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.
Novel Spectrum Sensing Algorithms for OFDM Cognitive Radio Networks.
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
Novel Spectrum Sensing Algorithms for OFDM Cognitive Radio Networks
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
Derivation of GFDM Based on OFDM Principles
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.
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.
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.
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.
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.
Companding transform based SPM compensation in coherent optical OFDM transmission.
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
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.
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.
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.
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.
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.
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.
Channel estimation in DFT-based offset-QAM OFDM systems.
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
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.
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.
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.
Energy-efficient optical network units for OFDM PON based on time-domain interleaved OFDM technique.
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
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.
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.
Pilot-based blind phase estimation for coherent optical OFDM system.
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
Per-symbol-based digital back-propagation approach for PDM-CO-OFDM transmission systems.
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
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.
Hybrid time-frequency domain equalization for LED nonlinearity mitigation in OFDM-based VLC systems.
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
Evaluation of multiple-channel OFDM based airborne ultrasonic communications.
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
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.
Toward user mobility for OFDM-based visible light communications.
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
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
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.
All-optical virtual private network and ONUs communication in optical OFDM-based PON system.
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
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.
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.
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).
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.
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.
Sparsity-Based Space-Time Adaptive Processing Using OFDM Radar
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.
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.
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
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).
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.
Coherent optical OFDM: theory and design.
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
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.
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.
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.
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.
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.
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.
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
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.
On-the-field performance of quintuple-play long-reach OFDM-based WDM-PON optical access networks.
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
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.
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.
Optical single-sideband OFDM transmission based on a two-segment EAM.
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
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.
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%.
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
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.
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
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
Low-bit rate feedback strategies for iterative IA-precoded MIMO-OFDM-based systems.
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
Low-Bit Rate Feedback Strategies for Iterative IA-Precoded MIMO-OFDM-Based Systems
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
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
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.
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.
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.
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.
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.
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.
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
Investigation of PMD in direct-detection optical OFDM with zero padding.
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
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.
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.
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.
Variable length adjacent partitioning for PTS based PAPR reduction of OFDM signal
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.
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.
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).
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.
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
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.
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.
Reverse polarity optical-OFDM (RPO-OFDM): dimming compatible OFDM for gigabit VLC links.
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
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.
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
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.
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.
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
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.
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.
Fiber nonlinearity-induced penalty reduction in CO-OFDM by ANN-based nonlinear equalization.
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
Plant Based Extracts and Cognition
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.
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.
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
Banded all-optical OFDM super-channels with low-bandwidth receivers.
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
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.
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…
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…
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
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.
Polarization demultiplexing in stokes space for coherent optical PDM-OFDM.
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
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.
Power-efficient method for IM-DD optical transmission of multiple OFDM signals.
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
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.
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
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.
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.
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.
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
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
Fast dispersion estimation in coherent optical 16QAM fast OFDM systems.
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
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…
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
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.
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
Performance analysis of a finite radon transform in OFDM system under different channel models
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.
A P300-based cognitive assessment battery
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
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.
A collaborative knowledge base for cognitive phenomics
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
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
Energy-efficient WDM-OFDM-PON employing shared OFDM modulation modules in optical line terminal.
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
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
OFDM Radar Space-Time Adaptive Processing by Exploiting Spatio-Temporal Sparsity
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.
Direct-detection optical OFDM superchannel for long-reach PON using pilot regeneration.
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
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.
Dispersion tolerance enhancement using an improved offset-QAM OFDM scheme.
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
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
Physical-layer network coding in coherent optical OFDM systems.
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
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.
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.
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.
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.
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.
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.
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.
First demonstration of OFDM ECDMA for low cost optical access networks.
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
Faith-based cognitive behavioral therapy: easing depression in the elderly with cognitive decline.
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
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.
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
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…
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…
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…
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.
A novel ECDM-OFDM-PON architecture for next-generation optical access network.
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
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.
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…
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
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.
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
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.
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.
Phased-array cancellation of nonlinear FWM in coherent OFDM dispersive multi-span links.
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
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.
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
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…
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.
Comparisons of spectrally-enhanced asymmetrically-clipped optical OFDM systems.
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
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.
MAGELLAN: A cognitive map-based model of human wayfinding
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
MAGELLAN: a cognitive map-based model of human wayfinding.
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
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.
Cognitively automated assembly processes: a simulation based evaluation of performance.
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
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…
Coherent optical DFT-spread OFDM transmission using orthogonal band multiplexing.
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
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
Zero-guard-interval coherent optical OFDM with overlapped frequency-domain CD and PMD equalization.
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
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
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.
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.
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.
Joint robustness security in optical OFDM access system with Turbo-coded subcarrier rotation.
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
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.
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.
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…
Cognitive control predicts use of model-based reinforcement learning.
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
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…
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…
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…
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…
Effects of a computer-based cognitive exercise program on age-related cognitive decline.
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
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.
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.
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.
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.
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…
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…
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…
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.
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
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.
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.
Performance analysis of an all-optical OFDM system in presence of non-linear phase noise.
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
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…
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).…
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.
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.
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
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.
450-nm GaN laser diode enables high-speed visible light communication with 9-Gbps QAM-OFDM.
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
Sprint-based exercise and cognitive function in adolescents.
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
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
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.
Mindfulness-based cognitive therapy: theory and practice.
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
Evidence-based Assessment of Cognitive Functioning in Pediatric Psychology
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
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.
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
Internet-based cognitive behaviour therapy for depression and anxiety.
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
Mindfulness-based cognitive therapy for depression: trends and developments
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
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
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).
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.
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…
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…
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…
Novel television-based cognitive training improves working memory and executive function.
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
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
Sex-based memory advantages and cognitive aging: a challenge to the cognitive reserve construct?
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
Sex-Based Memory Advantages and Cognitive Aging: A Challenge to the Cognitive Reserve Construct?
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
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.
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.
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…
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.
[Mindfulness-based cognitive therapy : current status and future applications].
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
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.
Cognitive process-based subtypes of developmental coordination disorder (DCD).
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
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.
Clinical diagnosis support system based on case based fuzzy cognitive maps and semantic web.
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
Requirements of older adults for a daily use of an internet-based cognitive training platform.
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
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
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.
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.
Physical-enhanced secure strategy in an OFDM-PON.
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
Equation-Method for correcting clipping errors in OFDM signals.
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
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.
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
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.
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
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.
Blood Glucose, Diet-Based Glycemic Load and Cognitive Aging Among Dementia-Free Older Adults
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
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.
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
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.
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
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…
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…
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…
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.
Extended reach OFDM-PON using super-Nyquist image induced aliasing.
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
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…
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.