide faster data transmission and higher bit rate and bandwidth. Taking advantages of both optical communication and wireless communication, OFDM Radio over Fiber (OFDM-RoF) system is characterized by its high speed, large capacity and high spectral efficiency. However, up to the present there are some problems to be solved, such as dispersion and nonlinearity effects. In this paper we will study the dispersion and nonlinearity effects and their elimination in OFDM-radio-over-fiber system.

  8. Extended reach OFDM-PON using super-Nyquist image induced aliasing.

    PubMed

    Guo, Changjian; Liang, Jiawei; Liu, Jie; Liu, Liu

    2015-08-24

    We investigate a novel dispersion compensating technique in double sideband (DSB) modulated and directed-detected (DD) passive optical network (PON) systems using super-Nyquist image induced aliasing. We show that diversity is introduced to the higher frequency components by deliberate aliasing using the super-Nyquist images. We then propose to use fractional sampling and per-subcarrier maximum ratio combining (MRC) to harvest this diversity. We evaluate the performance of conventional orthogonal frequency division multiplexing (OFDM) signals along with discrete Fourier transform spread (DFT-S) OFDM and code-division multiplexing OFDM (CDM-OFDM) signals using the proposed scheme. The results show that the DFT-S OFDM signal has the best performance due to spectrum spreading and its superior peak-to-average power ratio (PAPR). By using the proposed scheme, the reach of a 10-GHz bandwidth QPSK modulated OFDM-PON can be extended to around 90 km. We also experimentally show that the achievable data rate of the OFDM signals can be effectively increased using the proposed scheme when adaptive bit loading is applied, depending on the transmission distance. A 10.5% and 5.2% increase in the achievable bit rate can be obtained for DSB modulated OFDM-PONs in 48.3-km and 83.2-km standard single mode fiber (SSMF) transmission cases, respectively, without any modification on the transmitter. A 40-Gb/s OFDM transmission over 83.2-km SSMF is successfully demonstrated. PMID:26368156

  9. A Cognitive Diagnosis Model for Cognitively Based Multiple-Choice Options

    ERIC Educational Resources Information Center

    de la Torre, Jimmy

    2009-01-01

    Cognitive or skills diagnosis models are discrete latent variable models developed specifically for the purpose of identifying the presence or absence of multiple fine-grained skills. However, applications of these models typically involve dichotomous or dichotomized data, including data from multiple-choice (MC) assessments that are scored as…

  10. Joint Symbol Timing and CFO Estimation for OFDM/OQAM Systems in Multipath Channels

    NASA Astrophysics Data System (ADS)

    Fusco, Tilde; Petrella, Angelo; Tanda, Mario

    2009-12-01

    The problem of data-aided synchronization for orthogonal frequency division multiplexing (OFDM) systems based on offset quadrature amplitude modulation (OQAM) in multipath channels is considered. In particular, the joint maximum-likelihood (ML) estimator for carrier-frequency offset (CFO), amplitudes, phases, and delays, exploiting a short known preamble, is derived. The ML estimators for phases and amplitudes are in closed form. Moreover, under the assumption that the CFO is sufficiently small, a closed form approximate ML (AML) CFO estimator is obtained. By exploiting the obtained closed form solutions a cost function whose peaks provide an estimate of the delays is derived. In particular, the symbol timing (i.e., the delay of the first multipath component) is obtained by considering the smallest estimated delay. The performance of the proposed joint AML estimator is assessed via computer simulations and compared with that achieved by the joint AML estimator designed for AWGN channel and that achieved by a previously derived joint estimator for OFDM systems.

  11. Automatic Synthesis of Cost Effective FFT/IFFT Cores for VLSI OFDM Systems

    NASA Astrophysics Data System (ADS)

    L'Insalata, Nicola E.; Saponara, Sergio; Fanucci, Luca; Terreni, Pierangelo

    This work presents an FFT/IFFT core compiler particularly suited for the VLSI implementation of OFDM communication systems. The tool employs an architecture template based on the pipelined cascade principle. The generated cores support run-time programmable length and transform type selection, enabling seamless integration into multiple mode and multiple standard terminals. A distinctive feature of the tool is its accuracy-driven configuration engine which automatically profiles the internal arithmetic and generates a core with minimum operands bit-width and thus minimum circuit complexity. The engine performs a closed-loop optimization over three different internal arithmetic models (fixed-point, block floating-point and convergent block floating-point) using the numerical accuracy budget given by the user as a reference point. The flexibility and re-usability of the proposed macrocell are illustrated through several case studies which encompass all current state-of-the-art OFDM communications standards (WLAN, WMAN, xDSL, DVB-T/H, DAB and UWB). Implementations results of the generated macrocells are presented for two deep sub-micron standard-cells libraries (65 and 90nm) and commercially available FPGA devices. When compared with other tools for automatic FFT core generation, the proposed environment produces macrocells with lower circuit complexity expressed as gate count and RAM/ROM bits, while keeping the same system level performance in terms of throughput, transform size and numerical accuracy.

  12. New low-complexity and robust time synchronization technique for optical IMDD OFDM transmissions.

    PubMed

    Truong, Tuan-Anh; Arzel, Matthieu; Lin, Hao; Jahan, Bruno; Jezequel, Michel

    2014-06-16

    This paper provides an analysis of the performance of conventional preamble-based time synchronization techniques, which have been proposed for Orthogonal Frequency Division Multiplexing (OFDM) radio transmissions, in the context of optical Intensity Modulated and Direct Detected (IMDD) OFDM transmissions over single-mode fiber. A novel preamble structure along with a two-stage synchronization algorithm is proposed. Thanks to the particular structure of the preamble, a first coarse synchronization metric does not present minor peaks. In addition, without the knowledge of the preamble waveform the receiver can perform both coarse and fine synchronization steps. As maximal delay in arrival time between different frequency components of a signal depends on chromatic dispersion and the signal bandwidth, it is also observed that a slowly time-varying preamble is more robust than a fast time-varying one. By means of numerical simulations, the proposed method is shown to provide better performance when compared to other conventional methods in terms of timing offset variance with reduced receiver complexity. In unamplified transmissions the proposed technique guarantees a quasi-optimal transmission capacity even with a short cyclic prefix. PMID:24977530

  13. Novel Rx IQ mismatch compensation considering laser phase noise for CO-OFDM system

    NASA Astrophysics Data System (ADS)

    Ma, Xiurong; Ding, Zhaocai; Li, Kun; Wang, Xiao

    2015-08-01

    In this paper, a novel compensation scheme for receiver (Rx) in-phase/quadrature (IQ) mismatch is proposed in coherent optical orthogonal frequency division multiplexing (CO-OFDM) system in the presence of laser phase noise. In this scheme, laser phase noise and channel distortion were combined as a new channel transfer factor, the IQ mismatch factor and initial channel transfer factor can be estimated independently based on the relationship of IQ mismatch factors. And the channel transfer factor can be updated on a symbol-by-symbol basis which retrieves an estimation of the phase noise value by extracting and averaging the phase drift of all OFDM sub-channels. Numerical results indicate that when the phase and amplitude mismatch are 10° and 2 dB respectively, a 1.6 dB optical signal-to noise ratio is improved at laser linewidth of 60 kHz. Furthermore, the complexity of the proposed method is analyzed in terms of the number of required complex multiplications per bit.

  14. Cognitive Remediation: Potential Novel Brain-Based Treatment for Bipolar Disorder in Children and Adolescents

    PubMed Central

    Dickstein, Daniel P.; Cushman, Grace K.; Kim, Kerri L.; Weissman, Alexandra B.; Wegbreit, Ezra

    2015-01-01

    Bipolar disorder (BD) is among the most impairing psychiatric disorders affecting children and adolescents, despite our best psychopharmacological and psychotherapeutic treatments. Cognitive remediation, defined as a behavioral intervention designed to improve cognitive functions so as to reduce psychiatric illness, is an emerging brain-based treatment approach that has thus far not been studied in pediatric BD. The present article reviews the basic principles of cognitive remediation, describes what is known about cognitive remediation in psychiatric disorders, and delineates potential brain/behavior alterations implicated in pediatric BD that might be targets for cognitive remediation. Emerging data shows that cognitive remediation may be useful in children and adults with schizophrenia, ADHD, and anxiety disorders, and in adults with BD. Potential targets for cognitive remediation in pediatric BD include face processing, response inhibition, frustration, and cognitive flexibility. Further study is warranted to determine if cognitive remediation for these targets, or others, may serve as a novel, brain-based treatment for pediatric BD. PMID:26135596

  15. EEG-based research on brain functional networks in cognition.

    PubMed

    Wang, Niannian; Zhang, Li; Liu, Guozhong

    2015-01-01

    Recently, exploring the cognitive functions of the brain by establishing a network model to understand the working mechanism of the brain has become a popular research topic in the field of neuroscience. In this study, electroencephalography (EEG) was used to collect data from subjects given four different mathematical cognitive tasks: recite numbers clockwise and counter-clockwise, and letters clockwise and counter-clockwise to build a complex brain function network (BFN). By studying the connectivity features and parameters of those brain functional networks, it was found that the average clustering coefficient is much larger than its corresponding random network and the average shortest path length is similar to the corresponding random networks, which clearly shows the characteristics of the small-world network. The brain regions stimulated during the experiment are consistent with traditional cognitive science regarding learning, memory, comprehension, and other rational judgment results. The new method of complex networking involves studying the mathematical cognitive process of reciting, providing an effective research foundation for exploring the relationship between brain cognition and human learning skills and memory. This could help detect memory deficits early in young and mentally handicapped children, and help scientists understand the causes of cognitive brain disorders. PMID:26405867

  16. Music-based cognitive remediation therapy for patients with traumatic brain injury.

    PubMed

    Hegde, Shantala

    2014-01-01

    Traumatic brain injury (TBI) is one of the common causes of disability in physical, psychological, and social domains of functioning leading to poor quality of life. TBI leads to impairment in sensory, motor, language, and emotional processing, and also in cognitive functions such as attention, information processing, executive functions, and memory. Cognitive impairment plays a central role in functional recovery in TBI. Innovative methods such as music therapy to alleviate cognitive impairments have been investigated recently. The role of music in cognitive rehabilitation is evolving, based on newer findings emerging from the fields of neuromusicology and music cognition. Research findings from these fields have contributed significantly to our understanding of music perception and cognition, and its neural underpinnings. From a neuroscientific perspective, indulging in music is considered as one of the best cognitive exercises. With "plasticity" as its veritable nature, brain engages in producing music indulging an array of cognitive functions and the product, the music, in turn permits restoration and alters brain functions. With scientific findings as its basis, "neurologic music therapy" (NMT) has been developed as a systematic treatment method to improve sensorimotor, language, and cognitive domains of functioning via music. A preliminary study examining the effect of NMT in cognitive rehabilitation has reported promising results in improving executive functions along with improvement in emotional adjustment and decreasing depression and anxiety following TBI. The potential usage of music-based cognitive rehabilitation therapy in various clinical conditions including TBI is yet to be fully explored. There is a need for systematic research studies to bridge the gap between increasing theoretical understanding of usage of music in cognitive rehabilitation and application of the same in a heterogeneous condition such as TBI. PMID:24715887

  17. Empowering At-Risk Students to Stay in School Using a Cognitive-Based Information System.

    ERIC Educational Resources Information Center

    Chinien, Christian A.; And Others

    1997-01-01

    Junior high students who were at risk of dropping out of school (n=45) were taught using the Cognitive-Based Instructional System (CBIS). Positive cognitive skills change occurred in 38%; there were discrepancies between dropout prediction test results and teacher perceptions of students at risk; CBIS implementation would require a significant…

  18. Cognitive and Cognate-Based Treatments for Bilingual Aphasia: A Case Study

    ERIC Educational Resources Information Center

    Kohnert, Kathryn

    2004-01-01

    Two consecutive treatments were conducted to investigate skill learning and generalization within and across cognitive-linguistic domains in a 62-year-old Spanish-English bilingual man with severe non-fluent aphasia. Treatment 1 was a cognitive-based treatment that emphasized non-linguistic skills, such as visual scanning, categorization, and…

  19. Physically secured orthogonal frequency division multiplexing-passive optical network employing noise-based encryption and signal recovery process

    NASA Astrophysics Data System (ADS)

    Jin, Wei; Zhang, Chongfu; Yuan, Weicheng

    2016-02-01

    We propose a physically enhanced secure scheme for direct detection-orthogonal frequency division multiplexing-passive optical network (DD-OFDM-PON) and long reach coherent detection-orthogonal frequency division multiplexing-passive optical network (LRCO-OFDM-PON), by employing noise-based encryption and channel/phase estimation. The noise data generated by chaos mapping are used to substitute training sequences in preamble to realize channel estimation and frame synchronization, and also to be embedded on variable number of key-selected randomly spaced pilot subcarriers to implement phase estimation. Consequently, the information used for signal recovery is totally hidden as unpredictable noise information in OFDM frames to mask useful information and to prevent illegal users from correctly realizing OFDM demodulation, and thereby enhancing resistance to attackers. The levels of illegal-decryption complexity and implementation complexity are theoretically discussed. Through extensive simulations, the performances of the proposed channel/phase estimation and the security introduced by encrypted pilot carriers have been investigated in both DD-OFDM and LRCO-OFDM systems. In addition, in the proposed secure DD-OFDM/LRCO-OFDM PON models, both legal and illegal receiving scenarios have been considered. These results show that, by utilizing the proposed scheme, the resistance to attackers can be significantly enhanced in DD-OFDM-PON and LRCO-OFDM-PON systems without performance degradations.

  20. Can Smartphones Enhance Telephone-Based Cognitive Assessment (TBCA)?

    PubMed Central

    Kwan, Rick Yiu-Cho; Lai, Claudia Kam-Yuk

    2013-01-01

    TBCA has emerged to solve the limitations of administering cognitive assessments face-to-face. The recent development of telephones and knowledge advances in the area of cognitive impairment may affect the development of TBCA. The purpose of this paper is to discuss how smartphones can be used to enhance the applicability of TBCA, which has previously been administered by conventional telephone. This paper will first review, describe and critique the existing TBCA instruments. It will then discuss the recent developments in tele-technology, the popularity of tele-technology among the elderly, potential benefits and challenges in using smartphones for cognitive assessment, and possible future developments in this technology. In the systematic review, eighteen TBCA instruments were identified. They were found to be valid in differentiating between people with and without dementia. TBCA was previously found to be launched on a conventional telephone platform. The advances in understanding of cognitive impairment may demand that telephones be equipped with more advanced features. Recently, the development and penetration of smartphones among the elderly has been rapid. This may allow the smartphone to enhance its TBCA applicability by overcoming the limitations of the conventional telephone, rendering the TBCA more efficient in addressing the increasing demand and complexity of cognitive assessments in the future. However, more research and technology developments are needed before smartphones can become a valid platform for TBCA. PMID:24351736

  1. Cognitive Assessment of Movement-Based Computer Games

    NASA Technical Reports Server (NTRS)

    Kearney, Paul

    2008-01-01

    This paper examines the possibility that dance games such as Dance Dance Revolution or StepMania enhance the cognitive abilities that are critical to academic achievement. These games appear to place a high cognitive load on working memory requiring the player to convert a visual signal to a physical movement up to 7 times per second. Players see a pattern of directions displayed on the screen and they memorise these as a dance sequence. Other researchers have found that attention span and memory ability, both cognitive abilities required for academic achievement, are improved through the use of physical movement and exercise. This paper reviews these claims and documents tool development for on-going research by the author.

  2. Time-lenses for time-division multiplexing of optical OFDM channels.

    PubMed

    Geng, Zihan; Corcoran, Bill; Zhu, Chen; Lowery, Arthur James

    2015-11-16

    Time-lenses provide a promising platform for novel, broadband optical signal processing. However, in order to minimize system penalties, design constraints must be adequately taken into account. We investigate the impact of third-order-dispersion and nonlinear distortion on the performance of time-lens-based communication systems for the first time. Here, we propose a novel application of time-lenses - temporal compression and time-division multiplexing of optical OFDM channels, to provide a 1 Tb/s superchannel. Time-lens system performance degradations are investigated in our proposed system and the results are applicable to all four wave mixing based time-lens systems. Our work can help to optimize time-lens based communication systems. PMID:26698462

  3. Numerical investigation of all-optical add-drop multiplexing for spectrally overlapping OFDM signals.

    PubMed

    Sygletos, S; Fabbri, S; Giacoumidis, E; Sorokina, M; Marom, D M; Stephens, M F C; Klonidis, D; Tomkos, I; Ellis, A D

    2015-03-01

    We propose a novel architecture for all-optical add-drop multiplexing of OFDM signals. Sub-channel extraction is achieved by means of waveform replication and coherent subtraction from the OFDM super-channel. Numerical simulations have been carried out to benchmark the performance of the architecture against critical design parameters. PMID:25836815

  4. 12-mode OFDM transmission using reduced-complexity maximum likelihood detection.

    PubMed

    Lobato, Adriana; Chen, Yingkan; Jung, Yongmin; Chen, Haoshuo; Inan, Beril; Kuschnerov, Maxim; Fontaine, Nicolas K; Ryf, Roland; Spinnler, Bernhard; Lankl, Berthold

    2015-02-01

    We report the transmission of 163-Gb/s MDM-QPSK-OFDM and 245-Gb/s MDM-8QAM-OFDM transmission over 74 km of few-mode fiber supporting 12 spatial and polarization modes. A low-complexity maximum likelihood detector is employed to enhance the performance of a system impaired by mode-dependent loss. PMID:25680039

  5. Distinguishing the affective and cognitive bases of implicit attitudes to improve prediction of food choices.

    PubMed

    Trendel, Olivier; Werle, Carolina O C

    2016-09-01

    Eating behaviors largely result from automatic processes. Yet, in existing research, automatic or implicit attitudes toward food often fail to predict eating behaviors. Applying findings in cognitive neuroscience research, we propose and find that a central reason why implicit attitudes toward food are not good predictors of eating behaviors is that implicit attitudes are driven by two distinct constructs that often have diverging evaluative consequences: the automatic affective reactions to food (e.g., tastiness; the affective basis of implicit attitudes) and the automatic cognitive reactions to food (e.g., healthiness; the cognitive basis of implicit attitudes). More importantly, we find that the affective and cognitive bases of implicit attitudes directly and uniquely influence actual food choices under different conditions. While the affective basis of implicit attitude is the main driver of food choices, it is the only driver when cognitive resources during choice are limited. The cognitive basis of implicit attitudes uniquely influences food choices when cognitive resources during choice are plentiful but only for participants low in impulsivity. Researchers interested in automatic processes in eating behaviors could thus benefit by distinguishing between the affective and cognitive bases of implicit attitudes. PMID:26471802

  6. Prevalence and Cognitive Bases of Subjective Memory Complaints in Older Adults: Evidence from a Community Sample

    PubMed Central

    McClendon, McKee J.; Wallendal, Maggie S.; Hyde, Trevor F.; Larsen, Janet D.

    2014-01-01

    Objectives. To estimate the prevalence of subjective memory complaints (SMCs) in a sample of community-dwelling, older adults and to examine cognitive bases of these complaints. Participants. 499 community-dwelling adults, 65 and older. Measurements. A telephone survey consisting of cognitive tests and clinical and sociodemographic variables. SMCs were based on subjects' evaluations and subjects' perceptions of others' evaluations. Analysis. Logistic regression was used to model the risk for SMCs as a function of the cognitive, clinical, and sociodemographic variables. We tested for interactions of the cognitive variables with age, education, and gender. Results. 27.1% reported memory complaints. Among the younger age, better objective memory performance predicted lower risk for SMCs, while among the older age, better memory had no effect on risk. Among the better-educated people, better global cognitive functioning predicted lower risk for SMCs, while among the less-educated people, better global cognitive functioning had no effect on SMC risk. When predicting others' perceptions, better objective memory was associated with lower risk for SMCs. Conclusion. Objective memory performance and global cognitive functioning are associated with lower risk for SMCs, but these relationships are the strongest for the younger age and those with more education, respectively. Age and education may affect the ability to accurately appraise cognitive functioning. PMID:26317004

  7. Smartphone-based system to improve transportation access for the cognitively impaired.

    PubMed

    Anderson, Shane M; Riehle, Timothy H; Lichter, Patrick A; Brown, Allen W; Panescu, Dorin

    2015-08-01

    This project developed and evaluated a smartphone-based system to improve mobility and transportation access for the cognitively impaired. The proposed system is intended to allow the cognitively impaired to use public transportation systems, community transportation and dedicated transportation services for the disabled with greater ease and safety. Individuals with cognitive disabilities are often unable to operate an automobile, or may require a prolonged recovery period before resuming driving. Public transportation systems represent a significant means to allow these individuals to maintain independence. Yet public transportation systems can pose significant challenges to individuals with cognitive impairment. The goal of this project is to develop a system to reduce these barriers via a technological solution consisting of components developed both for the cognitively impaired user and their caregiver or family member. The first component consists of a cognitive prosthetic device featuring traditional memory cueing and reminders as well as custom location-based transportation specific functions. This cognitive mobility assistant will leverage the computing power and GPS location determination capabilities of inexpensive, powerful smart phones. The second component consists of a management application which offers caregivers the ability to configure and program the reminder and transit functions remotely via the Internet. Following completion of the prototype system a pilot human test was performed with cognitively disabled individuals and family members or caregivers to assess the usability and acceptability of both system components. PMID:26738091

  8. Wavelet packet transform-based optical orthogonal frequency-division multiplexing transmission using direct detection

    NASA Astrophysics Data System (ADS)

    Zhang, Hongbo; Yi, Xingwen; Chen, Lei; Zhang, Jing; Deng, Mingliang; Qiu, Kun

    2012-10-01

    As an alternate to fast Fourier transform-based orthogonal frequency-division multiplexing (OFDM), wavelet packet transform (WPT)-based OFDM (WPT-OFDM) does not require cyclic prefix to avoid inter-symbol-interference. The wavelet has many varieties and therefore, it can provide more freedom for system design to suit different applications. We propose a real-valued WPT-OFDM that uses intensity modulation/direct detection. We also conduct an experiment to verify its performance through a 75-km standard single-mode fiber.

  9. Flexible all-optical frequency allocation of OFDM subcarriers.

    PubMed

    Lowery, Arthur James; Schröder, Jochen; Du, Liang B

    2014-01-13

    We investigate the underlying mechanism that allows OFDM subcarriers in an all-optical OFDM system to be assigned to any optical frequency using an optical filter, even if that frequency is not generated by the comb-line source feeding the filters. We confirm our analysis using simulations, and present experimental results from a 252-subcarrier system that uses a mode-locked laser (MLL) as the comb source and a wavelength selective switch. The experimental results show that there is no correlation between the programmed frequency offset between a subcarrier and nearest comb line, and the received signal quality. Thus, subcarriers could be inserted into unused portions of an optical transmission system's spectrum without restriction on their particular center frequencies. Any percentage of cyclic prefix can be added to the OFDM symbol simply by reprogramming the optical filter to give wider subcarrier frequency spacing than the comb line spacing, which is useful for tailoring the CP to the dispersion of various optical transmission paths, to maximize the spectral efficiency. Finally, the MLL's center frequency need not be locked to a system reference. PMID:24515064

  10. Cognitive Effects of Mindfulness Training: Results of a Pilot Study Based on a Theory Driven Approach

    PubMed Central

    Wimmer, Lena; Bellingrath, Silja; von Stockhausen, Lisa

    2016-01-01

    The present paper reports a pilot study which tested cognitive effects of mindfulness practice in a theory-driven approach. Thirty-four fifth graders received either a mindfulness training which was based on the mindfulness-based stress reduction approach (experimental group), a concentration training (active control group), or no treatment (passive control group). Based on the operational definition of mindfulness by Bishop et al. (2004), effects on sustained attention, cognitive flexibility, cognitive inhibition, and data-driven as opposed to schema-based information processing were predicted. These abilities were assessed in a pre-post design by means of a vigilance test, a reversible figures test, the Wisconsin Card Sorting Test, a Stroop test, a visual search task, and a recognition task of prototypical faces. Results suggest that the mindfulness training specifically improved cognitive inhibition and data-driven information processing. PMID:27462287

  11. Evidence-based practice for pain identification in cognitively impaired nursing home residents.

    PubMed

    Sacoco, Christina; Ishikawa, Sally

    2014-09-01

    Pain identification of cognitively impaired elderly is very challenging. This project aimed to identify best practices for pain assessment in nursing home residents with cognitive impairment and to establish a standardized pain assessment guide to optimize nursing practice and resident outcomes. The Iowa Model of Evidence-Based Practice to Promote Quality of Care guided the project's process. Phase I of the project analyzed data gained from chart reviews on current practices of pain assessment, and Phase II used the results of Phase I to develop, implement, and evaluate an evidence-based practice standard for nursing assessment of pain for cognitively impaired residents. PMID:25155534

  12. Digital coherent superposition of optical OFDM subcarrier pairs with Hermitian symmetry for phase noise mitigation.

    PubMed

    Yi, Xingwen; Chen, Xuemei; Sharma, Dinesh; Li, Chao; Luo, Ming; Yang, Qi; Li, Zhaohui; Qiu, Kun

    2014-06-01

    Digital coherent superposition (DCS) provides an approach to combat fiber nonlinearities by trading off the spectrum efficiency. In analogy, we extend the concept of DCS to the optical OFDM subcarrier pairs with Hermitian symmetry to combat the linear and nonlinear phase noise. At the transmitter, we simply use a real-valued OFDM signal to drive a Mach-Zehnder (MZ) intensity modulator biased at the null point and the so-generated OFDM signal is Hermitian in the frequency domain. At receiver, after the conventional OFDM signal processing, we conduct DCS of the optical OFDM subcarrier pairs, which requires only conjugation and summation. We show that the inter-carrier-interference (ICI) due to phase noise can be reduced because of the Hermitain symmetry. In a simulation, this method improves the tolerance to the laser phase noise. In a nonlinear WDM transmission experiment, this method also achieves better performance under the influence of cross phase modulation (XPM). PMID:24921539

  13. Managing Cognitive Load during Document-Based Learning

    ERIC Educational Resources Information Center

    Rouet, Jean-Francois

    2009-01-01

    Designers of interactive learning environments face the issue of managing the learner's cognitive load, reducing irrelevant sources while optimizing useful sources of load. I propose a conceptual framework aimed at organizing the contributions of the papers presented in this special issue. The framework identifies three main dimensions, namely…

  14. Team-Based Complex Problem Solving: A Collective Cognition Perspective

    ERIC Educational Resources Information Center

    Hung, Woei

    2013-01-01

    Today, much problem solving is performed by teams, rather than individuals. The complexity of these problems has exceeded the cognitive capacity of any individual and requires a team of members to solve them. The success of solving these complex problems not only relies on individual team members who possess different but complementary expertise,…

  15. Technology-Based Cognitive Apprenticeship for Empowering Children with Disabilities

    ERIC Educational Resources Information Center

    Kasinath, H. M.

    2009-01-01

    The cognitive apprenticeship approach has been applied in a good deal of conceptual, quantitative and qualitative studies in various settings including technology integration. It has proved successful in promoting student's higher order thinking skills as well as in shaping the social interactions between teachers and students to goal-oriented…

  16. Design of Activities on Numerical Representations Based on Cognitive Research

    ERIC Educational Resources Information Center

    Kalifatidou, Eleftheria R.

    2008-01-01

    The results of the cognitive research on numbers' representations can provide a sound theoretical framework to develop educational activities on representing numbers. A program of such activities for a nursery school was designed in order to enable the children to externalize and strengthen their internal representations about numerosity and link…

  17. Expectations and Experience: Dissociable Bases for Cognitive Control?

    ERIC Educational Resources Information Center

    Bugg, Julie M.; Diede, Nathaniel T.; Cohen-Shikora, Emily R.; Selmeczy, Diana

    2015-01-01

    Classic theories emphasized the role of expectations in the intentional control of attention and action. However, recent theorizing has implicated experience-dependent, online adjustments as the primary basis for cognitive control--adjustments that appear to be implicit (Blais, Harris, Guerrero, & Bunge, 2012). The purpose of the current study…

  18. Generalizability of Cognitive Interview-Based Measures across Cultural Groups

    ERIC Educational Resources Information Center

    Solano-Flores, Guillermo; Li, Min

    2009-01-01

    We addressed the challenge of scoring cognitive interviews in research involving multiple cultural groups. We interviewed 123 fourth- and fifth-grade students from three cultural groups to probe how they related a mathematics item to their personal lives. Item meaningfulness--the tendency of students to relate the content and/or context of an item…

  19. Expectations and experience: Dissociable bases for cognitive control?

    PubMed

    Bugg, Julie M; Diede, Nathaniel T; Cohen-Shikora, Emily R; Selmeczy, Diana

    2015-09-01

    Classic theories emphasized the role of expectations in the intentional control of attention and action. However, recent theorizing has implicated experience-dependent, online adjustments as the primary basis for cognitive control--adjustments that appear to be implicit (Blais, Harris, Guerrero, & Bunge, 2012). The purpose of the current study was to evaluate whether explicit expectations play any role in cognitive control above and beyond experience. In a novel precued lists paradigm, participants were administered abbreviated lists of Stroop trials. For half of the lists, precues led participants to validly expect lists of varying proportion congruency (e.g., mostly congruent [MC], mostly incongruent [MI]; Experiments 1 to 4). The Stroop effect was greater in cued MC relative to uncued MC lists. By contrast, the Stroop effect was equivalent in cued MI and uncued MI lists. Only when preparation was encouraged via a speed manipulation (Experiment 3) or incentives (Experiment 4) did we find evidence of heightened control when an MI list was expected, in the form of a short-lived reduction in the Stroop effect on the first (experience-free) trial. These patterns suggest (a) expectations play a role in the relaxation of cognitive control, independent of experience (as also shown in Experiment 5, wherein expectations were varied while holding experience constant across lists), but (b) experience is the dominant basis for the sustained heightening of cognitive control (after the first trial). Theoretical implications of dissociating the contributions of expectations and experience to cognitive control are discussed, including interpretations of the list-wide proportion congruence effect. PMID:25689002

  20. High-efficiency optical coupling single-sideband modulation for OFDM-RoF-PON systems

    NASA Astrophysics Data System (ADS)

    Xue, Xuwei; Ji, Wei; Kang, Zhaoyuan; Huang, Kangrui; Li, Xiao

    2015-12-01

    We report on an OFDM-RoF-PON system based on novel optical coupling single-sideband (O-SSB) modulation for one wavelength carrying one baseband and two radio frequency (RF) signals. The impact of nonlinear distortion consisting of harmonic distortion (HD) and intermodulation distortion (IMD) in this system is theoretically investigated. Transmission over 0 km and 40 km of standard single mode fiber is successfully demonstrated and it is indicated that modulation index 0.6 is more adapted to O-SSB modulation. The error vector magnitude (EVM) of system based on O-SSB modulation after transmission over 40 km is <0.1. For O-SSB modulation, bit error rate (BER) after 40 km transmission is below forward error correction (FEC) limit of 10-3.

  1. Four-dimensional optical multiband-OFDM for beyond 1.4 Tb/s serial optical transmission.

    PubMed

    Djordjevic, Ivan; Batshon, Hussam G; Xu, Lei; Wang, Ting

    2011-01-17

    We propose a four-dimensional (4D) coded multiband-OFDM scheme suitable for beyond 1.4 Tb/s serial optical transport. The proposed scheme organizes the N-dimensional (ND) signal constellation points in the form of signal matrix; employs 2D-inverse FFT and 2D-FFT to perform modulation and demodulation, respectively; and exploits both orthogonal polarizations. This scheme can fully exploit advantages of OFDM to deal with chromatic dispersion, PMD and PDL effects; and multidimensional signal constellations to improve OSNR sensitivity of conventional optical OFDM. The improvement of 4D-OFDM over corresponding polarization-multiplexed QAM (with the same number of constellation points) ranges from 1.79 dB for 16 signal constellation point-four-dimensional-OFDM (16-4D-OFDM) up to 4.53 dB for 128-4D-OFDM. PMID:21263627

  2. Achievable rate maximization for decode-and-forward MIMO-OFDM networks with an energy harvesting relay.

    PubMed

    Du, Guanyao; Yu, Jianjun

    2016-01-01

    This paper investigates the system achievable rate for the multiple-input multiple-output orthogonal frequency division multiplexing (MIMO-OFDM) system with an energy harvesting (EH) relay. Firstly we propose two protocols, time switching-based decode-and-forward relaying (TSDFR) and a flexible power splitting-based DF relaying (PSDFR) protocol by considering two practical receiver architectures, to enable the simultaneous information processing and energy harvesting at the relay. In PSDFR protocol, we introduce a temporal parameter to describe the time division pattern between the two phases which makes the protocol more flexible and general. In order to explore the system performance limit, we discuss the system achievable rate theoretically and formulate two optimization problems for the proposed protocols to maximize the system achievable rate. Since the problems are non-convex and difficult to solve, we first analyze them theoretically and get some explicit results, then design an augmented Lagrangian penalty function (ALPF) based algorithm for them. Numerical results are provided to validate the accuracy of our analytical results and the effectiveness of the proposed ALPF algorithm. It is shown that, PSDFR outperforms TSDFR to achieve higher achievable rate in such a MIMO-OFDM relaying system. Besides, we also investigate the impacts of the relay location, the number of antennas and the number of subcarriers on the system performance. Specifically, it is shown that, the relay position greatly affects the system performance of both protocols, and relatively worse achievable rate is achieved when the relay is placed in the middle of the source and the destination. This is different from the MIMO-OFDM DF relaying system without EH. Moreover, the optimal factor which indicates the time division pattern between the two phases in the PSDFR protocol is always above 0.8, which means that, the common division of the total transmission time into two equal phases in

  3. NSAID Use and Incident Cognitive Impairment in a Population-based Cohort.

    PubMed

    Wichmann, Margarete A; Cruickshanks, Karen J; Carlsson, Cynthia M; Chappell, Rick; Fischer, Mary E; Klein, Barbara E K; Klein, Ronald; Schubert, Carla R

    2016-01-01

    Nonsteroidal anti-inflammatory drugs (NSAIDs) may prevent dementia, but previous studies have yielded conflicting results. This study estimated the association of prior NSAID use with incident cognitive impairment in the population-based Epidemiology of Hearing Loss Study (EHLS, n=2422 without cognitive impairment in 1998-2000). Prospectively collected medication data from 1988-1990, 1993-1995, and 1998-2000 were used to categorize NSAID use history at the cognitive baseline (1998-2000). Aspirin use and nonaspirin NSAID use were separately examined. Cox regression models were used to estimate the associations between NSAID use history at baseline and incident cognitive impairment in 2003-2005 or 2009-2010. Logistic regression analyses were used to estimate associations with a second outcome, mild cognitive impairment/dementia, available in 2009-2010. Participants using aspirin at baseline but not 5 years prior were more likely to develop cognitive impairment (adjusted hazard ratio=1.77; 95% confidence interval=1.11, 2.82; model 2), with nonsignificant associations for longer term use. Nonaspirin NSAID use was not associated with incident cognitive impairment or mild cognitive impairment/dementia odds. These results provided no evidence to support a potential protective effect of NSAIDs against dementia. PMID:26079710

  4. PERFORMANCE OF A COMPUTER-BASED ASSESSMENT OF COGNITIVE FUNCTION MEASURES IN TWO COHORTS OF SENIORS

    PubMed Central

    Espeland, Mark A.; Katula, Jeffrey A.; Rushing, Julia; Kramer, Arthur F.; Jennings, Janine M.; Sink, Kaycee M.; Nadkarni, Neelesh K.; Reid, Kieran F.; Castro, Cynthia M.; Church, Timothy; Kerwin, Diana R.; Williamson, Jeff D.; Marottoli, Richard A.; Rushing, Scott; Marsiske, Michael; Rapp, Stephen R.

    2013-01-01

    Background Computer-administered assessment of cognitive function is being increasingly incorporated in clinical trials, however its performance in these settings has not been systematically evaluated. Design The Seniors Health and Activity Research Program (SHARP) pilot trial (N=73) developed a computer-based tool for assessing memory performance and executive functioning. The Lifestyle Interventions and Independence for Seniors (LIFE) investigators incorporated this battery in a full scale multicenter clinical trial (N=1635). We describe relationships that test scores have with those from interviewer-administered cognitive function tests and risk factors for cognitive deficits and describe performance measures (completeness, intra-class correlations). Results Computer-based assessments of cognitive function had consistent relationships across the pilot and full scale trial cohorts with interviewer-administered assessments of cognitive function, age, and a measure of physical function. In the LIFE cohort, their external validity was further demonstrated by associations with other risk factors for cognitive dysfunction: education, hypertension, diabetes, and physical function. Acceptable levels of data completeness (>83%) were achieved on all computer-based measures, however rates of missing data were higher among older participants (odds ratio=1.06 for each additional year; p<0.001) and those who reported no current computer use (odds ratio=2.71; p<0.001). Intra-class correlations among clinics were at least as low (ICC≤0.013) as for interviewer measures (ICC≤0.023), reflecting good standardization. All cognitive measures loaded onto the first principal component (global cognitive function), which accounted for 40% of the overall variance. Conclusion Our results support the use of computer-based tools for assessing cognitive function in multicenter clinical trials of older individuals. PMID:23589390

  5. Efficacy of cognitive rehabilitation therapies for mild cognitive impairment (MCI) in older adults: Working toward a theoretical model and evidence-based interventions

    PubMed Central

    Huckans, Marilyn; Hutson, Lee; Twamley, Elizabeth; Jak, Amy; Kaye, Jeffrey; Storzbach, Daniel

    2013-01-01

    Objective To evaluate the efficacy of cognitive rehabilitation therapies (CRTs) for mild cognitive impairment (MCI). Our review revealed a need for evidence-based treatments for MCI and a lack of a theoretical rehabilitation model to guide the development and evaluation of these interventions. We have thus proposed a theoretical rehabilitation model of MCI that yields key intervention targets - cognitive compromise, functional compromise, neuropsychiatric symptoms, and modifiable risk and protective factors known to be associated with MCI and dementia. Our model additionally defines specific cognitive rehabilitation approaches that may directly or indirectly target key outcomes - restorative cognitive training, compensatory cognitive training, lifestyle interventions, and psychotherapeutic techniques. Methods Fourteen randomized controlled trials met inclusion criteria and were reviewed. Results Studies markedly varied in terms of intervention approaches and selected outcome measures and were frequently hampered by design limitations. The bulk of the evidence suggested that CRTs can change targeted behaviors in individuals with MCI and that CRTs are associated with improvements in objective cognitive performance, but the pattern of effects on specific cognitive domains was inconsistent across studies. Other important outcomes (i.e., daily functioning, quality of life, neuropsychiatric symptom severity) were infrequently assessed across studies. Few studies evaluated long-term outcomes or the impact of CRTs on conversion rates from MCI to dementia or normal cognition. Conclusions Overall, results from trials are promising but inconclusive. Additional well-designed and adequately powered trials are warranted and required before CRTs for MCI can be considered evidence based. PMID:23471631

  6. Efficacy of cognitive rehabilitation therapies for mild cognitive impairment (MCI) in older adults: working toward a theoretical model and evidence-based interventions.

    PubMed

    Huckans, Marilyn; Hutson, Lee; Twamley, Elizabeth; Jak, Amy; Kaye, Jeffrey; Storzbach, Daniel

    2013-03-01

    To evaluate the efficacy of cognitive rehabilitation therapies (CRTs) for mild cognitive impairment (MCI). Our review revealed a need for evidence-based treatments for MCI and a lack of a theoretical rehabilitation model to guide the development and evaluation of these interventions. We have thus proposed a theoretical rehabilitation model of MCI that yields key intervention targets-cognitive compromise, functional compromise, neuropsychiatric symptoms, and modifiable risk and protective factors known to be associated with MCI and dementia. Our model additionally defines specific cognitive rehabilitation approaches that may directly or indirectly target key outcomes-restorative cognitive training, compensatory cognitive training, lifestyle interventions, and psychotherapeutic techniques. Fourteen randomized controlled trials met inclusion criteria and were reviewed. Studies markedly varied in terms of intervention approaches and selected outcome measures and were frequently hampered by design limitations. The bulk of the evidence suggested that CRTs can change targeted behaviors in individuals with MCI and that CRTs are associated with improvements in objective cognitive performance, but the pattern of effects on specific cognitive domains was inconsistent across studies. Other important outcomes (i.e., daily functioning, quality of life, neuropsychiatric symptom severity) were infrequently assessed across studies. Few studies evaluated long-term outcomes or the impact of CRTs on conversion rates from MCI to dementia or normal cognition. Overall, results from trials are promising but inconclusive. Additional well-designed and adequately powered trials are warranted and required before CRTs for MCI can be considered evidence-based. PMID:23471631

  7. Effect of Neuroscience-Based Cognitive Skill Training on Growth of Cognitive Deficits Associated with Learning Disabilities in Children Grades 2-4

    ERIC Educational Resources Information Center

    Avtzon, Sarah Abitbol

    2012-01-01

    Working memory, executive functions, and cognitive processes associated with specific academic areas, are empirically identified as being the core underlying cognitive deficits in students with specific learning disabilities. Using Hebb's theory of neuroplasticity and the principle of automaticity as theoretical bases, this experimental study…

  8. Going beyond the unitary curve: incorporating richer cognition into agent-based water resources models

    NASA Astrophysics Data System (ADS)

    Kock, B. E.

    2008-12-01

    The increased availability and understanding of agent-based modeling technology and techniques provides a unique opportunity for water resources modelers, allowing them to go beyond traditional behavioral approaches from neoclassical economics, and add rich cognition to social-hydrological models. Agent-based models provide for an individual focus, and the easier and more realistic incorporation of learning, memory and other mechanisms for increased cognitive sophistication. We are in an age of global change impacting complex water resources systems, and social responses are increasingly recognized as fundamentally adaptive and emergent. In consideration of this, water resources models and modelers need to better address social dynamics in a manner beyond the capabilities of neoclassical economics theory and practice. However, going beyond the unitary curve requires unique levels of engagement with stakeholders, both to elicit the richer knowledge necessary for structuring and parameterizing agent-based models, but also to make sure such models are appropriately used. With the aim of encouraging epistemological and methodological convergence in the agent-based modeling of water resources, we have developed a water resources-specific cognitive model and an associated collaborative modeling process. Our cognitive model emphasizes efficiency in architecture and operation, and capacity to adapt to different application contexts. We describe a current application of this cognitive model and modeling process in the Arkansas Basin of Colorado. In particular, we highlight the potential benefits of, and challenges to, using more sophisticated cognitive models in agent-based water resources models.

  9. Effectiveness of Game-Based Learning: Influence of Cognitive Style

    NASA Astrophysics Data System (ADS)

    Milovanović, Miloš; Minović, Miroslav; Kovačević, Ivana; Minović, Jelena; Starčević, Dušan

    Today students have grown up using devices like computers, mobile phones, and video consoles for almost any activity; from studies and work to entertainment or communication. Motivating them with traditional teaching methods such as lectures and written materials becomes more difficult daily. That is why digital games are becoming more and more considered to have a promising role in education process. We decided to conduct a study among university students. Purpose of that study was to try to find some empirical evidence to support the claim that educational games can be used as an effective form of teaching. We also invested an effort to measure effects of different teaching approaches with the respect of individual differences in cognitive styles. Initial results provide a good argument for use of educational games in teaching. In addition, we reported some influence of cognitive style on effectiveness of using educational games.

  10. Mechanism based approaches for rescuing and enhancing cognition

    PubMed Central

    Lynch, Gary; Gall, Christine M.

    2013-01-01

    Progress toward pharmacological means for enhancing memory and cognition has been retarded by the widely discussed failure of behavioral studies in animals to predict human outcomes. As a result, a number of groups have targeted cognition-related neurobiological mechanisms in animal models, with the assumption that these basic processes are highly conserved across mammals. Here we survey one such approach that begins with a form of synaptic plasticity intimately related to memory encoding in animals and likely operative in humans. An initial section will describe a detailed hypothesis concerning the signaling and structural events (a “substrate map”) that convert learning associated patterns of afferent activity into extremely stable increases in fast, excitatory transmission. We next describe results suggesting that all instances of intellectual impairment so far tested in rodent models involve a common endpoint failure in the substrate map. This will be followed by a clinically plausible proposal for obviating the ultimate defect in these models. We then take up the question of whether it is reasonable to expect, from either general principles or a very limited set of experimental results, that enhancing memory will expand the cognitive capabilities of high functioning brains. The final section makes several suggestions about how to improve translation of behavioral results from animals to humans. Collectively, the material covered here points to the following: (1) enhancement, in the sense of rescue, is not an unrealistic possibility for a broad array of neuropsychiatric disorders; (2) serendipity aside, developing means for improving memory in normals will likely require integration of information about mechanisms with new behavioral testing strategies; (3) a shift in emphasis from synapses to networks is a next, logical step in the evolution of the cognition enhancement field. PMID:23966908

  11. Mechanism based approaches for rescuing and enhancing cognition.

    PubMed

    Lynch, Gary; Gall, Christine M

    2013-01-01

    Progress toward pharmacological means for enhancing memory and cognition has been retarded by the widely discussed failure of behavioral studies in animals to predict human outcomes. As a result, a number of groups have targeted cognition-related neurobiological mechanisms in animal models, with the assumption that these basic processes are highly conserved across mammals. Here we survey one such approach that begins with a form of synaptic plasticity intimately related to memory encoding in animals and likely operative in humans. An initial section will describe a detailed hypothesis concerning the signaling and structural events (a "substrate map") that convert learning associated patterns of afferent activity into extremely stable increases in fast, excitatory transmission. We next describe results suggesting that all instances of intellectual impairment so far tested in rodent models involve a common endpoint failure in the substrate map. This will be followed by a clinically plausible proposal for obviating the ultimate defect in these models. We then take up the question of whether it is reasonable to expect, from either general principles or a very limited set of experimental results, that enhancing memory will expand the cognitive capabilities of high functioning brains. The final section makes several suggestions about how to improve translation of behavioral results from animals to humans. Collectively, the material covered here points to the following: (1) enhancement, in the sense of rescue, is not an unrealistic possibility for a broad array of neuropsychiatric disorders; (2) serendipity aside, developing means for improving memory in normals will likely require integration of information about mechanisms with new behavioral testing strategies; (3) a shift in emphasis from synapses to networks is a next, logical step in the evolution of the cognition enhancement field. PMID:23966908

  12. Reliability and validity of the NeuroCognitive Performance Test, a web-based neuropsychological assessment

    PubMed Central

    Morrison, Glenn E.; Simone, Christa M.; Ng, Nicole F.; Hardy, Joseph L.

    2015-01-01

    The NeuroCognitive Performance Test (NCPT) is a brief, repeatable, web-based cognitive assessment platform that measures performance across several cognitive domains. The NCPT platform is modular and includes 18 subtests that can be arranged into customized batteries. Here we present normative data from a sample of 130,140 healthy volunteers for an NCPT battery consisting of 8 subtests. Participants took the NCPT remotely and without supervision. Factor structure and effects of age, education, and gender were evaluated with this normative dataset. Test-retest reliability was evaluated in a subset of participants who took the battery again an average of 78.8 days later. The eight NCPT subtests group into 4 putative cognitive domains, have adequate to good test-retest reliability, and are sensitive to expected age- and education-related cognitive effects. Concurrent validity to standard neuropsychological tests was demonstrated in 73 healthy volunteers. In an exploratory analysis the NCPT battery could differentiate those who self-reported Mild Cognitive Impairment or Alzheimer's disease from matched healthy controls. Overall these results demonstrate the reliability and validity of the NCPT battery as a measure of cognitive performance and support the feasibility of web-based, unsupervised testing, with potential utility in clinical and research settings. PMID:26579035

  13. Expert music performance: cognitive, neural, and developmental bases.

    PubMed

    Brown, Rachel M; Zatorre, Robert J; Penhune, Virginia B

    2015-01-01

    In this chapter, we explore what happens in the brain of an expert musician during performance. Understanding expert music performance is interesting to cognitive neuroscientists not only because it tests the limits of human memory and movement, but also because studying expert musicianship can help us understand skilled human behavior in general. In this chapter, we outline important facets of our current understanding of the cognitive and neural basis for music performance, and developmental factors that may underlie musical ability. We address three main questions. (1) What is expert performance? (2) How do musicians achieve expert-level performance? (3) How does expert performance come about? We address the first question by describing musicians' ability to remember, plan, execute, and monitor their performances in order to perform music accurately and expressively. We address the second question by reviewing evidence for possible cognitive and neural mechanisms that may underlie or contribute to expert music performance, including the integration of sound and movement, feedforward and feedback motor control processes, expectancy, and imagery. We further discuss how neural circuits in auditory, motor, parietal, subcortical, and frontal cortex all contribute to different facets of musical expertise. Finally, we address the third question by reviewing evidence for the heritability of musical expertise and for how expertise develops through training and practice. We end by discussing outlooks for future work. PMID:25725910

  14. Breakfast is associated with enhanced cognitive function in schoolchildren. An internet based study.

    PubMed

    Wesnes, Keith A; Pincock, Claire; Scholey, Andrew

    2012-12-01

    In this study, 1386 children aged between 6 and 16years, from schools throughout the UK, logged on to a web site before lunch during Farmhouse Breakfast Week 2004. They answered a number of questions concerning their food and drink consumption that day and performed cognitive tests of attention and episodic memory. Children who had had breakfast showed superior performance on tests of attention and memory, confirming a previous laboratory based study using the same cognitive tests. This study adds weight to the growing body of literature indicating that breakfast plays a positive role in maintaining cognitive function during the morning. PMID:22902600

  15. Performance Analysis of the Blind Minimum Output Variance Estimator for Carrier Frequency Offset in OFDM Systems

    NASA Astrophysics Data System (ADS)

    Yang, Feng; Li, Kwok H.; Teh, Kah C.

    2006-12-01

    Carrier frequency offset (CFO) is a serious drawback in orthogonal frequency division multiplexing (OFDM) systems. It must be estimated and compensated before demodulation to guarantee the system performance. In this paper, we examine the performance of a blind minimum output variance (MOV) estimator. Based on the derived probability density function (PDF) of the output magnitude, its mean and variance are obtained and it is observed that the variance reaches the minimum when there is no frequency offset. This observation motivates the development of the proposed MOV estimator. The theoretical mean-square error (MSE) of the MOV estimator over an AWGN channel is obtained. The analytical results are in good agreement with the simulation results. The performance evaluation of the MOV estimator is extended to a frequency-selective fading channel and the maximal-ratio combining (MRC) technique is applied to enhance the MOV estimator's performance. Simulation results show that the MRC technique significantly improves the accuracy of the MOV estimator.

  16. 20 Gb/s optical OFDM transmission for long haul transmission

    NASA Astrophysics Data System (ADS)

    Aldhaibani, Abdullahomar; Aljunid, Syed Alwee; Fadhil, Hilal; Safar, Anuar Mat

    2015-05-01

    Optical OFDM system is considered to be the essential backbone of the next generation of ultra-high-speed networks. A dispersion effect is considered one of the common limitations in optical OFDMA system especially at very high date rate. When the pulse width reaches less than a few pico-seconds, not only the second-order but even higher-order dispersion must be taken into account. In this paper OOFDM system designed with traditional dispersion compensating devices such as Dispersion compensating fiber (DCF) used in multi spans with single mode fiber to reach to 288 km distance at 20 Gb/s. moreover, single side band (SSB) used to reduce the dispersion as well. Therefore, the overall system performance based on SNR, spectral analyzer and constellation diagram for the single side band (SSB) OOFDM system gives a good result with 16 QAM modulation.

  17. NB-PLC channel modelling with cyclostationary noise addition & OFDM implementation for smart grid

    NASA Astrophysics Data System (ADS)

    Thomas, Togis; Gupta, K. K.

    2016-03-01

    Power line communication (PLC) technology can be a viable solution for the future ubiquitous networks because it provides a cheaper alternative to other wired technology currently being used for communication. In smart grid Power Line Communication (PLC) is used to support communication with low rate on low voltage (LV) distribution network. In this paper, we propose the channel modelling of narrowband (NB) PLC in the frequency range 5 KHz to 500 KHz by using ABCD parameter with cyclostationary noise addition. Behaviour of the channel was studied by the addition of 11KV/230V transformer, by varying load location and load. Bit error rate (BER) Vs signal to noise ratio SNR) was plotted for the proposed model by employing OFDM. Our simulation results based on the proposed channel model show an acceptable performance in terms of bit error rate versus signal to noise ratio, which enables communication required for smart grid applications.

  18. Linearly interpolated sub-symbol optical phase noise suppression in CO-OFDM system.

    PubMed

    Hong, Xuezhi; Hong, Xiaojian; He, Sailing

    2015-02-23

    An optical phase noise suppression algorithm, LI-SCPEC, based on phase linear interpolation and sub-symbol processing is proposed for CO-OFDM system. By increasing the temporal resolution of carrier phase tracking through dividing one symbol into several sub-blocks, i.e., sub-symbols, inter-carrier-interference (ICI) mitigation is achieved in the proposed algorithm. Linear interpolation is employed to obtain a reliable temporal reference for sub-symbol phase estimation. The new algorithm, with only a few number of sub-symbols (N(B) = 4), can provide a considerably larger laser linewidth tolerance than several other ICI mitigation algorithms as demonstrated by Monte-Carlo simulations. Numerical analysis verifies that the best performance is achieved with an optimal and moderate number of sub-symbols. Complexity analysis shows that the required number of complex-valued multiplications is independent of the number of sub-symbols used in the proposed algorithm. PMID:25836506

  19. A New SIR-Based Sigmoid Power Control Game in Cognitive Radio Networks

    PubMed Central

    Al-Gumaei, Yousef Ali; Noordin, Kamarul Ariffin; Reza, Ahmed Wasif; Dimyati, Kaharudin

    2014-01-01

    Interference resulting from Cognitive Radios (CRs) is the most important aspect of cognitive radio networks that leads to degradation in Quality of Service (QoS) in both primary and CR systems. Power control is one of the efficient techniques that can be used to reduce interference and satisfy the Signal-to-Interference Ratio (SIR) constraint among CRs. This paper proposes a new distributed power control algorithm based on game theory approach in cognitive radio networks. The proposal focuses on the channel status of cognitive radio users to improve system performance. A new cost function for SIR-based power control via a sigmoid weighting factor is introduced. The existence of Nash Equilibrium and convergence of the algorithm are also proved. The advantage of the proposed algorithm is the possibility to utilize and implement it in a distributed manner. Simulation results show considerable savings on Nash Equilibrium power compared to relevant algorithms while reduction in achieved SIR is insignificant. PMID:25286044

  20. A new SIR-based sigmoid power control game in cognitive radio networks.

    PubMed

    Al-Gumaei, Yousef Ali; Noordin, Kamarul Ariffin; Reza, Ahmed Wasif; Dimyati, Kaharudin

    2014-01-01

    Interference resulting from Cognitive Radios (CRs) is the most important aspect of cognitive radio networks that leads to degradation in Quality of Service (QoS) in both primary and CR systems. Power control is one of the efficient techniques that can be used to reduce interference and satisfy the Signal-to-Interference Ratio (SIR) constraint among CRs. This paper proposes a new distributed power control algorithm based on game theory approach in cognitive radio networks. The proposal focuses on the channel status of cognitive radio users to improve system performance. A new cost function for SIR-based power control via a sigmoid weighting factor is introduced. The existence of Nash Equilibrium and convergence of the algorithm are also proved. The advantage of the proposed algorithm is the possibility to utilize and implement it in a distributed manner. Simulation results show considerable savings on Nash Equilibrium power compared to relevant algorithms while reduction in achieved SIR is insignificant. PMID:25286044

  1. Simulation-Based Assessment to Evaluate Cognitive Performance in an Anesthesiology Residency Program

    PubMed Central

    Sidi, Avner; Baslanti, Tezcan Ozrazgat; Gravenstein, Nikolaus; Lampotang, Samsun

    2014-01-01

    Background Problem solving in a clinical context requires knowledge and experience, and most traditional examinations for learners do not capture skills that are required in some situations where there is uncertainty about the proper course of action. Objective We sought to evaluate anesthesiology residents for deficiencies in cognitive performance within and across 3 clinical domains (operating room, trauma, and cardiac resuscitation) using simulation-based assessment. Methods Individual basic knowledge and cognitive performance in each simulation-based scenario were assessed in 47 residents using a 15- to 29-item scenario-specific checklist. For every scenario and item we calculated group error scenario rate (frequency) and individual (resident) item success. For all analyses, alpha was designated as 0.05. Results Postgraduate year (PGY)-3 and PGY-4 residents' cognitive items error rates were higher and success rates lower compared to basic and technical performance in each domain tested (P < .05). In the trauma and resuscitation scenarios, the cognitive error rate by PGY-4 residents was fairly high (0.29–0.5) and their cognitive success rate was low (0.5–0.68). The most common cognitive errors were anchoring, availability bias, premature closure, and confirmation bias. Conclusions Simulation-based assessment can differentiate between higher-order (cognitive) and lower-order (basic and technical) skills expected of relatively experienced (PGY-3 and PGY-4) anesthesiology residents. Simulation-based assessments can also highlight areas of relative strength and weakness in a resident group, and this information can be used to guide curricular modifications to address deficiencies in tasks requiring higher-order processing and cognition. PMID:24701316

  2. Comparison of the compensation effects of fiber nonlinear impairments with mid-span optical phase conjugation between PDM CO-OFDM system and PDM QPSK system

    NASA Astrophysics Data System (ADS)

    Xu, Fei; Guo, Meng-Qi; Wang, Lei; Qiao, Yao-Jun; Tian, Hui-Ping

    2016-08-01

    The compensation effects of fiber nonlinearity in 112 Gb/s polarization division multiplexing (PDM) coherent optical systems by mid-span optical phase conjugation (OPC) based on four wave mixing (FWM) effect are studied. Comparisons of the compensation results between PDM coherent optical-orthogonal frequency division multiplexing (CO-OFDM) system and the single carrier (SC) PDM quadrature phase shift keying (QPSK) system are provided as well. The results demonstrate that nonlinear compensation effect with mid-span OPC in PDM CO-OFDM system is much more obvious than that in SC PDM QPSK system. Project supported by the National Natural Science Foundation of China (Grant Nos. 61271192, 61427813, and 61331010) and the National Basic Research Program of China (Grant No. 2013AA013401).

  3. Layered ACO-OFDM for intensity-modulated direct-detection optical wireless transmission.

    PubMed

    Wang, Qi; Qian, Chen; Guo, Xuhan; Wang, Zhaocheng; Cunningham, David G; White, Ian H

    2015-05-01

    Layered asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) with high spectral efficiency is proposed in this paper for optical wireless transmission employing intensity modulation with direct detection. In contrast to the conventional ACO-OFDM, which only utilizes odd subcarriers for modulation, leading to an obvious spectral efficiency loss, in layered ACO-OFDM, the subcarriers are divided into different layers and modulated by different kinds of ACO-OFDM, which are combined for simultaneous transmission. In this way, more subcarriers are used for data transmission and the spectral efficiency is improved. An iterative receiver is also proposed for layered ACO-OFDM, where the negative clipping distortion of each layer is subtracted once it is detected so that the signals from different layers can be recovered. Theoretical analysis shows that the proposed scheme can improve the spectral efficiency by up to 2 times compared with conventional ACO-OFDM approaches with the same modulation order. Meanwhile, simulation results confirm a considerable signal-to-noise ratio gain over ACO-OFDM at the same spectral efficiency. PMID:25969323

  4. Optimization of coherent optical OFDM transmitter using DP-IQ modulator with nonlinear response

    NASA Astrophysics Data System (ADS)

    Chang, Sun Hyok; Kang, Hun-Sik; Moon, Sang-Rok; Lee, Joon Ki

    2016-07-01

    In this paper, we investigate the performance of dual polarization orthogonal frequency division multiplexing (DP-OFDM) signal generation when the signal is generated by a DP-IQ optical modulator. The DP-IQ optical modulator is made of four parallel Mach-Zehnder modulators (MZMs) which have nonlinear responses and limited extinction ratios. We analyze the effects of the MZM in the DP-OFDM signal generation by numerical simulation. The operating conditions of the DP-IQ modulator are optimized to have the best performance of the DP-OFDM signal.

  5. Study of dual-polarization OQAM-OFDM PON with direct detection

    NASA Astrophysics Data System (ADS)

    Luo, Qing-long; Feng, Min; Bai, Cheng-lin; Hu, Wei-sheng

    2016-01-01

    An offset quadrature amplitude modulation orthogonal frequency-division multiplexing (OQAM-OFDM) passive optical network (PON) architecture with direct detection is brought up to increase the transmission range and improve the system performance. In optical line terminal (OLT), OQAM-OFDM signals at 40 Gbit/s are transmitted as downstream. At each optical network unit (ONU), the optical OQAM-OFDM signal is demodulated with direct detection. The results show that the transmission distance can exceed 20 km with negligible penalty under the experimental conditions.

  6. Exploring Music-Based Rehabilitation for Parkinsonism through Embodied Cognitive Science.

    PubMed

    Schiavio, Andrea; Altenmüller, Eckart

    2015-01-01

    Recent embodied approaches in cognitive sciences emphasize the constitutive roles of bodies and environment in driving cognitive processes. Cognition is thus seen as a distributed system based on the continuous interaction of bodies, brains, and environment. These categories, moreover, do not relate only causally, through a sequential input-output network of computations; rather, they are dynamically enfolded in each other, being mutually implemented by the concrete patterns of actions adopted by the cognitive system. However, while this claim has been widely discussed across various disciplines, its relevance and potential beneficial applications for music therapy remain largely unexplored. With this in mind, we provide here an overview of the embodied approaches to cognition, discussing their main tenets through the lenses of music therapy. In doing so, we question established methodological and theoretical paradigms and identify possible novel strategies for intervention. In particular, we refer to the music-based rehabilitative protocols adopted for Parkinson's disease patients. Indeed, in this context, it has recently been observed that music therapy not only affects movement-related skills but that it also contributes to stabilizing physiological functions and improving socio-affective behaviors. We argue that these phenomena involve previously unconsidered aspects of cognition and (motor) behavior, which are rooted in the action-perception cycle characterizing the whole living system. PMID:26539155

  7. Studying distributed cognition of simulation-based team training with DiCoT.

    PubMed

    Rybing, Jonas; Nilsson, Heléne; Jonson, Carl-Oscar; Bang, Magnus

    2016-03-01

    Health care organizations employ simulation-based team training (SBTT) to improve skill, communication and coordination in a broad range of critical care contexts. Quantitative approaches, such as team performance measurements, are predominantly used to measure SBTTs effectiveness. However, a practical evaluation method that examines how this approach supports cognition and teamwork is missing. We have applied Distributed Cognition for Teamwork (DiCoT), a method for analysing cognition and collaboration aspects of work settings, with the purpose of assessing the methodology's usefulness for evaluating SBTTs. In a case study, we observed and analysed four Emergo Train System® simulation exercises where medical professionals trained emergency response routines. The study suggests that DiCoT is an applicable and learnable tool for determining key distributed cognition attributes of SBTTs that are of importance for the simulation validity of training environments. Moreover, we discuss and exemplify how DiCoT supports design of SBTTs with a focus on transfer and validity characteristics. Practitioner Summary: In this study, we have evaluated a method to assess simulation-based team training environments from a cognitive ergonomics perspective. Using a case study, we analysed Distributed Cognition for Teamwork (DiCoT) by applying it to the Emergo Train System®. We conclude that DiCoT is useful for SBTT evaluation and simulator (re)design. PMID:26275026

  8. Exploring Music-Based Rehabilitation for Parkinsonism through Embodied Cognitive Science

    PubMed Central

    Schiavio, Andrea; Altenmüller, Eckart

    2015-01-01

    Recent embodied approaches in cognitive sciences emphasize the constitutive roles of bodies and environment in driving cognitive processes. Cognition is thus seen as a distributed system based on the continuous interaction of bodies, brains, and environment. These categories, moreover, do not relate only causally, through a sequential input–output network of computations; rather, they are dynamically enfolded in each other, being mutually implemented by the concrete patterns of actions adopted by the cognitive system. However, while this claim has been widely discussed across various disciplines, its relevance and potential beneficial applications for music therapy remain largely unexplored. With this in mind, we provide here an overview of the embodied approaches to cognition, discussing their main tenets through the lenses of music therapy. In doing so, we question established methodological and theoretical paradigms and identify possible novel strategies for intervention. In particular, we refer to the music-based rehabilitative protocols adopted for Parkinson’s disease patients. Indeed, in this context, it has recently been observed that music therapy not only affects movement-related skills but that it also contributes to stabilizing physiological functions and improving socio-affective behaviors. We argue that these phenomena involve previously unconsidered aspects of cognition and (motor) behavior, which are rooted in the action-perception cycle characterizing the whole living system. PMID:26539155

  9. Student Characteristics, Sense of Community, and Cognitive Achievement in Web-Based and Lab-Based Learning Environments

    ERIC Educational Resources Information Center

    Overbaugh, Richard C.; Lin, ShinYi

    2006-01-01

    This study investigated differential effects of learning styles and learning orientation on sense of community and cognitive achievement in Web-based and lab-based university course formats. Students in the Web-based sections achieved higher scores at the "remember" and "understand" levels, but not at the "apply" or "analyze" levels. In terms of…

  10. Web-Based Cognitive Training: Patient Adherence and Intensity of Treatment in an Outpatient Memory Clinic

    PubMed Central

    Pais, Joana; Alves, Ivânia; Ruano, Luís; Mateus, Cátia; Barreto, Rui; Bento, Virgílio; Colunas, Márcio; Rocha, Nelson; Coutinho, Paula

    2014-01-01

    Background Cognitive training has been playing an increasing role in the treatment of patients with cognitive deficits. This type of intervention, namely its intensity, can be optimized by incorporating information technology-based systems. Objective The intent of the study was to determine the treatment intensity and patient adherence to home-based cognitive training strategies (Web-based cognitive training). Methods A cohort of 45 patients with neurologic and psychiatric diseases attending an outpatient memory clinic (average age 50.7 years, SD 17.0; average education 7.8 years, SD 4.9) was followed over 18 months. Participants were challenged to use a Web-based cognitive training system, “COGWEB”, on a daily basis, and fulfilled at least four weeks of training supervised remotely. Additionally, 11 patients attended face-to-face sessions. Results The average duration of continuous cognitive training was 18.8 weeks (SD 18.9). Each patient performed on average 363.5 minutes/week (SD 136.6). At 6-month follow-up, 82.8% complied with their treatment plan. The average proportion of complete weeks was 0.75 (SD 0.22). Patients with dementia trained more intensively (444.6 minutes/week), followed by patients with static brain lesion (414.5 minutes/week; P=.01). The group that held face-to-face sessions performed more training overall (481.4 vs 366.9 minutes/week), achieving a stronger expression and statistical significance in the last week of training (652.6 versus 354.9 minutes/week, P=.027). Conclusions Overall, the weekly training intensity was high. Patients with dementia and static lesions performed more cognitive training. Face-to-face sessions were associated with higher intensities. The combination of classical methods with information technology systems seems to ensure greater training intensity. PMID:24808451

  11. Early Childhood OCD: Preliminary Findings from a Family-Based Cognitive-Behavioral Approach

    ERIC Educational Resources Information Center

    Freeman, Jennifer B.; Garcia, Abbe M.; Coyne, Lisa; Ale, Chelsea; Prezeworski, Amy; Himle, Michael; Compton, Scott; Leonard, Henrietta L.

    2008-01-01

    A study was conducted to compare the relative usefulness of family-based cognitive-behavioral therapy (CBT) against family-based relaxation treatment for children with obsessive-compulsive disorder (OCD). Results showed that children with early childhood-onset OCD benefited from the CBT program as it effectively decreased OCD symptoms and helped…

  12. An Examination of Game-Based Learning from Theories of Flow Experience and Cognitive Load

    ERIC Educational Resources Information Center

    Lai, Chih-Hung; Chu, Chih-Ming; Liu, Hsiang-Hsuan; Yang, Shun-Bo; Chen, Wei-Hsuan

    2013-01-01

    This study aims to discuss whether game-based learning with the integration of games and digital learning could enhance not only the flow experience in learning but achieve the same flow experience in pure games. In addition, the authors discovered that whether the game-based learning could make learners to reveal higher cognitive load. The…

  13. Clinical Trial of Abstinence-Based Vouchers and Cognitive-Behavioral Therapy for Cannabis Dependence

    ERIC Educational Resources Information Center

    Budney, Alan J.; Moore, Brent A.; Rocha, Heath L.; Higgins, Stephen T.

    2006-01-01

    Ninety cannabis-dependent adults seeking treatment were randomly assigned to receive cognitive-behavioral therapy, abstinence-based voucher incentives, or their combination. Treatment duration was 14 weeks, and outcomes were assessed for 12 months post treatment. Findings suggest that (a) abstinence-based vouchers were effective for engendering…

  14. Effects of Multimedia on Cognitive Load, Self-Efficacy, and Multiple Rule-Based Problem Solving

    ERIC Educational Resources Information Center

    Zheng, Robert; McAlack, Matthew; Wilmes, Barbara; Kohler-Evans, Patty; Williamson, Jacquee

    2009-01-01

    This study investigates effects of multimedia on cognitive load, self-efficacy and learners' ability to solve multiple rule-based problems. Two hundred twenty-two college students were randomly assigned to interactive and non-interactive multimedia groups. Based on Engelkamp's multimodal theory, the present study investigates the role of…

  15. Operationalizing Cognitive Constructs in the Design of Computer-Based Instruction.

    ERIC Educational Resources Information Center

    Hettinger, Gary A.

    This study of the application of cognitive style theory to the development of computer-based instruction explored two questions, i.e., whether computer-based courseware can be designed to address specific learner characteristics, and, if so, which characteristics. Several factors involved in the optimization of instruction are described: learner…

  16. "Kracking" the Missing Data Problem: Applying Krackhardt's Cognitive Social Structures to School-Based Social Networks

    ERIC Educational Resources Information Center

    Neal, Jennifer Watling

    2008-01-01

    Social network analysis can enrich school-based research on children's peer relationships. Unfortunately, accurate network analysis requires near-complete data on all students and is underutilized in school-based research because of low rates of parental consent. This article advocates Krackhardt's cognitive social structures (CSS) as a solution…

  17. Effects of Computer-Based Cognitive Restructuring on Rationally Mediated Self-Esteem.

    ERIC Educational Resources Information Center

    Horan, John J.

    1996-01-01

    Students in grade 11 and grade 12 with below-average self-esteem (N=56) were classified by gender and randomly assigned to either computer-based cognitive restructuring or a relaxation-training control condition. The computer intervention targeted irrational beliefs linked to low self-esteem. Results indicate that the computer-based technique…

  18. Mindfulness-Based Cognitive Therapy: Evaluating Current Evidence and Informing Future Research

    ERIC Educational Resources Information Center

    Coelho, Helen F.; Canter, Peter H.; Ernst, Edzard

    2007-01-01

    Mindfulness-based cognitive therapy (MBCT) is a recently developed class-based program designed to prevent relapse or recurrence of major depression (Z. V. Segal, J. M. G. Williams, & J. Teasdale, 2002). Although research in this area is in its infancy, MBCT is generally discussed as a promising therapy in terms of clinical effectiveness. The aim…

  19. TO-56-can packaged colorless WRC-FPLD for QAM OFDM transmission at 42 Gbit/s over 25-km SMF.

    PubMed

    Cheng, Min-Chi; Chi, Yu-Chieh; Tsai, Cheng-Ting; Lin, Chung-Yu; Lin, Gong-Ru

    2015-08-24

    The weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) with colorless and channelized mode features is a new-class optical transmitter fulfilling the need of next-generation communications. By packaging the colorless WRC-FPLD transmitter with a 10-GHz transistor-outline-56-can (TO-56-can), the premier demonstration on directly modulated 42-Gbit/s/channel quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) transmission is demonstrated via wavelength injection-locking. Enlarging the injection level effectively up-shifts the relaxation oscillation peak and suppresses the relative intensity noise, which facilitates the TO-56-can packaged WRC-FPLD to improve its modulation throughput bandwidth to 9 GHz and enhance its signal-to-noise ratio to 22 dB. By pre-amplifying the directly modulated QAM-OFDM data with a total raw bit rate of 42 Gbit/s, the receiving bit-error-rate (BER) under back-to-back transmission can be reduced below the forward-error-correction (FEC) limited BER of 3.8 × 10(-3). Such a colorless WRC-FPLD enables the QAM-OFDM transmission over a 25-km long single-mode-fiber based metropolitan access network with its BER matching the FEC criterion at a receiving power of -2 dBm. PMID:26368236

  20. Positive imagery cognitive bias modification (CBM) and internet-based cognitive behavioral therapy (iCBT): A randomized controlled trial

    PubMed Central

    Williams, Alishia D.; O’Moore, Kathleen; Blackwell, Simon E.; Smith, Jessica; Holmes, Emily A.; Andrews, Gavin

    2015-01-01

    Background Accruing evidence suggests that positive imagery-based cognitive bias modification (CBM) could have potential as a standalone targeted intervention for depressive symptoms or as an adjunct to existing treatments. We sought to establish the benefit of this form of CBM when delivered prior to Internet cognitive behavioral therapy (iCBT) for depression Methods A randomized controlled trial (RCT) of a 1-week Internet-delivered positive CBM vs. an active control condition for participants (N=75, 69% female, mean age=42) meeting diagnostic criteria for major depression; followed by a 10-week iCBT program for both groups. Results Modified intent-to-treat marginal and mixed effect models demonstrated no significant difference between conditions following the CBM intervention or the iCBT program. In both conditions there were significant reductions (Cohen׳s d .57–1.58, 95% CI=.12–2.07) in primary measures of depression and interpretation bias (PHQ9, BDI-II, AST-D). Large effect size reductions (Cohen׳s d .81–1.32, 95% CI=.31–1.79) were observed for secondary measures of distress, disability, anxiety and repetitive negative thinking (K10, WHODAS, STAI, RTQ). Per protocol analyses conducted in the sample of participants who completed all seven sessions of CBM indicated between-group superiority of the positive over control group on depression symptoms (PHQ9, BDI-II) and psychological distress (K10) following CBM (Hedges g .55–.88, 95% CI=−.03–1.46) and following iCBT (PHQ9, K10). The majority (>70%) no longer met diagnostic criteria for depression at 3-month follow-up. Limitations The control condition contained many active components and therefore may have represented a smaller ‘dose’ of the positive condition. Conclusions Results provide preliminary support for the successful integration of imagery-based CBM into an existing Internet-based treatment for depression. PMID:25805405

  1. [Establishment and practice of traditional Chinese medicine property cognitive model based on three elements].

    PubMed

    Zhang, Bing; Jin, Rui; Huang, Jianmei; Liu, Xiaoqing; Xue, Chunmiao; Lin, Zhijian

    2012-08-01

    Traditional Chinese medicine (TCM) property theory is believed to be a key and difficult point of basic theory studies of TCM. Complex concepts, components and characteristics of TCM property have long puzzled researchers and urged them to develop new angles and approaches. In the view of cognitive science, TCM property theory is a cognitive process of storing, extracting, rebuilding and summarizing the sensory information about TCMs and their effects during the medical practice struggling against diseases under the guidance of traditional Chinese philosophical thinking. The cognitive process of TCM property has particular cognitive elements and strategies. Taking into account clinical application characteristics of TCMs, this study defines the particular cognitive elements. In the combination of research methods of modern chemistry, biology and mathematics, and on the basis early-stage work for five years, we have built a TCM property cognition model based on three elements and practiced with drugs with pungent and hot properties as example, in the hope of interpreting TCM properties with modern science and providing thoughts for the nature of medical properties and instruction for rational clinical prescription. PMID:23189745

  2. Demostration of 520 Gb/s/λ pre-equalized DFT-spread PDM-16QAM-OFDM signal transmission.

    PubMed

    Li, Fan; Yu, Jianjun; Cao, Zizheng; Chen, Ming; Zhang, Junwen; Li, Xinying

    2016-02-01

    In this paper, we successfully transmit 8 × 520 Gb/s pre-equalized DFT-spread PDM-16QAM orthogonal frequency-division multiplexing (OFDM) signal over 840 km SMF with BER under 2.4 × 10(-2). We discuss how to obtain accurate tranceivers' response during pre-equalization for DFT-spread OFDM with coherent detection and we find conventional OFDM symbols training sequences (TSs) outperform DFT-spread OFDM symbols TSs in obtaining channel response for pre-equalization and equalization. Additionally, the optimal IFFT/FFT size is explored for the pre-equalized DFT-spread PDM-16QAM-OFDM transmission systems. It is the first time to realize 400 Gb/s/λ net rate OFDM signal transmission. PMID:26906836

  3. Blind and semi-blind ML detection for space-time block-coded OFDM wireless systems

    NASA Astrophysics Data System (ADS)

    Zaib, Alam; Al-Naffouri, Tareq Y.

    2014-12-01

    This paper investigates the joint maximum likelihood (ML) data detection and channel estimation problem for Alamouti space-time block-coded (STBC) orthogonal frequency-division multiplexing (OFDM) wireless systems. The joint ML estimation and data detection is generally considered a hard combinatorial optimization problem. We propose an efficient low-complexity algorithm based on branch-estimate-bound strategy that renders exact joint ML solution. However, the computational complexity of blind algorithm becomes critical at low signal-to-noise ratio (SNR) as the number of OFDM carriers and constellation size are increased especially in multiple-antenna systems. To overcome this problem, a semi-blind algorithm based on a new framework for reducing the complexity is proposed by relying on subcarrier reordering and decoding the carriers with different levels of confidence using a suitable reliability criterion. In addition, it is shown that by utilizing the inherent structure of Alamouti coding, the estimation performance improvement or the complexity reduction can be achieved. The proposed algorithms can reliably track the wireless Rayleigh fading channel without requiring any channel statistics. Simulation results presented against the perfect coherent detection demonstrate the effectiveness of blind and semi-blind algorithms over frequency-selective channels with different fading characteristics.

  4. Evaluation of cognitive loads imposed by traditional paper-based and innovative computer-based instructional strategies.

    PubMed

    Khalil, Mohammed K; Mansour, Mahmoud M; Wilhite, Dewey R

    2010-01-01

    Strategies of presenting instructional information affect the type of cognitive load imposed on the learner's working memory. Effective instruction reduces extraneous (ineffective) cognitive load and promotes germane (effective) cognitive load. Eighty first-year students from two veterinary schools completed a two-section questionnaire that evaluated their perspectives on the educational value of a computer-based instructional program. They compared the difference between cognitive loads imposed by paper-based and computer-based instructional strategies used to teach the anatomy of the canine skeleton. Section I included 17 closed-ended items, rated on a five-point Likert scale, that assessed the use of graphics, content, and the learning process. Section II included a nine-point mental effort rating scale to measure the level of difficulty of instruction; students were asked to indicate the amount of mental effort invested in the learning task using both paper-based and computer-based presentation formats. The closed-ended data were expressed as means and standard deviations. A paired t test with an alpha level of 0.05 was used to determine the overall mean difference between the two presentation formats. Students positively evaluated their experience with the computer-based instructional program with a mean score of 4.69 (SD=0.53) for use of graphics, 4.70 (SD=0.56) for instructional content, and 4.45 (SD=0.67) for the learning process. The mean difference of mental effort (1.50) between the two presentation formats was significant, t=8.26, p≤.0001, df=76, for two-tailed distribution. Consistent with cognitive load theory, innovative computer-based instructional strategies decrease extraneous cognitive load compared with traditional paper-based instructional strategies. PMID:21135402

  5. Colorless ONU implementation for WDM-PON using direct-detection optical OFDM

    NASA Astrophysics Data System (ADS)

    Feng, Min; Luo, Qing-long; Bai, Cheng-lin

    2013-03-01

    A novel architecture for the colorless optical network unit (ONU) is proposed and experimentally demonstrated with direct-detection optical orthogonal frequency division multiplexing (DDO-OFDM). In this architecture, polarization-division multiplexing is used to reduce the cost at ONU. In optical line terminal (OLT), quadrature amplitude modulation (QAM) intensity-modulated OFDM signal with x-polarization at 10 Gbit/s is transmitted as downstream. At each ONU, the optical OFDM signal is demodulated with direct detection, and γ-polarization signal is modulated for upstream on-off keying (OOK) data at 5 Gbit/s. Simulation results show that the power penalty is negligible for both optical OFDM downstream and the on-off keying upstream signals after over 50 km single-mode fiber (SMF) transmission.

  6. Effects of School-Based Physical Activity Interventions on Cognition and Academic Achievement: A Systematic Review.

    PubMed

    Mura, Gioia; Vellante, Marcello; Nardi, Antonio Egidio; Machado, Sergio; Carta, Mauro Giovanni

    2015-01-01

    Schools are an ideal setting to implement physical activity programs targeted at youths' learning and intellectual abilities, as exercise has been associated with improvement in cognitive skills and academic proficiency. A systematic review of the literature was performed to examine the effects of school-based physical activity interventions on academic achievement and cognitive outcomes. A search for relevant papers was carried out on PubMed/Medline, Scopus and Google Scholar. Only quasi-experimental and experimental studies were included, if focused on school-based physical activity interventions targeting 3 to 18 year-old healthy pupils, and designed to establish a relationship between exercise performed in a school setting and cognitive/academic performance. Thirty-one papers were retrieved by the search, reporting the findings of twenty-eight school-based physical activity interventions. Most of the included studies were published in the past five years. A large majority of the studies showed positive results in terms of academic achievement and, above all, cognitive skills. In the recent years, the number of studies on school-based physical interventions aimed to establish a relationship between physical activity performed in school setting and cognitive/academic outcomes significantly increased, as well as high quality assessments and designs. This review highlights the effectiveness of school-based physical activity interventions on academic achievement and, above all, on youths' cognitive performance. Some interesting findings come from studies assessing brain functional changes, from interventions targeting culturally diverse or low-income samples, and from interventions where physical activity is in the form of active videogames. PMID:26556088

  7. Modeling and compensation of transmitter nonlinearity in coherent optical OFDM.

    PubMed

    Amiralizadeh, Siamak; Nguyen, An T; Rusch, Leslie A

    2015-10-01

    We present a comprehensive study of nonlinear distortions from an optical OFDM transmitter. Nonlinearities are introduced by the combination of effects from the digital-to-analog converter (DAC), electrical power amplifier (PA) and optical modulator in the presence of high peak-to-average power ratio (PAPR). We introduce parameters to quantify the transmitter nonlinearity. High input backoff avoids OFDM signal compression from the PA, but incurs high penalties in power efficiency. At low input backoff, common PAPR reduction techniques are not effective in suppressing the PA nonlinear distortion. A bit error distribution investigation shows a technique combining nonlinear predistortion with PAPR mitigation could achieve good power efficiency by allowing low input backoff. We use training symbols to extract the transmitter nonlinear function. We show that piecewise linear interpolation (PLI) leads to an accurate transmitter nonlinearity characterization. We derive a semi-analytical solution for bit error rate (BER) that validates the PLI approximation accurately captures transmitter nonlinearity. The inverse of the PLI estimate of the nonlinear function is used as a predistorter to suppress transmitter nonlinearity. We investigate performance of the proposed scheme by Monte Carlo simulations. Our simulations show that when DAC resolution is more than 4 bits, BER below forward error correction limit of 3.8 × 10(-3) can be achieved by using predistortion with very low input power backoff for electrical PA and optical modulator. PMID:26480133

  8. Measurement of Social Cognition in Amyotrophic Lateral Sclerosis: A Population Based Study

    PubMed Central

    Pinto-Grau, Marta; Lonergan, Katie; Elamin, Marwa; Bede, Peter; Costello, Emmet; Hardiman, Orla; Pender, Niall

    2016-01-01

    Background: Amyotrophic lateral sclerosis (ALS) is a rapidly progressive neurodegenerative disease. Executive dysfunction is common in patients with ALS, with up to 50% of patients performing within an impaired range. There is evidence that social cognitive deficits associated with ALS are a function of deficits in executive function. The ‘Reading the Mind in the Eyes’ Test is a recognized test of social cognitive function, although the reliability of this instrument remains to be established. Methodology: Patients with ALS (n = 106), and age and IQ matched controls (n = 50) were recruited and asked to perform the Reading the Mind in the Eyes Test as part of an on-going population-based study of cognitive function. ALS patients were sub-stratified based on the presence, and/or extent of executive dysfunction. Results: Cronbach’s Alpha of .73 was observed, indicating good reliability on this measure. Split-half reliability analysis further confirms these findings (p = 0.826). The Reading the Mind in the Eyes test had excellent psychometric properties when discriminating between ALS patients who are cognitively intact, and those who have executive impairment, with an overall medium difficulty. There was a large magnitude significant difference between patients and controls (p< 0.001; η2 = .19). Post-hoc analysis revealed that controls performed significantly higher than patients with executive impairment (p< 0.001), and patients with single executive deficits (p = 0.002). Conclusion: Executive dysfunction impacts on social cognitive performance. This study contributes not only to the psychometric knowledge of this measure, but also to the usability, efficacy, and reliability of social cognitive assessment in ALS. Using population-specific normative data, we confirm the Reading the Mind in the Eyes Test is a reliable measure of social cognitive processes in ALS. PMID:27556398

  9. Simplified model for nonlinear noise calculation in coherent optical OFDM systems.

    PubMed

    Uzunidis, Dimitris; Matrakidis, Chris; Stavdas, Alexandros

    2014-11-17

    A simplified closed form expression for the noise power due to four-wave mixing in coherent OFDM systems is derived. The proposed model is in very good agreement with the exact model. The derived analytical expressions can be used in performance evaluation of systems employing CO-OFDM with any number of subcarriers and/or as an integral part of physical layer aware routing algorithms. PMID:25402073

  10. Non-Systematic Complex Number RS Coded OFDM by Unique Word Prefix

    NASA Astrophysics Data System (ADS)

    Huemer, Mario; Hofbauer, Christian; Huber, Johannes B.

    2012-01-01

    In this paper we expand our recently introduced concept of UW-OFDM (unique word orthogonal frequency division multiplexing). In UW-OFDM the cyclic prefixes (CPs) are replaced by deterministic sequences, the so-called unique words (UWs). The UWs are generated by appropriately loading a set of redundant subcarriers. By that a systematic complex number Reed Solomon (RS) code construction is introduced in a quite natural way, because an RS code may be defined as the set of vectors, for which a block of successive zeros occurs in the other domain w.r.t. a discrete Fourier transform. (For a fixed block different to zero, i.e., a UW, a coset code of an RS code is generated.) A remaining problem in the original systematic coded UW-OFDM concept is the fact that the redundant subcarrier symbols disproportionately contribute to the mean OFDM symbol energy. In this paper we introduce the concept of non-systematic coded UW-OFDM, where the redundancy is no longer allocated to dedicated subcarriers, but distributed over all subcarriers. We derive optimum complex valued code generator matrices matched to the BLUE (best linear unbiased estimator) and to the LMMSE (linear minimum mean square error) data estimator, respectively. With the help of simulations we highlight the advantageous spectral properties and the superior BER (bit error ratio) performance of non-systematic coded UW-OFDM compared to systematic coded UW-OFDM as well as to CP-OFDM in AWGN (additive white Gaussian noise) and in frequency selective environments.

  11. A Cognitive Support System to Scaffold Students' Problem-Based Learning in a Web-Based Learning Environment

    ERIC Educational Resources Information Center

    Ge, Xun; Planas, Lourdes G.; Er, Nelson

    2010-01-01

    An experimental study was conducted to investigate the effects of question prompts and peer review on scaffolding students' problem-based learning in a web-based cognitive support system. Ninety-six pharmacy students were randomly assigned to a treatment or control condition. The students in both conditions were asked to generate solutions to a…

  12. Development of a self-administered web-based test for longitudinal cognitive assessment.

    PubMed

    Ruano, Luis; Sousa, Andreia; Severo, Milton; Alves, Ivânia; Colunas, Márcio; Barreto, Rui; Mateus, Cátia; Moreira, Sandra; Conde, Eduardo; Bento, Virgílio; Lunet, Nuno; Pais, Joana; Tedim Cruz, Vítor

    2016-01-01

    Sequential testing with brief cognitive tools has been recommended to improve cognitive screening and monitoring, however the few available tools still depend on an external evaluator and periodic visits. We developed a self-administered computerized test intended for longitudinal cognitive testing (Brain on Track). The test can be performed from a home computer and is composed of several subtests, expected to evaluate different cognitive domains, all including random elements to minimize learning effects. An initial (A) and a refined version of the test (B) were applied to patients with mild cognitive impairment or early dementia (n = 88) and age and education-matched controls. A subsample of a population-based cohort (n = 113) performed the test at home every three months to evaluate test-retest reliability. The test's final version Cronbach's alpha was 0.90, test scores were significantly different between patients and controls (p = 0.001), the area under the receiver operating characteristic curve was 0.75 and the smallest real difference (43.04) was lower than the clinical relevant difference (56.82). In the test-retest reliability analysis 9/10 subtests showed two-way mixed single intraclass consistency correlation coefficient >0.70. These results imply good internal consistency, discriminative ability and reliability when performed at home, encouraging further longitudinal clinical and population-based studies. PMID:26743329

  13. Development of a self-administered web-based test for longitudinal cognitive assessment

    PubMed Central

    Ruano, Luis; Sousa, Andreia; Severo, Milton; Alves, Ivânia; Colunas, Márcio; Barreto, Rui; Mateus, Cátia; Moreira, Sandra; Conde, Eduardo; Bento, Virgílio; Lunet, Nuno; Pais, Joana; Tedim Cruz, Vítor

    2016-01-01

    Sequential testing with brief cognitive tools has been recommended to improve cognitive screening and monitoring, however the few available tools still depend on an external evaluator and periodic visits. We developed a self-administered computerized test intended for longitudinal cognitive testing (Brain on Track). The test can be performed from a home computer and is composed of several subtests, expected to evaluate different cognitive domains, all including random elements to minimize learning effects. An initial (A) and a refined version of the test (B) were applied to patients with mild cognitive impairment or early dementia (n = 88) and age and education-matched controls. A subsample of a population-based cohort (n = 113) performed the test at home every three months to evaluate test-retest reliability. The test’s final version Cronbach’s alpha was 0.90, test scores were significantly different between patients and controls (p = 0.001), the area under the receiver operating characteristic curve was 0.75 and the smallest real difference (43.04) was lower than the clinical relevant difference (56.82). In the test-retest reliability analysis 9/10 subtests showed two-way mixed single intraclass consistency correlation coefficient >0.70. These results imply good internal consistency, discriminative ability and reliability when performed at home, encouraging further longitudinal clinical and population-based studies. PMID:26743329

  14. 107 Gb/s coherent optical OFDM transmission over 1000-km SSMF fiber using orthogonal band multiplexing.

    PubMed

    Shieh, W; Yang, Q; Ma, Y

    2008-04-28

    Coherent optical OFDM (CO-OFDM) has emerged as an attractive modulation format for the forthcoming 100 Gb/s Ethernet. However, even the spectral-efficient implementation of CO-OFDM requires digital-to-analog converters (DAC) and analog-to-digital converters (ADC) to operate at the bandwidth which may not be available today or may not be cost-effective. In order to resolve the electronic bandwidth bottleneck associated with DAC/ADC devices, we propose and elucidate the principle of orthogonal-band-multiplexed OFDM (OBM-OFDM) to subdivide the entire OFDM spectrum into multiple orthogonal bands. With this scheme, the DAC/ADCs do not need to operate at extremely high sampling rate. The corresponding mapping to the mixed-signal integrated circuit (IC) design is also revealed. Additionally, we show the proof-of-concept transmission experiment through optical realization of OBM-OFDM. To the best of our knowledge, we present the first experimental demonstration of 107 Gb/s QPSK-encoded CO-OFDM signal transmission over 1000 km standard-single- mode-fiber (SSMF) without optical dispersion compensation and without Raman amplification. The demonstrated system employs 2x2 MIMO-OFDM signal processing and achieves high electrical spectral efficiency with direct-conversion at both transmitter and receiver. PMID:18545341

  15. A novel power-efficient scheme asymmetrically and symmetrically clipping optical (ASCO)-OFDM for IM/DD optical systems

    NASA Astrophysics Data System (ADS)

    Wu, Nan; Bar-Ness, Yeheskel

    2015-12-01

    In this paper, we propose a novel scheme of orthogonal frequency division multiplexing (OFDM) for intensity modulation direct detection (IM/DD) optical systems. By using this novel scheme of an OFDM optical system, not only odd subcarriers but also even subcarriers can be modulated to transmit a clipping optical signal. A conventional asymmetrically clipping optical (ACO)-OFDM is applied to modulate odd subcarriers while even subcarriers are modulated by a novel technique called a symmetrically clipping optical (SCO)-OFDM. Although both the asymmetrically clipping noise caused by ACO-OFDM and the symmetrically clipping noise caused by SCO-OFDM fall onto the even subcarriers, the former interference can be estimated and removed at the receiver. Thus, SCO-OFDM symbols carried on the even subcarriers can be recovered by subtracting the estimated ACO-OFDM clipping noise from the received signal. Then the SCO-OFDM clipping noise can be removed by subtraction due to its special transmission format. Note that no DC bias added on all subcarriers makes this novel scheme achieve better performance in terms of both power efficiency and symbol error rate (SER).

  16. PAPR reduction technique by inserting a power-concentrated subcarrier for CO-OFDM

    NASA Astrophysics Data System (ADS)

    Kang, Sungyong; Lee, Jaehoon; Jeong, Jichai

    2015-09-01

    Optical orthogonal frequency division multiplexing (OFDM) signals suffer from the nonlinear effects of an electric-to-optical modulator and fiber due to high peak to average power ratio (PAPR) characteristics. We propose a power-concentrated subcarrier method for use in OFDM systems to reduce PAPR of the OFDM signal without increasing system complexity or side information. The PAPR can be reduced by simply inserting a power-concentrated subcarrier (PCS) to replace the zero in the end of the signal spectrum at the zero padding stage. The simulation is performed with a conventional CO-OFDM transmission system with a PCS under dispersion and a nonlinear effective fiber to estimate PAPR using complementary cumulative distribution function (CCDF), error vector magnitude (EVM), and bit-error-rate (BER) characteristics. After a 2000-km transmission, the conventional CO-OFDM had an optimal fiber launch power of -6 dBm from the BER characteristics. In contrast, the proposed CO-OFDM with a PCS improves transmission performance in terms of log(BER) as much as -0.67 by an increased fiber launch power of -1 dBm with 60% concentrated-power of the PCS.

  17. Frequency Adaptability and Waveform Design for OFDM Radar Space-Time Adaptive Processing

    SciTech Connect

    Sen, Satyabrata; Glover, Charles Wayne

    2012-01-01

    We propose an adaptive waveform design technique for an orthogonal frequency division multiplexing (OFDM) radar signal employing a space-time adaptive processing (STAP) technique. We observe that there are inherent variabilities of the target and interference responses in the frequency domain. Therefore, the use of an OFDM signal can not only increase the frequency diversity of our system, but also improve the target detectability by adaptively modifying the OFDM coefficients in order to exploit the frequency-variabilities of the scenario. First, we formulate a realistic OFDM-STAP measurement model considering the sparse nature of the target and interference spectra in the spatio-temporal domain. Then, we show that the optimal STAP-filter weight-vector is equal to the generalized eigenvector corresponding to the minimum generalized eigenvalue of the interference and target covariance matrices. With numerical examples we demonstrate that the resultant OFDM-STAP filter-weights are adaptable to the frequency-variabilities of the target and interference responses, in addition to the spatio-temporal variabilities. Hence, by better utilizing the frequency variabilities, we propose an adaptive OFDM-waveform design technique, and consequently gain a significant amount of STAP-performance improvement.

  18. Underwater wireless transmission of high-speed QAM-OFDM signals using a compact red-light laser.

    PubMed

    Xu, Jing; Song, Yuhang; Yu, Xiangyu; Lin, Aobo; Kong, Meiwei; Han, Jun; Deng, Ning

    2016-04-18

    We first study the transmission property of red light in water in terms of extinction coefficient and channel bandwidth via Monte Carlo simulation, with an interesting finding that red light outperforms blue-green light in highly turbid water. We further propose and experimentally demonstrate a broadband underwater wireless optical communication system based on a simple and cost-effective TO56 red-light laser diode. We demonstrate a 1.324-Gb/s transmission at a bit error rate (BER) of 2.02 × 10-3 over a 6-m underwater channel, by using 128-QAM OFDM signals and a low-cost 150-MHz positive-intrinsic-negative photodetector, with a record spectral efficiency higher than 7.32 bits/Hz. By using an avalanche photodetector and 32-QAM OFDM signals, we have achieved a record bit rate of 4.883 Gb/s at a BER of 3.20 × 10-3 over a 6-m underwater channel. PMID:27137249

  19. Analog implementation of radix-2, 16-FFT processor for OFDM receivers: non-linearity behaviours and system performance analysis

    NASA Astrophysics Data System (ADS)

    Mokhtarian, N.; Hodtani, G. A.

    2015-12-01

    Analog implementations of decoders have been widely studied by considering circuit complexity, as well as power and speed, and their integration with other analog blocks is an extension of analog decoding research. In the front-end blocks of orthogonal frequency-division multiplexing (OFDM) systems, combination of an analog fast Fourier transform (FFT) with an analog decoder is suitable. In this article, the implementation of a 16-symbol FFT processor based on analog complementary metal-oxide-semiconductor current mirrors within circuit and system levels is presented, and the FFT is implemented using a butterfly diagram, where each node is implemented using analog circuits. Implementation details include consideration of effects of transistor mismatch and inherent noises and effects of circuit non-linearity in OFDM system performance. It is shown that not only can transistor inherent noises be measured but also transistor mismatch can be applied as an input-referred noise source that can be used in system- and circuit-level studies. Simulations of a radix-2, 16-symbol FFT show that proposed circuits consume very low power, and impacts of noise, mismatch and non-linearity for each node of this processor are very small.

  20. Low complexity PAPR reduction techniques for clipping and quantization noise mitigation in direct-detection O-OFDM systems

    NASA Astrophysics Data System (ADS)

    Nadal, Laia; Svaluto Moreolo, Michela; Fàbrega, Josep M.; Junyent, Gabriel

    2014-06-01

    We present different distortionless peak-to-average power ratio (PAPR) reduction techniques that can be easily applied, without any symmetry restriction, in direct-detection (DD) optical orthogonal frequency division multiplexing (O-OFDM) systems based on the fast Hartley transform (FHT). The performance of DD O-OFDM systems is limited by the constraints on system components such as digital-to-analog converter (DAC), analog-to-digital converter (ADC), the Mach-Zehnder modulator (MZM) and electrical amplifiers. In this paper, in order to relax the constraints on these components, we propose to symmetrically clip the transmitted signal and apply low complexity (LC) distortionless PAPR reduction schemes able to mitigate, at the same time, PAPR, quantization and clipping noise. We demonstrate that, applying LC-selective mapping (SLM) without any additional transform block, the PAPR reduction is 1.5dB with only one additional FHT block using LC-partial transmit sequence (PTS) with random partitions; up to 3.1dB reduction is obtained. Moreover, the sensitivity performance and the power efficiency are enhanced. In fact, applying LC PAPR reduction techniques with one additional transform block and a 6 bit DAC resolution, the required receiver power for 8 dB clipping level and for a 10-3BER is reduced by 5.1dB.

  1. Low-complexity optical phase noise suppression in CO-OFDM system using recursive principal components elimination.

    PubMed

    Hong, Xiaojian; Hong, Xuezhi; He, Sailing

    2015-09-01

    A low-complexity optical phase noise suppression approach based on recursive principal components elimination, R-PCE, is proposed and theoretically derived for CO-OFDM systems. Through frequency domain principal components estimation and elimination, signal distortion caused by optical phase noise is mitigated by R-PCE. Since matrix inversion and domain transformation are completely avoided, compared with the case of the orthogonal basis expansion algorithm (L = 3) that offers a similar laser linewidth tolerance, the computational complexities of multiple principal components estimation are drastically reduced in the R-PCE by factors of about 7 and 5 for q = 3 and 4, respectively. The feasibility of optical phase noise suppression with the R-PCE and its decision-aided version (DA-R-PCE) in the QPSK/16QAM CO-OFDM system are demonstrated by Monte-Carlo simulations, which verify that R-PCE with only a few number of principal components q ( = 3) provides a significantly larger laser linewidth tolerance than conventional algorithms, including the common phase error compensation algorithm and linear interpolation algorithm. Numerical results show that the optimal performance of R-PCE and DA-R-PCE can be achieved with a moderate q, which is beneficial for low-complexity hardware implementation. PMID:26368499

  2. An Exploration Based Cognitive Bias Test for Mice: Effects of Handling Method and Stereotypic Behaviour

    PubMed Central

    Novak, Janja; Bailoo, Jeremy D.; Melotti, Luca; Rommen, Jonas; Würbel, Hanno

    2015-01-01

    Behavioural tests to assess affective states are widely used in human research and have recently been extended to animals. These tests assume that affective state influences cognitive processing, and that animals in a negative affective state interpret ambiguous information as expecting a negative outcome (displaying a negative cognitive bias). Most of these tests however, require long discrimination training. The aim of the study was to validate an exploration based cognitive bias test, using two different handling methods, as previous studies have shown that standard tail handling of mice increases physiological and behavioural measures of anxiety compared to cupped handling. Therefore, we hypothesised that tail handled mice would display a negative cognitive bias. We handled 28 female CD-1 mice for 16 weeks using either tail handling or cupped handling. The mice were then trained in an eight arm radial maze, where two adjacent arms predicted a positive outcome (darkness and food), while the two opposite arms predicted a negative outcome (no food, white noise and light). After six days of training, the mice were also given access to the four previously unavailable intermediate ambiguous arms of the radial maze and tested for cognitive bias. We were unable to validate this test, as mice from both handling groups displayed a similar pattern of exploration. Furthermore, we examined whether maze exploration is affected by the expression of stereotypic behaviour in the home cage. Mice with higher levels of stereotypic behaviour spent more time in positive arms and avoided ambiguous arms, displaying a negative cognitive bias. While this test needs further validation, our results indicate that it may allow the assessment of affective state in mice with minimal training—a major confound in current cognitive bias paradigms. PMID:26154309

  3. An Exploration Based Cognitive Bias Test for Mice: Effects of Handling Method and Stereotypic Behaviour.

    PubMed

    Novak, Janja; Bailoo, Jeremy D; Melotti, Luca; Rommen, Jonas; Würbel, Hanno

    2015-01-01

    Behavioural tests to assess affective states are widely used in human research and have recently been extended to animals. These tests assume that affective state influences cognitive processing, and that animals in a negative affective state interpret ambiguous information as expecting a negative outcome (displaying a negative cognitive bias). Most of these tests however, require long discrimination training. The aim of the study was to validate an exploration based cognitive bias test, using two different handling methods, as previous studies have shown that standard tail handling of mice increases physiological and behavioural measures of anxiety compared to cupped handling. Therefore, we hypothesised that tail handled mice would display a negative cognitive bias. We handled 28 female CD-1 mice for 16 weeks using either tail handling or cupped handling. The mice were then trained in an eight arm radial maze, where two adjacent arms predicted a positive outcome (darkness and food), while the two opposite arms predicted a negative outcome (no food, white noise and light). After six days of training, the mice were also given access to the four previously unavailable intermediate ambiguous arms of the radial maze and tested for cognitive bias. We were unable to validate this test, as mice from both handling groups displayed a similar pattern of exploration. Furthermore, we examined whether maze exploration is affected by the expression of stereotypic behaviour in the home cage. Mice with higher levels of stereotypic behaviour spent more time in positive arms and avoided ambiguous arms, displaying a negative cognitive bias. While this test needs further validation, our results indicate that it may allow the assessment of affective state in mice with minimal training-a major confound in current cognitive bias paradigms. PMID:26154309

  4. Evidence-based practice and the need for paradigmatic pluralism in cognitive behavioural psychotherapy.

    PubMed

    Grant, A

    2009-05-01

    The scientist-practitioner model, which is based on positivistic methodological assumptions, is influential in the development, training and practice of cognitive behavioural psychotherapists. As the emergence of 'Nurse Cognitive Behavioural Therapist' training in the early 1970s in Britain, many of those trained have been mental health nurses and with the emergence of the Increased Access to Psychological Therapies agenda many more are likely to undergo training. Despite some acceptance of its relevance, the scientist-practitioner model is subject of criticism on the grounds of its achievability and contemporary relevance, and its exclusion of other modalities of counselling and psychotherapy without an, as yet, disseminated evidence base. In line with key policy-related work, the empirical and political issues inscribed within the scientist-practitioner model have direct implications for the educational preparation and ongoing professional development of cognitive behavioural practitioners. Specifically, in this polemical paper it is argued that there is a moral and educational need for 'senior' practitioners to question the philosophy of science assumptions underpinning the overwhelming dominance of the quantitative-experimental approach in cognitive behavioural psychotherapy. Such a critically evaluative and pluralistic stance would arguably distinguish senior practitioners in terms of them being able to make broad rather than narrow appraisals of the evidence base for their practice. A recognition of the relevance of paradigmatic and epistemological pluralism in cognitive behavioural work would, it is argued, confer considerable advantages on our practice communities and clients. A range of emerging implications for cognitive behavioural education, practice and relational ethics are described and discussed. PMID:19383016

  5. Mindfulness-Based Cognitive Therapy (MBCT) Reduces the Association Between Depressive Symptoms and Suicidal Cognitions in Patients With a History of Suicidal Depression

    PubMed Central

    2015-01-01

    Objective: In patients with a history of suicidal depression, recurrence of depressive symptoms can easily reactivate suicidal thinking. In this study, we investigated whether training in mindfulness, which is aimed at helping patients “decenter” from negative thinking, could help weaken the link between depressive symptoms and suicidal cognitions. Method: Analyses were based on data from a recent randomized controlled trial, in which previously suicidal patients were allocated to mindfulness-based cognitive therapy (MBCT), an active control treatment, cognitive psychoeducation (CPE), which did not include any meditation practice, or treatment as usual (TAU). After the end of the treatment phase, we compared the associations between depressive symptoms, as assessed through self-reports on the Beck Depression Inventory–II (Beck, Steer, & Brown, 1996), and suicidal thinking, as assessed through the Suicidal Cognitions Scale (Rudd et al., 2001). Results: In patients with minimal to moderate symptoms at the time of assessment, comparisons of the correlations between depressive symptoms and suicidal cognitions showed significant differences between the groups. Although suicidal cognitions were significantly related to levels of symptoms in the 2 control groups, there was no such relation in the MBCT group. Conclusion: The findings suggest that, in patients with a history of suicidal depression, training in mindfulness can help to weaken the association between depressive symptoms and suicidal thinking, and thus reduce an important vulnerability for relapse to suicidal depression. PMID:26302249

  6. Permutations of Control: Cognitive Considerations for Agent-Based Learning Environments

    ERIC Educational Resources Information Center

    Baylor, Amy L.

    2004-01-01

    While there has been a significant amount of research on technical issues regarding the development of agent-based learning environments (e.g., see the special issue of Journal of "Interactive Learning Research," 10(3/4)), there is less information regarding cognitive foundations for these environments. The management of control is a prime issue…

  7. Chinese-Speaking Learners' Cognitive Comprehension Problems with English Video-Based Materials

    ERIC Educational Resources Information Center

    Lin, Lu-Fang

    2014-01-01

    This study surveyed the problems 213 university students confronted while viewing an online video-based English program. Data were collected through self-reports and one-to-one interviews. The content analysis approach was used. Totally, 18 problems were identified and categorized into three cognitive-processing stages: perception, parsing, and…

  8. Applications of Cognitive Load Theory to Multimedia-Based Foreign Language Learning: An Overview

    ERIC Educational Resources Information Center

    Chen, I-Jung; Chang, Chi-Cheng; Lee, Yen-Chang

    2009-01-01

    This article reviews the multimedia instructional design literature based on cognitive load theory (CLT) in the context of foreign language learning. Multimedia are of particular importance in language learning materials because they incorporate text, image, and sound, thus offering an integrated learning experience of the four language skills…

  9. Evaluating a Web-Based Cognitive-Behavioral Therapy for Maladaptive Perfectionism in University Students

    ERIC Educational Resources Information Center

    Radhu, Natasha; Daskalakis, Zafiris J.; Arpin-Cribbie, Chantal A.; Irvine, Jane; Ritvo, Paul

    2012-01-01

    Objective: This study assessed a Web-based cognitive-behavioral therapy (CBT) for maladaptive perfectionism, investigating perfectionism, anxiety, depression, negative automatic thoughts, and perceived stress. Participants: Participants were undergraduate students defined as maladaptive perfectionists through a screening questionnaire at an urban…

  10. An Evidence-Based Systematic Review on Cognitive Interventions for Individuals with Dementia

    ERIC Educational Resources Information Center

    Hopper, Tammy; Bourgeois, Michelle; Pimentel, Jane; Qualls, Constance Dean; Hickey, Ellen; Frymark, Tobi; Schooling, Tracy

    2013-01-01

    Purpose: To evaluate the current state of research evidence related to cognitive interventions for individuals with Alzheimer's disease or related dementias. Method: A systematic search of the literature was conducted across 27 electronic databases based on a set of a priori questions, inclusion/exclusion criteria, and search parameters. Studies…

  11. Technology-Based Training in Cognitive Behavioral Therapy for Substance Abuse Counselors

    ERIC Educational Resources Information Center

    Weingardt, Kenneth R.; Villafranca, Steven W.; Levin, Cindy

    2006-01-01

    This study compared the learning outcomes achieved by 166 practicing substance abuse counselors who were randomized to one of three conditions: (1) a Web-Based Training (WBT) module designed to familiarize practitioners with the "Coping with Craving" module from the NIDA treatment manual, "A Cognitive-Behavioral Approach: Treating Cocaine…

  12. Cognitively Based Assessment and the Integration of Summative and Formative Assessments

    ERIC Educational Resources Information Center

    Embretson, Susan

    2010-01-01

    This article presents the author's comments on Randy Elliot Bennett's article "Cognitively Based Assessment of, for, and as Learning" (CBAL), which appeared in issue 8(2-3). The article presents an integrated approach to assessment in which a theory of action for the intended consequences (i.e., benefits) drives both assessments and instructional…

  13. Permutations of Control: Cognitive Considerations for Agent-Based Learning Environments.

    ERIC Educational Resources Information Center

    Baylor, Amy L.

    2001-01-01

    Discussion of intelligent agents and their use in computer learning environments focuses on cognitive considerations. Presents four dimension of control that should be considered in designing agent-based learning environments: learner control, from constructivist to instructivist; feedback; relationship of learner to agent; and learner confidence…

  14. The Application of Social Cognitive Theory to Web-Based Learning through NetPorts

    ERIC Educational Resources Information Center

    Wang, Shu-Ling; Lin, Sunny S. J.

    2007-01-01

    Although the Web allows for flexible learning, research has found that online students tend to lack focus, willingness to participate, confidence, and discipline. This study thus attempts to promote Web-based self-regulated learning from the social cognitive perspective, which emphasizes the interactions among personal, behavioral, and…

  15. Performance of a computer-based assessment of cognitive function measures in two cohorts of seniors

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Computer-administered assessment of cognitive function is being increasingly incorporated in clinical trials, however its performance in these settings has not been systematically evaluated. The Seniors Health and Activity Research Program (SHARP) pilot trial (N=73) developed a computer-based tool f...

  16. Mining Students' Learning Patterns and Performance in Web-Based Instruction: A Cognitive Style Approach

    ERIC Educational Resources Information Center

    Chen, Sherry Y.; Liu, Xiaohui

    2011-01-01

    Personalization has been widely used in Web-based instruction (WBI). To deliver effective personalization, there is a need to understand different preferences of each student. Cognitive style has been identified as one of the most pertinent factors that affect students' learning preferences. Therefore, it is essential to investigate how learners…

  17. Study of Personalized Network Tutoring System Based on Emotional-cognitive Interaction

    NASA Astrophysics Data System (ADS)

    Qi, Manfei; Ma, Ding; Wang, Wansen

    Aiming at emotion deficiency in present Network tutoring system, a lot of negative effects is analyzed and corresponding countermeasures are proposed. The model of Personalized Network tutoring system based on Emotional-cognitive interaction is constructed in the paper. The key techniques of realizing the system such as constructing emotional model and adjusting teaching strategies are also introduced.

  18. The Effects of a Cognitive-Based Intervention on Drug Awareness in Private School Preadolescent Students

    ERIC Educational Resources Information Center

    Parsons, Phyllis M.

    2005-01-01

    The effects of a Cognitive-Based Intervention on Drug Awareness in Private School Preadolescent Students. Parsons, Phyllis M., 2005: Applied Dissertation, Nova Southeastern University, Fischler School of Education and Human Services. Adolescents/Substance Abuse/Prevention/Family Influence/Drug Education. This applied dissertation was designed to…

  19. Mindfulness-Based Cognitive Therapy to Prevent Relapse in Recurrent Depression

    ERIC Educational Resources Information Center

    Kuyken, Willem; Byford, Sarah; Taylor, Rod S.; Watkins, Ed; Holden, Emily; White, Kat; Barrett, Barbara; Byng, Richard; Evans, Alison; Mullan, Eugene; Teasdale, John D.

    2008-01-01

    For people at risk of depressive relapse, mindfulness-based cognitive therapy (MBCT) has an additive benefit to usual care (H. F. Coelho, P. H. Canter, & E. Ernst, 2007). This study asked if, among patients with recurrent depression who are treated with antidepressant medication (ADM), MBCT is comparable to treatment with maintenance ADM (m-ADM)…

  20. Internet-Based Cognitive-Behavioral Therapy for Complicated Grief: A Randomized Controlled Trial

    ERIC Educational Resources Information Center

    Wagner, Birgit; Knaevelsrud, Christine; Maercker, Andreas

    2006-01-01

    The present study investigates the efficacy of an Internet-based cognitive-behavioral therapy program for bereaved people suffering complicated grief. The program combines established methods of psychotherapy with new technology--therapists and patients communicated exclusively by e-mail. Bereaved individuals diagnosed with complicated grief (n =…

  1. Effects of Computer-Based Visual Representation on Mathematics Learning and Cognitive Load

    ERIC Educational Resources Information Center

    Yung, Hsin I.; Paas, Fred

    2015-01-01

    Visual representation has been recognized as a powerful learning tool in many learning domains. Based on the assumption that visual representations can support deeper understanding, we examined the effects of visual representations on learning performance and cognitive load in the domain of mathematics. An experimental condition with visual…

  2. Center-Based Child Care and Cognitive Skills Development: Importance of Timing and Household Resources

    ERIC Educational Resources Information Center

    Votruba-Drzal, Elizabeth; Coley, Rebekah Levine; Koury, Amanda S.; Miller, Portia

    2013-01-01

    Growing evidence has linked center-based early care and education settings to improvements in children's cognitive skills. Additional research is needed to more carefully delineate when and for whom these associations are most pronounced. Using data from the Early Childhood Longitudinal Study, Birth Cohort (N ˜ 6,350; Flanagan & West, 2004),…

  3. Telephone-Administered Cognitive Behavioral Therapy for Veterans Served by Community-Based Outpatient Clinics

    ERIC Educational Resources Information Center

    Mohr, David C.; Carmody, Timothy; Erickson, Lauren; Jin, Ling; Leader, Julie

    2011-01-01

    Objective: Multiple trials have found telephone-administered cognitive behavioral therapy (T-CBT) to be effective for the treatment of depression. The aim of this study was to evaluate T-CBT for the treatment of depression among veterans served by community-based outpatient clinics (CBOCs) outside of major urban areas. Method: Eighty-five veterans…

  4. Technology and Cognition Merge with Challenge-Based Learning Cycles Online

    ERIC Educational Resources Information Center

    Cobbett, Shelley L.

    2013-01-01

    Teaching and learning in Web-based courses has become a global phenomenon. Educators are grappling with merging cognition and technology to offer students quality, relevant online courses. The development of social presence in the online environment is of paramount importance and requires individuals to engage in meaningful interactions about, and…

  5. Mindfulness-Based Cognitive Therapy: Further Issues in Current Evidence and Future Research

    ERIC Educational Resources Information Center

    Williams, J. Mark G.; Russell, Ian; Russell, Daphne

    2008-01-01

    The authors respond to the article by H. F. Coelho, P. H. Canter, and E. Ernst (2007), which reviewed the current status of mindfulness-based cognitive therapy (MBCT). First, they clarify the randomization procedures in the 2 main MBCT trials. Second, they report posttreatment and follow-up data to show that trial participants allocated to…

  6. Cognitive Abilities that Predict Success in a Computer-Based Training Program

    ERIC Educational Resources Information Center

    Ownby, Raymond L.; Czaja, Sara J.; Loewenstein, David; Rubert, Mark

    2008-01-01

    Purpose: The purposes of this study were (a) to identify cognitive abilities and other factors related to successful completion of training for computer-based tasks that simulated real jobs and (b) to create a brief assessment battery useful in assessing older adults for these kinds of jobs. Design and Methods: Participants from three age groups…

  7. The Beast of Aggregating Cognitive Load Measures in Technology-Based Learning

    ERIC Educational Resources Information Center

    Leppink, Jimmie; van Merriënboer, Jeroen J. G.

    2015-01-01

    An increasing part of cognitive load research in technology-based learning includes a component of repeated measurements, that is: participants are measured two or more times on the same performance, mental effort or other variable of interest. In many cases, researchers aggregate scores obtained from repeated measurements to one single sum or…

  8. Cognitive Control Predicts Use of Model-Based Reinforcement-Learning

    PubMed Central

    Otto, A. Ross; Skatova, Anya; Madlon-Kay, Seth; Daw, Nathaniel D.

    2015-01-01

    Accounts of decision-making and its neural substrates have long posited the operation of separate, competing valuation systems in the control of choice behavior. Recent theoretical and experimental work suggest that this classic distinction between behaviorally and neurally dissociable systems for habitual and goal-directed (or more generally, automatic and controlled) choice may arise from two computational strategies for reinforcement learning (RL), called model-free and model-based RL, but the cognitive or computational processes by which one system may dominate over the other in the control of behavior is a matter of ongoing investigation. To elucidate this question, we leverage the theoretical framework of cognitive control, demonstrating that individual differences in utilization of goal-related contextual information—in the service of overcoming habitual, stimulus-driven responses—in established cognitive control paradigms predict model-based behavior in a separate, sequential choice task. The behavioral correspondence between cognitive control and model-based RL compellingly suggests that a common set of processes may underpin the two behaviors. In particular, computational mechanisms originally proposed to underlie controlled behavior may be applicable to understanding the interactions between model-based and model-free choice behavior. PMID:25170791

  9. From Theory to PrACTice: A Cognitive Remediation Program Based on a Neuropsychological Model of Schizophrenia

    PubMed Central

    Fabre, Delphine; Vehier, Aurélie; Chesnoy-Servanin, Gabrielle; Gouiller, Nicolas; D’Amato, Thierry; Saoud, Mohamed

    2015-01-01

    Cognitive dysfunction is one of the hallmark deficits of schizophrenia. A wide range of studies illustrate how it is strongly interconnected to clinical presentation and daily life functioning [see Ref. (1, 2)]. Hence, cognition is an important treatment target in schizophrenia. To address the challenge of cognitive enhancement in schizophrenia, a large number of cognitive remediation programs have been developed and evaluated over the past several decades. First, an overview of these programs is presented highlighting their specificity to cognitive deficit in schizophrenia using an integrated method. In this case, cognitive training focuses on enhancing several elementary cognitive functions considered as a prerequisite to social skills or vocational training modules. These programs are based on the neurodevelopmental hypothesis of schizophrenia. However, moderate improvement for patients who benefit from these therapies has been observed as described in Wykes et al. review (3). Next, neuropsychological models of schizophrenia are then presented. They highlight the critical role of the internally generated intentions in appropriate willful actions. The cognitive control mechanism deals with this ability. Interestingly, available cognitive remediation programs have not been influenced by these models. Hence, we propose another alternative to set up a specific cognitive remediation program for schizophrenia patients by targeting the cognitive control mechanism. We describe the PrACTice program that is in the process of being validated. PMID:26648877

  10. [User friendliness of computer-based cognitive training for psychogeriatric patients with mild to moderate cognitive impairments].

    PubMed

    van der Ploeg, Eva S; Hoorweg, Angela; van der Lee, Jacqueline

    2016-04-01

    Cognitive impairment associated with dementia is characterized by a continuous decline. Cognitive training is a method to train specific brain functions such as memory and attention to prevent or slow down cognitive decline. A small number of studies has shown that cognitive training on a computer has a positive effect on both cognition and mood in people with cognitive impairment. This pilot study tested if serious games could be integrated in a psychogeriatric rehabilitation center. Fourteen psychogeriatric patients participated twice weekly in cognitive training sessions on a computer. Both the participants and the facilitator reported positive interactions and outcomes. However, after five weeks only half of the sample still participated in the training. This was partly because of patient turn-over as well as incorporating this new task in the facilitators' daily work. Fear of failure, physical limitations and rapidly decreasing cognitive function led to drop out according to the facilitator. The engagement of patients in the games and the role of the facilitator seemed essential for success, especially monitoring (and adjusting) the difficulty level of the program for every individual participant. PMID:26821167

  11. Regional Gray Matter Density Associated with Cognitive Reflectivity–Impulsivity: Evidence from Voxel-Based Morphometry

    PubMed Central

    Yokoyama, Ryoichi; Nozawa, Takayuki; Takeuchi, Hikaru; Taki, Yasuyuki; Sekiguchi, Atsushi; Nouchi, Rui; Kotozaki, Yuka; Nakagawa, Seishu; Miyauchi, Carlos Makoto; Iizuka, Kunio; Shinada, Takamitsu; Yamamoto, Yuki; Hanawa, Sugiko; Araki, Tsuyoshi; Hashizume, Hiroshi; Kunitoki, Keiko; Hanihara, Mayu; Sassa, Yuko; Kawashima, Ryuta

    2015-01-01

    When faced with a problem or choice, humans can use two different strategies: “cognitive reflectivity,” which involves slow responses and fewer mistakes, or “cognitive impulsivity,” which comprises of quick responses and more mistakes. Different individuals use these two strategies differently. To our knowledge, no study has directly investigated the brain regions involved in reflectivity–impulsivity; therefore, this study focused on associations between these cognitive strategies and the gray matter structure of several brain regions. In order to accomplish this, we enrolled 776 healthy, right-handed individuals (432 men and 344 women; 20.7 ± 1.8 years) and used voxel-based morphometry with administration of a cognitive reflectivity–impulsivity questionnaire. We found that high cognitive reflectivity was associated with greater regional gray matter density in the ventral medial prefrontal cortex. Our finding suggests that this area plays an important role in defining an individual’s trait associated with reflectivity and impulsivity. PMID:25803809

  12. Model-Based Inference of Cognitive Processes from Unobtrusive Gait Velocity Measurements

    PubMed Central

    Austin, Daniel.; Leen, Todd; Hayes, Tamara L.; Kaye, Jeff; Jimison, Holly; Pavel, Misha

    2011-01-01

    In this paper we describe a preliminary modeling and analysis of a unique data set comprising unobtrusive and continuous measurements of gait velocity in the elder participants' residences. The data have been collected as a part of a longitudinal study aimed at early detection of cognitive decline. We motivate these analyses by first presenting evidence that suggests significant relationship between gait parameters and cognitive functions. We then describe a simple, model-based approach to the analysis of gait velocity using a weighted correlation function estimates. One of the main challenges is due to the fact that the daily estimates of the gait parameters vary with the number of walks. We illustrate the importance of using weighted as opposed to unweighted estimates on a sample of different houses. The correlation functions appear to capture behavioral differences that can be related to the cognitive functioning of the participants. PMID:21096044

  13. Computer-based cognitive retraining for adults with chronic acquired brain injury: a pilot study.

    PubMed

    Li, Kitsum; Robertson, Julie; Ramos, Joshua; Gella, Stephanie

    2013-10-01

    This study evaluated the effectiveness of a computer-based cognitive retraining (CBCR) program on improving memory and attention deficits in individuals with a chronic acquired brain injury (ABI). Twelve adults with a chronic ABI demonstrating deficits in memory and attention were recruited from a convenience sample from the community. Using a quasi-experimental one-group pretest-posttest design, a significant improvement was found in both memory and attention scores postintervention using the cognitive screening tool. This study supported the effectiveness of CBCR programs in improving cognitive deficits in memory and attention in individuals with chronic ABI. Further research is recommended to validate these findings with a larger ABI population and to investigate transfer to improvement in occupational performance that supports daily living skills. PMID:24102589

  14. Creation and Global Deployment of a Mobile, Application-Based Cognitive Simulator for Cardiac Surgical Procedures.

    PubMed

    Brewer, Zachary E; Ogden, William David; Fann, James I; Burdon, Thomas A; Sheikh, Ahmad Y

    2016-01-01

    Several modern learning frameworks (eg, cognitive apprenticeship, anchored instruction, and situated cognition) posit the utility of nontraditional methods for effective experiential learning. Thus, development of novel educational tools emphasizing the cognitive framework of operative sequences may be of benefit to surgical trainees. We propose the development and global deployment of an effective, mobile cognitive cardiac surgical simulator. In methods, 16 preclinical medical students were assessed. Overall, 4 separate surgical modules (sternotomy, cannulation, decannulation, and sternal closure) were created utilizing the Touch Surgery (London, UK) platform. Modules were made available to download free of charge for use on mobile devices. Usage data were collected over a 6-month period. Educational efficacy of the modules was evaluated by randomizing a cohort of medical students to either module usage or traditional, reading-based self-study, followed by a multiple-choice learning assessment tool. In results, downloads of the simulator achieved global penetrance, with highest usage in the USA, Brazil, Italy, UK, and India. Overall, 5368 unique users conducted a total of 1971 hours of simulation. Evaluation of the medical student cohort revealed significantly higher assessment scores in those randomized to module use versus traditional reading (75% ± 9% vs 61% ± 7%, respectively; P < 0.05). In conclusion, this study represents the first effort to create a mobile, interactive cognitive simulator for cardiac surgery. Simulators of this type may be effective for the training and assessment of surgical students. We investigated whether an interactive, mobile-computing-based cognitive task simulator for cardiac surgery could be developed, deployed, and validated. Our findings suggest that such simulators may be a useful learning tool. PMID:27568126

  15. A diet based on multiple functional concepts improves cognitive performance in healthy subjects

    PubMed Central

    2013-01-01

    plasma concentrations of cardiometabolic risk markers (fasting cholesterol, blood glucose, blood pressure) and cardiovascular risk scores (Framingham and Reynols), and positivly associated with apolipoprotein A1 (p < 0.05). Conclusions The results indicate that diet characteristics may modulate cognitive performance. A relationship seems to exist between cardiometabolic risk markers and cognitive performance in apparently healthy subjects. The results provide additional motives for diet based prevention of metabolic disturbances related to the MetS. PMID:23855966

  16. Towards a web 2.0 based software for the design and the facilitation of cognitive stimulation workshops.

    PubMed

    Klinger, Evelyne; Martinet, Elise; Perret, David

    2011-01-01

    Cognitive stimulation workshops (CSW) are recommended for elderly people with a decline in cognitive functions, for example, mild cognitive impairment. Information and Communication Technology (ICT) has the potential to enrich and facilitate preparation, facilitation and assessment of CSW interventions. We present the first steps of our co-design approach towards a Web 2.0 based software, called STIMULEE, for the design and the facilitation of CSW. Its achievement will provide novel therapeutic practices to our clinical partners. PMID:21685659

  17. A Randomized Trial to Measure the Impact of a Community-Based Cognitive Training Intervention on Balance and Gait in Cognitively Intact Black Older Adults

    PubMed Central

    Smith-Ray, Renae L.; Makowski-Woidan, Beth; Hughes, Susan L.

    2015-01-01

    Introduction Fall prevention is important for maintaining mobility and independence into old age. Approaches for reducing falls include exercise, tai chi, and home modifications; however, causes of falling are multifactorial and include not just physical but cognitive factors. Cognitive decline occurs with age, but older adults with the greatest declines in executive function experience more falls. The purpose of this study was twofold: to demonstrate the feasibility of a community-based cognitive training program for cognitively intact Black older adults and to analyze its impact on gait and balance in this population. Method This pilot study used a pretest/posttest randomized trial design with assignment to an intervention or control group. Participants assigned to the intervention completed a computer-based cognitive training class that met 2 days a week for 60 min over 10 weeks. Classes were held at senior/community centers. Primary outcomes included balance as measured by the Berg Balance Scale (BBS), 10-meter gait speed, and 10-meter gait speed under visuospatial dual-task condition. All measures were assessed at baseline and immediately post-intervention. Results Participants were community-dwelling Black adults with a mean age of 72.5 and history of falls (N = 45). Compared to controls, intervention participants experienced statistically significant improvements in BBS and gait speed. Mean performance on distracted gait speed also improved more for intervention participants compared to controls. Conclusion Findings from this pilot randomized trial demonstrate the feasibility of a community-based cognitive training intervention. They provide initial evidence that cognitive training may be an efficacious approach toward improving balance and gait in older adults known to have a history of falls. PMID:25274713

  18. Improving the learning of clinical reasoning through computer-based cognitive representation

    PubMed Central

    Wu, Bian; Wang, Minhong; Johnson, Janice M.; Grotzer, Tina A.

    2014-01-01

    Objective Clinical reasoning is usually taught using a problem-solving approach, which is widely adopted in medical education. However, learning through problem solving is difficult as a result of the contextualization and dynamic aspects of actual problems. Moreover, knowledge acquired from problem-solving practice tends to be inert and fragmented. This study proposed a computer-based cognitive representation approach that externalizes and facilitates the complex processes in learning clinical reasoning. The approach is operationalized in a computer-based cognitive representation tool that involves argument mapping to externalize the problem-solving process and concept mapping to reveal the knowledge constructed from the problems. Methods Twenty-nine Year 3 or higher students from a medical school in east China participated in the study. Participants used the proposed approach implemented in an e-learning system to complete four learning cases in 4 weeks on an individual basis. For each case, students interacted with the problem to capture critical data, generate and justify hypotheses, make a diagnosis, recall relevant knowledge, and update their conceptual understanding of the problem domain. Meanwhile, students used the computer-based cognitive representation tool to articulate and represent the key elements and their interactions in the learning process. Results A significant improvement was found in students’ learning products from the beginning to the end of the study, consistent with students’ report of close-to-moderate progress in developing problem-solving and knowledge-construction abilities. No significant differences were found between the pretest and posttest scores with the 4-week period. The cognitive representation approach was found to provide more formative assessment. Conclusions The computer-based cognitive representation approach improved the learning of clinical reasoning in both problem solving and knowledge construction. PMID:25518871

  19. Optical performance monitoring for OFDM using low bandwidth coherent receivers.

    PubMed

    Chen, Simin; Anderson, Trevor; Hewitt, Don; Tran, An V; Zhu, Chen; Du, Liang B; Lowery, Arthur J; Skafidas, Efstratios

    2012-12-17

    We propose using low bandwidth coherent receivers for distributed optical performance monitoring. We demonstrate optical signal-to-noise ratio (OSNR) monitoring of both 20-Gb/s single-polarization and 40-Gb/s polarization-multiplexed coherent optical orthogonal frequency-division multiplexing (CO-OFDM) signals with a 0.8-GHz receiver using both data-aided (DA) and non-data-aided (NDA) approaches. The sampling rate of the performance monitor is much lower than the signal baud rate, so provides a cost-effective solution for distributed optical performance monitoring. The proposed method is demonstrated experimentally and through simulation. The results show that after calibration the OSNR monitoring error is less than 1 dB and the two approaches are not affected by fiber dispersion after 800-km transmission and 30-ps differential group delay (DGD). PMID:23263110

  20. Lesion mapping of cognitive control and value-based decision making in the prefrontal cortex

    PubMed Central

    Gläscher, Jan; Adolphs, Ralph; Damasio, Hanna; Bechara, Antoine; Rudrauf, David; Calamia, Matthew; Paul, Lynn K.; Tranel, Daniel

    2012-01-01

    A considerable body of previous research on the prefrontal cortex (PFC) has helped characterize the regional specificity of various cognitive functions, such as cognitive control and decision making. Here we provide definitive findings on this topic, using a neuropsychological approach that takes advantage of a unique dataset accrued over several decades. We applied voxel-based lesion-symptom mapping in 344 individuals with focal lesions (165 involving the PFC) who had been tested on a comprehensive battery of neuropsychological tasks. Two distinct functional-anatomical networks were revealed within the PFC: one associated with cognitive control (response inhibition, conflict monitoring, and switching), which included the dorsolateral prefrontal cortex and anterior cingulate cortex and a second associated with value-based decision-making, which included the orbitofrontal, ventromedial, and frontopolar cortex. Furthermore, cognitive control tasks shared a common performance factor related to set shifting that was linked to the rostral anterior cingulate cortex. By contrast, regions in the ventral PFC were required for decision-making. These findings provide detailed causal evidence for a remarkable functional-anatomical specificity in the human PFC. PMID:22908286

  1. Performance analysis of OFDM modulation on indoor broadband PLC channels

    NASA Astrophysics Data System (ADS)

    Antonio Cortés, José; Díez, Luis; Cañete, Francisco Javier; Sánchez-Martínez, Juan José; Entrambasaguas, José Tomás

    2011-12-01

    Indoor broadband power-line communications is a suitable technology for home networking applications. In this context, orthogonal frequency-division multiplexing (OFDM) is the most widespread modulation technique. It has recently been adopted by the ITU-T Recommendation G.9960 and is also used by most of the commercial systems, whose number of carriers has gone from about 100 to a few thousands in less than a decade. However, indoor power-line channels are frequency-selective and exhibit periodic time variations. Hence, increasing the number of carriers does not always improves the performance, since it reduces the distortion because of the frequency selectivity, but increases the one caused by the channel time variation. In addition, the long impulse response of power-line channels obliges to use an insufficient cyclic prefix. Increasing its value reduces the distortion, but also the symbol rate. Therefore, there are optimum values for both modulation parameters. This article evaluates the performance of an OFDM system as a function of the number of carriers and the cyclic prefix length, determining their most appropriate values for the indoor power-line scenario. This task must be accomplished by means of time-consuming simulations employing a linear time-varying filtering, since no consensus on a tractable statistical channel model has been reached yet. However, this study presents a simpler procedure in which the distortion because of the frequency selectivity is computed using a time-invariant channel response, and an analytical expression is derived for the one caused by the channel time variation.

  2. Cognitive, on-road, and simulator-based driving assessment after stroke.

    PubMed

    Hird, Megan A; Vetivelu, Abeiramey; Saposnik, Gustavo; Schweizer, Tom A

    2014-01-01

    Driving is a complex activity that requires intact cognitive, behavioral, and motor function. Stroke is one of the most prevalent neurologic impairments and can affect all of these functions. However, diagnosis of stroke is not a definitive indicator of driving impairment. Determining fitness to drive after stroke is a very complex process and is typically based on cognitive assessments, on-road performance, simulator-based assessment, or a combination of the three. The aim of this review was to provide (1) a systematic review of the literature on cognitive, on-road, and simulator assessment after stroke, and (2) address the existing limitations and inconsistencies in stroke and driving research. Our results indicated that of 1413 total stroke patients, 748 definitively passed and 367 definitely failed an on-road assessment, with minimal information provided about clinical presentation. In addition, although the Stroke Driver Screening Assessment, the Useful Field of View Test, and the Rey-O Complex Figure test may have some utility in predicting driving performance, most cognitive measures have been inconsistently and minimally explored. Several limitations were observed across studies such as procedural inconsistencies, including outcome variables used (eg, driving cessation and pass/fail classification) and the heterogeneity of patient samples (eg, time since stroke and stroke location). Due, in part, to the larger variability in results of cognitive, on-road, and simulator-based assessment, there is no consensus regarding a valid and reliable driving assessment for physicians. Future studies should assess poststroke driving fitness by differentiating different stages, severities, and locations of stroke. PMID:25306401

  3. A Randomized Controlled Trial of Acceptance-Based Behavior Therapy and Cognitive Therapy for Test Anxiety: A Pilot Study

    ERIC Educational Resources Information Center

    Brown, Lily A.; Forman, Evan M.; Herbert, James D.; Hoffman, Kimberly L.; Yuen, Erica K.; Goetter, Elizabeth M.

    2011-01-01

    Many university students suffer from test anxiety that is severe enough to impair performance. Given mixed efficacy results of previous cognitive-behavior therapy (CBT) trials and a theoretically driven rationale, an acceptance-based behavior therapy (ABBT) approach was compared to traditional CBT (i.e., Beckian cognitive therapy; CT) for the…

  4. Self-Instructional Module Based on Cognitive Load Theory: A Study on Information Retention among Trainee Teachers

    ERIC Educational Resources Information Center

    Ong, Chiek Pin; Tasir, Zaidatun

    2015-01-01

    The aim of the research is to study the information retention among trainee teachers using a self-instructional printed module based on Cognitive Load Theory for learning spreadsheet software. Effective pedagogical considerations integrating the theoretical concepts related to cognitive load are reflected in the design and development of the…

  5. Cognitive Correlates of Functional Performance in Older Adults: Comparison of Self-Report, Direct Observation, and Performance-Based Measures

    PubMed Central

    Schmitter-Edgecombe, Maureen; Parsey, Carolyn; Cook, Diane J.

    2013-01-01

    Neuropsychologists are often asked to answer questions about the effects of cognitive deficits on everyday functioning. This study examined the relationship between and the cognitive correlates of self-report, performance-based, and direct observation measures commonly used as proxy measures for everyday functioning. Participants were 88 community-dwelling, cognitively healthy older adults (age 50–86 years). Participants completed standardized neuropsychological tests and questionnaires, and performed eight activities of daily living (e.g., water plants, fill a medication dispenser) while under direct observation in a campus apartment. All proxy measures of everyday function were sensitive to the effects of healthy cognitive aging. After controlling for age, cognitive predictors explained a unique amount of the variance for only the performance-based behavioral simulation measure (i.e., Revised Observed Tasks of Daily Living). The self-report instrumental activities of daily living (IADL) and the performance-based everyday problem-solving test (i.e., EPT) did not correlate with each other; however, both were unique predictors of the direct observation measure. These findings suggest that neuropsychologists must be cautious in making predictions about the quality of everyday activity completion in cognitively healthy older adults from specific cognitive functions. The findings further suggest that a self-report of IADLs and the performance-based EPT may be useful measures for assessing everyday functional status in cognitively healthy older adults. PMID:21729400

  6. The Impact of Classroom-Based Meditation Practice on Cognitive Engagement, Mindfulness and Academic Performance of Undergraduate College Students

    ERIC Educational Resources Information Center

    Napora, Lisa

    2013-01-01

    This study explored the potential of classroom-based meditation practice as a tool to facilitate learning. Moreover, the impact of meditation on cognitive engagement, mindfulness and academic performance of undergraduate college students was investigated. Additionally, the relationships between mindfulness and cognitive engagement, and between…

  7. How Cognitive Styles Affect the Learning Behaviors of Online Problem-Solving Based Discussion Activity: A Lag Sequential Analysis

    ERIC Educational Resources Information Center

    Wu, Sheng-Yi; Hou, Huei-Tse

    2015-01-01

    Cognitive styles play an important role in influencing the learning process, but to date no relevant study has been conducted using lag sequential analysis to assess knowledge construction learning patterns based on different cognitive styles in computer-supported collaborative learning activities in online collaborative discussions. This study…

  8. Cognitive-Behavioral Psychotherapy for Anxiety and Depressive Disorders in Children and Adolescents: An Evidence-Based Medicine Review

    ERIC Educational Resources Information Center

    Compton, Scott N.; March, John S.; Brent, David; Albano, Anne Marie; Weersing, V. Robin; Curry, John

    2004-01-01

    Objective: To review the literature on the cognitive-behavioral treatment of children and adolescents with anxiety and depressive disorders within the conceptual framework of evidence-based medicine. Method: The psychiatric and psychological literature was systematically searched for controlled trials applying cognitive-behavioral treatment to…

  9. Developing the Therapeutic Potential of Embodied Cognition and Metaphors in Nature-Based Therapy: Lessons from Theory to Practice

    ERIC Educational Resources Information Center

    Corazon, Sus S.; Schilhab, Theresa S. S.; Stigsdotter, Ulrika K.

    2011-01-01

    This paper theoretically examines the interplay between cognition and bodily involvement in relation to nature-based therapy and proposes implications for practice. With support from theory within embodied cognition and neuroscientific studies, it is argued that explicit learning is actively supported by bodily involvement with the environment.…

  10. Seven practical principles for improving patient education: Evidence-based ideas from cognition science

    PubMed Central

    Pusic, Martin V; Ching, Kevin; Yin, Hsiang Shonna; Kessler, David

    2014-01-01

    An important role of the paediatrician is that of a teacher – every clinician is an educator to patients and their families. This education, however, often occurs under difficult or time-pressured learning conditions. The authors present principles derived from three basic theories of human cognition that may help to guide clinicians’ instruction of parents and patients. Cognitive load theory holds that an individual’s capacity to process information is finite. By controlling information flow rate, decreasing reliance on working memory and removing extraneous cognitive load, learning is improved. Dual code theory suggests that humans have separate cognitive ‘channels’ for text/audio information versus visual information. By constructing educational messages that take advantage of both channels simultaneously, information uptake may be improved. Multimedia theory is based on the notion that there is an optimal blend of media to accomplish a given learning objective. The authors suggest seven practical strategies that clinicians may use to improve patient education. PMID:24665218

  11. 1-Tb/s single-channel coherent optical OFDM transmission over 600-km SSMF fiber with subwavelength bandwidth access.

    PubMed

    Ma, Yiran; Yang, Qi; Tang, Yan; Chen, Simin; Shieh, William

    2009-05-25

    A 1-Tb/s single-channel coherent optical OFDM (CO-OFDM) signal consisting of continuous 4,104 spectrally-overlapped subcarriers is generated using a novel device of recirculating frequency shifter (RFS). The RFS produces 320.6-GHz wide spectrum using a single laser with superior flatness and tone-to-noise ratio (TNR). The 1-Tb/s CO-OFDM signal is comprised of 36 uncorrelated orthogonal bands achieved by adjusting the delay of the RFS to an integer number of OFDM symbol periods. The 1- Tb/s CO-OFDM signal with a spectral efficiency of 3.3 bit/s/Hz is successfully received after transmission over 600-km SSMF fiber without either Raman amplification or dispersion compensation. PMID:19466194

  12. Spectrum sensing and resource allocation for multicarrier cognitive radio systems under interference and power constraints

    NASA Astrophysics Data System (ADS)

    Dikmese, Sener; Srinivasan, Sudharsan; Shaat, Musbah; Bader, Faouzi; Renfors, Markku

    2014-12-01

    Multicarrier waveforms have been commonly recognized as strong candidates for cognitive radio. In this paper, we study the dynamics of spectrum sensing and spectrum allocation functions in cognitive radio context using very practical signal models for the primary users (PUs), including the effects of power amplifier nonlinearities. We start by sensing the spectrum with energy detection-based wideband multichannel spectrum sensing algorithm and continue by investigating optimal resource allocation methods. Along the way, we examine the effects of spectral regrowth due to the inevitable power amplifier nonlinearities of the PU transmitters. The signal model includes frequency selective block-fading channel models for both secondary and primary transmissions. Filter bank-based wideband spectrum sensing techniques are applied for detecting spectral holes and filter bank-based multicarrier (FBMC) modulation is selected for transmission as an alternative multicarrier waveform to avoid the disadvantage of limited spectral containment of orthogonal frequency-division multiplexing (OFDM)-based multicarrier systems. The optimization technique used for the resource allocation approach considered in this study utilizes the information obtained through spectrum sensing and knowledge of spectrum leakage effects of the underlying waveforms, including a practical power amplifier model for the PU transmitter. This study utilizes a computationally efficient algorithm to maximize the SU link capacity with power and interference constraints. It is seen that the SU transmission capacity depends critically on the spectral containment of the PU waveform, and these effects are quantified in a case study using an 802.11-g WLAN scenario.

  13. Disrupted white matter integrity is associated with cognitive deficits in patients with amnestic mild cognitive impairment: An atlas-based study

    PubMed Central

    Liu, Duan; Wang, Zan; Shu, Hao; Zhang, Zhijun

    2016-01-01

    Objective: This study investigated white matter integrity in patients with amnestic mild cognitive impairment by diffusion tensor imaging. Methods: A total of 83 patients with amnestic mild cognitive impairment and 85 elderly healthy controls underwent neuropsychological testing and a diffusion tensor imaging scan. Whole-brain white matter data were parcellated into 50 regions based on the anatomical ICBM-DTI-81 atlas, and regional diffusion metrics consisting of fractional anisotropy, mean diffusivity, radial diffusivity, and axial diffusivity were calculated for each region. Diffusion tensor imaging indices were compared between groups, and it was determined that between-group differences were significantly correlated with neurocognitive performance. Results: Relative to the healthy controls group, the amnestic mild cognitive impairment group exhibited poorer cognitive performance in all neuropsychological tests except the complex figure test (p = 0.083) and showed decreased mean fractional anisotropy in the fornix, increased mean diffusivity in the fornix and bilateral uncinate fasciculus, elevated axial diffusivity in the fornix and genu of corpus callosum, and elevated radial diffusivity in the fornix and bilateral uncinate fasciculus (p < 0.05). Behaviorally, integrity of the bilateral uncinate fasciculus was correlated positively with episodic memory function, while left uncinate fasciculus integrity was positively associated with language function in the amnestic mild cognitive impairment group (p < 0.05). Conclusion: White matter abnormalities in neural pathways associated with memory were correlated with neurocognitive deficiencies in amnestic mild cognitive impairment. Given that amnestic mild cognitive impairment is putatively a prodromal syndrome for Alzheimer’s disease, this study furthers our understanding of the white matter changes associated with Alzheimer’s disease pathogenesis in the predementia stage. PMID:27354916

  14. An Energy-Efficient Game-Theory-Based Spectrum Decision Scheme for Cognitive Radio Sensor Networks.

    PubMed

    Salim, Shelly; Moh, Sangman

    2016-01-01

    A cognitive radio sensor network (CRSN) is a wireless sensor network in which sensor nodes are equipped with cognitive radio. In this paper, we propose an energy-efficient game-theory-based spectrum decision (EGSD) scheme for CRSNs to prolong the network lifetime. Note that energy efficiency is the most important design consideration in CRSNs because it determines the network lifetime. The central part of the EGSD scheme consists of two spectrum selection algorithms: random selection and game-theory-based selection. The EGSD scheme also includes a clustering algorithm, spectrum characterization with a Markov chain, and cluster member coordination. Our performance study shows that EGSD outperforms the existing popular framework in terms of network lifetime and coordination overhead. PMID:27376290

  15. SVM-based spectrum mobility prediction scheme in mobile cognitive radio networks.

    PubMed

    Wang, Yao; Zhang, Zhongzhao; Ma, Lin; Chen, Jiamei

    2014-01-01

    Spectrum mobility as an essential issue has not been fully investigated in mobile cognitive radio networks (CRNs). In this paper, a novel support vector machine based spectrum mobility prediction (SVM-SMP) scheme is presented considering time-varying and space-varying characteristics simultaneously in mobile CRNs. The mobility of cognitive users (CUs) and the working activities of primary users (PUs) are analyzed in theory. And a joint feature vector extraction (JFVE) method is proposed based on the theoretical analysis. Then spectrum mobility prediction is executed through the classification of SVM with a fast convergence speed. Numerical results validate that SVM-SMP gains better short-time prediction accuracy rate and miss prediction rate performance than the two algorithms just depending on the location and speed information. Additionally, a rational parameter design can remedy the prediction performance degradation caused by high speed SUs with strong randomness movements. PMID:25143975

  16. A spatial reference frame model of Beijing based on spatial cognitive experiment

    NASA Astrophysics Data System (ADS)

    Zhang, Jie; Zhang, Jing; Liu, Yu

    2006-10-01

    Orientation relation in the spatial relation is very important in GIS. People can obtain orientation information by making use of map reading and the cognition of the surrounding environment, and then create the spatial reference frame. City is a kind of special spatial environment, a person with life experiences has some spatial knowledge about the city where he or she lives in. Based on the spatial knowledge of the city environment, people can position, navigate and understand the meaning embodied in the environment correctly. Beijing as a real geographic space, its layout is very special and can form a kind of new spatial reference frame. Based on the characteristics of the layout of Beijing city, this paper will introduce a new spatial reference frame of Beijing and use two psychological experiments to validate its cognitive plausibility.

  17. An Energy-Efficient Game-Theory-Based Spectrum Decision Scheme for Cognitive Radio Sensor Networks

    PubMed Central

    Salim, Shelly; Moh, Sangman

    2016-01-01

    A cognitive radio sensor network (CRSN) is a wireless sensor network in which sensor nodes are equipped with cognitive radio. In this paper, we propose an energy-efficient game-theory-based spectrum decision (EGSD) scheme for CRSNs to prolong the network lifetime. Note that energy efficiency is the most important design consideration in CRSNs because it determines the network lifetime. The central part of the EGSD scheme consists of two spectrum selection algorithms: random selection and game-theory-based selection. The EGSD scheme also includes a clustering algorithm, spectrum characterization with a Markov chain, and cluster member coordination. Our performance study shows that EGSD outperforms the existing popular framework in terms of network lifetime and coordination overhead. PMID:27376290

  18. A novel pattern mining approach for identifying cognitive activity in EEG based functional brain networks.

    PubMed

    Thilaga, M; Vijayalakshmi, R; Nadarajan, R; Nandagopal, D

    2016-06-01

    The complex nature of neuronal interactions of the human brain has posed many challenges to the research community. To explore the underlying mechanisms of neuronal activity of cohesive brain regions during different cognitive activities, many innovative mathematical and computational models are required. This paper presents a novel Common Functional Pattern Mining approach to demonstrate the similar patterns of interactions due to common behavior of certain brain regions. The electrode sites of EEG-based functional brain network are modeled as a set of transactions and node-based complex network measures as itemsets. These itemsets are transformed into a graph data structure called Functional Pattern Graph. By mining this Functional Pattern Graph, the common functional patterns due to specific brain functioning can be identified. The empirical analyses show the efficiency of the proposed approach in identifying the extent to which the electrode sites (transactions) are similar during various cognitive load states. PMID:27401999

  19. A structural difference based image clutter metric with brain cognitive model constraints

    NASA Astrophysics Data System (ADS)

    Xu, Dejiang; Shi, Zelin; Luo, Haibo

    2013-03-01

    Previous clutter metrics have less than the desired accuracy in predicting targeting performance, in this paper, a structural difference based image clutter metric is proposed based on the given definition of image clutter metric. According to the sensitivity of human visual perception to image structural information, a structural similarity measure between the target and clutter images is firstly established. Previous clutter metrics not considering brain cognitive characteristics, we define an information content weight measure by introducing the widely accepted brain cognitive information extracting model in the field of image quality assessment (IQA), and then, pool the structural similarity measure to be a clutter metric, which can be entitled BSD metric. Comparative field tests show that BSD metric makes a more significant improvement than previously proposed metrics in predicting target acquisition performance including detection probability and search time.

  20. a Framework of Cognitive Indoor Navigation Based on Characteristics of Indoor Spatial Environment

    NASA Astrophysics Data System (ADS)

    Si, R.; Arikawa, M.

    2015-05-01

    People are easy to get confused in indoor spatial environment. Thus, indoor navigation systems on mobile devices are expected in a wide variety of application domains. Limited by the accuracy of indoor positioning, indoor navigating systems are not common in our society. However, automatic positioning is not all about location-based services (LBS), other factors, such as good map design and user interfaces, are also important to satisfy users of LBS. Indoor spatial environment and people's indoor spatial cognition are different than those in outdoor environment, which asks for different design of LBS. This paper introduces our design methods of indoor navigation system based on the characteristics of indoor spatial environment and indoor spatial cognition.

  1. Evaluation of manual-based cognitive-behavioral therapy for bulimia nervosa in a service setting.

    PubMed

    Tuschen-Caffier, B; Pook, M; Frank, M

    2001-03-01

    In the present study manual-based cognitive-behavioral therapy for bulimia nervosa was evaluated on an unselected sample of an out-patient service facility. A total of 73 female patients who asked for treatment received the primary diagnosis of bulimia nervosa. Of these, 67 took up treatment. Treatment was completed by 66 patients. Outcome variables were the number of binge episodes along with questionnaire scores for restraint eating, emotional eating, body dissatisfaction and depressiveness. At the end of treatment and 1 year after the end of treatment significant improvements were found in all outcome variables. Effect sizes for outcome variables were within the range of those of controlled research. Therefore, the present study delivered empirical evidence that manual-based cognitive-behavioral therapy is an effective treatment for bulimia nervosa not only within the restricted area of research. PMID:11227811

  2. TENI: A comprehensive battery for cognitive assessment based on games and technology.

    PubMed

    Delgado, Marcela Tenorio; Uribe, Paulina Arango; Alonso, Andrés Aparicio; Díaz, Ricardo Rosas

    2016-01-01

    TENI (Test de Evaluación Neuropsicológica Infantil) is an instrument developed to assess cognitive abilities in children between 3 and 9 years of age. It is based on a model that incorporates games and technology as tools to improve the assessment of children's capacities. The test was standardized with two Chilean samples of 524 and 82 children living in urban zones. Evidence of reliability and validity based on current standards is presented. Data show good levels of reliability for all subtests. Some evidence of validity in terms of content, test structure, and association with other variables is presented. This instrument represents a novel approach and a new frontier in cognitive assessment. Further studies with clinical, rural, and cross-cultural populations are required. PMID:25396766

  3. Detection of Subtle Cognitive Changes after mTBI Using a Novel Tablet-Based Task.

    PubMed

    Fischer, Tara D; Red, Stuart D; Chuang, Alice Z; Jones, Elizabeth B; McCarthy, James J; Patel, Saumil S; Sereno, Anne B

    2016-07-01

    This study examined the potential for novel tablet-based tasks, modeled after eye tracking techniques, to detect subtle sensorimotor and cognitive deficits after mild traumatic brain injury (mTBI). Specifically, we examined whether performance on these tablet-based tasks (Pro-point and Anti-point) was able to correctly categorize concussed versus non-concussed participants, compared with performance on other standardized tests for concussion. Patients admitted to the emergency department with mTBI were tested on the Pro-point and Anti-point tasks, a current standard cognitive screening test (i.e., the Standard Assessment of Concussion [SAC]), and another eye movement-based tablet test, the King-Devick(®) (KD). Within hours after injury, mTBI patients showed significant slowing in response times, compared with both orthopedic and age-matched control groups, in the Pro-point task, demonstrating deficits in sensorimotor function. Mild TBI patients also showed significant slowing, compared with both control groups, on the Anti-point task, even when controlling for sensorimotor slowing, indicating deficits in cognitive function. Performance on the SAC test revealed similar deficits of cognitive function in the mTBI group, compared with the age-matched control group; however, the KD test showed no evidence of cognitive slowing in mTBI patients, compared with either control group. Further, measuring the sensitivity and specificity of these tasks to accurately predict mTBI with receiver operating characteristic analysis indicated that the Anti-point and Pro-point tasks reached excellent levels of accuracy and fared better than current standardized tools for assessment of concussion. Our findings suggest that these rapid tablet-based tasks are able to reliably detect and measure functional impairment in cognitive and sensorimotor control within hours after mTBI. These tasks may provide a more sensitive diagnostic measure for functional deficits that could prove key to

  4. Cognitive Correlates of Functional Abilities in Individuals with Mild Cognitive Impairment: Comparison of Questionnaire, Direct Observation and Performance-based Measures

    PubMed Central

    Schmitter-Edgecombe, Maureen; Parsey, Carolyn M.

    2014-01-01

    The relationship between and the cognitive correlates of several proxy measures of functional status were studied in a population with mild cognitive impairment (MCI). Participants were 51 individuals diagnosed with MCI and 51 cognitively healthy older adults (OA). Participants completed performance-based functional status tests, standardized neuropsychological tests, and performed eight activities of daily living (e.g., watered plants, filled medication dispenser) while under direct observation in a campus apartment. An informant interview about everyday functioning was also conducted. Compared to the OA control group, the MCI group performed more poorly on all proxy measures of everyday functioning. The informant-report of instrumental activities of daily living (IADL) did not correlate with the two performance-based measures; however, both the informant-report IADL and the performance-based everyday problem-solving test correlated with the direct observation measure. After controlling for age and education, cognitive predictors did not explain a significant amount of variance in the performance-based measures; however, performance on a delayed memory task was a unique predictor for the informant-report IADL, and processing speed predicted unique variance for the direct observation score. These findings indicate that differing methods for evaluating functional status are not assessing completely overlapping aspects of everyday functioning in the MCI population. PMID:24766574

  5. A comparative study of frequency offset estimations in real and complex OFDM systems using different algorithms

    NASA Astrophysics Data System (ADS)

    Sahu, Swagatika; Mohanty, Saumendra; Srivastav, Richa

    2013-01-01

    Orthogonal Frequency Division Multiplexing (OFDM) is an emerging multi-carrier modulation scheme, which has been adopted for several wireless standards such as IEEE 802.11a and HiperLAN2, etc. A well-known problem of OFDM is its sensitivity to frequency offset between the transmitted and received carrier frequencies. In (OFDM) system Carrier frequency offsets (CFOs) between the transmitter and the receiver destroy the orthogonality between carriers and degrade the system performance significantly. The main problem with frequency offset is that it introduces interference among the multiplicity of carriers in the OFDM signal.The conventional algorithms given by P. Moose and Schmidl describes how carrier frequency offset of an OFDM system can be estimated using training sequences. Simulation results show that the improved carrier frequency offset estimation algorithm which uses a complex training sequence for frequency offset estimation, performs better than conventional P. Moose and Schmidl algorithm, which can effectively improve the frequency estimation accuracy and provides a wide acquisition range for the carrier frequency offset with low complexity. This paper introduces the BER comparisons of different algorithms with the Improved Algorithms for different Real and Complex modulations schemes, considering random carrier offsets . This paper also introduces the BER performances with different CFOs for different Real and Complex modulation schemes for the Improved algorithm.

  6. Spectrally efficient polarization multiplexed direct-detection OFDM system without frequency gap.

    PubMed

    Wei, Chia-Chien; Zeng, Wei-Siang; Lin, Chun-Ting

    2016-01-25

    We experimentally demonstrate a spectrally efficient direct-detection orthogonal frequency-division multiplexing (DD-OFDM) system. In addition to polarization-division multiplexing, removing the frequency gap further improves the spectral efficiency of the OFDM system. The frequency gap between a reference carrier and OFDM subcarriers avoids subcarrier-to-subcarrier beating interference (SSBI) in traditional DD-OFDM systems. Without dynamic polarization control, the resulting interference after square-law direct detection in the proposed gap-less system is polarization-dependent and composed of linear inter-carrier interference (ICI) and nonlinear SSBI. Thus, this work proposes an iterative multiple-input multiple-output detection scheme to remove the mixed polarization-dependent interference. Compared to the previous scheme, which only removes ICI, the proposed scheme can further eliminate SSBI to achieve the improvement of ∼ 7 dB in signal-to-noise ratio. Without the need for polarization control, we successfully utilize 7-GHz bandwidth to transmit a 39.5-Gbps polarization multiplexed OFDM signal over 100 km. PMID:26832560

  7. PAPR-Constrained Pareto-Optimal Waveform Design for OFDM-STAP Radar

    SciTech Connect

    Sen, Satyabrata

    2014-01-01

    We propose a peak-to-average power ratio (PAPR) constrained Pareto-optimal waveform design approach for an orthogonal frequency division multiplexing (OFDM) radar signal to detect a target using the space-time adaptive processing (STAP) technique. The use of an OFDM signal does not only increase the frequency diversity of our system, but also enables us to adaptively design the OFDM coefficients in order to further improve the system performance. First, we develop a parametric OFDM-STAP measurement model by considering the effects of signaldependent clutter and colored noise. Then, we observe that the resulting STAP-performance can be improved by maximizing the output signal-to-interference-plus-noise ratio (SINR) with respect to the signal parameters. However, in practical scenarios, the computation of output SINR depends on the estimated values of the spatial and temporal frequencies and target scattering responses. Therefore, we formulate a PAPR-constrained multi-objective optimization (MOO) problem to design the OFDM spectral parameters by simultaneously optimizing four objective functions: maximizing the output SINR, minimizing two separate Cramer-Rao bounds (CRBs) on the normalized spatial and temporal frequencies, and minimizing the trace of CRB matrix on the target scattering coefficients estimations. We present several numerical examples to demonstrate the achieved performance improvement due to the adaptive waveform design.

  8. One Tbps superchannel generated by Optical Flat Comb Source WDM-Nyquist and OFDM system simulative investigation

    NASA Astrophysics Data System (ADS)

    Hraghi, Abir; Menif, Mourad

    2014-09-01

    In this paper, we implement an Optical Flat Comb Source generating a coherent super-channel operating at 1 Tbps using WDM-Nyquist and OFDM approaches with new flex-grid channel spacing. The new flex-grid defines WDM channel spacing having a multiple of 12.5 GHz. We compare through simulation the performance of two techniques for generating Dual Polarization-Quadrature Amplitude Modulation based on 16 (DP-16QAM), 64 (DP-64QAM) and 128 (DP-128QAM). We first study the performance of WDM-Nyquist and OFDM super-channels implementing DP- 16QAM, DP-64QAM and DP-128QAM in back-to-back scenarios in terms of receiver sensitivity and Optical Signal-to- Noise Ratio (OSNR) requirement with 12.5 GHz flex-grid spacing. We find that DP-16QAM has the best receiver sensitivity and the lower OSNR penalty compared to the other modulation formats in WDM-Nyquist system. With DP- 128QAM sensitivity as reference, we can observe a benefit of 10 dB for DP-16QAM with a BER equal to 3.8 10-3. In addition, we can observe a benefit of 12.4 dB in OSNR for DP-16QAM compared to DP-128QAM for a BER equal to 3.8 10-3. Also, we study the impact of the optical and electrical shaping filters. Finally, we investigate the performance of WDM-Nyquist and OFDM terabit system with 12.5 GHz flex-grid spacing over long-haul dispersion compensated links using Standard Single Mode Fiber (SSMF). We find that DP-16QAM is the suitable modulation format in dispersion compensated WDM-Nyquist systems using SSMF fiber. In addition, we prove that the use of Raman amplification improve the maximum reach of the super-channel by increasing the span distance between the amplifier module. Indeed, using the Raman amplification the maximum reach increase from 812 km to 955 km in a WDM-Nyquist system based on DP-16QAM with 12.5 GHz flex-grid spacing.

  9. The Effect of Occupation-based Cognitive Rehabilitation for Traumatic Brain Injury: A Meta-analysis of Randomized Controlled Trials.

    PubMed

    Park, Hae Yean; Maitra, Kinsuk; Martinez, Kristina Marie

    2015-06-01

    Traumatic brain injury (TBI) is the leading cause of death and disability among people younger than 35 years in the United States. Cognitive difficulty is a common consequence of TBI. To address cognitive deficits of patients with TBI, various cognitive rehabilitation approaches have been used for the clinical setting. The purpose of this study was to investigate the overall effect of occupation-based cognitive rehabilitation on patients' improvement in cognitive performance components, activity of daily living (ADL) performance, and values, beliefs and spirituality functions of patients with TBI. The papers used in this study were retrieved from the Cochrane Database, EBSCO (CINAHL), PsycINFO, PubMed and Web of Science published between 1997 and 2014. The keywords for searching were cognitive, rehabilitation, occupation, memory, attention, problem-solving, executive function, ADL, values, beliefs, spirituality, randomized controlled trials and TBI. For the meta-analysis, we examined 60 effect sizes from nine studies that are related to the occupation-based cognitive rehabilitation on persons with TBI. In persons with TBI, overall mental functions, ADL, and values, beliefs and spirituality were significantly improved in the groups that received occupation-based cognitive rehabilitation compared with comparison groups (mean d = 0.19, p < .05). Evidence from the present meta-analytic study suggests that occupation-based cognitive rehabilitation would be beneficial for individuals with TBI for improving daily functioning and positively be able to affect their psychosocial functions. Collecting many outcome measures in studies with relatively few participants and the final data are less reliable than the whole instrument itself. Future research should evaluate the effectiveness of specific occupation-based cognitive rehabilitations programmes in order to improve consistency among rehabilitation providers. PMID:25808426

  10. Efficient Compensation of Transmitter and Receiver IQ Imbalance in OFDM Systems

    NASA Astrophysics Data System (ADS)

    Tandur, Deepaknath; Moonen Eurasip Member, Marc

    2010-12-01

    Radio frequency impairments such as in-phase/quadrature-phase (IQ) imbalances can result in a severe performance degradation in direct-conversion architecture-based communication systems. In this paper, we consider the case of transmitter and receiver IQ imbalance together with frequency selective channel distortion. The proposed training-based schemes can decouple the compensation of transmitter and receiver IQ imbalance from the compensation of channel distortion in an orthogonal frequency division multiplexing (OFDM) systems. The presence of frequency selective channel fading is a requirement for the estimation of IQ imbalance parameters when both transmitter/receiver IQ imbalance are present. However, the proposed schemes are equally applicable over a frequency flat/frequency selective channel when either transmitter or only receiver IQ imbalance is present. Once the transmitter and receiver IQ imbalance parameters are estimated, a standard channel equalizer can be applied to estimate/compensate for the channel distortion. The proposed schemes result in an overall lower training overhead and a lower computational requirement, compared to the joint compensation of transmitter/receiver IQ imbalance and channel distortion. Simulation results demonstrate that the proposed schemes provide a very efficient compensation with performance close to the ideal case without any IQ imbalance.

  11. Natural Language Query in the Biochemistry and Molecular Biology Domains Based on Cognition Search™

    PubMed Central

    Goldsmith, Elizabeth J.; Mendiratta, Saurabh; Akella, Radha; Dahlgren, Kathleen

    2009-01-01

    Motivation: With the increasing volume of scientific papers and heterogeneous nomenclature in the biomedical literature, it is apparent that an improvement over standard pattern matching available in existing search engines is required. Cognition Search Information Retrieval (CSIR) is a natural language processing (NLP) technology that possesses a large dictionary (lexicon) and large semantic databases, such that search can be based on meaning. Encoded synonymy, ontological relationships, phrases, and seeds for word sense disambiguation offer significant improvement over pattern matching. Thus, the CSIR has the right architecture to form the basis for a scientific search engine. Result: Here we have augmented CSIR to improve access to the MEDLINE database of scientific abstracts. New biochemical, molecular biological and medical language and acronyms were introduced from curated web-based sources. The resulting system was used to interpret MEDLINE abstracts. Meaning-based search of MEDLINE abstracts yields high precision (estimated at >90%), and high recall (estimated at >90%), where synonym, ontology, phrases and sense seeds have been encoded. The present implementation can be found at http://MEDLINE.cognition.com. Contact: Elizabeth.goldsmith@UTsouthwestern.edu Kathleen.dahlgren@cognition.com PMID:21347167

  12. Development and Experimental Evaluation of Cyclostationarity-Based Signal Identification Equipment for Cognitive Radios

    NASA Astrophysics Data System (ADS)

    Harada, Hiroki; Fujii, Hiromasa; Miura, Shunji; Kayama, Hidetoshi; Okano, Yoshiki; Imai, Tetsuro

    An important and widely considered signal identification technique for cognitive radios is cyclostationarity-based feature detection because this method does not require time and frequency synchronization and prior information except for information concerning cyclic autocorrelation features of target signals. This paper presents the development and experimental evaluation of cyclostationarity-based signal identification equipment. A spatial channel emulator is used in conjunction with the equipment that provides an environment to evaluate realistic spectrum sharing scenarios. The results reveal the effectiveness of the cyclostationarity-based signal identification methodology in realistic spectrum sharing scenarios, especially in terms of the capability to identify weak signals.

  13. Cognitive development in introductory physics: A research-based approach to curriculum reform

    NASA Astrophysics Data System (ADS)

    Teodorescu, Raluca Elena

    This project describes the research on a classification of physics problems in the context of introductory physics courses. This classification, called the Taxonomy of Introductory Physics Problems (TIPP), relates physics problems to the cognitive processes required to solve them. TIPP was created for designing and clarifying educational objectives, for developing assessments that can evaluate individual component processes of the problem-solving process, and for guiding curriculum design in introductory physics courses, specifically within the context of a "thinking-skills" curriculum. TIPP relies on the following resources: (1) cognitive research findings adopted by physics education research, (2) expert-novice research discoveries acknowledged by physics education research, (3) an educational psychology taxonomy for educational objectives, and (4) various collections of physics problems created by physics education researchers or developed by textbook authors. TIPP was used in the years 2006--2008 to reform the first semester of the introductory algebra-based physics course (called Phys 11) at The George Washington University. The reform sought to transform our curriculum into a "thinking-skills" curriculum that trades "breadth for depth" by focusing on fewer topics while targeting the students' cognitive development. We employed existing research on the physics problem-solving expert-novice behavior, cognitive science and behavioral science findings, and educational psychology recommendations. Our pedagogy relies on didactic constructs such as the GW-ACCESS problem-solving protocol, learning progressions and concept maps that we have developed and implemented in our introductory physics course. These tools were designed based on TIPP. Their purpose is: (1) to help students build local and global coherent knowledge structures, (2) to develop more context-independent problem-solving abilities, (3) to gain confidence in problem solving, and (4) to establish

  14. Effects of momentum-based dumbbell training on cognitive function in older adults with mild cognitive impairment: a pilot randomized controlled trial

    PubMed Central

    Lü, Jiaojiao; Sun, Mingyun; Liang, Leichao; Feng, Yi; Pan, Xiaoyu; Liu, Yu

    2016-01-01

    Purpose The purpose of this study was to explore the effects of an innovative momentum-based dumbbell-training intervention on cognitive function in older adults with mild cognitive impairment (MCI). Subjects and methods A total of 45 community-dwelling older adults with MCI were randomly assigned to either a dumbbell-training group (DTG; n=22) or a control group (CG; n=23). Participants in the DTG participated in exercise sessions three times weekly for 12 weeks. The primary outcome measures were cognitive function, including the Alzheimer’s Disease Assessment Scale (ADAS) – Cognitive subscale, Trail Making Test part B, Digit Span Test (DST) – forward, and DST – backward, with secondary outcome measures being Timed Up and Go, functional reach, and the Activities-Specific Balance Confidence Scale. Results In an intent-to-treat analysis, participants in the DTG had significantly improved ADAS – Cognitive subscale scores compared to those in the CG (5.02 points, P=0.012). There was a significant within-group change (improvement) in Trail Making Test part B (33.32 seconds, P<0.001) and DST – backward (0.41 points, P=0.025) scores. No change was observed for the DST – forward measure. Participants in the DTG also improved their functional mobility compared to those in the CG (Timed Up and Go, 0.81 seconds; P=0.043). Conclusion There is preliminary evidence showing the potential benefit of momentum-based dumbbell training for improving cognitive function in older adults with MCI. PMID:26766905

  15. Curriculum Providing Cognitive Knowledge and Problem-Solving Skills for Anesthesia Systems-Based Practice

    PubMed Central

    Wachtel, Ruth E.; Dexter, Franklin

    2010-01-01

    Background Residency programs accredited by the ACGME are required to teach core competencies, including systems-based practice (SBP). Projects are important for satisfying this competency, but the level of knowledge and problem-solving skills required presupposes a basic understanding of the field. The responsibilities of anesthesiologists include the coordination of patient flow in the surgical suite. Familiarity with this topic is crucial for many improvement projects. Intervention A course in operations research for surgical services was originally developed for hospital administration students. It satisfies 2 of the Institute of Medicine's core competencies for health professionals: evidence-based practice and work in interdisciplinary teams. The course lasts 3.5 days (eg, 2 weekends) and consists of 45 cognitive objectives taught using 7 published articles, 10 lectures, and 156 computer-assisted problem-solving exercises based on 17 case studies. We tested the hypothesis that the cognitive objectives of the curriculum provide the knowledge and problem-solving skills necessary to perform projects that satisfy the SBP competency. Standardized terminology was used to define each component of the SBP competency for the minimum level of knowledge needed. The 8 components of the competency were examined independently. Findings Most cognitive objectives contributed to at least 4 of the 8 core components of the SBP competency. Each component of SBP is addressed at the minimum requirement level of exemplify by at least 6 objectives. There is at least 1 cognitive objective at the level of summarize for each SBP component. Conclusions A curriculum in operating room management can provide the knowledge and problem-solving skills anesthesiologists need for participation in projects that satisfy the SBP competency. PMID:22132289

  16. Cognition-based and affect-based trust as mediators of leader behavior influences on team performance.

    PubMed

    Schaubroeck, John; Lam, Simon S K; Peng, Ann Chunyan

    2011-07-01

    We develop a model in which cognitive and affective trust in the leader mediate the relationship between leader behavior and team psychological states that, in turn, drive team performance. The model is tested on a sample of 191 financial services teams in Hong Kong and the U.S. Servant leadership influenced team performance through affect-based trust and team psychological safety. Transformational leadership influenced team performance indirectly through cognition-based trust. Cognition-based trust directly influenced team potency and indirectly (through affect-based trust) influenced team psychological safety. The effects of leader behavior on team performance were fully mediated through the trust in leader variables and the team psychological states. Servant leadership explained an additional 10% of the variance in team performance beyond the effect of transformational leadership. We discuss implications of these results for research on the relationship between leader behavior and team performance, and for efforts to enhance leader development by combining knowledge from different leadership theories. PMID:21299271

  17. A hybrid CATV/16-QAM-OFDM visible laser light communication system

    NASA Astrophysics Data System (ADS)

    Lin, Chun-Yu; Li, Chung-Yi; Lu, Hai-Han; Chen, Chia-Yi; Jhang, Tai-Wei; Ruan, Sheng-Siang; Wu, Kuan-Hung

    2014-10-01

    A visible laser light communication (VLLC) system employing a vertical cavity surface emitting laser and spatial light modulator with hybrid CATV/16-QAM-OFDM modulating signals over a 5 m free-space link is proposed and demonstrated. With the assistance of a push-pull scheme, low-noise amplifier, and equalizer, good performances of composite second-order and composite triple beat are obtained, accompanied by an acceptable carrier-to-noise ratio performance for a CATV signal, and a low bit error rate value and clear constellation map are achieved for a 16-QAM-OFDM signal. Such a hybrid CATV/16-QAM-OFDM VLLC system would be attractive for providing services including CATV, Internet and telecommunication services.

  18. Decision-aided sampling frequency offset compensation for reduced-guard-interval coherent optical OFDM systems.

    PubMed

    Wang, Wei; Zhuge, Qunbi; Morsy-Osman, Mohamed; Gao, Yuliang; Xu, Xian; Chagnon, Mathieu; Qiu, Meng; Hoang, Minh Thang; Zhang, Fangyuan; Li, Rui; Plant, David V

    2014-11-01

    We propose a decision-aided algorithm to compensate the sampling frequency offset (SFO) between the transmitter and receiver for reduced-guard-interval (RGI) coherent optical (CO) OFDM systems. In this paper, we first derive the cyclic prefix (CP) requirement for preventing OFDM symbols from SFO induced inter-symbol interference (ISI). Then we propose a new decision-aided SFO compensation (DA-SFOC) algorithm, which shows a high SFO tolerance and reduces the CP requirement. The performance of DA-SFOC is numerically investigated for various situations. Finally, the proposed algorithm is verified in a single channel 28 Gbaud polarization division multiplexing (PDM) RGI CO-OFDM experiment with QPSK, 8 QAM and 16 QAM modulation formats, respectively. Both numerical and experimental results show that the proposed DA-SFOC method is highly robust against the standard SFO in optical fiber transmission. PMID:25401902

  19. ML Frame Synchronization for OFDM Systems Using a Known Pilot and Cyclic Prefixes

    NASA Astrophysics Data System (ADS)

    Huh, Heon

    Orthogonal frequency-division multiplexing (OFDM) is a popular air interface technology that is adopted as a standard modulation scheme for 4G communication systems owing to its excellent spectral efficiency. For OFDM systems, synchronization problems have received much attention along with peak-to-average power ratio (PAPR) reduction. In addition to frequency offset estimation, frame synchronization is a challenging problem that must be solved to achieve optimal system performance. In this paper, we present a maximum likelihood (ML) frame synchronizer for OFDM systems. The synchronizer exploits a synchronization word and cyclic prefixes together to improve the synchronization performance. Numerical results show that the performance of the proposed frame synchronizer is better than that of conventional schemes. The proposed synchronizer can be used as a reference for evaluating the performance of other suboptimal frame synchronizers. We also modify the proposed frame synchronizer to reduce the implementation complexity and propose a near-ML synchronizer for time-varying fading channels.

  20. Performance-based interpretation bias in clinically anxious youths: relationships with attention, anxiety, and negative cognition.

    PubMed

    Rozenman, Michelle; Amir, Nader; Weersing, V Robin

    2014-09-01

    This preliminary investigation sought to examine basic interpretive biases, as assessed via performance-based means, in the context of anxious symptomatology, attention, and negative cognition in children and adolescents. At a single assessment, 26 youths diagnosed with primary separation anxiety, social phobia, or generalized anxiety disorder completed performance-based assessments of interpretation and attention. Youths and parents also completed diagnostic interviews and youths completed a measure of negative self-statements. Components of interpretation (threat-valence judgments and speed of responding) were examined, and interpretation was explored as a correlate of youth anxiety, attention bias, and negative self-statements. Results found percentage of negative interpretations endorsed as the strongest predictor of anxiety symptoms; this index was also correlated with attention bias. Slower rejection of benign interpretations was also associated with youth-reported negative self-statements.This initial investigation provides support for a relationship between interpretation bias and anxiety and preliminary evidence for a relationship between attention and interpretation biases. Continued research dismantling the stages of basic cognition within the chain of information processing may provide a better understanding of the mechanisms underlying anxiety disorders in youths and lead to continued development and refinement of cognitive interventions. PMID:25022771

  1. Future Cognitive Ability: US IQ Prediction until 2060 Based on NAEP.

    PubMed

    Rindermann, Heiner; Pichelmann, Stefan

    2015-01-01

    The US National Assessment of Educational Progress (NAEP) measures cognitive competences in reading and mathematics of US students (last 2012 survey N = 50,000). The long-term development based on results from 1971 to 2012 allows a prediction of future cognitive trends. For predicting US averages also demographic trends have to be considered. The largest groups' (White) average of 1978/80 was set at M = 100 and SD = 15 and was used as a benchmark. Based on two past NAEP development periods for 17-year-old students, 1978/80 to 2012 (more optimistic) and 1992 to 2012 (more pessimistic), and demographic projections from the US Census Bureau, cognitive trends until 2060 for the entire age cohort and ethnic groups were estimated. Estimated population averages for 2060 are 103 (optimistic) or 102 (pessimistic). The average rise per decade is dec = 0.76 or 0.45 IQ points. White-Black and White-Hispanic gaps are declining by half, Asian-White gaps treble. The catch-up of minorities (their faster ability growth) contributes around 2 IQ to the general rise of 3 IQ; however, their larger demographic increase reduces the general rise at about the similar amount (-1.4 IQ). Because minorities with faster ability growth also rise in their population proportion the interactive term is positive (around 1 IQ). Consequences for economic and societal development are discussed. PMID:26460731

  2. Future Cognitive Ability: US IQ Prediction until 2060 Based on NAEP

    PubMed Central

    2015-01-01

    The US National Assessment of Educational Progress (NAEP) measures cognitive competences in reading and mathematics of US students (last 2012 survey N = 50,000). The long-term development based on results from 1971 to 2012 allows a prediction of future cognitive trends. For predicting US averages also demographic trends have to be considered. The largest groups’ (White) average of 1978/80 was set at M = 100 and SD = 15 and was used as a benchmark. Based on two past NAEP development periods for 17-year-old students, 1978/80 to 2012 (more optimistic) and 1992 to 2012 (more pessimistic), and demographic projections from the US Census Bureau, cognitive trends until 2060 for the entire age cohort and ethnic groups were estimated. Estimated population averages for 2060 are 103 (optimistic) or 102 (pessimistic). The average rise per decade is dec = 0.76 or 0.45 IQ points. White-Black and White-Hispanic gaps are declining by half, Asian-White gaps treble. The catch-up of minorities (their faster ability growth) contributes around 2 IQ to the general rise of 3 IQ; however, their larger demographic increase reduces the general rise at about the similar amount (-1.4 IQ). Because minorities with faster ability growth also rise in their population proportion the interactive term is positive (around 1 IQ). Consequences for economic and societal development are discussed. PMID:26460731

  3. Comparing features extractors in EEG-based cognitive fatigue detection of demanding computer tasks.

    PubMed

    Rifai Chai; Smith, Mitchell R; Nguyen, Tuan N; Sai Ho Ling; Coutts, Aaron J; Nguyen, Hung T

    2015-08-01

    An electroencephalography (EEG)-based classification system could be used as a tool for detecting cognitive fatigue from demanding computer tasks. The most widely used feature extractor in EEG-based fatigue classification is power spectral density (PSD). This paper investigates PSD and three alternative feature extraction methods, in order to find the best feature extractor for the classification of cognitive fatigue during cognitively demanding tasks. These compared methods are power spectral entropy (PSE), wavelet, and autoregressive (AR). Bayesian neural network was selected as the classifier in this study. The results showed that the use of PSD and PSE methods provide an average accuracy of 60% for each computer task. This finding is slightly improved using the wavelet method which has an average accuracy of 61%. The AR method is the best feature extractor compared with the PSD, PSE and wavelet in this study with accuracy of 75.95% in AX-continuous performance test (AX-CPT), 75.23% in psychomotor vigilance test (PVT) and 76.02% in Stroop task (p-value <; 0.05). PMID:26738050

  4. 4×100 Gb/s WDM DD-OFDM using EAM for next generation Ethernet transceivers over SMF

    NASA Astrophysics Data System (ADS)

    Torres-Ferrera, P.; Vázquez, S. O.; Gutiérrez-Castrejón, R.

    2016-04-01

    The technical feasibility (pre-FEC BER<3.8×10-5) of an unamplified 4×100 Gb/s wavelength division multiplexed direct-detection optical orthogonal frequency division multiplexing (OFDM) system that uses electro-absorption modulators is numerically demonstrated for 2 and 10-km reach of single-mode fiber in C-band. Based on the use of specifications of currently available (realistic) components, error-free operation is achieved by finding optimum values for bias voltage and electrical gain in the modulator, and by employing a simple, yet powerful, peak-to-average power ratio (PAPR)-reduction technique. A performance comparison with a Mach-Zehnder driven system is presented too. The architecture here put forward can be used to define next-generation 400 Gb/s Ethernet standard.

  5. Peak-to-Average-Power-Ratio (PAPR) reduction in WiMAX and OFDM/A systems

    NASA Astrophysics Data System (ADS)

    Khademi, Seyran; Svantesson, Thomas; Viberg, Mats; Eriksson, Thomas

    2011-12-01

    A peak to average power ratio (PAPR) reduction method is proposed that exploits the precoding or beamforming mode in WiMAX. The method is applicable to any OFDM/A systems that implements beamforming using dedicated pilots which use the same beamforming antenna weights for both pilots and data. Beamforming performance depends on the relative phase shift between antennas, but is unaffected by a phase shift common to all antennas. PAPR, on the other hand, changes with a common phase shift and this paper exploits that property. An effective optimization technique based on sequential quadratic programming is proposed to compute the common phase shift. The proposed technique has several advantages compared with traditional PAPR reduction techniques in that it does not require any side-information and has no effect on power and bit-error-rate while providing better PAPR reduction performance than most other methods.

  6. Dual-polarization OFDM-OQAM for communications over optical fibers with coherent detection.

    PubMed

    Horlin, François; Fickers, Jessica; Emplit, Philippe; Bourdoux, André; Louveaux, Jérome

    2013-03-11

    In order to improve the spectral efficiency of coherent optical communication systems, it has recently been proposed to make use of the orthogonal frequency-division multiplexing offset quadrature amplitude modulation (OFDM-OQAM). Multiple optical channels spaced in the frequency domain by the symbol rate can be transmitted orthogonally, even if each channel overlaps significantly in frequency with its two adjacent channels. The solutions proposed until now in the literature unfortunately only address a single polarization communication, and therefore do not benefit from the capacity gain reached when two polarizations are used to transmit independent information signals. The aim of the present paper is to propose a receiver architecture that can decouple the two polarizations. We build an equalizer per channel at twice the symbol rate and optimize it based on the minimum mean square error (MMSE) criterion. We demonstrate the efficiency of the resulting system compared to the Nyquist wavelength-division multiplexing (N-WDM) system both in terms of performance and complexity. We also assess the system sensitivity to transmit synchronization errors and show that system can even work under significant synchronization errors. PMID:23482211

  7. Quantification of MDL-induced signal degradation in MIMO-OFDM mode-division multiplexing systems.

    PubMed

    Tian, Yu; Li, Juhao; Zhu, Paikun; Wu, Zhongying; Chen, Yuanxiang; He, Yongqi; Chen, Zhangyuan

    2016-08-22

    Mode-division multiplexing (MDM) transmission over few-mode optical fiber has emerged as a promising technology to enhance transmission capacity, in which multiple-input-multiple-output (MIMO) digital signal processing (DSP) after coherent detection is used to demultiplex the signals. Compared with conventional single-mode systems, MIMO-MDM systems suffer non-recoverable signal degradation induced by mode-dependent loss (MDL). In this paper, the MDL-induced signal degradation in orthogonal-frequency-division-multiplexing (OFDM) MDM systems is theoretically quantified in terms of mode-average error vector magnitude (EVM) through frequency domain norm analysis. A novel scalar MDL metric is proposed considering the probability distribution of the practical MDM input signals, and a closed-form expression for EVM measured after zero-force (ZF) MIMO equalization is derived. Simulation results show that the EVM estimations utilizing the novel MDL metric remain unbiased for unrepeated links. For a 6 × 100 km 20-mode MDM transmission system, the estimation accuracy is improved by more than 90% compared with that utilizing traditional condition number (CN) based MDL metric. The proposed MDL metric can be used to predict the MDL-induced SNR penalty in a theoretical manner, which will be beneficial for the design of practical MIMO-MDM systems. PMID:27557176

  8. Math anxiety: A review of its cognitive consequences, psychophysiological correlates, and brain bases.

    PubMed

    Suárez-Pellicioni, Macarena; Núñez-Peña, María Isabel; Colomé, Àngels

    2016-02-01

    A decade has passed since the last published review of math anxiety, which was carried out by Ashcraft and Ridley (2005). Given the considerable interest aroused by this topic in recent years and the growing number of publications related to it, the present article aims to provide a full and updated review of the field, ranging from the initial studies of the impact of math anxiety on numerical cognition, to the latest research exploring its electrophysiological correlates and brain bases from a cognitive neuroscience perspective. Finally, this review describes the factors and mechanisms that have been claimed to play a role in the origins and/or maintenance of math anxiety, and it examines in detail the main explanations proposed to account for the negative effects of math anxiety on performance: competition for working memory resources, a deficit in a low-level numerical representation, and inhibition/attentional control deficit. PMID:26250692

  9. Performance bounds on micro-Doppler estimation and adaptive waveform design using OFDM signals

    NASA Astrophysics Data System (ADS)

    Sen, Satyabrata; Barhen, Jacob; Glover, Charles W.

    2014-05-01

    We analyze the performance of a wideband orthogonal frequency division multiplexing (OFDM) signal in estimating the micro-Doppler frequency of a target having multiple rotating scatterers (e.g., rotor blades of a helicopter, propellers of a submarine). The presence of rotating scatterers introduces Doppler frequency modulation in the received signal by generating sidebands about the transmitted frequencies. This is called the micro-Doppler effects. The use of a frequency-diverse OFDM signal in this context enables us to independently analyze the micro-Doppler characteristics with respect to a set of orthogonal subcarrier frequencies. Therefore, to characterize the accuracy of micro-Doppler frequency estimation, we compute the Craḿer-Rao Bound (CRB) on the angular-velocity estimate of the target while considering the scatterer responses as deterministic but unknown nuisance parameters. Additionally, to improve the accuracy of the estimation procedure, we formulate and solve an optimization problem by minimizing the CRB on the angular-velocity estimate with respect to the transmitting OFDM spectral coefficients. We present several numerical examples to demonstrate the CRB variations at different values of the signal-to-noise ratio (SNR) and the number of OFDM subcarriers. The CRB values not only decrease with the increase in the SNR values, but also reduce as we increase the number of subcarriers implying the significance of frequency-diverse OFDM waveforms. The improvement in estimation accuracy due to the adaptive waveform design is also numerically analyzed. Interestingly, we find that the relative decrease in the CRBs on the angular-velocity estimate is more pronounced for larger number of OFDM subcarriers.

  10. Performance Bounds on Micro-Doppler Estimation and Adaptive Waveform Design Using OFDM Signals

    SciTech Connect

    Sen, Satyabrata; Barhen, Jacob; Glover, Charles Wayne

    2014-01-01

    We analyze the performance of a wideband orthogonal frequency division multiplexing (OFDM) signal in estimating the micro-Doppler frequency of a target having multiple rotating scatterers (e.g., rotor blades of a helicopter, propellers of a submarine). The presence of rotating scatterers introduces Doppler frequency modulation in the received signal by generating sidebands about the transmitted frequencies. This is called the micro-Doppler effects. The use of a frequency-diverse OFDM signal in this context enables us to independently analyze the micro-Doppler characteristics with respect to a set of orthogonal subcarrier frequencies. Therefore, to characterize the accuracy of micro-Doppler frequency estimation, we compute the Cram er-Rao Bound (CRB) on the angular-velocity estimate of the target while considering the scatterer responses as deterministic but unknown nuisance parameters. Additionally, to improve the accuracy of the estimation procedure, we formulate and solve an optimization problem by minimizing the CRB on the angular-velocity estimate with respect to the transmitting OFDM spectral coefficients. We present several numerical examples to demonstrate the CRB variations at different values of the signal-to-noise ratio (SNR) and the number of OFDM subcarriers. The CRB values not only decrease with the increase in the SNR values, but also reduce as we increase the number of subcarriers implying the significance of frequency-diverse OFDM waveforms. The improvement in estimation accuracy due to the adaptive waveform design is also numerically analyzed. Interestingly, we find that the relative decrease in the CRBs on the angular-velocity estimate is more pronounced for larger number of OFDM subcarriers.

  11. Adapting Ancient Wisdom for the Treatment of Depression: Mindfulness-Based Cognitive Therapy Group Training

    PubMed Central

    Chartier, Maggie; Bitner, Robin; Peng, Tracy; Coffelt, Nicole; McLane, Maura; Eisendrath, Stuart

    2012-01-01

    This paper outlines and discusses two models of training for group Mindfulness-Based Cognitive Therapy (MBCT) which we have called In vivo and Intensive. MBCT training and practice focuses on present moment experience versus content, focused on gaining a metacognitive perspective on one's thoughts and internal processes. Trainees and trainers share their reflections on the training process as well as the experiential and acceptance-based framework of MBCT reflected in the training process itself. Suggestions for optimizing training across multiple mental health disciplines and settings are also discussed. PMID:25309026

  12. Adapting Ancient Wisdom for the Treatment of Depression: Mindfulness-Based Cognitive Therapy Group Training.

    PubMed

    Chartier, Maggie; Bitner, Robin; Peng, Tracy; Coffelt, Nicole; McLane, Maura; Eisendrath, Stuart

    2010-12-01

    This paper outlines and discusses two models of training for group Mindfulness-Based Cognitive Therapy (MBCT) which we have called In vivo and Intensive. MBCT training and practice focuses on present moment experience versus content, focused on gaining a metacognitive perspective on one's thoughts and internal processes. Trainees and trainers share their reflections on the training process as well as the experiential and acceptance-based framework of MBCT reflected in the training process itself. Suggestions for optimizing training across multiple mental health disciplines and settings are also discussed. PMID:25309026

  13. Mindfulness-based cognitive therapy with older adults: an exploratory study.

    PubMed

    Foulk, Mariko A; Ingersoll-Dayton, Berit; Kavanagh, Janet; Robinson, Elizabeth; Kales, Helen C

    2014-01-01

    An 8-week mindfulness-based cognitive therapy (MBCT) group for older adults with depression and/or anxiety is described. This article is based on an exploratory study of this therapeutic approach and changes in participants' symptoms associated with participation. Pre-post data from 5 MBCT groups showed significant improvements in reported anxiety, ruminative thoughts, and sleep problems and a reduction in depressive symptoms. Case examples are presented to illustrate these symptom changes. Findings showed that this nonpharmacological intervention is acceptable to older adults and is associated with positive changes. Suggestions are provided for both practitioners and researchers interested in using MBCT with older adults. PMID:24329497

  14. Obtained Diversity Gain in OFDM Systems under the Influence of IQ Imbalance

    NASA Astrophysics Data System (ADS)

    Jin, Younghwan; Kwon, Jihyeon; Lee, Yuro; Lee, Dongchan; Ahn, Jaemin

    In this paper, we analyze the effects of IQ (In-phase/Quadrature-phase) imbalance at both transmitter and receiver of OFDM (Orthogonal Frequency Division Multiplexing) system and show that more diversity gain can be achieved even though there are unwanted IQ imbalance. When mixed sub-carriers within an OFDM symbol due to the IQ imbalance undergo frequency selective channels, additional diversity effects are expected during the demodulation process. Simulation results on the symbol error rate (SER) performance with ML (Maximum Likelihood) and OSIC (Ordered Successive Interference Cancellation) receiver show that significant performance gain can be achieved with the diversity gain caused by the IQ imbalance combined with the frequency selective channels.

  15. Comparison study of time reversal OFDM acoustic communication with vector and scalar sensors

    NASA Astrophysics Data System (ADS)

    Wang, Zhongkang; Zhang, Hongtao; Xie, Zhe

    2012-11-01

    To compare the performance of time reversal orthogonal frequency division multiplexing (OFDM) acoustic communication on vector and scalar sensors, the vector and scalar acoustic fields were modeled. Time reversal OFDM acoustic communication was then simulated for each sensor type. These results are compared with data from the CAPEx'09 experiment. The abilityof particle velocity channels to achieve reliable acoustic communication, as predicted by the model, is confirmed with the experiment data. Experimental results show that vector receivers can reduce the required array size, in comparisonto hydrophone arrays, whileproviding comparable communication performance.

  16. Spectrally-efficient all-optical OFDM by WSS and AWG.

    PubMed

    Hoxha, J; Morosi, J; Shimizu, S; Martelli, P; Boffi, P; Wada, N; Cincotti, G

    2015-05-01

    We report on the transmission experiment of seven 12.5-GHz spaced all optical-orthogonal frequency division multiplexed (AO-OFDM) subcarriers over a 35-km fiber link, using differential quadrature phase shift keying (DQPSK) modulation and direct detection. The system does not require chromatic dispersion compensation, optical time gating at the receiver (RX) or cyclic prefix (CP), achieving the maximum spectral efficiency. We use a wavelength selective switch (WSS) at the transmitter (TX) to allow subcarrier assignment flexibility and optimal filter shaping; an arrayed waveguide grating (AWG) AO-OFDM demultiplexer is used at the RX, to reduce the system cost and complexity. PMID:25969193

  17. GFDM performance in terms of BER, PAPR and OOB and comparison to OFDM system

    NASA Astrophysics Data System (ADS)

    Antapurkar, Shwetal K.; Pandey, Avinash; Gupta, K. K.

    2016-03-01

    Generalized frequency division multiplexing is a multicarrier modulation technique which can be foreseen as a potential alternative for upcoming wireless networks. GFDM attractive features include reduced out-of-band radiation(OOB) and low peak-to-average ratio(PAPR), which are the crucial shortcomings of OFDM used in present day wireless communication networks. This paper gives detailed description of GFDM system model and further studies and validates through simulations, the performance of GFDM in terms of OOB, PAPR and Bit Error Rate (BER) and compares the results obtained with OFDM system.

  18. Predictors of Retest Effects in a Longitudinal Study of Cognitive Aging in a Diverse Community-Based Sample.

    PubMed

    Gross, Alden L; Benitez, Andreana; Shih, Regina; Bangen, Katherine J; Glymour, M Maria M; Sachs, Bonnie; Sisco, Shannon; Skinner, Jeannine; Schneider, Brooke C; Manly, Jennifer J

    2015-08-01

    Better performance due to repeated testing can bias long-term trajectories of cognitive aging and correlates of change. We examined whether retest effects differ as a function of individual differences pertinent to cognitive aging: race/ethnicity, age, sex, language, years of education, literacy, and dementia risk factors including apolipoprotein E ε4 status, baseline cognitive performance, and cardiovascular risk. We used data from the Washington Heights-Inwood Columbia Aging Project, a community-based cohort of older adults (n=4073). We modeled cognitive change and retest effects in summary factors for general cognitive performance, memory, executive functioning, and language using multilevel models. Retest effects were parameterized in two ways, as improvement between the first and subsequent testings, and as the square root of the number of prior testings. We evaluated whether the retest effect differed by individual characteristics. The mean retest effect for general cognitive performance was 0.60 standard deviations (95% confidence interval [0.46, 0.74]), and was similar for memory, executive functioning, and language. Retest effects were greater for participants in the lowest quartile of cognitive performance (many of whom met criteria for dementia based on a study algorithm), consistent with regression to the mean. Retest did not differ by other characteristics. Retest effects are large in this community-based sample, but do not vary by demographic or dementia-related characteristics. Differential retest effects may not limit the generalizability of inferences across different groups in longitudinal research. PMID:26527240

  19. Telephone-based screening tools for mild cognitive impairment and dementia in aging studies: a review of validated instruments

    PubMed Central

    Castanho, Teresa C.; Amorim, Liliana; Zihl, Joseph; Palha, Joana A.; Sousa, Nuno; Santos, Nadine C.

    2013-01-01

    The decline of cognitive function in old age is a great challenge for modern society. The simultaneous increase in dementia and other neurodegenerative diseases justifies a growing need for accurate and valid cognitive assessment instruments. Although in-person testing is considered the most effective and preferred administration mode of assessment, it can pose not only a research difficulty in reaching large and diverse population samples, but it may also limit the assessment and follow-up of individuals with either physical or health limitations or reduced motivation. Therefore, telephone-based cognitive screening instruments can be an alternative and attractive strategy to in-person assessments. In order to give a current view of the state of the art of telephone-based tools for cognitive assessment in aging, this review highlights some of the existing instruments with particular focus on data validation, cognitive domains assessed, administration time and instrument limitations and advantages. From the review of the literature, performed using the databases EBSCO, Science Direct and PubMed, it was possible to verify that while telephone-based tools are useful in research and clinical practice, providing a promising approach, the methodologies still need refinement in the validation steps, including comparison with either single instruments or neurocognitive test batteries, to improve specificity and sensitivity to validly detect subtle changes in cognition that may precede cognitive impairment. PMID:24611046

  20. D Visibility Analysis in Urban Environment - Cognition Research Based on Vge

    NASA Astrophysics Data System (ADS)

    Lin, T. P.; Lin, H.; Hu, M. Y.

    2013-09-01

    The author in this research attempts to illustrate a measurable relationship between the physical environment and human's visual perception, including the distance, visual angle impact and visual field (a 3D isovist conception) against human's cognition way, by using a 3D visibility analysis method based on the platform of Virtual Geographic Environment (VGE). The whole project carries out in the CUHK campus (the Chinese University of Hong Kong), by adopting a virtual 3D model of the whole campus and survey in real world. A possible model for the simulation of human cognition in urban spaces is expected to be the output of this research, such as what the human perceive from the environment, how their feelings and behaviours are and how they affect the surrounding world. Kevin Lynch raised 5 elements of urban design in 1960s, which are "vitality, sense, fit, access and control". As the development of urban design, several problems around the human's cognitive and behaviour have come out. Due to the restriction of sensing knowledge in urban spaces, the research among the "sense" and the "fit" of urban design were not quite concerned in recent decades. The geo-spatial cognition field comes into being in 1997 and developed in recent 15 years, which made great effort in way-finding and urban behaviour simulation based on the platform of GIS (geographic information system) or VGE. The platform of VGE is recognized as a proper tool for the analysis of human's perception in urban places, because of its efficient 3D spatial data management and excellent 3D visualization for output result. This article will generally describe the visibility analysis method based on the 3D VGE platform. According to the uncertainty and variety of human perception existed in this research, the author attempts to arrange a survey of observer investigation and validation for the analysis results. Four figures related with space and human's perception will be mainly concerned in this proposal

  1. A Rehabilitation Tool Designed for Intensive Web-Based Cognitive Training: Description and Usability Study

    PubMed Central

    Pais, Joana; Bento, Virgílio; Mateus, Cátia; Colunas, Márcio; Alves, Ivânia; Coutinho, Paula; Rocha, Nelson Pacheco

    2013-01-01

    Background Cognitive deficits are among the most disabling of neurological diseases and have a serious impact on the quality of life of patients and families. Cognitive training has been proven successful in improving or compensating for neuropsychological deficits after acute brain injury, but its efficacy highly depends on the intensity of treatment over an extended period of time. Therefore, cognitive training indicates expensive human resources and renders the rehabilitation process vulnerable to physical and economic barriers for the majority of patients. Objective The aim of this study was to develop and test a new Web-based rehabilitation tool that provides intensive cognitive training at home under clinical prescription and monitoring, at affordable costs. Methods From a pool of 60 original exercises, designed and used over the past 10 years for cognitive training at our center, we developed 27 exercises on a computer game format, with automatic increase or decrease of difficulty levels. These exercises were assembled in a clean, user-friendly design and covered various cognitive domains such as attention (n=4), memory (n=11), language (n=3), calculus (n=3), praxis (n=2), and executive functions (n=3). A Web 2.0 platform was also designed to provide medical prescription of cognitive training sessions, performed at the patient’s home. These sessions included continuous monitoring of compliance, performance, and evolution; algorithms for automatic adjustment and long-term learning through use, and database recording of all activities. The end-user interaction test included 80 patients from our memory clinic from several groups including subjective memory complaints (n=20), traumatic brain injury (n=20), stroke and other static brain lesions (n=20), and mild Alzheimer’s disease (n=20). During a 1-hour session, patients and their relatives were taught to use the system and allowed to practice using it. At the end of the session, they were asked to complete

  2. An evaluation of volume-based morphometry for prediction of mild cognitive impairment and Alzheimer's disease

    PubMed Central

    Schmitter, Daniel; Roche, Alexis; Maréchal, Bénédicte; Ribes, Delphine; Abdulkadir, Ahmed; Bach-Cuadra, Meritxell; Daducci, Alessandro; Granziera, Cristina; Klöppel, Stefan; Maeder, Philippe; Meuli, Reto; Krueger, Gunnar

    2014-01-01

    Voxel-based morphometry from conventional T1-weighted images has proved effective to quantify Alzheimer's disease (AD) related brain atrophy and to enable fairly accurate automated classification of AD patients, mild cognitive impaired patients (MCI) and elderly controls. Little is known, however, about the classification power of volume-based morphometry, where features of interest consist of a few brain structure volumes (e.g. hippocampi, lobes, ventricles) as opposed to hundreds of thousands of voxel-wise gray matter concentrations. In this work, we experimentally evaluate two distinct volume-based morphometry algorithms (FreeSurfer and an in-house algorithm called MorphoBox) for automatic disease classification on a standardized data set from the Alzheimer's Disease Neuroimaging Initiative. Results indicate that both algorithms achieve classification accuracy comparable to the conventional whole-brain voxel-based morphometry pipeline using SPM for AD vs elderly controls and MCI vs controls, and higher accuracy for classification of AD vs MCI and early vs late AD converters, thereby demonstrating the potential of volume-based morphometry to assist diagnosis of mild cognitive impairment and Alzheimer's disease. PMID:25429357

  3. Whatever the cost? Information integration in memory-based inferences depends on cognitive effort.

    PubMed

    Hilbig, Benjamin E; Michalkiewicz, Martha; Castela, Marta; Pohl, Rüdiger F; Erdfelder, Edgar

    2015-05-01

    One of the most prominent models of probabilistic inferences from memory is the simple recognition heuristic (RH). The RH theory assumes that judgments are based on recognition in isolation, such that other information is ignored. However, some prior research has shown that available knowledge is not generally ignored. In line with the notion of adaptive strategy selection--and, thus, a trade-off between accuracy and effort--we hypothesized that information integration crucially depends on how easily accessible information beyond recognition is, how much confidence decision makers have in this information, and how (cognitively) costly it is to acquire it. In three experiments, we thus manipulated (a) the availability of information beyond recognition, (b) the subjective usefulness of this information, and (c) the cognitive costs associated with acquiring this information. In line with the predictions, we found that RH use decreased substantially, the more easily and confidently information beyond recognition could be integrated, and increased substantially with increasing cognitive costs. PMID:25504054

  4. Transforming Spatial Reasoning Skills in the Undergraduate Geoscience Classroom Through Interventions Based on Cognitive Science Research

    NASA Astrophysics Data System (ADS)

    Ormand, C. J.; Shipley, T. F.; Tikoff, B.; Manduca, C. A.; Dutrow, B. L.; Goodwin, L. B.; Hickson, T.; Atit, K.; Gagnier, K. M.; Resnick, I.

    2013-12-01

    Spatial visualization is an essential skill in many, if not all, STEM disciplines. It is a prerequisite for understanding subjects as diverse as fluid flow through 3D fault systems, magnetic and gravitational fields, atmospheric and oceanic circulation patterns, cellular and molecular structures, engineering design, topology, and much, much more. Undergraduate geoscience students, in both introductory and upper-level courses, bring a wide range of spatial skill levels to the classroom. However, spatial thinking improves with practice, and can improve more rapidly with intentional training. As a group of geoscience faculty members and cognitive psychologists, we are collaborating to apply the results of cognitive science research to the development of teaching materials to improve undergraduate geology majors' spatial thinking skills. This approach has the potential to transform undergraduate STEM education by removing one significant barrier to success in the STEM disciplines. Two promising teaching strategies have emerged from recent cognitive science research into spatial thinking: gesturing and predictive sketching. Studies show that students who gesture about spatial relationships perform better on spatial tasks than students who don't gesture, perhaps because gesture provides a mechanism for cognitive offloading. Similarly, students who sketch their predictions about the interiors of geologic block diagrams perform better on penetrative thinking tasks than students who make predictions without sketching. We are developing new teaching materials for Mineralogy, Structural Geology, and Sedimentology & Stratigraphy courses using these two strategies. Our data suggest that the research-based teaching materials we are developing may boost students' spatial thinking skills beyond the baseline gains we have measured in the same courses without the new curricular materials.

  5. A Score Based on Screening Tests to Differentiate Mild Cognitive Impairment from Subjective Memory Complaints

    PubMed Central

    de Gobbi Porto, Fábio Henrique; Spíndola, Lívia; de Oliveira, Maira Okada; Figuerêdo do Vale, Patrícia Helena; Orsini, Marco; Nitrini, Ricardo; Dozzi Brucki, Sonia Maria

    2013-01-01

    It is not easy to differentiate patients with mild cognitive impairment (MCI) from subjective memory complainers (SMC). Assessments with screening cognitive tools are essential, particularly in primary care where most patients are seen. The objective of this study was to evaluate the diagnostic accuracy of screening cognitive tests and to propose a score derived from screening tests. Elderly subjects with memory complaints were evaluated using the Mini Mental State Examination (MMSE) and the Brief Cognitive Battery (BCB). We added two delayed recalls in the MMSE (a delayed recall and a late-delayed recall, LDR), and also a phonemic fluency test of letter P fluency (LPF). A score was created based on these tests. The diagnoses were made on the basis of clinical consensus and neuropsychological testing. Receiver operating characteristic curve analyses were used to determine area under the curve (AUC), the sensitivity and specificity for each test separately and for the final proposed score. MMSE, LDR, LPF and delayed recall of BCB scores reach statistically significant differences between groups (P=0.000, 0.03, 0.001 and 0.01, respectively). Sensitivity, specificity and AUC were MMSE: 64%, 79% and 0.75 (cut off <29); LDR: 56%, 62% and 0.62 (cut off <3); LPF: 71%, 71% and 0.71 (cut off <14); delayed recall of BCB: 56%, 82% and 0.68 (cut off <9). The proposed score reached a sensitivity of 88% and 76% and specificity of 62% and 75% for cut off over 1 and over 2, respectively. AUC were 0.81. In conclusion, a score created from screening tests is capable of discriminating MCI from SMC with moderate to good accurancy. PMID:24147213

  6. Differential effect of motivational features on training improvements in school-based cognitive training.

    PubMed

    Katz, Benjamin; Jaeggi, Susanne; Buschkuehl, Martin; Stegman, Alyse; Shah, Priti

    2014-01-01

    Cognitive training often utilizes game-like motivational features to keep participants engaged. It is unclear how these elements, such as feedback, reward, and theming impact player performance during training. Recent research suggests that motivation and engagement are closely related to improvements following cognitive training. We hypothesized that training paradigms featuring game-like motivational elements would be more effective than a version with no motivational elements. Five distinct motivational features were chosen for examination: a real-time scoring system, theme changes, prizes, end-of-session certificates, and scaffolding to explain the lives and leveling system included in the game. One version of the game was created with all these motivational elements included, and one was created with all of them removed. Other versions removed a single element at a time. Seven versions of a game-like n-back working memory task were then created and administered to 128 students in second through eight grade at school-based summer camps in southeastern Michigan. The inclusion of real-time scoring during play, a popular motivational component in both entertainment games and cognitive training, was found to negatively impact training improvements over the three day period. Surprisingly, scaffolding to explain lives and levels also negatively impacted training gains. The other game adjustments did not significantly impact training improvement compared to the original version of the game with all features included. These findings are preliminary and are limited by both the small sample size and the brevity of the intervention. Nonetheless, these findings suggest that certain motivational elements may distract from the core cognitive training task, reducing task improvement, especially at the initial stage of learning. PMID:24795603

  7. Differential effect of motivational features on training improvements in school-based cognitive training

    PubMed Central

    Katz, Benjamin; Jaeggi, Susanne; Buschkuehl, Martin; Stegman, Alyse; Shah, Priti

    2014-01-01

    Cognitive training often utilizes game-like motivational features to keep participants engaged. It is unclear how these elements, such as feedback, reward, and theming impact player performance during training. Recent research suggests that motivation and engagement are closely related to improvements following cognitive training. We hypothesized that training paradigms featuring game-like motivational elements would be more effective than a version with no motivational elements. Five distinct motivational features were chosen for examination: a real-time scoring system, theme changes, prizes, end-of-session certificates, and scaffolding to explain the lives and leveling system included in the game. One version of the game was created with all these motivational elements included, and one was created with all of them removed. Other versions removed a single element at a time. Seven versions of a game-like n-back working memory task were then created and administered to 128 students in second through eight grade at school-based summer camps in southeastern Michigan. The inclusion of real-time scoring during play, a popular motivational component in both entertainment games and cognitive training, was found to negatively impact training improvements over the three day period. Surprisingly, scaffolding to explain lives and levels also negatively impacted training gains. The other game adjustments did not significantly impact training improvement compared to the original version of the game with all features included. These findings are preliminary and are limited by both the small sample size and the brevity of the intervention. Nonetheless, these findings suggest that certain motivational elements may distract from the core cognitive training task, reducing task improvement, especially at the initial stage of learning. PMID:24795603

  8. Predictors of retest effects in a longitudinal study of cognitive aging in a diverse community-based sample

    PubMed Central

    Gross, Alden L.; Benitez, Andreana; Shih, Regina; Bangen, Katherine J.; Glymour, M Maria M; Sachs, Bonnie; Sisco, Shannon; Skinner, Jeannine; Schneider, Brooke C.; Manly, Jennifer J.

    2016-01-01

    OBJECTIVE Better performance due to repeated testing can bias long-term trajectories of cognitive aging and correlates of change. We examined whether retest effects differ as a function of individual differences pertinent to cognitive aging: race/ethnicity, age, sex, language, years of education, and dementia risk factors including APOE ε4 status, baseline cognitive performance, and cardiovascular risk. METHOD We used data from the Washington Heights-Inwood Columbia Aging Project, a community-based cohort of older adults (n=4,073). We modeled cognitive change and retest effects in summary factors for general cognitive performance, memory, executive functioning, and language using multilevel models. Retest effects were parameterized in two ways, as improvement between the first and subsequent testings, and as the square root of the number of prior testings. We evaluated whether the retest effect differed by individual characteristics. RESULTS The mean retest effect for general cognitive performance was 0.60 standard deviations (95%CI: 0.46, 0.74), and was similar for memory, executive functioning, and language. Retest effects were greater for participants in the lowest quartile of cognitive performance, consistent with regression to the mean. Retest did not differ by other characteristics. CONCLUSIONS Retest effects are large in this community-based sample, but do not vary by demographic or dementia-related characteristics. Differential retest effects may not limit the generalizability of inferences across different groups in longitudinal research. PMID:26527240

  9. Elaborate analysis and design of filter-bank-based sensing for wideband cognitive radios

    NASA Astrophysics Data System (ADS)

    Maliatsos, Konstantinos; Adamis, Athanasios; Kanatas, Athanasios G.

    2014-12-01

    The successful operation of a cognitive radio system strongly depends on its ability to sense the radio environment. With the use of spectrum sensing algorithms, the cognitive radio is required to detect co-existing licensed primary transmissions and to protect them from interference. This paper focuses on filter-bank-based sensing and provides a solid theoretical background for the design of these detectors. Optimum detectors based on the Neyman-Pearson theorem are developed for uniform discrete Fourier transform (DFT) and modified DFT filter banks with root-Nyquist filters. The proposed sensing framework does not require frequency alignment between the filter bank of the sensor and the primary signal. Each wideband primary channel is spanned and monitored by several sensor subchannels that analyse it in narrowband signals. Filter-bank-based sensing is proved to be robust and efficient under coloured noise. Moreover, the performance of the weighted energy detector as a sensing technique is evaluated. Finally, based on the Locally Most Powerful and the Generalized Likelihood Ratio test, real-world sensing algorithms that do not require a priori knowledge are proposed and tested.

  10. W-band OFDM Radio-over-Fiber system with power detector for vector signal down-conversion.

    PubMed

    Lin, Chun-Ting; Wu, Meng-Fan; Ho, Chun-Hung; Li, Che-Hao; Lin, Chi-Hsiang; Huang, Hou-Tzu

    2015-06-01

    This Letter proposes a W-band OFDM RoF system at 103.5 GHz employing power detector to support vector signal down-conversion. Additional RF tone is generated and transmitted from central office to replace the local oscillator at a wireless receiver. With a proper frequency gap and power ratio between the RF tone and the OFDM-modulated signal, the impact from signal-to-signal beating interference can be minimized. The data rate can achieve a 40 Gbps 16 QAM OFDM signal over 25 km fiber and 2 m wireless transmission. PMID:26030536

  11. Multichannel broadcast based on home channel for cognitive radio sensor networks.

    PubMed

    Zeng, Fanzi; Tang, Yuting; Pu, Jianjie

    2014-01-01

    Considering the limited resources and the dynamic spectrum distribution in the cognitive radio sensor networks (CRSN), a half-duplex Multichannel broadcast protocol for CRSN is presented based on the home channel. This protocol maintains the networks topology only through the home channel, so there is no need for the public channel to transmit the control information and no need for the synchronization. After network initialization, node broadcasts data via home channel in half-duplex transmission way. The simulation results show that, compared with complete broadcast, the proposed protocol effectively reduces broadcast delay and overhead. PMID:25161397

  12. The Experimental Research on E-Learning Instructional Design Model Based on Cognitive Flexibility Theory

    NASA Astrophysics Data System (ADS)

    Cao, Xianzhong; Wang, Feng; Zheng, Zhongmei

    The paper reports an educational experiment on the e-Learning instructional design model based on Cognitive Flexibility Theory, the experiment were made to explore the feasibility and effectiveness of the model in promoting the learning quality in ill-structured domain. The study performed the experiment on two groups of students: one group learned through the system designed by the model and the other learned by the traditional method. The results of the experiment indicate that the e-Learning designed through the model is helpful to promote the intrinsic motivation, learning quality in ill-structured domains, ability to resolve ill-structured problem and creative thinking ability of the students.

  13. The Spectrum Sensing Algorithm Based AdaBoost in Cognitive Radio

    NASA Astrophysics Data System (ADS)

    Tian, Deyong; Wang, Xin

    To solve the low detection rate of the primary user in the cognitive radio environment, we propose a spectrum sensing method based on AdaBoost in the case of low SNR. In this paper, a set of received signal spectrum features are first calculated and extracted the discriminant feature vector as training samples and testing samples for classification. Finally, we utilize the trained AdaBoost to detect the primary user. Test result shows that the proposed algorithm is not affected by uncertainty factors of noise and has high performance to classification detection compared with ANN, SVM and maximum-minimum eigenvalue (MME).

  14. Benzodiazepine use and risk of incident dementia or cognitive decline: prospective population based study

    PubMed Central

    Dublin, Sascha; Yu, Onchee; Walker, Rod; Anderson, Melissa; Hubbard, Rebecca A; Crane, Paul K; Larson, Eric B

    2016-01-01

    Objective To determine whether higher cumulative use of benzodiazepines is associated with a higher risk of dementia or more rapid cognitive decline. Design Prospective population based cohort. Setting Integrated healthcare delivery system, Seattle, Washington. Participants 3434 participants aged ≥65 without dementia at study entry. There were two rounds of recruitment (1994-96 and 2000-03) followed by continuous enrollment beginning in 2004. Main outcomes measures The cognitive abilities screening instrument (CASI) was administered every two years to screen for dementia and was used to examine cognitive trajectory. Incident dementia and Alzheimer’s disease were determined with standard diagnostic criteria. Benzodiazepine exposure was defined from computerized pharmacy data and consisted of the total standardized daily doses (TSDDs) dispensed over a 10 year period (a rolling window that moved forward in time during follow-up). The most recent year was excluded because of possible use for prodromal symptoms. Multivariable Cox proportional hazard models were used to examine time varying use of benzodiazepine and dementia risk. Analyses of cognitive trajectory used linear regression models with generalized estimating equations. Results Over a mean follow-up of 7.3 years, 797 participants (23.2%) developed dementia, of whom 637 developed Alzheimer’s disease. For dementia, the adjusted hazard ratios associated with cumulative benzodiazepine use compared with non-use were 1.25 (95% confidence interval 1.03 to 1.51) for 1-30 TSDDs; 1.31 (1.00 to 1.71) for 31-120 TSDDs; and 1.07 (0.82 to 1.39) for ≥121 TSDDs. Results were similar for Alzheimer’s disease. Higher benzodiazepine use was not associated with more rapid cognitive decline. Conclusion The risk of dementia is slightly higher in people with minimal exposure to benzodiazepines but not with the highest level of exposure. These results do not support a causal association between benzodiazepine use and

  15. Identifying potential misfit items in cognitive process of learning engineering mathematics based on Rasch model

    NASA Astrophysics Data System (ADS)

    Ataei, Sh; Mahmud, Z.; Khalid, M. N.

    2014-04-01

    The students learning outcomes clarify what students should know and be able to demonstrate after completing their course. So, one of the issues on the process of teaching and learning is how to assess students' learning. This paper describes an application of the dichotomous Rasch measurement model in measuring the cognitive process of engineering students' learning of mathematics. This study provides insights into the perspective of 54 engineering students' cognitive ability in learning Calculus III based on Bloom's Taxonomy on 31 items. The results denote that some of the examination questions are either too difficult or too easy for the majority of the students. This analysis yields FIT statistics which are able to identify if there is data departure from the Rasch theoretical model. The study has identified some potential misfit items based on the measurement of ZSTD where the removal misfit item was accomplished based on the MNSQ outfit of above 1.3 or less than 0.7 logit. Therefore, it is recommended that these items be reviewed or revised to better match the range of students' ability in the respective course.

  16. Thinking about online sources: Exploring students' epistemic cognition in internet-based chemistry learning

    NASA Astrophysics Data System (ADS)

    Dai, Ting

    This dissertation investigated the relation between epistemic cognition---epistemic aims and source beliefs---and learning outcome in an Internet--based research context. Based on a framework of epistemic cognition (Chinn, Buckland, & Samarapungavan, 2011), a context--specific epistemic aims and source beliefs questionnaire (CEASBQ) was developed and administered to 354 students from college--level introductory chemistry courses. A series of multitrait--multimethod model comparisons provided evidence for construct convergent and discriminant validity for three epistemic aims--- true beliefs, justified beliefs, explanatory connection, which were all distinguished from, yet correlated with, mastery goals. Students' epistemic aims were specific to the chemistry topics in research. Multidimensional scaling results indicated that students' source evaluation was based on two dimensions--- professional expertise and first--hand knowledge, suggesting a multidimensional structure of source beliefs. Most importantly, online learning outcome was found to be significantly associated with two epistemic aims---justified beliefs and explanatory connection: The more students sought justifications in the online research, the lower they tended to score on the learning outcome measure, whereas the more students sought explanatory connections between information, the higher they scored on the outcome measure. There was a significant but small positive association between source beliefs and learning outcome. The influences of epistemic aims and source beliefs on learning outcome were found to be above and beyond the effects of a number of covariates, including prior knowledge and perceived ability with online sources.

  17. Computer-Based Cognitive Training for Executive Functions after Stroke: A Systematic Review

    PubMed Central

    van de Ven, Renate M.; Murre, Jaap M. J.; Veltman, Dick J.; Schmand, Ben A.

    2016-01-01

    Background: Stroke commonly results in cognitive impairments in working memory, attention, and executive function, which may be restored with appropriate training programs. Our aim was to systematically review the evidence for computer-based cognitive training of executive dysfunctions. Methods: Studies were included if they concerned adults who had suffered stroke or other types of acquired brain injury, if the intervention was computer training of executive functions, and if the outcome was related to executive functioning. We searched in MEDLINE, PsycINFO, Web of Science, and The Cochrane Library. Study quality was evaluated based on the CONSORT Statement. Treatment effect was evaluated based on differences compared to pre-treatment and/or to a control group. Results: Twenty studies were included. Two were randomized controlled trials that used an active control group. The other studies included multiple baselines, a passive control group, or were uncontrolled. Improvements were observed in tasks similar to the training (near transfer) and in tasks dissimilar to the training (far transfer). However, these effects were not larger in trained than in active control groups. Two studies evaluated neural effects and found changes in both functional and structural connectivity. Most studies suffered from methodological limitations (e.g., lack of an active control group and no adjustment for multiple testing) hampering differentiation of training effects from spontaneous recovery, retest effects, and placebo effects. Conclusions: The positive findings of most studies, including neural changes, warrant continuation of research in this field, but only if its methodological limitations are addressed. PMID:27148007

  18. A cognitive robotic system based on the Soar cognitive architecture for mobile robot navigation, search, and mapping missions

    NASA Astrophysics Data System (ADS)

    Hanford, Scott D.

    Most unmanned vehicles used for civilian and military applications are remotely operated or are designed for specific applications. As these vehicles are used to perform more difficult missions or a larger number of missions in remote environments, there will be a great need for these vehicles to behave intelligently and autonomously. Cognitive architectures, computer programs that define mechanisms that are important for modeling and generating domain-independent intelligent behavior, have the potential for generating intelligent and autonomous behavior in unmanned vehicles. The research described in this presentation explored the use of the Soar cognitive architecture for cognitive robotics. The Cognitive Robotic System (CRS) has been developed to integrate software systems for motor control and sensor processing with Soar for unmanned vehicle control. The CRS has been tested using two mobile robot missions: outdoor navigation and search in an indoor environment. The use of the CRS for the outdoor navigation mission demonstrated that a Soar agent could autonomously navigate to a specified location while avoiding obstacles, including cul-de-sacs, with only a minimal amount of knowledge about the environment. While most systems use information from maps or long-range perceptual capabilities to avoid cul-de-sacs, a Soar agent in the CRS was able to recognize when a simple approach to avoiding obstacles was unsuccessful and switch to a different strategy for avoiding complex obstacles. During the indoor search mission, the CRS autonomously and intelligently searches a building for an object of interest and common intersection types. While searching the building, the Soar agent builds a topological map of the environment using information about the intersections the CRS detects. The agent uses this topological model (along with Soar's reasoning, planning, and learning mechanisms) to make intelligent decisions about how to effectively search the building. Once the

  19. UMTS Base Station-like Exposure, Well-Being, and Cognitive Performance

    PubMed Central

    Regel, Sabine J.; Negovetic, Sonja; Röösli, Martin; Berdiñas, Veronica; Schuderer, Jürgen; Huss, Anke; Lott, Urs; Kuster, Niels; Achermann, Peter

    2006-01-01

    Background Radio-frequency electromagnetic fields (RF EMF) of mobile communication systems are widespread in the living environment, yet their effects on humans are uncertain despite a growing body of literature. Objectives We investigated the influence of a Universal Mobile Telecommunications System (UMTS) base station-like signal on well-being and cognitive performance in subjects with and without self-reported sensitivity to RF EMF. Methods We performed a controlled exposure experiment (45 min at an electric field strength of 0, 1, or 10 V/m, incident with a polarization of 45° from the left back side of the subject, weekly intervals) in a randomized, double-blind crossover design. A total of 117 healthy subjects (33 self-reported sensitive, 84 nonsensitive subjects) participated in the study. We assessed well-being, perceived field strength, and cognitive performance with questionnaires and cognitive tasks and conducted statistical analyses using linear mixed models. Organ-specific and brain tissue–specific dosimetry including uncertainty and variation analysis was performed. Results In both groups, well-being and perceived field strength were not associated with actual exposure levels. We observed no consistent condition-induced changes in cognitive performance except for two marginal effects. At 10 V/m we observed a slight effect on speed in one of six tasks in the sensitive subjects and an effect on accuracy in another task in nonsensitive subjects. Both effects disappeared after multiple end point adjustment. Conclusions In contrast to a recent Dutch study, we could not confirm a short-term effect of UMTS base station-like exposure on well-being. The reported effects on brain functioning were marginal and may have occurred by chance. Peak spatial absorption in brain tissue was considerably smaller than during use of a mobile phone. No conclusions can be drawn regarding short-term effects of cell phone exposure or the effects of long-term base station

  20. All-optical OFDM network coding scheme for all-optical virtual private communication in PON

    NASA Astrophysics Data System (ADS)

    Li, Lijun; Gu, Rentao; Ji, Yuefeng; Bai, Lin; Huang, Zhitong

    2014-03-01

    A novel optical orthogonal frequency division multiplexing (OFDM) network coding scheme is proposed over passive optical network (PON) system. The proposed scheme for all-optical virtual private network (VPN) does not only improve transmission efficiency, but also realize full-duplex communication mode in a single fiber. Compared with the traditional all-optical VPN architectures, the all-optical OFDM network coding scheme can support higher speed, more flexible bandwidth allocation, and higher spectrum efficiency. In order to reduce the difficulty of alignment for encoding operation between inter-communication traffic, the width of OFDM subcarrier pulse is stretched in our proposed scheme. The feasibility of all-optical OFDM network coding scheme for VPN is verified, and the relevant simulation results show that the full-duplex inter-communication traffic stream can be transmitted successfully. Furthermore, the tolerance of misalignment existing in inter-ONUs traffic is investigated and analyzed for all-optical encoding operation, and the difficulty of pulse alignment is proved to be lower.

  1. Proposal of ICI cancellation using opposite weightings on symmetric subcarrier pairs in CO-OFDM systems

    NASA Astrophysics Data System (ADS)

    Zhang, Jing; Chen, Xuemei; Deng, Mingliang; Zeng, Dengke; Yang, Heming; Qiu, Kun

    2015-08-01

    We propose a novel ICI cancellation using opposite weighting on symmetric subcarrier pairs to combat the linear phase noise of laser source and the nonlinear phase noise resulted from the fiber nonlinearity. We compare the proposed ICI cancellation scheme with conventional OFDM and the ICI self-cancellation at the same raw bit rate of 35.6 Gb/s. In simulations, the proposed ICI cancellation scheme shows better phase noise tolerance compared with conventional OFDM and has similar phase noise tolerance with the ICI self-cancellation. The laser linewidth is about 13 MHz at BER of 2 × 10-3 with ICI cancellation scheme while it is 5 MHz in conventional OFDM. We also study the nonlinearity tolerance and find that the proposed ICI cancellation scheme is better compared with the other two schemes which due to the first order nonlinearity mitigation. The launch power is 7 dBm for the proposed ICI cancellation scheme and its SNR improves by 4 dB or 3 dB compared with the ICI self-cancellation or conventional OFDM at BER of 1.1 × 10-3, respectively.

  2. A robust and scalable neuromorphic communication system by combining synaptic time multiplexing and MIMO-OFDM.

    PubMed

    Srinivasa, Narayan; Zhang, Deying; Grigorian, Beayna

    2014-03-01

    This paper describes a novel architecture for enabling robust and efficient neuromorphic communication. The architecture combines two concepts: 1) synaptic time multiplexing (STM) that trades space for speed of processing to create an intragroup communication approach that is firing rate independent and offers more flexibility in connectivity than cross-bar architectures and 2) a wired multiple input multiple output (MIMO) communication with orthogonal frequency division multiplexing (OFDM) techniques to enable a robust and efficient intergroup communication for neuromorphic systems. The MIMO-OFDM concept for the proposed architecture was analyzed by simulating large-scale spiking neural network architecture. Analysis shows that the neuromorphic system with MIMO-OFDM exhibits robust and efficient communication while operating in real time with a high bit rate. Through combining STM with MIMO-OFDM techniques, the resulting system offers a flexible and scalable connectivity as well as a power and area efficient solution for the implementation of very large-scale spiking neural architectures in hardware. PMID:24807453

  3. An OFDM Receiver with Frequency Domain Diversity Combined Impulsive Noise Canceller for Underwater Network.

    PubMed

    Saotome, Rie; Hai, Tran Minh; Matsuda, Yasuto; Suzuki, Taisaku; Wada, Tomohisa

    2015-01-01

    In order to explore marine natural resources using remote robotic sensor or to enable rapid information exchange between ROV (remotely operated vehicles), AUV (autonomous underwater vehicle), divers, and ships, ultrasonic underwater communication systems are used. However, if the communication system is applied to rich living creature marine environment such as shallow sea, it suffers from generated Impulsive Noise so-called Shrimp Noise, which is randomly generated in time domain and seriously degrades communication performance in underwater acoustic network. With the purpose of supporting high performance underwater communication, a robust digital communication method for Impulsive Noise environments is necessary. In this paper, we propose OFDM ultrasonic communication system with diversity receiver. The main feature of the receiver is a newly proposed Frequency Domain Diversity Combined Impulsive Noise Canceller. The OFDM receiver utilizes 20-28 KHz ultrasonic channel and subcarrier spacing of 46.875 Hz (MODE3) and 93.750 Hz (MODE2) OFDM modulations. In addition, the paper shows Impulsive Noise distribution data measured at a fishing port in Okinawa and at a barge in Shizuoka prefectures and then proposed diversity OFDM transceivers architecture and experimental results are described. By the proposed Impulsive Noise Canceller, frame bit error rate has been decreased by 20-30%. PMID:26351656

  4. Blind polarization demultiplexing by constructing a cost function for coherent optical PDM-OFDM.

    PubMed

    Yu, Zhenming; Chen, Minghua; Chen, Hongwei; Yi, Xingwen; Yang, Sigang; Xie, Shizhong

    2015-07-13

    We propose a training symbols-free polarization demultiplexing method by constructing a cost function (CCF-PDM) for coherent optical PDM-OFDM. This method is applicable for high-speed, wide-bandwidth OFDM signals, different subcarrier modulation formats and long-haul transmission. It shows comparable performance with that of conventional method but without overhead and converges fast. Since the neighboring subcarriers experience similar polarization effects, we set the initial matrix parameters by the neighboring subcarrier to reduce the number of iteration for the gradient algorithm and prevent swapping the data of the two orthogonal polarizations. We verify this method in experiment by transmitting 66.6-Gb/s PDM-OFDM signal with 4QAM subcarrier modulation over 5440 km SSMF and 133.3-Gb/s PDM-OFDM signal with 16QAM subcarrier modulation over 960 km SSMF respectively. We compare its performance with that of training symbols. We also analyze the convergence speed of this method. PMID:26191909

  5. A combined PAPR-reduction technique for asymmetrically clipped optical OFDM system

    NASA Astrophysics Data System (ADS)

    Zhou, Ji; Zhang, Zhenshan; Zhang, Tiantian; Guo, Mengqi; Tang, Xizi; Wang, Zhansheng; Qiao, Yaojun

    2016-05-01

    In this paper, we propose a combined peak-to-average power ratio (PAPR) reduction technique for asymmetrically clipped optical orthogonal frequency division multiplexing (ACO-OFDM) system. The proposed PAPR-reduction technique combines discrete Fourier transform (DFT)-spread technique with peak-clipping technique. For a tradeoff between PAPR and BER performance, the clipping ratio (CR) in peak-clipping technique is set to 2.2. Under this CR, a 6 dB of PAPR reduction can be obtained by the combined PAPR-reduction technique at the probability of 10-3 and BER performance is barely affected by the clipping distortion. The transmission experiment over 100-km SSMF has been implemented to verify the feasibility of the proposed scheme. At the forward error correction (FEC) limit, ACO-OFDM with the combined PAPR-reduction technique has 1.8 dB improvement of received sensitivity compared to ACO-OFDM with DFT-spread technique and 3.8 dB improvement compared to conventional ACO-OFDM.

  6. Study of IQ imbalance effect in direct-detection optical OFDM systems

    NASA Astrophysics Data System (ADS)

    Li, Xinying; Shao, Yufeng; Zou, Shumin; Hou, Chunning; Zheng, Xi; Liu, Xiao; Zhang, Junwen; Fang, Wuliang; Chi, Nan

    2009-11-01

    In-phase/quadrature-phase (IQ) imbalance can result in severe performance degradation in optical direct-detection orthogonal-frequency-division-multiplexing (DD-OFDM) systems. We build two optical back-to-back DD-OFDM systems, which implement double-sideband (DSB) and single-sideband (SSB) modulation, respectively. The tolerance to IQ imbalance of these two systems is analyzed and compared using error vector magnitude (EVM) and symbol error rate (SER). We find that, in the back-to-back case, the DSB system has stronger robustness to IQ imbalance than the SSB System. We further build two optical DD-OFDM systems each with 40-km transmission, which respectively implement DSB and SSB transmission. Similarly, we analyze and compare the tolerance to IQ imbalance of these two systems in terms of EVM and SER. We find that, however, in the case of 40-km transmission, the SSB system has stronger robustness to IQ imbalance than the DSB system. As a result, we conclude that, in the case of transmission, SSB modulation can enhance the tolerance to IQ imbalance of DD-OFDM systems.

  7. An OFDM Receiver with Frequency Domain Diversity Combined Impulsive Noise Canceller for Underwater Network

    PubMed Central

    Saotome, Rie; Hai, Tran Minh; Matsuda, Yasuto; Suzuki, Taisaku; Wada, Tomohisa

    2015-01-01

    In order to explore marine natural resources using remote robotic sensor or to enable rapid information exchange between ROV (remotely operated vehicles), AUV (autonomous underwater vehicle), divers, and ships, ultrasonic underwater communication systems are used. However, if the communication system is applied to rich living creature marine environment such as shallow sea, it suffers from generated Impulsive Noise so-called Shrimp Noise, which is randomly generated in time domain and seriously degrades communication performance in underwater acoustic network. With the purpose of supporting high performance underwater communication, a robust digital communication method for Impulsive Noise environments is necessary. In this paper, we propose OFDM ultrasonic communication system with diversity receiver. The main feature of the receiver is a newly proposed Frequency Domain Diversity Combined Impulsive Noise Canceller. The OFDM receiver utilizes 20–28 KHz ultrasonic channel and subcarrier spacing of 46.875 Hz (MODE3) and 93.750 Hz (MODE2) OFDM modulations. In addition, the paper shows Impulsive Noise distribution data measured at a fishing port in Okinawa and at a barge in Shizuoka prefectures and then proposed diversity OFDM transceivers architecture and experimental results are described. By the proposed Impulsive Noise Canceller, frame bit error rate has been decreased by 20–30%. PMID:26351656

  8. Cognitive and Socio-Affective Outcomes of Project-Based Learning: Perceptions of Greek Second Chance School Students

    ERIC Educational Resources Information Center

    Koutrouba, Konstantina; Karageorgou, Elissavet

    2013-01-01

    The present questionnaire-based study was conducted in 2010 in order to examine 677 Greek Second Chance School (SCS) students' perceptions about the cognitive and socio-affective outcomes of project-based learning. Data elaboration, statistical and factor analysis showed that the participants found that project-based learning offered a second…

  9. Effects of Web Based Inquiry Science Environment on Cognitive Outcomes in Biological Science in Correlation to Emotional Intelligence

    ERIC Educational Resources Information Center

    Manoj, T. I.; Devanathan, S.

    2010-01-01

    This research study is the report of an experiment conducted to find out the effects of web based inquiry science environment on cognitive outcomes in Biological science in correlation to Emotional intelligence. Web based inquiry science environment (WISE) provides a platform for creating inquiry-based science projects for students to work…

  10. Spatial cognition

    NASA Technical Reports Server (NTRS)

    Kaiser, Mary Kister; Remington, Roger

    1988-01-01

    Spatial cognition is the ability to reason about geometric relationships in the real (or a metaphorical) world based on one or more internal representations of those relationships. The study of spatial cognition is concerned with the representation of spatial knowledge, and our ability to manipulate these representations to solve spatial problems. Spatial cognition is utilized most critically when direct perceptual cues are absent or impoverished. Examples are provided of how human spatial cognitive abilities impact on three areas of space station operator performance: orientation, path planning, and data base management. A videotape provides demonstrations of relevant phenomena (e.g., the importance of orientation for recognition of complex, configural forms). The presentation is represented by abstract and overhead visuals only.

  11. Augmentation of Evidence-Based Psychotherapy for PTSD With Cognitive Enhancers.

    PubMed

    Marin, Marie-France; Lonak, Sylwia Fowler; Milad, Mohammed R

    2015-06-01

    Exposure-based therapy has proven to be useful to treat various anxiety disorders as well as post-traumatic stress disorder (PTSD). Despite its efficacy, a fair proportion of patients remain symptomatic after treatment. Different lines of research have put considerable efforts to investigate ways to enhance the efficacy of exposure-based therapy, which could ultimately lead to better clinical outcomes for patients. Given that this type of therapy relies on extinction learning principles, neuroscience research has tested different adjuncts that could be used as cognitive enhancers through their impact on extinction learning and its consolidation. The current review will summarize some of the latest compounds that have received attention and show some promise to be used in clinical settings to improve the efficacy of exposure-based therapy. PMID:25894356

  12. Neuroplasticity-based cognitive and linguistic skills training improves reading and writing skills in college students.

    PubMed

    Rogowsky, Beth A; Papamichalis, Pericles; Villa, Laura; Heim, Sabine; Tallal, Paula

    2013-01-01

    This study reports an evaluation of the effect of computer-based cognitive and linguistic training on college students' reading and writing skills. The computer-based training included a series of increasingly challenging software programs that were designed to strengthen students' foundational cognitive skills (memory, attention span, processing speed, and sequencing) in the context of listening and higher level reading tasks. Twenty-five college students (12 native English language; 13 English Second Language), who demonstrated poor writing skills, participated in the training group. The training group received daily training during the spring semester (11 weeks) with the Fast ForWord Literacy (FFW-L) and upper levels of the Fast ForWord Reading series (Levels 3-5). The comparison group (n = 28) selected from the general college population did not receive training. Both the training and comparison groups attended the same university. All students took the Gates MacGinitie Reading Test (GMRT) and the Oral and Written Language Scales (OWLS) Written Expression Scale at the beginning (Time 1) and end (Time 2) of the spring college semester. Results from this study showed that the training group made a statistically greater improvement from Time 1 to Time 2 in both their reading skills and their writing skills than the comparison group. The group who received training began with statistically lower writing skills before training, but exceeded the writing skills of the comparison group after training. PMID:23533100

  13. [Music therapy and neuropsychology: a proposal to music therapy based on the cognitive processing of music].

    PubMed

    Satoh, Masayuki; Takeda, Katsuhiko; Kuzuhara, Shigeki

    2007-11-01

    In the last decade, a considerable number of studies have been made on the cognitive processing of music. A patient with pure amusia due to the infarction of anterior portion of bilateral temporal lobes revealed the disturbance of the discrimination of chords. Using positron emission tomography, these regions were activated when musically naive normal subjects listened to the harmony compared to the rhythm of identical music. So, we concluded that anterior temporal portion might participate in the recognition of chords. Several articles reported that the musician's brain was different from nonmusicians' functionally and anatomically. This difference was considered to be caused by the musical training for a long time. Recent studies clarified that the reorganization might occur by musical training for a few months. Melodic intonation therapy (MIT) is a method aimed to improve speech output of aphasic patients, using short melodic phrase with a word. The literatures of mental processing of music suggested that right hemisphere might participate in the expression of music, namely singing and playing instrumentals. So, it was supposed that MIT utilized the compensational function of right hemisphere for damaged left hemisphere. We also reported that mental singing improved the gait disturbance of patients with Parkinson's disease. Music therapy is changing from a social science model based on the individual experiences to a neuroscience-guided model based on brain function and cognitive processing of the perception and expression of music. PMID:18210821

  14. Neuroplasticity-Based Cognitive and Linguistic Skills Training Improves Reading and Writing Skills in College Students

    PubMed Central

    Rogowsky, Beth A.; Papamichalis, Pericles; Villa, Laura; Heim, Sabine; Tallal, Paula

    2013-01-01

    This study reports an evaluation of the effect of computer-based cognitive and linguistic training on college students’ reading and writing skills. The computer-based training included a series of increasingly challenging software programs that were designed to strengthen students’ foundational cognitive skills (memory, attention span, processing speed, and sequencing) in the context of listening and higher level reading tasks. Twenty-five college students (12 native English language; 13 English Second Language), who demonstrated poor writing skills, participated in the training group. The training group received daily training during the spring semester (11 weeks) with the Fast ForWord Literacy (FFW-L) and upper levels of the Fast ForWord Reading series (Levels 3–5). The comparison group (n = 28) selected from the general college population did not receive training. Both the training and comparison groups attended the same university. All students took the Gates MacGinitie Reading Test (GMRT) and the Oral and Written Language Scales (OWLS) Written Expression Scale at the beginning (Time 1) and end (Time 2) of the spring college semester. Results from this study showed that the training group made a statistically greater improvement from Time 1 to Time 2 in both their reading skills and their writing skills than the comparison group. The group who received training began with statistically lower writing skills before training, but exceeded the writing skills of the comparison group after training. PMID:23533100

  15. Spectrum Handoffs Based on Preemptive Repeat Priority Queue in Cognitive Radio Networks.

    PubMed

    Yang, Xiaolong; Tan, Xuezhi; Ye, Liang; Ma, Lin

    2016-01-01

    Cognitive radio can significantly improve the spectrum efficiency, and spectrum handoff is considered as an important functionality to guarantee the quality of service (QoS) of primary users (PUs) and the continuity of data transmission of secondary users (SUs). In this paper, we propose an analytical framework based on a preemptive repeat identical (PRI) M/G/1 queuing network model to characterize spectrum handoff behaviors with general service time distribution of both primary and secondary connections, multiple interruptions and transmission delay resulting from the appearance of primary connections. Then, we derive the close-expression of the extended data delivery and the system sojourn time in both staying and changing scenarios. In addition, based on analysis of spectrum handoff behaviors resulting from multiple interruptions caused by the appearance of the primary connections, we investigate the traffic-adaptive policy, by which the considered SU will optimally adjust its handoff spectrum policy. Moreover, we investigate the admissible region and provide the reference for designing the admission control rule for the arriving secondary connection requests. Finally, simulation results verify that our proposed analytical framework is reasonable and can provide the reference for executing the optimal spectrum handoff strategy and designing the admission control rule for the SU in cognitive radio networks. PMID:27447644

  16. Senior-driven design and development of tablet-based cognitive games.

    PubMed

    Marques, João; Vasconcelos, Ana; Teixeira, Luís F

    2013-01-01

    This paper describes the design and development of a tablet-based gaming platform targeting the senior population, aiming at improving their overall wellbeing by stimulating their cognitive capabilities and promoting social interaction between players. To achieve these goals, we started by performing a study of the specific characteristics of the senior user as well as what makes a game appealing to the player. Furthermore we investigated why the tablet proves to be an advantageous device to our target audience. Based on the results of our research, we developed a solution that incorporates cognitive and social mechanisms into its games, while performing iterative evaluations together with the final user by adopting a user-centered design methodology. In each design phase, a pre-selected group of senior participants experimented with the game platform and provided feedback to improve its features and usability. Through a series of short-term and a long-term evaluation, the game platform proved to be appealing to its intended users, providing an enjoyable gaming experience. PMID:23739372

  17. Spectrum Handoffs Based on Preemptive Repeat Priority Queue in Cognitive Radio Networks

    PubMed Central

    Yang, Xiaolong; Tan, Xuezhi; Ye, Liang; Ma, Lin

    2016-01-01

    Cognitive radio can significantly improve the spectrum efficiency, and spectrum handoff is considered as an important functionality to guarantee the quality of service (QoS) of primary users (PUs) and the continuity of data transmission of secondary users (SUs). In this paper, we propose an analytical framework based on a preemptive repeat identical (PRI) M/G/1 queuing network model to characterize spectrum handoff behaviors with general service time distribution of both primary and secondary connections, multiple interruptions and transmission delay resulting from the appearance of primary connections. Then, we derive the close-expression of the extended data delivery and the system sojourn time in both staying and changing scenarios. In addition, based on analysis of spectrum handoff behaviors resulting from multiple interruptions caused by the appearance of the primary connections, we investigate the traffic-adaptive policy, by which the considered SU will optimally adjust its handoff spectrum policy. Moreover, we investigate the admissible region and provide the reference for designing the admission control rule for the arriving secondary connection requests. Finally, simulation results verify that our proposed analytical framework is reasonable and can provide the reference for executing the optimal spectrum handoff strategy and designing the admission control rule for the SU in cognitive radio networks. PMID:27447644

  18. Toward a research-based assessment of dyslexia: using cognitive measures to identify reading disabilities.

    PubMed

    Bell, Sherry Mee; McCallum, R Steve; Cox, Elizabeth A

    2003-01-01

    One hundred five participants from a random sample of elementary and middle school children completed measures of reading achievement and cognitive abilities presumed, based on a synthesis of current dyslexia research, to underlie reading. Factor analyses of these cognitive variables (including auditory processing, phonological awareness, short-term auditory memory, visual memory, rapid automatized naming, and visual processing speed) produced three empirically and theoretically derived factors (auditory processing, visual processing/speed, and memory), each of which contributed to the prediction of reading and spelling skills. Factor scores from the three factors combined predicted 85% of the variance associated with letter/sight word naming, 70% of the variance associated with reading comprehension, 73% for spelling, and 61% for phonetic decoding. The auditory processing factor was the strongest predictor, accounting for 27% to 43% of the variance across the different achievement areas. The results provide practitioner and researcher with theoretical and empirical support for the inclusion of measures of the three factors, in addition to specific measures of reading achievement, in a standardized assessment of dyslexia. Guidelines for a thorough, research-based assessment are provided. PMID:15493433

  19. Utilization of multi-band OFDM modulation to increase traffic rate of phosphor-LED wireless VLC.

    PubMed

    Yeh, Chien-Hung; Chen, Hsing-Yu; Chow, Chi-Wai; Liu, Yen-Liang

    2015-01-26

    To increase the traffic rate in phosphor-LED visible light communication (VLC), a multi-band orthogonal frequency division multiplexed (OFDM) modulation is first proposed and demonstrated. In the measurement, we do not utilize optical blue filter to increase modulation bandwidth of phosphor-LED in the VLC system. In this proposed scheme, different bands of OFDM signals are applied to different LED chips in a LED lamp, this can avoid the power fading and nonlinearity issue by applying the same OFDM signal to all the LED chips in a LED lamp. Here, the maximum increase percentages of traffic rates are 41.1%, 17.8% and 17.8% under received illuminations of 200, 500 and 1000 Lux, respectively, when the proposed three-band OFDM modulation is used in the VLC system. In addition, the analysis and verification by experiments are also performed. PMID:25835873

  20. Going up in Smoke? A Review of nAChRs-based Treatment Strategies for Improving Cognition in Schizophrenia

    PubMed Central

    Boggs, Douglas L.; Carlson, Jon; Cortes-Briones, Jose; Krystal, John H.; D’Souza, D. Cyril

    2015-01-01

    Cognitive impairment is known to be a core deficit in schizophrenia. Existing treatments for schizophrenia have limited efficacy against cognitive impairment. The ubiquitous use of nicotine in this population is thought to reflect an attempt by patients to self-medicate certain symptoms associated with the illness. Concurrently there is evidence that nicotinic receptors that have lower affinity for nicotine are more important in cognition. Therefore, a number of medications that target nicotinic acetylcholine receptors (nAChRs) have been tested or are in development. In this article we summarize the clinical evidence of nAChRs dysfunction in schizophrenia and review clinical studies testing either nicotine or nicotinic medications for the treatment of cognitive impairment in schizophrenia. Some evidence suggests beneficial effects of nAChRs based treatments for the attentional deficits associated with schizophrenia. Standardized cognitive test batteries have failed to capture consistent improvements from drugs acting at nAChRs. However, more proximal measures of brain function, such as ERPs relevant to information processing impairments in schizophrenia, have shown some benefit. Further work is necessary to conclude that nAChRs based treatments are of clinical utility in the treatment of cognitive deficits of schizophrenia. PMID:24345265

  1. Early Cognitive Deficits in Type 2 Diabetes: A Population-Based Study

    PubMed Central

    Marseglia, Anna; Fratiglioni, Laura; Laukka, Erika J.; Santoni, Giola; Pedersen, Nancy L.; Bäckman, Lars; Xu, Weili

    2016-01-01

    Evidence links type 2 diabetes to dementia risk. However, our knowledge on the initial cognitive deficits in diabetic individuals and the factors that might promote such deficits is still limited. This study aimed to identify the cognitive domains initially impaired by diabetes and the factors that play a role in this first stage. Within the population-based Swedish National Study on Aging and Care–Kungsholmen, 2305 cognitively intact participants aged ≥60 y were identified. Attention/working memory, perceptual speed, category fluency, letter fluency, semantic memory, and episodic memory were assessed. Diabetes (controlled and uncontrolled) and prediabetes were ascertained by clinicians, who also collected information on vascular disorders (hypertension, heart diseases, and stroke) and vascular risk factors (VRFs, including smoking and overweight/obesity). Data were analyzed with linear regression models. Overall, 196 participants (8.5%) had diabetes, of which 144 (73.5%) had elevated glycaemia (uncontrolled diabetes); 571 (24.8%) persons had prediabetes. In addition, diabetes, mainly uncontrolled, was related to lower performance in perceptual speed (β – 1.10 [95% CI – 1.98, – 0.23]), category fluency (β – 1.27 [95% CI – 2.52, – 0.03]), and digit span forward (β – 0.35 [95% CI – 0.54, – 0.17]). Critically, these associations were present only among APOE ɛ4 non–carriers. The associations of diabetes with perceptual speed and category fluency were present only among participants with VRFs or vascular disorders. Diabetes, especially uncontrolled diabetes, is associated with poorer performance in perceptual speed, category fluency, and attention/primary memory. VRFs, vascular disorders, and APOE status play a role in these associations. PMID:27314527

  2. Cognitive decline in short and long sleepers: A prospective population-based study (NEDICES)

    PubMed Central

    Benito-León, Julián; Louis, Elan D.; Bermejo-Pareja, Félix

    2013-01-01

    Background It is not clear whether cognitive decline progresses more quickly in long sleepers than in short sleepers or than in participants with usual sleep duration. We assessed cognitive decline as a function of self-reported sleep duration in a prospective population-based cohort (NEDICES). Methods Participants were evaluated at baseline and 3 years later. Baseline demographic variables were recorded and participants indicated their daily sleep usual duration as the sum of nighttime sleep and daytime napping. The average daily total usual sleep duration was grouped into three categories: ≤5 hours (short sleepers), 6 to 8 hours (reference category), and ≥9 hours (long sleepers). At baseline and at follow-up, a 37-item version of the Mini-Mental State Examination (37-MMSE) was administered. Results The final sample, 2,715 participants (72.9±6.1 years), comprised 298 (11%) short sleepers, 1,086 (40%) long sleepers, and 1,331 (49%) in the reference group (6 to 8 hours). During the three year follow-up period, the 37-MMSE declined by 0.5±4.0 points in short sleepers, 0.6±4.3 points in long sleepers, and 0.2±3.8 points in the reference group (p=0.08). The difference between short sleepers and the reference group was not significant (p=0.142); however, the difference between long sleepers and the reference group was significant (p=0.040). In analyses adjusted for baseline age and other potential confounders, this difference remained robust. Conclusions In this study, cognitive test scores among long sleepers declined more rapidly than observed in a reference group. Additional studies are needed to confirm these results. PMID:24094933

  3. Indices of cognitive function measured in rugby union players using a computer-based test battery.

    PubMed

    MacDonald, Luke A; Minahan, Clare L

    2016-09-01

    The purpose of this study was to investigate the intra- and inter-day reliability of cognitive performance using a computer-based test battery in team-sport athletes. Eighteen elite male rugby union players (age: 19 ± 0.5 years) performed three experimental trials (T1, T2 and T3) of the test battery: T1 and T2 on the same day and T3, on the following day, 24 h later. The test battery comprised of four cognitive tests assessing the cognitive domains of executive function (Groton Maze Learning Task), psychomotor function (Detection Task), vigilance (Identification Task), visual learning and memory (One Card Learning Task). The intraclass correlation coefficients (ICCs) for the Detection Task, the Identification Task and the One Card Learning Task performance variables ranged from 0.75 to 0.92 when comparing T1 to T2 to assess intraday reliability, and 0.76 to 0.83 when comparing T1 and T3 to assess inter-day reliability. The ICCs for the Groton Maze Learning Task intra- and inter-day reliability were 0.67 and 0.57, respectively. We concluded that the Detection Task, the Identification Task and the One Card Learning Task are reliable measures of psychomotor function, vigilance, visual learning and memory in rugby union players. The reliability of the Groton Maze Learning Task is questionable (mean coefficient of variation (CV) = 19.4%) and, therefore, results should be interpreted with caution. PMID:26756946

  4. Comparison of evidence-based interventions on outcomes of hospitalized, cognitively impaired older adults

    PubMed Central

    Naylor, Mary D; Hirschman, Karen B; Hanlon, Alexandra L; Bowles, Kathryn H; Bradway, Christine; McCauley, Kathleen M; Pauly, Mark V

    2014-01-01

    Aim This article reports the effects of three evidence-based interventions of varying intensity, each designed to improve outcomes of hospitalized cognitively impaired older adults. Patients & methods In this comparative effectiveness study, 202 older adults with cognitive impairment (assessed within 24 h of index hospitalization) were enrolled at one of three hospitals within an academic health system. Each hospital was randomly assigned one of the following interventions: Augmented Standard Care (ASC; lower dose: n = 65), Resource Nurse Care (RNC; medium dose: n = 71) or the Transitional Care Model (TCM; higher dose: n = 66). Since randomization at the patient level was not feasible due to potential contamination, generalized boosted modeling that estimated multigroup propensity score weights was used to balance baseline patient characteristics between groups. Analyses compared the three groups on time with first rehospitalization or death, the number and days of all-cause rehospitalizations per patient and functional status through 6-month postindex hospitalization. Results In total, 25% of the ASC group were rehospitalized or died by day 33 compared with day 58 for the RNC group versus day 83 for the TCM group. The largest differences between the three groups on time to rehospitalization or death were observed early in the Kaplan–Meier curve (at 30 days: ASC = 22% vs RNC = 19% vs TCM = 9%). The TCM group also demonstrated lower mean rehospitalization rates per patient compared with the RNC (p < 0.001) and ASC groups (p = 0.06) at 30 days. At 90-day postindex hospitalization, the TCM group continued to demonstrate lower mean rehospitalization rates per patient only when compared with the ASC group (p = 0.02). No significant group differences in functional status were observed. Conclusion Findings suggest that the TCM intervention, compared with interventions of lower intensity, has the potential to decrease costly resource use outcomes in the immediate

  5. Feasibility, Reliability, and Validity of a Smartphone Based Application for the Assessment of Cognitive Function in the Elderly

    PubMed Central

    Brouillette, Robert M.; Foil, Heather; Fontenot, Stephanie; Correro, Anthony; Allen, Ray; Martin, Corby K.; Bruce-Keller, Annadora J.; Keller, Jeffrey N.

    2013-01-01

    While considerable knowledge has been gained through the use of established cognitive and motor assessment tools, there is a considerable interest and need for the development of a battery of reliable and validated assessment tools that provide real-time and remote analysis of cognitive and motor function in the elderly. Smartphones appear to be an obvious choice for the development of these “next-generation” assessment tools for geriatric research, although to date no studies have reported on the use of smartphone-based applications for the study of cognition in the elderly. The primary focus of the current study was to assess the feasibility, reliability, and validity of a smartphone-based application for the assessment of cognitive function in the elderly. A total of 57 non-demented elderly individuals were administered a newly developed smartphone application-based Color-Shape Test (CST) in order to determine its utility in measuring cognitive processing speed in the elderly. Validity of this novel cognitive task was assessed by correlating performance on the CST with scores on widely accepted assessments of cognitive function. Scores on the CST were significantly correlated with global cognition (Mini-Mental State Exam: r = 0.515, p<0.0001) and multiple measures of processing speed and attention (Digit Span: r = 0.427, p<0.0001; Trail Making Test: r = −0.651, p<0.00001; Digit Symbol Test: r = 0.508, p<0.0001). The CST was not correlated with naming and verbal fluency tasks (Boston Naming Test, Vegetable/Animal Naming) or memory tasks (Logical Memory Test). Test re-test reliability was observed to be significant (r = 0.726; p = 0.02). Together, these data are the first to demonstrate the feasibility, reliability, and validity of using a smartphone-based application for the purpose of assessing cognitive function in the elderly. The importance of these findings for the establishment of smartphone-based assessment batteries of

  6. Feasibility, reliability, and validity of a smartphone based application for the assessment of cognitive function in the elderly.

    PubMed

    Brouillette, Robert M; Foil, Heather; Fontenot, Stephanie; Correro, Anthony; Allen, Ray; Martin, Corby K; Bruce-Keller, Annadora J; Keller, Jeffrey N

    2013-01-01

    While considerable knowledge has been gained through the use of established cognitive and motor assessment tools, there is a considerable interest and need for the development of a battery of reliable and validated assessment tools that provide real-time and remote analysis of cognitive and motor function in the elderly. Smartphones appear to be an obvious choice for the development of these "next-generation" assessment tools for geriatric research, although to date no studies have reported on the use of smartphone-based applications for the study of cognition in the elderly. The primary focus of the current study was to assess the feasibility, reliability, and validity of a smartphone-based application for the assessment of cognitive function in the elderly. A total of 57 non-demented elderly individuals were administered a newly developed smartphone application-based Color-Shape Test (CST) in order to determine its utility in measuring cognitive processing speed in the elderly. Validity of this novel cognitive task was assessed by correlating performance on the CST with scores on widely accepted assessments of cognitive function. Scores on the CST were significantly correlated with global cognition (Mini-Mental State Exam: r = 0.515, p<0.0001) and multiple measures of processing speed and attention (Digit Span: r = 0.427, p<0.0001; Trail Making Test: r = -0.651, p<0.00001; Digit Symbol Test: r = 0.508, p<0.0001). The CST was not correlated with naming and verbal fluency tasks (Boston Naming Test, Vegetable/Animal Naming) or memory tasks (Logical Memory Test). Test re-test reliability was observed to be significant (r = 0.726; p = 0.02). Together, these data are the first to demonstrate the feasibility, reliability, and validity of using a smartphone-based application for the purpose of assessing cognitive function in the elderly. The importance of these findings for the establishment of smartphone-based assessment batteries of cognitive

  7. A spiritually based approach to breast cancer awareness: cognitive response analysis of communication effectiveness.

    PubMed

    Holt, Cheryl L; Lee, Crystal; Wright, Katrina

    2008-01-01

    The purpose of this study was to compare the communication effectiveness of a spiritually based approach to breast cancer early detection education with a secular approach, among African American women, by conducting a cognitive response analysis. A total of 108 women from 6 Alabama churches were randomly assigned by church to receive a spiritually based or secular educational booklet discussing breast cancer early detection. Based on the elaboration likelihood model (Petty & Cacioppo, 1981), after reading the booklets participants were asked to complete a thought-listing task, writing down any thoughts they experienced and rating them as positive, negative, or neutral. Two independent coders then used 5 dimensions to code participants' thoughts. Compared with the secular booklet, the spiritually based booklet resulted in significantly more thoughts involving personal connection, self-assessment, and spiritually based responses. These results suggest that a spiritually based approach to breast cancer awareness may be more effective than the secular approach because it caused women to more actively process the message, stimulating central route processing. The incorporation of spiritually based content into church-based breast cancer education could be a promising health communication approach for African American women. PMID:18443989

  8. Emerging Innovative Teacher Education from Situated Cognition in a Web-Based Environment

    ERIC Educational Resources Information Center

    Lin, Tzu-Chiang; Hsu, Ying-Shao; Cheng, Yeong-Jing

    2011-01-01

    In this paper, the authors first discuss the main rationales of situated cognition and its connections with innovation in teacher education. The challenges that might occur in applying situated cognition in teacher education programs, including insufficient opportunities for cognition apprenticeship, limited social interactions, and constraints in…

  9. The Efficacy of Exposure-Based Cognitive Therapy with Survivors of Childhood Sexual Abuse.

    ERIC Educational Resources Information Center

    Gardner, Yun Hui

    Recent research has revealed the efficacy of cognitive behavioral interventions with sexual abuse survivors. Cognitive behavioral treatment (CBT) interventions require trauma survivors to confront their painful memories directly. This allows for assessment of cognitive distortions that need to be challenged and reframed. The extent and amount of…

  10. A novel biomarker of amnestic MCI based on dynamic cross-frequency coupling patterns during cognitive brain responses

    PubMed Central

    Dimitriadis, Stavros I.; Laskaris, Nikolaos A.; Bitzidou, Malamati P.; Tarnanas, Ioannis; Tsolaki, Magda N.

    2015-01-01

    The detection of mild cognitive impairment (MCI), the transitional stage between normal cognitive changes of aging and the cognitive decline caused by AD, is of paramount clinical importance, since MCI patients are at increased risk of progressing into AD. Electroencephalographic (EEG) alterations in the spectral content of brainwaves and connectivity at resting state have been associated with early-stage AD. Recently, cognitive event-related potentials (ERPs) have entered into the picture as an easy to perform screening test. Motivated by the recent findings about the role of cross-frequency coupling (CFC) in cognition, we introduce a relevant methodological approach for detecting MCI based on cognitive responses from a standard auditory oddball paradigm. By using the single trial signals recorded at Pz sensor and comparing the responses to target and non-target stimuli, we first demonstrate that increased CFC is associated with the cognitive task. Then, considering the dynamic character of CFC, we identify instances during which the coupling between particular pairs of brainwave frequencies carries sufficient information for discriminating between normal subjects and patients with MCI. In this way, we form a multiparametric signature of impaired cognition. The new composite biomarker was tested using data from a cohort that consists of 25 amnestic MCI patients and 15 age-matched controls. Standard machine-learning algorithms were employed so as to implement the binary classification task. Based on leave-one-out cross-validation, the measured classification rate was found reaching very high levels (95%). Our approach compares favorably with the traditional alternative of using the morphology of averaged ERP response to make the diagnosis and the usage of features from spectro-temporal analysis of single-trial responses. This further indicates that task-related CFC measurements can provide invaluable analytics in AD diagnosis and prognosis. PMID:26539070

  11. A novel biomarker of amnestic MCI based on dynamic cross-frequency coupling patterns during cognitive brain responses.

    PubMed

    Dimitriadis, Stavros I; Laskaris, Nikolaos A; Bitzidou, Malamati P; Tarnanas, Ioannis; Tsolaki, Magda N

    2015-01-01

    The detection of mild cognitive impairment (MCI), the transitional stage between normal cognitive changes of aging and the cognitive decline caused by AD, is of paramount clinical importance, since MCI patients are at increased risk of progressing into AD. Electroencephalographic (EEG) alterations in the spectral content of brainwaves and connectivity at resting state have been associated with early-stage AD. Recently, cognitive event-related potentials (ERPs) have entered into the picture as an easy to perform screening test. Motivated by the recent findings about the role of cross-frequency coupling (CFC) in cognition, we introduce a relevant methodological approach for detecting MCI based on cognitive responses from a standard auditory oddball paradigm. By using the single trial signals recorded at Pz sensor and comparing the responses to target and non-target stimuli, we first demonstrate that increased CFC is associated with the cognitive task. Then, considering the dynamic character of CFC, we identify instances during which the coupling between particular pairs of brainwave frequencies carries sufficient information for discriminating between normal subjects and patients with MCI. In this way, we form a multiparametric signature of impaired cognition. The new composite biomarker was tested using data from a cohort that consists of 25 amnestic MCI patients and 15 age-matched controls. Standard machine-learning algorithms were employed so as to implement the binary classification task. Based on leave-one-out cross-validation, the measured classification rate was found reaching very high levels (95%). Our approach compares favorably with the traditional alternative of using the morphology of averaged ERP response to make the diagnosis and the usage of features from spectro-temporal analysis of single-trial responses. This further indicates that task-related CFC measurements can provide invaluable analytics in AD diagnosis and prognosis. PMID:26539070

  12. Strengths-based cognitive-behavioural therapy: a four-step model to build resilience.

    PubMed

    Padesky, Christine A; Mooney, Kathleen A

    2012-01-01

    Padesky and Mooney's four-step Strengths-Based cognitive-behavioural therapy (CBT) model is designed to help clients build positive qualities. This article shows how it can be used to build and strengthen personal resilience. A structured search for client strengths is central to the approach, and methods designed to bring hidden strengths into client awareness are demonstrated through therapist-client dialogues. Development of positive qualities requires a shift in therapy perspective and different therapy methods from those employed when therapy is designed to ameliorate distress. Required adjustments to classic CBT are highlighted with specific recommendations for clinical modifications designed to support client development of resilience such as a focus on current strengths, the constructive use of imagery and client-generated metaphors. Although the focus of this article is on resilience, this Strengths-Based CBT model offers a template that also can be used to develop other positive human qualities. PMID:22653834

  13. APPLYING SPARSE CODING TO SURFACE MULTIVARIATE TENSOR-BASED MORPHOMETRY TO PREDICT FUTURE COGNITIVE DECLINE

    PubMed Central

    Zhang, Jie; Stonnington, Cynthia; Li, Qingyang; Shi, Jie; Bauer, Robert J.; Gutman, Boris A.; Chen, Kewei; Reiman, Eric M.; Thompson, Paul M.; Ye, Jieping; Wang, Yalin

    2016-01-01

    Alzheimer’s disease (AD) is a progressive brain disease. Accurate diagnosis of AD and its prodromal stage, mild cognitive impairment, is crucial for clinical trial design. There is also growing interests in identifying brain imaging biomarkers that help evaluate AD risk presymptomatically. Here, we applied a recently developed multivariate tensor-based morphometry (mTBM) method to extract features from hippocampal surfaces, derived from anatomical brain MRI. For such surface-based features, the feature dimension is usually much larger than the number of subjects. We used dictionary learning and sparse coding to effectively reduce the feature dimensions. With the new features, an Adaboost classifier was employed for binary group classification. In tests on publicly available data from the Alzheimers Disease Neuroimaging Initiative, the new framework outperformed several standard imaging measures in classifying different stages of AD. The new approach combines the efficiency of sparse coding with the sensitivity of surface mTBM, and boosts classification performance. PMID:27499829

  14. Family-based training program improves brain function, cognition, and behavior in lower socioeconomic status preschoolers

    PubMed Central

    Neville, Helen J.; Stevens, Courtney; Pakulak, Eric; Bell, Theodore A.; Fanning, Jessica; Klein, Scott; Isbell, Elif

    2013-01-01

    Using information from research on the neuroplasticity of selective attention and on the central role of successful parenting in child development, we developed and rigorously assessed a family-based training program designed to improve brain systems for selective attention in preschool children. One hundred forty-one lower socioeconomic status preschoolers enrolled in a Head Start program were randomly assigned to the training program, Head Start alone, or an active control group. Electrophysiological measures of children’s brain functions supporting selective attention, standardized measures of cognition, and parent-reported child behaviors all favored children in the treatment program relative to both control groups. Positive changes were also observed in the parents themselves. Effect sizes ranged from one-quarter to half of a standard deviation. These results lend impetus to the further development and broader implementation of evidence-based education programs that target at-risk families. PMID:23818591

  15. Effects of Smart-Tablet-Based Neurofeedback Training on Cognitive Function in Children with Attention Problems.

    PubMed

    Shin, Min-Sup; Jeon, Hyejin; Kim, Miyoung; Hwang, Taeho; Oh, Seo Jin; Hwangbo, Minsu; Kim, Ki Joong

    2016-05-01

    We sought to determine whether smart-tablet-based neurofeedback could improve executive function-including attention, working memory, and self-regulation-in children with attention problems. Forty children (10-12 years old) with attention problems, as determined by ratings on the Conners Parent Rating Scale, were assigned to either a neurofeedback group that received 16 sessions or a control group. A comprehensive test battery that assessed general intelligence, visual and auditory attention, attentional shifting, response inhibition and behavior rating scales were administered to both groups before neurofeedback training. Several neuropsychological tests were conducted at posttraining and follow-up assessment. Scores on several neuropsychological tests and parent behavior rating scales showed significant improvement in the training group but not in the controls. The improvements remained through the follow-up assessment. This study suggests that the smart-tablet-based neurofeedback training program might improve cognitive function in children with attention problems. PMID:26681772

  16. Dual-polarization multi-band OFDM versus single-carrier DP-QPSK for 100 Gb/s long-haul WDM transmission over legacy infrastructure.

    PubMed

    Karaki, J; Giacoumidis, E; Grot, D; Guillossou, T; Gosset, C; Le Bidan, R; Le Gall, T; Jaouën, Y; Pincemin, E

    2013-07-15

    The transmission performance of coherent dual-polarization multi-band OFDM (DP-MB-OFDM) and QPSK (DP-QPSK) are experimentally compared for 100 Gb/s long-haul transport over legacy infrastructure combining G.652 fiber and 10 Gb/s WDM system. It is shown that DP-MB-OFDM and DP-QPSK have nearly the same performance at 100 Gb/s after transmission over a 10 × 100-km fiber line. Furthermore, the origin of performance degradations and limitations of the DP-MB-OFDM is explored numerically, as well as the impact of transmission distance and sub-band spacing. PMID:23938547

  17. The Effect of Beck’s Cognitive Therapy and Mindfulness-Based Cognitive Therapy on Sociotropic and Autonomous Personality Styles in Patients With Depression

    PubMed Central

    Abolghasemi, Abbas; Gholami, Hossin; Narimani, Mohammad; Gamji, Masood

    2015-01-01

    Background: Depression is characterized by a great risk of relapse and recurrence. Mindfulness-based cognitive therapy (MBCT) and cognitive therapy are efficacious psychosocial interventions for recurrent depression. Objectives: The aim of the present research was to compare the effect of Beck’s cognitive therapy (BCT) and MBCT on reduction of depression and sociotropic and autonomous personality styles in Iranian depressed patients. Patients and Methods: The study sample consisted of 30 subjects randomly selected from patients with depression in Mashhad city, Iran. The subjects were assigned randomly to experimental groups. The 2 techniques used for treatment were BCT and MBCT. The data collection instruments used in the research consisted of psychological interview, the Beck Depression Inventory II and the revised Personal Style Inventory (RPSI). The research data was analyzed using repeated measures analysis of variance (ANOVA). Results: BCT and MBCT were effective in reducing depression, but BCT and MBCT did not cause any change in the sociotropic and autonomous personality styles in patients with depression. Conclusions: The results provide support for the role of BCT and MBCT plays in reducing depression. However, the results did not approve their role in changing sociotropic and autonomous personality styles in patients with depression. PMID:26834809

  18. Cognitive decline impairs financial and health literacy among community-based older persons without dementia

    PubMed Central

    Boyle, Patricia A.; Yu, Lei; Wilson, Robert S.; Segawa, Eisuke; Buchman, Aron S.; Bennett, David A.

    2013-01-01

    Literacy is an important determinant of health and well-being across the lifespan but is critical in aging, when many influential health and financial decisions are made. Prior studies suggest that older persons exhibit lower literacy than younger persons, particularly in the domains of financial and health literacy, but the reasons why remain unknown. The objectives of this study were to: a) examine pathways linking diverse resources (i.e., education, word knowledge, cognitive function, and decision making style) to health and financial literacy among older persons and determine the extent to which the relation of age with literacy represents a direct effect versus an indirect effect due to decrements in specific cognitive functions (i.e., executive functions and episodic memory), and b) test the hypothesis that declines in executive function and episodic memory are associated with lower literacy among older persons without dementia. 645 community-based older persons without dementia underwent detailed assessments of diverse resources, including education, word knowledge, cognitive function (i.e., executive function, episodic memory) and decision making style (i.e., risk aversion), and completed a measure of literacy that included items similar to those assessed in the Health and Retirement Study, such as numeracy, financial concepts such as compound inflation and knowledge of stocks and bonds, and important health concepts such as understanding of drug risk and Medicare Part D. Path analysis revealed a strong effect of age on literacy, with about half of the effect of age on literacy due to decrements in executive functions and episodic memory. In addition, executive function had an indirect effect on literacy via decision making style (i.e., risk aversion), and education and word knowledge had independent effects on literacy. Finally, among (n=447) persons with repeated cognitive assessments available for up to 14 years, regression analysis supported the

  19. Multiple Sclerosis: Changes in Thalamic Resting-State Functional Connectivity Induced by a Home-based Cognitive Rehabilitation Program.

    PubMed

    De Giglio, Laura; Tona, Francesca; De Luca, Francesca; Petsas, Nikolaos; Prosperini, Luca; Bianchi, Valentina; Pozzilli, Carlo; Pantano, Patrizia

    2016-07-01

    Purpose To investigate thalamic connectivity changes after use of a video game-based cognitive rehabilitation program, as thalamic damage and alterations in thalamocortical functional connectivity (FC) are important factors in cognitive dysfunction in patients with multiple sclerosis (MS). Materials and Methods This prospective study was approved by the local ethical committee. Twenty-four patients with MS and cognitive impairment were randomly assigned to either an intervention or a wait-list group. Patients were evaluated with cognitive tests and 3-T resting-state functional magnetic resonance (MR) imaging at baseline and after an 8-week period. In addition, 11 healthy subjects underwent baseline resting-state functional MR imaging. Patients in the intervention group performed the video game-based cognitive rehabilitation program, while those in the wait-list group served as control subjects. Repeated measures analysis of variance was used to test efficacy of the intervention. The thalamic resting-state network was identified with a seed-based method; both first-level and high-level analyses were performed by using software tools. Results Patients showed lower baseline FC compared with healthy subjects. A significant improvement was seen in results of the Paced Auditory Serial Addition Test and the Stroop Test after 8 weeks of cognitive rehabilitation (F = 6.616, [P = .018] and F = 5.325 [P = .030], respectively). At follow-up, the intervention group had an increased FC in the cingulum, precuneus, and bilateral parietal cortex and a lower FC in the cerebellum and in left prefrontal cortex compared with the wait-list group (P < .05, family-wise error corrected); correlations were found between FC changes in these regions and cognitive improvement (P < .05, family-wise error corrected). Conclusion The results of this study show the relevance of thalamic regulation of the brain networks involved in cognition and suggest that changes in thalamic resting-state network

  20. Effects of a social cognitive theory-based hip fracture prevention web site for older adults.

    PubMed

    Nahm, Eun-Shim; Barker, Bausell; Resnick, Barbara; Covington, Barbara; Magaziner, Jay; Brennan, Patricia Flatley

    2010-01-01

    The purposes of this study were to develop a Social Cognitive Theory-based, structured Hip Fracture Prevention Web site for older adults and conduct a preliminary evaluation of its effectiveness. The Theory-based, structured Hip Fracture Prevention Web site is composed of learning modules and a moderated discussion board. A total of 245 older adults recruited from two Web sites and a newspaper advertisement were randomized into the Theory-based, structured Hip Fracture Prevention Web site and the conventional Web sites groups. Outcomes included (1) knowledge (hip fractures and osteoporosis), (2) self-efficacy and outcome expectations, and (3) calcium intake and exercise and were assessed at baseline, end of treatment (2 weeks), and follow-up (3 months). Both groups showed significant improvement in most outcomes. For calcium intake, only the Theory-based, structured Hip Fracture Prevention Web site group showed improvement. None of the group and time interactions were significant. The Theory-based, structured Hip Fracture Prevention Web site group, however, was more satisfied with the intervention. The discussion board usage was significantly correlated with outcome gains. Despite several limitations, the findings showed some preliminary effectiveness of Web-based health interventions for older adults and the use of a Theory-based, structured Hip Fracture Prevention Web site as a sustainable Web structure for online health behavior change interventions. PMID:20978408