Science.gov

Sample records for fading nakagami channels

  1. Outage Capacity Analysis of TAS/MRC Systems over Arbitrary Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Hung, Chia-Chun; Chiang, Ching-Tai; Lin, Shyh-Neng; Wu, Rong-Ching

    A simple closed-form approximation for the outage capacity of Transmit Antenna Selection/Maximal-Ratio Combining (TAS/MRC) systems over independent and identically distributed (i.i.d) Nakagami-m fading channels is derived while the fading index is a positive integer. When the Nakagami-m fading index is not an integer, the approximate outage capacity is derived as a single infinite series of Gamma function. Computer simulations verify the accuracy of the approximate results.

  2. A subspace-based parameter estimation algorithm for Nakagami-m fading channels

    NASA Astrophysics Data System (ADS)

    Dianat, Sohail; Rao, Raghuveer

    2010-04-01

    Estimation of channel fading parameters is an important task in the design of communication links such as maximum ratio combining (MRC). The MRC weights are directly related to the fading channel coefficients. In this paper, we propose a subspace based parameter estimation algorithm for the estimation of the parameters of Nakagami-m fading channels in the presence of additive white Gaussian noise. Comparisons of our proposed approach are made with other techniques available in the literature. The performance of the algorithm with respect to the Cramer-Rao bound (CRB) is investigated. Computer simulation results for different signal to noise ratios (SNR) are presented.

  3. Performance Analysis of OFDM in Frequency Selective, Slowly Fading Nakagami Channels

    DTIC Science & Technology

    2001-12-01

    Rayleigh is a special case of the Nakagami - m distribution. 3...35 This is why we consider the Rayleigh distribution to be a special case of the Nakagami PDF. In Figure 11 the Nakagami - m PDF is illustrated...obtain ( )4 1 3 1 b b M qP Q Mq M γ−   =   −  (3.29) 44 Once again, to obtain the BER in Nakagami fading, we must average the

  4. Performance Analysis of a JTIDS/Link-16-type Waveform Transmitted over Slow, Flat Nakagami Fading Channels in the Presence of Narrowband Interference

    DTIC Science & Technology

    2008-12-01

    L-branch maximal-ratio combining with Rayleigh -fading signals, the resulting signal is Nakagami with m L= . It can be shown that when diversity L is...used and the channel is modeled as a Nakagami - m fading channel, the performance is identical to that obtained for a Rayleigh fading channel with...when 1m = the Nakagami - m pdf corresponds to the Rayleigh pdf since ( )1 !n nΓ + = . Generally speaking, for 1m < , the fading is more severe than

  5. Performance Analysis of Amplify-and-Forward Relaying over Shadowed Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Cai, Chunxiao; Cai, Yueming; Yang, Weiwei

    2011-11-01

    In the paper, the closed-form approximation for outage probability and symbol error probability are presented for amplify-and-forward cooperative network over shadowed Nakagami-m Fading Channels. Our results are verified through comparison with Monte Carlo simulations. It shows that our theoretical results can provide good approximations to the numerical results.

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

    NASA Astrophysics Data System (ADS)

    Ahmad Ansari, Ejaz; Rajatheva, Nandana

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

  7. Outage Probability of Interference-limited Switch and Stay Diversity System over Gamma Shadowed Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Djordjevic, Goran T.; Antic, Dragan

    2013-12-01

    In this paper, the outage performance of a dual-branch switch and stay combining (SSC) diversity receiver operating over composite multipath Nakagami-m fading/gamma shadowing channels in the presence of a co-channel interference is determined. For a single channel composite fading environment, we derive the new analytical expressions for the probability density function and cumulative distribution function of the instantaneous signal-to-interference (SIR) ratio that can be used as alternatives to the previously published results. In the case of non-identically distributed and power unbalanced SSC branches with arbitrary fading parameters, the outage performance is determined. The choice of optimal switching threshold in minimum outage probability sense is discussed. The results show the outage probability dependence on simultaneous effects of the SIR unbalancing, as well as multipath fading and shadowing severities. The analytical results are confirmed by Monte Carlo simulations.

  8. Accurate Bit-Error Rate Evaluation for TH-PPM Systems in Nakagami Fading Channels Using Moment Generating Functions

    NASA Astrophysics Data System (ADS)

    Liang, Bin; Gunawan, Erry; Law, Choi Look; Teh, Kah Chan

    Analytical expressions based on the Gauss-Chebyshev quadrature (GCQ) rule technique are derived to evaluate the bit-error rate (BER) for the time-hopping pulse position modulation (TH-PPM) ultra-wide band (UWB) systems under a Nakagami-m fading channel. The analyses are validated by the simulation results and adopted to assess the accuracy of the commonly used Gaussian approximation (GA) method. The influence of the fading severity on the BER performance of TH-PPM UWB system is investigated.

  9. Outage Performance of Cooperative Relay Selection with Multiple Source and Destination Antennas over Dissimilar Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Lee, Wooju; Yoon, Dongweon

    Cooperative relay selection, in which one of multiple relays is selected to retransmit the source signal to the destination, has received considerable attention in recent years, because it is a simple way to obtain cooperative diversity in wireless networks. The exact expression of outage probability for a decode-and-forward cooperative relay selection with multiple source and destination antennas over Rayleigh fading channels was recently derived in [9]. In this letter, we derive the exact expressions of outage probability and diversity-multiplexing tradeoff over independent and non-identically distributed Nakagami-m fading channels as an extension of [9]. We then analyze the effects of various parameters such as fading conditions, number of relays, and number of source and destination antennas on the outage probability.

  10. Performance Analysis of Error Probabilities for Arbitrary 2-D Signaling with I/Q Unbalances over Nakagami-m Fading Channels

    NASA Astrophysics Data System (ADS)

    Lee, Jaeyoon; Yoon, Dongweon; Park, Sang Kyu

    Recently, we provided closed-form expressions involving two-dimensional (2-D) joint Gaussian Q-function for the symbol error rate (SER) and bit error rate (BER) of an arbitrary 2-D signal with I/Q unbalances over an additive white Gaussian noise (AWGN) channel [1]. In this letter, we extend the expressions to Nakagami-m fading channels. Using Craig representation of the 2-D joint Gaussian Q-function, we derive an exact and general expression for the error probabilities of arbitrary 2-D signaling with I/Q phase and amplitude unbalances over Nakagami-m fading channels.

  11. Parallel Decentralized Network for the Detection of Unknown Signals Through Wireless Nakagami Fading Channels

    NASA Astrophysics Data System (ADS)

    El-Bahaie, Ebtehal H.; Al-Hussaini, Emad K.

    2010-12-01

    In this paper analytical and simulation results for the decentralized detection of unknown signals are introduced. Parallel sensor network scheme is assumed. Additive White Gaussian Noise (AWGN) and Nakagami fading are assumed in both links, that is, from the source to the decentralized local sensors and from the sensors to the fusion center. Furthermore, diversity employing Square Law Combining (SLC) or Square Law Selection (SLS) is considered at each sensor, for both independent and correlated branches. Appreciable improvements are obtained with the increase of the number of sensors and the diversity employment.

  12. Analytic Nakagami fading parameter estimation in dependent noise channel using copula

    NASA Astrophysics Data System (ADS)

    Gholizadeh, Mohammad Hossein; Amindavar, Hamidreza; Ritcey, James A.

    2013-12-01

    In this paper, the probability density function (PDF) estimation is introduced in the framework of estimating the Nakagami fading parameter. This approach provides an analytic procedure for finding the fading parameter. Using the copula theory, an accurate PDF estimate is obtained even when the desired signal is corrupted in a noisy environment. In the real world, the noise samples could be highly dependent on the main signal. Copula-based models are a general set of statistical models defined for any multivariate random variable. Thus, they depict the statistical behavior of a received signal including two dependent terms, representative of the desired signal and noise. Previous works in the Nakagami parameter determination have mainly examined estimation based on either a noiseless sample model or an independent trivial noisy one. In this paper, we consider a more comprehensive situation about the noise destruction and our investigation is done in low signal-to-noise ratios. The parametric bootstrap method approves the accuracy of the analytically estimated PDF, and simulation results show that the new estimator has superior performance over conventional estimators.

  13. Average Fade Duration of Dual Selection Diversity over Correlated Unbalanced Nakagami-m Fading Channels in the Presence of Cochannel Interference

    NASA Astrophysics Data System (ADS)

    Panajotović, Aleksandra; Sekulović, Nikola; Drača, Dragan; Stefanović, Mihajlo; Stefanović, Časlav

    2013-12-01

    A dual selection combining (SC) receiver with correlated and unbalanced diversity branches operating in interference-limited Nakagami-m fading environment is considered in this paper. Actually, average fade duration (AFD) of SC system applying desired signal decision algorithm is obtained. Numerical results can be used to examine the effects of fading severity, input signal-to-interference ratio (SIR) unbalance and level of branch correlation on the AFD, as well as the correctness of proposed analytical formulation.

  14. Moments Of Microdiversity EGC Receivers And Macrodiversity SC Receiver Output Signal Over Gamma Shadowed Nakagami-m Multipath Fading Channel

    NASA Astrophysics Data System (ADS)

    Djordjević, Nebojša; Jaksić, Branimir S.; Matović, Ana; Matović, Marija; Smilić, Marko

    2015-11-01

    A system with macrodiversity selection combining (SC) receiver and for microdiversity equal gain combining (EGC) receivers is considered. Received signal is subjected, simultaneously to multipath fading and shadowing, resulting in signal envelope and signal power variation. Closed form expressions for moments of macrodiversity SC receiver output signal envelope are calculated. Numerical expressions are plotted to present the influences of Gamma shadowing severity and Nakagami-m severity on moments of proposed system output signal.

  15. Performance of a space-time block coded code division multiple access system over Nakagami-m fading channels

    NASA Astrophysics Data System (ADS)

    Yu, Xiangbin; Dong, Tao; Xu, Dazhuan; Bi, Guangguo

    2010-09-01

    By introducing an orthogonal space-time coding scheme, multiuser code division multiple access (CDMA) systems with different space time codes are given, and corresponding system performance is investigated over a Nakagami-m fading channel. A low-complexity multiuser receiver scheme is developed for space-time block coded CDMA (STBC-CDMA) systems. The scheme can make full use of the complex orthogonality of space-time block coding to simplify the high decoding complexity of the existing scheme. Compared to the existing scheme with exponential decoding complexity, it has linear decoding complexity. Based on the performance analysis and mathematical calculation, the average bit error rate (BER) of the system is derived in detail for integer m and non-integer m, respectively. As a result, a tight closed-form BER expression is obtained for STBC-CDMA with an orthogonal spreading code, and an approximate closed-form BER expression is attained for STBC-CDMA with a quasi-orthogonal spreading code. Simulation results show that the proposed scheme can achieve almost the same performance as the existing scheme with low complexity. Moreover, the simulation results for average BER are consistent with the theoretical analysis.

  16. A Reliability Study of RFID Technology in a Fading Channel

    DTIC Science & Technology

    2007-06-01

    systems. Bit and tag error probabilities are computed for various OOK and M-CSK modulation schemes in a varying Nakagami - m fading channel, and the best...performing schemes are identified for future employment. 15. NUMBER OF PAGES 69 14. SUBJECT TERMS RFID, Fading Channel, Nakagami , On-off...and tag error probabilities are computed for various OOK and M-CSK modulation schemes in a varying Nakagami - m fading channel, and the best performing

  17. Optimal Power Allocation for CC-HARQ-based Cognitive Radio with Statistical CSI in Nakagami Slow Fading Channels

    NASA Astrophysics Data System (ADS)

    Xu, Ding; Li, Qun

    2017-01-01

    This paper addresses the power allocation problem for cognitive radio (CR) based on hybrid-automatic-repeat-request (HARQ) with chase combining (CC) in Nakagamimslow fading channels. We assume that, instead of the perfect instantaneous channel state information (CSI), only the statistical CSI is available at the secondary user (SU) transmitter. The aim is to minimize the SU outage probability under the primary user (PU) interference outage constraint. Using the Lagrange multiplier method, an iterative and recursive algorithm is derived to obtain the optimal power allocation for each transmission round. Extensive numerical results are presented to illustrate the performance of the proposed algorithm.

  18. Reliability of a jammed binary transmission over a Nakagami channel

    NASA Astrophysics Data System (ADS)

    Zenon, Syroka

    2014-05-01

    This study presents a mathematic and numerical analysis of the probability of error in a binary transmission over a fading radio channel described by Nakagami-m distribution and its special cases. The transmission is jammed by a signal occupying the entire (or comparable) band before detection.

  19. Distortion outage minimization in Nakagami fading using limited feedback

    NASA Astrophysics Data System (ADS)

    Wang, Chih-Hong; Dey, Subhrakanti

    2011-12-01

    We focus on a decentralized estimation problem via a clustered wireless sensor network measuring a random Gaussian source where the clusterheads amplify and forward their received signals (from the intra-cluster sensors) over orthogonal independent stationary Nakagami fading channels to a remote fusion center that reconstructs an estimate of the original source. The objective of this paper is to design clusterhead transmit power allocation policies to minimize the distortion outage probability at the fusion center, subject to an expected sum transmit power constraint. In the case when full channel state information (CSI) is available at the clusterhead transmitters, the optimization problem can be shown to be convex and is solved exactly. When only rate-limited channel feedback is available, we design a number of computationally efficient sub-optimal power allocation algorithms to solve the associated non-convex optimization problem. We also derive an approximation for the diversity order of the distortion outage probability in the limit when the average transmission power goes to infinity. Numerical results illustrate that the sub-optimal power allocation algorithms perform very well and can close the outage probability gap between the constant power allocation (no CSI) and full CSI-based optimal power allocation with only 3-4 bits of channel feedback.

  20. Outage Probability of SINR for Underlay Cognitive Radio Systems in Nakagami Fading

    NASA Astrophysics Data System (ADS)

    Jarrouj, Jiana; Blagojevic, Vesna; Ivanis, Predrag

    2014-11-01

    In this paper underlay cognitive radio system is analyzed in Nakagami fading environment, for the case when the available channel state information (CSI) of the link from the secondary transmitter to the primary receiver is outdated. We considered the case when both interference and transmit power constraints are applied. The impact of the co-channel interference that originates from the primary user is analyzed in details. The exact closed-form expressions for probability density function, outage probability, and the moments of signal-to-interference and noise ratio (SINR) at the secondary user's receiver are derived. The analytical expressions are verified by using independent Monte Carlo simulation method.

  1. An Alternative Method to Compute the Bit Error Probability of Modulation Schemes Subject to Nakagami-[InlineEquation not available: see fulltext.] Fading

    NASA Astrophysics Data System (ADS)

    Queiroz, Wamberto J. L.; Lopes, Waslon T. A.; Madeiro, Francisco; Alencar, Marcelo S.

    2010-12-01

    This paper presents an alternative method for determining exact expressions for the bit error probability (BEP) of modulation schemes subject to Nakagami-[InlineEquation not available: see fulltext.] fading. In this method, the Nakagami-[InlineEquation not available: see fulltext.] fading channel is seen as an additive noise channel whose noise is modeled as the ratio between Gaussian and Nakagami-[InlineEquation not available: see fulltext.] random variables. The method consists of using the cumulative density function of the resulting noise to obtain closed-form expressions for the BEP of modulation schemes subject to Nakagami-[InlineEquation not available: see fulltext.] fading. In particular, the proposed method is used to obtain closed-form expressions for the BEP of [InlineEquation not available: see fulltext.]-ary quadrature amplitude modulation ([InlineEquation not available: see fulltext.]-QAM), [InlineEquation not available: see fulltext.]-ary pulse amplitude modulation ([InlineEquation not available: see fulltext.]-PAM), and rectangular quadrature amplitude modulation ([InlineEquation not available: see fulltext.]-QAM) under Nakagami-[InlineEquation not available: see fulltext.] fading. The main contribution of this paper is to show that this alternative method can be used to reduce the computational complexity for detecting signals in the presence of fading.

  2. ARQ on fading channels

    NASA Astrophysics Data System (ADS)

    Beirouti, Patrick; Leib, Harry; Morgera, Salvatore D.

    A recursive procedure for obtaining a (2 to the power n)-state extended Gilbert-Elliott fading channel model suitable for n-bit block codes is described. The extended model may be used for numerical assessment of the throughput of a variety of popular automatic repeat-request schemes used over fading channels such as those encountered in mobile communications systems. Computationally efficient lower and upper performance bounds are also developed for low memory fading channels. It is found that the throughput of the stop-and-wait protocol exhibits a maximum; therefore, there exists an optimum codeword length for this automatic repeat-request scheme.

  3. Performance Analysis of Beamforming in Fixed-gain AF Relay Networks with Asymmetric Correlated Fading Channels

    NASA Astrophysics Data System (ADS)

    Li, Min

    2014-07-01

    In this paper, the performance of beamforming (BF) for a dual-hop amplify-and-forward (AF) relay network, where the source and destination are each equipped with multiple antennas, is investigated. It is assumed that the source-relay and relay-destination channels experience mixed fading distributions, namely, correlated Nakagami-m/Rician and correlated Rician/Nakagami-m, respectively. By considering fixed-gain relaying, analytical expressions for outage probability (OP) and average symbol error rate (ASER) are derived in closed-form. Numerical results are presented to demonstrate the efficacy of our performance analysis, also illustrate the impact of channel correlation, fading severity, Rician factor and antenna configuration on the performance of the system. It is shown that the correlated Nakagami-m/Rician fading channel can achieve better performance than the correlated Rician/Nakagami-m fading channel with the increase of fading severity parameter, and the correlated Rician/Nakagami-m fading channel may outperform the correlated Nakagami-m/Rician fading channel by enlarging the Rician factor.

  4. Fading channel simulator

    SciTech Connect

    Argo, P.E.; Fitzgerald, T.J.

    1991-12-31

    This invention relates to high frequency (HF) radio signal propagation through fading channels and, more particularly, to simulation of fading channels in order to characterize HF radio system performance in transmitting and receiving signals through such fading channels. Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

  5. Error Probability of MRC in Frequency Selective Nakagami Fading in the Presence of CCI and ACI

    NASA Astrophysics Data System (ADS)

    Rahman, Mohammad Azizur; Sum, Chin-Sean; Funada, Ryuhei; Sasaki, Shigenobu; Baykas, Tuncer; Wang, Junyi; Harada, Hiroshi; Kato, Shuzo

    An exact expression of error rate is developed for maximal ratio combining (MRC) in an independent but not necessarily identically distributed frequency selective Nakagami fading channel taking into account inter-symbol, co-channel and adjacent channel interferences (ISI, CCI and ACI respectively). The characteristic function (CF) method is adopted. While accurate analysis of MRC performance cannot be seen in frequency selective channel taking ISI (and CCI) into account, such analysis for ACI has not been addressed yet. The general analysis presented in this paper solves a problem of past and present interest, which has so far been studied either approximately or in simulations. The exact method presented also lets us obtain an approximate error rate expression based on Gaussian approximation (GA) of the interferences. It is shown, especially while the channel is lightly faded, has fewer multipath components and a decaying delay profile, the GA may be substantially inaccurate at high signal-to-noise ratio. However, the exact results also reveal an important finding that there is a range of parameters where the simpler GA is reasonably accurate and hence, we don't have to go for more involved exact expression.

  6. Outage Analysis of Dual-hop Cognitive Networks with Relay Selection over Nakagami-m Fading Environment

    NASA Astrophysics Data System (ADS)

    Zhang, Zongsheng; Pi, Xurong

    2014-09-01

    In this paper, we investigate the outage performance of decode-and-forward cognitive relay networks for Nakagami-m fading channels, with considering both best relay selection and interference constraints. Focusing on the relay selection and making use of the underlay cognitive approach, an exact closed-form outage probability expression is derived in an independent, non-identical distributed Nakagami-m environment. The closed-form outage probability provides an efficient means to evaluate the effects of the maximum allowable interference power, number of cognitive relays, and channel conditions between the primary user and cognitive users. Finally, we present numerical results to validate the theory analysis. Moreover, from the simulation results, we obtain that the system can obtain the full diversity.

  7. Fading channel simulator

    DOEpatents

    Argo, Paul E.; Fitzgerald, T. Joseph

    1993-01-01

    Fading channel effects on a transmitted communication signal are simulated with both frequency and time variations using a channel scattering function to affect the transmitted signal. A conventional channel scattering function is converted to a series of channel realizations by multiplying the square root of the channel scattering function by a complex number of which the real and imaginary parts are each independent variables. The two-dimensional inverse-FFT of this complex-valued channel realization yields a matrix of channel coefficients that provide a complete frequency-time description of the channel. The transmitted radio signal is segmented to provide a series of transmitted signal and each segment is subject to FFT to generate a series of signal coefficient matrices. The channel coefficient matrices and signal coefficient matrices are then multiplied and subjected to inverse-FFT to output a signal representing the received affected radio signal. A variety of channel scattering functions can be used to characterize the response of a transmitter-receiver system to such atmospheric effects.

  8. Performance of the IEEE 802.11a Wireless Lan Standard Over Frequency-Selective, Slow, Ricean Fading Channels

    DTIC Science & Technology

    2002-09-01

    modeled as a random variable. Typical models are the Rayleigh , Ricean, and Nakagami - m distributions. In this thesis, two widely used models for...and [2], frequency-selective, Rayleigh fading channels [3], and frequency-selective, slow, Nakagami channels [4]. Unlike the above referenced work...signal component where i qM M M = × ; therefore, the probability of symbol error for rectangular QAM can be expressed as ( )error on error on . i q i

  9. A Simple Exact Error Rate Analysis for DS-CDMA with Arbitrary Pulse Shape in Flat Nakagami Fading

    NASA Astrophysics Data System (ADS)

    Rahman, Mohammad Azizur; Sasaki, Shigenobu; Kikuchi, Hisakazu; Harada, Hiroshi; Kato, Shuzo

    A simple exact error rate analysis is presented for random binary direct sequence code division multiple access (DS-CDMA) considering a general pulse shape and flat Nakagami fading channel. First of all, a simple model is developed for the multiple access interference (MAI). Based on this, a simple exact expression of the characteristic function (CF) of MAI is developed in a straight forward manner. Finally, an exact expression of error rate is obtained following the CF method of error rate analysis. The exact error rate so obtained can be much easily evaluated as compared to the only reliable approximate error rate expression currently available, which is based on the Improved Gaussian Approximation (IGA).

  10. On Statistics of Log-Ratio of Arithmetic Mean to Geometric Mean for Nakagami-m Fading Power

    NASA Astrophysics Data System (ADS)

    Wang, Ning; Cheng, Julian; Tellambura, Chintha

    To assess the performance of maximum-likelihood (ML) based Nakagami m parameter estimators, current methods rely on Monte Carlo simulation. In order to enable the analytical performance evaluation of ML-based m parameter estimators, we study the statistical properties of a parameter Δ, which is defined as the log-ratio of the arithmetic mean to the geometric mean for Nakagami-m fading power. Closed-form expressions are derived for the probability density function (PDF) of Δ. It is found that for large sample size, the PDF of Δ can be well approximated by a two-parameter Gamma PDF.

  11. OFDM Transmission Characteristics where the Delay Profile Exceeds the Guard Interval in Nakagami-Rice Fading Environment

    NASA Astrophysics Data System (ADS)

    Karasawa, Yoshio; Vanmany, Changarkame

    In order to evaluate the effect of Nakagami-Rice fading on Orthogonal Frequency Division Multiplex (OFDM) signal transmission when the delay profile exceeds the guard interval, a simple prediction model is developed by extending the Equivalent Transmission-Path (ETP) model for Rayleigh fading. The validity of the model is demonstrated by comparing the calculated values of BER to those obtained by computer simulation. Using the newly developed ETP-OFDM model, digital transmission characteristics of the OFDM signal in a multipath environment when the delay profile exceeds the guard interval are shown as a function of K factor, delay spread, guard interval and OFDM symbol period.

  12. Performance Analysis of IEEE 802.11g Waveform Transmitted Over a Fading Channel with Pulse-Noise Interference

    DTIC Science & Technology

    2006-06-01

    subchannel and (b) an OFDM signal......................7 Figure 3. The Nakagami - m PDF...diffractions, and scattering processes and, at the same time, achieve high data rates. The Nakagami - m distribution was used to model different fading...is the Nakagami distribution, where the amplitude of the received signal cα is modeled as a Nakagami - m random variable. 11 The probability

  13. Comparasion of Energy Detection in Cognitive Radio over different fading channels

    NASA Astrophysics Data System (ADS)

    Buttar, Simar

    2012-07-01

    With the advance of wireless communications, the problem of bandwidth scarcity has become more prominent. Cognitive radio technology has come out as a way to solve this problem by allowing the unlicensed users to use the licensed bands opportunistically. To sense the existence of licensed users, many spectrum sensing techniques have been devised. In this paper, energy detection and cyclic prefix is used for spectrum sensing.The comparison of ROC curves has been done for various wireless fading channels using squaring and cubingoperation,the improvement has gone as high as up to 0.6 times for AWGN channel and 0.4 times for Rayleigh channel as we go from squaring to cubing operation in an energy detector. Closed form expressions for Probability of detection for AWGN and Rayleigh channels are described.Nakagami fading channel shows worst results .

  14. Hardware Emulation of Wireless Communication Fading Channels

    DTIC Science & Technology

    2011-01-01

    vol. 19, no. 6 , pp. 1009-1018, Jun. 2001. [9] B. E. Baddour and N. C. Beaulieu, “Accurate simulation of multiple cross- correlated Rician fading...Rayleigh fading waveforms,” IEEE Trans. Commun., vol. 6 , no. 6 , pp. 256-258, Nov. 2002. [18] Y. R. Zheng and C. Xiao, “ Simulation models with correct...waveforms in the baseband equivalent channel due to the bandlimited nature of wireless systems [ 6 ]. Software-based channel simulators usually employ

  15. On the performance analysis of SSC diversity system over η-μ fading channels

    NASA Astrophysics Data System (ADS)

    Khatalin, Sari

    2016-06-01

    In this paper, we study key performance measures of dual-branch switch-and-stay combining (SSC) system operating in ? fading environment. Specifically, analytical expressions for the kth order moment, average signal-to-noise ratio, amount of fading and outage probability are obtained for an SSC system operating over ? fading channels. Expressions of the average bit error rate (BER) for coherent detection and non-coherent detection were also derived with SSC for various modulation schemes. The BER expressions for the coherent detection case were derived using the moment generating function-based approach. Some of the final expressions are presented in the form of infinite series. Therefore, those series are truncated and upper bounds are derived for truncation errors. Expressions to determine the optimum adaptive switching thresholds are also presented. Corresponding results for Nakagami-q and Nakagami-m fading are derived in this paper as special cases. Numerical results are provided to demonstrate the applications of the new results.

  16. Bit Error Rate Performance of Partially Coherent Dual-Branch SSC Receiver over Composite Fading Channels

    NASA Astrophysics Data System (ADS)

    Milić, Dejan N.; Đorđević, Goran T.

    2013-01-01

    In this paper, we study the effects of imperfect reference signal recovery on the bit error rate (BER) performance of dual-branch switch and stay combining receiver over Nakagami-m fading/gamma shadowing channels with arbitrary parameters. The average BER of quaternary phase shift keying is evaluated under the assumption that the reference carrier signal is extracted from the received modulated signal. We compute numerical results illustrating simultaneous influence of average signal-to-noise ratio per bit, fading severity, shadowing, phase-locked loop bandwidth-bit duration (BLTb) product, and switching threshold on BER performance. The effects of BLTb on receiver performance under different channel conditions are emphasized. Optimal switching threshold is determined which minimizes BER performance under given channel and receiver parameters.

  17. Consensus Algorithms Over Fading Channels

    DTIC Science & Technology

    2010-10-01

    studying the effect of fading and collisions on the performance of wireless consensus gossiping and in comparing its cost (measured in terms of number of...not assumed to be symmetric under A2. III. RELATED WORK There has been a resurgence of interest in characterizing consen- sus and gossip algorithms...tree, and then distribute the consensus value, with a finite number of exchanges. The price paid is clearly that of finding the appropriate routing

  18. Detection performance of cooperative spectrum sensing with hard decision fusion in fading channels

    NASA Astrophysics Data System (ADS)

    Nallagonda, S.; Chandra, A.; Roy, S. D.; Kundu, S.; Kukolev, P.; Prokes, A.

    2016-02-01

    In this paper, we investigate the detection performance of cooperative spectrum sensing (CSS) using energy detector in several fading scenarios. The fading environments comprise relatively less-studied Hoyt and Weibull channels in addition to the conventional Rayleigh, Rician, Nakagami-m and log-normal shadowing channels. We have presented an analytical framework for evaluating different probabilities related to spectrum sensing, i.e. missed detection, false alarm and total error due to both of them, for all the fading/shadowing models mentioned. The major theoretical contribution is, however, the derivation of closed-form expressions for probability of detection. Based on our developed framework, we present performance results of CSS under various hard decision fusion strategies such as OR rule, AND rule and Majority rule. Effects of sensing channel signal-to-noise ratio, detection threshold, fusion rules, number of cooperating cognitive radios (CRs) and fading/shadowing parameters on the sensing performance have been illustrated. The performance improvement achieved with CSS over a single CR-based sensing is depicted in terms of total error probability. Further, an optimal threshold that minimises total error probability has been indicated for all the fading/shadowing channels.

  19. Performance Analysis of IEEE 802.11g TCM Waveforms Transmitted over a Channel with Pulse-Noise Interference

    DTIC Science & Technology

    2007-06-01

    are less or more severe than the Rayleigh model since, for m =1, the Nakagami PDF is a Rayleigh PDF. For small m (1/ 2 1) m , fading is very severe...flat, slowly fading Nakagami channel with m =1/2 in AWGN. ................................................... 36 Figure 19. Magnified performance of 8...PSK and r=2/3 convolutionally encoded bits with HDD for different numbers of memory elements and a flat, slowly fading Nakagami channel with m =1/2

  20. Wireless Fading Channel Models: From Classical to Stochastic Differential Equations

    SciTech Connect

    Olama, Mohammed M; Djouadi, Seddik M; Charalambous, Prof. Charalambos

    2010-01-01

    expanded to three-dimensions (3D) by Aulin. An indoor STF was introduced. Most of these STF models provide information on the frequency response of the channel, described by the Doppler power spectral density (DPSD). Aulin presented a methodology to find the Doppler power spectrum by computing the Fourier transform of the autocorrelation function of the channel impulse response with respect to time. A different approach, leading to the same Doppler power spectrum relation was presented by Gans. These STF models suggest various distributions for the received signal amplitude such as Rayleigh, Rician, or Nakagami. Models based on autoregressive and moving averages (AR) are proposed. However, these models assume that the channel state is completely observable, which in reality is not the case due to additive noise, and requires long observation intervals. First order Markov models for Raleigh fading have been proposed, and the usefulness of a finite-state Markov channel model is argued. Mobile-to-mobile (or ad hoc) wireless networks comprise nodes that freely and dynamically self-organize into arbitrary and/or temporary network topology without any fixed infrastructure support. They require direct communication between a mobile transmitter and a mobile receiver over a wireless medium. Such mobile-to-mobile communication systems differ from the conventional cellular systems, where one terminal, the base station, is stationary, and only the mobile station is moving. As a consequence, the statistical properties of mobile-to-mobile links are different from cellular ones. Copious ad hoc networking research exists on layers in the open system interconnection (OSI) model above the physical layer. However, neglecting the physical layer while modeling wireless environment is error prone and should be considered more carefully. The experimental results show that the factors at the physical layer not only affect the absolute performance of a protocol, but because their impact on

  1. Digital Communications Over Non-Fading and Fading Channels

    DTIC Science & Technology

    2008-09-01

    quality of the demodulated bits entering the channel decoder as shown in Figure 1. Figure 1. Information bit...error and channel bit error relationship [4]. The probability of channel bit error, prior to the channel decoder , directly impacts the output...systems with convolutional coding and hard decision decoding for various commonly used code rates, the relationship between information bit error bP

  2. Performance of adaptive matched filter receivers over fading multipath channels

    NASA Astrophysics Data System (ADS)

    Pahlavan, Kaveh; Matthews, James W.

    1990-12-01

    A unified discrete channel model from the information source up to the sampler was developed for fading multipath channels. Different methods for adaptive channel measurement are studied. The performance of a discrete matched filter using different adaptation techniques and working over a troposcatter channel is predicted. It is shown that the effects of channel measurement noise are less damaging for the decision-directed adaptation technique as compared to any kind of reference-directed adaptation.

  3. Performance Characterization of a Hybrid Satellite-Terrestrial System with Co-Channel Interference over Generalized Fading Channels

    PubMed Central

    Javed, Umer; He, Di; Liu, Peilin

    2016-01-01

    The transmission of signals in a hybrid satellite-terrestrial system (HSTS) in the presence of co-channel interference (CCI) is considered in this study. Specifically, we examine the problem of amplify-and-forward (AF)-based relaying in a hybrid satellite-terrestrial link, where the relay node is operating in the presence of a dominant co-channel interferer. It is assumed that direct connection between a source node (satellite) and a destination node (terrestrial receiver) is not available due to masking by obstacles in the surrounding. The destination node is only able to receive signals from the satellite with the help of a relay node located at the ground. In the proposed HSTS, the satellite-relay channel follows the shadowed Rice fading; and the channels of interferer-relay and relay-destination links experience generalized Nakagami-m fading. For the considered AF-based HSTS, we first develop the analytical expression for the moment generating function (MGF) of the overall output signal-to-interference-plus-noise ratio (SINR). Then, based on the derived exact MGF, we derive novel expressions for the average symbol error rate (SER) of the considered HSTS for the following digital modulation techniques: M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM) and M-ary pulse amplitude modulation (M-PAM). To significantly reduce the computational complexity for utility in system-level simulations, simple analytical approximation for the exact SER in the high signal-to-noise ratio (SNR) regime is presented to provide key insights. Finally, numerical results and the corresponding analysis are presented to demonstrate the effectiveness of the developed performance evaluation framework and to view the impact of CCI on the considered HSTS under varying channel conditions and with different modulation schemes. PMID:27527182

  4. Performance Characterization of a Hybrid Satellite-Terrestrial System with Co-Channel Interference over Generalized Fading Channels.

    PubMed

    Javed, Umer; He, Di; Liu, Peilin

    2016-08-05

    The transmission of signals in a hybrid satellite-terrestrial system (HSTS) in the presence of co-channel interference (CCI) is considered in this study. Specifically, we examine the problem of amplify-and-forward (AF)-based relaying in a hybrid satellite-terrestrial link, where the relay node is operating in the presence of a dominant co-channel interferer. It is assumed that direct connection between a source node (satellite) and a destination node (terrestrial receiver) is not available due to masking by obstacles in the surrounding. The destination node is only able to receive signals from the satellite with the help of a relay node located at the ground. In the proposed HSTS, the satellite-relay channel follows the shadowed Rice fading; and the channels of interferer-relay and relay-destination links experience generalized Nakagami-m fading. For the considered AF-based HSTS, we first develop the analytical expression for the moment generating function (MGF) of the overall output signal-to-interference-plus-noise ratio (SINR). Then, based on the derived exact MGF, we derive novel expressions for the average symbol error rate (SER) of the considered HSTS for the following digital modulation techniques: M-ary phase shift keying (M-PSK), M-ary quadrature amplitude modulation (M-QAM) and M-ary pulse amplitude modulation (M-PAM). To significantly reduce the computational complexity for utility in system-level simulations, simple analytical approximation for the exact SER in the high signal-to-noise ratio (SNR) regime is presented to provide key insights. Finally, numerical results and the corresponding analysis are presented to demonstrate the effectiveness of the developed performance evaluation framework and to view the impact of CCI on the considered HSTS under varying channel conditions and with different modulation schemes.

  5. Performance of Digital Communications over Selective Fading Channels.

    DTIC Science & Technology

    1983-09-01

    J. G. Proakis , Digital Communications, McGraw-Hill, New York, 1983. ’ [45] R. D. Gitlin, E. Y. Ho and 3. E. Mazo, "Passband equalization of...7 D-A142 427 PERFORNANCE OF DIGITAL COMMUNICATIONS OVER SELECTIVE 1/2 FADING CHRNNELS(U) ILLINOIS UNIV AT URBANA COORDINATED SCIENCE LAB F D GARBER...PERIOD COVERED Technical Report PERFORMANCE OF DIGITAL COMMUNICATIONS OVER 6. PERFORMING ORG. REPORT NUMBER SELECTIVE FADING CHANNELS R-998; UILU-ENG

  6. Trellis coded modulation for transmission over fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Simon, Marvin K. (Inventor); Divasalar, Dariush (Inventor)

    1990-01-01

    The combination of trellis coding and multiple phase-shift keyed (MPSK) signaling with asymmetry (nonuniform spacing) to the signal set is disclosed with regard to its suitability for a fading mobile satellite communication channel. For MPSK signaling, introducing nonuniformity in the phase spacing between signal points provides an improvement in performance over that achievable with trellis codes symmetric MPSK signaling, all this without increasing the average or peak power, or changing the bandwidth constraints imposed on the system. Block interleaving may be used to reduce error and pilot tone(s) may be used for improving the error correction performance of the trellis decoder in the presence of channel fading.

  7. The design of trellis codes for fading channels

    NASA Technical Reports Server (NTRS)

    Divsalar, Dariush; Simon, Marvin K.

    1987-01-01

    The appropriate criterion for optimum trellis coded modulation design on the additive white Gaussian noise channel is maximization of the free Euclidean distance. When trellis coded modulation is used on a Rician fading channel with interleaving/deinterleaving, the design of the code for optimum performance is guided by other factors, in particular the length of the shortest error event path, and the product of branch distances (possibly normalized by the Euclidean distance of the path) along that path. Although maximum free distance (d sub free) is still an important consideration, it plays a less significant role the more severe the fading is on the channel. These considerations lead to the definition of a new distance measure for optimization of trellis codes transmitted over Rician fading channels. If no interleaving/deinterleaving is used, then once again the design of the trellis code is guided by maximizing d sub free. It is also shown that allowing for multiple symbols per trellis branch, i.e., multiple trellis coded modulation (MTCM), provides an additional degree of freedom for designing a code to meet the above optimization criteria on the fading channel. It is here where the MTCM technique exploits its full potential.

  8. New 16-PSK trellis codes for fading channels

    NASA Technical Reports Server (NTRS)

    Du, Jun; Vucetic, Branka; Zhang, Lin

    1990-01-01

    Growth in satellite mobile communications leads to increasing requirements for high data rate transmission that can be met by more efficient modulation schemes (M greater than 8). The 16-PSK trellis coded modulation technique is a very promising solution. A class of new 16-PSK trellis codes with improved error rate are designed based on the criteria on fading channels.

  9. Convolutional fountain distribution over fading wireless channels

    NASA Astrophysics Data System (ADS)

    Usman, Mohammed

    2012-08-01

    Mobile broadband has opened the possibility of a rich variety of services to end users. Broadcast/multicast of multimedia data is one such service which can be used to deliver multimedia to multiple users economically. However, the radio channel poses serious challenges due to its time-varying properties, resulting in each user experiencing different channel characteristics, independent of other users. Conventional methods of achieving reliability in communication, such as automatic repeat request and forward error correction do not scale well in a broadcast/multicast scenario over radio channels. Fountain codes, being rateless and information additive, overcome these problems. Although the design of fountain codes makes it possible to generate an infinite sequence of encoded symbols, the erroneous nature of radio channels mandates the need for protecting the fountain-encoded symbols, so that the transmission is feasible. In this article, the performance of fountain codes in combination with convolutional codes, when used over radio channels, is presented. An investigation of various parameters, such as goodput, delay and buffer size requirements, pertaining to the performance of fountain codes in a multimedia broadcast/multicast environment is presented. Finally, a strategy for the use of 'convolutional fountain' over radio channels is also presented.

  10. Utilizing space frequency COFDM on multipath fading channels

    NASA Astrophysics Data System (ADS)

    Kellerman, Fred C.

    2007-04-01

    This paper will investigate the use of an enhanced rate one Alamouti Space Frequency (SF) multiple antenna Orthogonal Frequency Division Multiplex (OFDM) radio communication system. A two transmit, single receive antenna system will be simulated to operate under conditions of multipath fading with noise. A simple modification to the standard coherent Alamouti receive combiner will be applied and shown to improve bit error rate (BER) performance on rapidly fading multipath HF channels. Orthogonal Frequency Division Multiplexing frequency domain techniques will be utilized to effectively eliminate the Inter-Symbol Interference (ISI) resulting from the effects of multipath. Numerically simulated results will be shown for several multipath fading High Frequency (HF) radio channels. Inner convolutional error correction coding will be applied in addition to the Alamouti coding and numerically simulated BER results presented. Various HF channel conditions will be simulated including the 2 ms, 10 Hz, 2 ms, 5 Hz, CCIR poor (2 ms, 1 Hz) and extra poor (2 ms, 2 Hz) channel conditions. Performance under conditions of correlated transmit antennas will also be investigated.

  11. Evaluations of SSC Diversity Receiver over EGK Fading Channels

    NASA Astrophysics Data System (ADS)

    Anastasov, Jelena A.; Djordjevic, Goran T.; Panic, Stefan R.; Stefanovic, Mihajlo C.

    2014-09-01

    In this paper, a detailed performance analysis of switch-and-stay combining receivers over non identical distributed extended generalized K fading channels is presented. The analysis has been performed in both noise and interference-limited environments (the level of interference or noise is ignored, respectively). The expressions for the output signal-to-noise (SNR) and signal-to-interference (SIR) probability density function and cumulative distribution function, in a form of Fox's H functions, are presented. Based on this, analytical expressions for evaluating the moments, outage probability, average bit error rate and average channel capacity are derived. The influence of fading and shadowing phenomena, as well as the influence of unbalanced input SNR/SIR on the most important performance metrics is obtained. Presented numerical results are confirmed by Monte Carlo simulations.

  12. Optimal Performance Monitoring of Hybrid Mid-Infrared Wavelength MIMO Free Space Optical and RF Wireless Networks in Fading Channels

    NASA Astrophysics Data System (ADS)

    Schmidt, Barnet Michael

    An optimal performance monitoring metric for a hybrid free space optical and radio-frequency (RF) wireless network, the Outage Capacity Objective Function, is analytically developed and studied. Current and traditional methods of performance monitoring of both optical and RF wireless networks are centered on measurement of physical layer parameters, the most common being signal-to-noise ratio, error rate, Q factor, and eye diagrams, occasionally combined with link-layer measurements such as data throughput, retransmission rate, and/or lost packet rate. Network management systems frequently attempt to predict or forestall network failures by observing degradations of these parameters and to attempt mitigation (such as offloading traffic, increasing transmitter power, reducing the data rate, or combinations thereof) prior to the failure. These methods are limited by the frequent low sensitivity of the physical layer parameters to the atmospheric optical conditions (measured by optical signal-to-noise ratio) and the radio frequency fading channel conditions (measured by signal-to-interference ratio). As a result of low sensitivity, measurements of this type frequently are unable to predict impending failures sufficiently in advance for the network management system to take corrective action prior to the failure. We derive and apply an optimal measure of hybrid network performance based on the outage capacity of the hybrid optical and RF channel, the outage capacity objective function. The objective function provides high sensitivity and reliable failure prediction, and considers both the effects of atmospheric optical impairments on the performance of the free space optical segment as well as the effect of RF channel impairments on the radio frequency segment. The radio frequency segment analysis considers the three most common RF channel fading statistics: Rayleigh, Ricean, and Nakagami-m. The novel application of information theory to the underlying physics of the

  13. Capacity Analysis of MIMO Rayleigh Channel with Spatial Fading Correlation

    NASA Astrophysics Data System (ADS)

    Trung, Ha Duyen; Benjapolakul, Watit; Araki, Kiyomichi

    MIMO (Multiple Input Multiple Output) communications systems equipped with array antennas at both the transmitter and receiver sides are a promising scheme to realize higher rate and/or reliable data transmission. In this paper, capacity analysis of MIMO Rayleigh channel with spatial correlation at the receiver of multipath taken into account is presented. In general, a model configuration of local scattering around a mobile station in MIMO environment is carried out by simulation to examine spatial correlation coefficients. Based on statistical properties of the eigenvalues of correlated complex random Wishart matrices, the exact closed-form expressions of distribution of the eigenvalues are investigated. Then, the general closed-form evaluation of integral form is proposed based on Meijer's G-function. The results demonstrate that the ergodic capacities are improved by increasing the number of the antennas and the SNR's. Compared with i. i. d. (independent identically distributed) Rayleigh channel, the incremental improvement of correlated Rayleigh channel is reduced by spatial fading correlation. The analytical results validated by Monte-Carlo simulations show a good agreement.

  14. Multicarrier chaotic communications in multipath fading channels without channel estimation

    SciTech Connect

    Wang, Shilian Zhang, Zhili

    2015-01-15

    A multi-carrier chaotic shift keying(MC-CSK) communication scheme with low probability of interception(LPI) is proposed in this article. We apply chaotic spreading sequences in the frequency domain, mapping a different chip of a chaotic sequence to an individual orthogonal frequency division multiplexing(OFDM) subcarrier. In each block size of $M$ OFDM symbols, we use one pilot OFDM symbol inserted time-spaced in all-frequency to transmit the reference chaotic signal and use the other M-1 OFDM symbols to transmit the information-bearing signals each spreaded by the reference chaotic signal. At the receiver, we construct a differential detector after DFT and recover the information bits from the correlations between the pilot OFDM symbol and the other M-1 OFDM symbols in each block size of M. Performance analysis and computer simulations show that the MC-CSK outperforms differential chaos shift keying(DCSK) in AWGN channels with high bandwidth efficiency for the block size of M=2 and that the MC-CSK exploits effectively the frequent diversity of the multipath channel.

  15. Outage Probability of MRC for κ-μ Shadowed Fading Channels under Co-Channel Interference

    PubMed Central

    Chen, Changfang; Shu, Minglei; Wang, Yinglong; Yang, Ming; Zhang, Chongqing

    2016-01-01

    In this paper, exact closed-form expressions are derived for the outage probability (OP) of the maximal ratio combining (MRC) scheme in the κ-μ shadowed fading channels, in which both the independent and correlated shadowing components are considered. The scenario assumes the received desired signals are corrupted by the independent Rayleigh-faded co-channel interference (CCI) and background white Gaussian noise. To this end, first, the probability density function (PDF) of the κ-μ shadowed fading distribution is obtained in the form of a power series. Then the incomplete generalized moment-generating function (IG-MGF) of the received signal-to-interference-plus-noise ratio (SINR) is derived in the closed form. By using the IG-MGF results, closed-form expressions for the OP of MRC scheme are obtained over the κ-μ shadowed fading channels. Simulation results are included to validate the correctness of the analytical derivations. These new statistical results can be applied to the modeling and analysis of several wireless communication systems, such as body centric communications. PMID:27851817

  16. Estimation of FBMC/OQAM fading channels using dual Kalman filters.

    PubMed

    Aldababseh, Mahmoud; Jamoos, Ali

    2014-01-01

    We address the problem of estimating time-varying fading channels in filter bank multicarrier (FBMC/OQAM) wireless systems based on pilot symbols. The standard solution to this problem is the least square (LS) estimator or the minimum mean square error (MMSE) estimator with possible adaptive implementation using recursive least square (RLS) algorithm or least mean square (LMS) algorithm. However, these adaptive filters cannot well-exploit fading channel statistics. To take advantage of fading channel statistics, the time evolution of the fading channel is modeled by an autoregressive process and tracked by Kalman filter. Nevertheless, this requires the autoregressive parameters which are usually unknown. Thus, we propose to jointly estimate the FBMC/OQAM fading channels and their autoregressive parameters based on dual optimal Kalman filters. Once the fading channel coefficients at pilot symbol positions are estimated by the proposed method, the fading channel coefficients at data symbol positions are then estimated by using some interpolation methods such as linear, spline, or low-pass interpolation. The comparative simulation study we carried out with existing techniques confirms the effectiveness of the proposed method.

  17. Estimation of FBMC/OQAM Fading Channels Using Dual Kalman Filters

    PubMed Central

    Aldababseh, Mahmoud

    2014-01-01

    We address the problem of estimating time-varying fading channels in filter bank multicarrier (FBMC/OQAM) wireless systems based on pilot symbols. The standard solution to this problem is the least square (LS) estimator or the minimum mean square error (MMSE) estimator with possible adaptive implementation using recursive least square (RLS) algorithm or least mean square (LMS) algorithm. However, these adaptive filters cannot well-exploit fading channel statistics. To take advantage of fading channel statistics, the time evolution of the fading channel is modeled by an autoregressive process and tracked by Kalman filter. Nevertheless, this requires the autoregressive parameters which are usually unknown. Thus, we propose to jointly estimate the FBMC/OQAM fading channels and their autoregressive parameters based on dual optimal Kalman filters. Once the fading channel coefficients at pilot symbol positions are estimated by the proposed method, the fading channel coefficients at data symbol positions are then estimated by using some interpolation methods such as linear, spline, or low-pass interpolation. The comparative simulation study we carried out with existing techniques confirms the effectiveness of the proposed method. PMID:24701181

  18. A Serial Unequal Error Protection Codes System Using MMSE-FDE for Fading Channels

    NASA Astrophysics Data System (ADS)

    Yamazaki, Satoshi; Asano, David K.

    In our previous research, to achieve unequal error protection (UEP), we proposed a scheme which encodes the data by randomly switching between several codes which use different signal constellations and showed the effectiveness in AWGN channels. In this letter, we propose our UEP system using MMSE-FDE for fast and selective fading by using the fact that importance levels are changed every few symbols, i.e., every block, in the proposed system. We confirmed the improvement in BER performance and the effectiveness of adaptive equalization for the proposed system in fading channels. Moreover, in fading channels we confirmed the validity of the theoretical tradeoff shown in static conditions.

  19. The performance of trellis coded multilevel DPSK on a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Simon, Marvin K.; Divsalar, Dariush

    1987-01-01

    The performance of trellis coded multilevel differential phase-shift-keying (MDPSK) over Rician and Rayleigh fading channels is discussed. For operation at L-Band, this signalling technique leads to a more robust system than the coherent system with dual pilot tone calibration previously proposed for UHF. The results are obtained using a combination of analysis and simulation. The analysis shows that the design criterion for trellis codes to be operated on fading channels with interleaving/deinterleaving is no longer free Euclidean distance. The correct design criterion for optimizing bit error probability of trellis coded MDPSK over fading channels will be presented along with examples illustrating its application.

  20. Performance Analysis of Pilot-Aided Forward CDMA Cellular Channel

    DTIC Science & Technology

    2001-09-01

    in the DS- CDMA cellular systems. For example, performance analysis in a Nakagami or a Ricean instead of a Rayleigh fading channel could be done...operating in a Rayleigh -fading, Lognormal-shadowing environment. We develop an upper bound on the probability of bit error, including all the participating...Wireless, Performance Analysis, Rayleigh Fading, Lognormal Shadowing, Hata Model, Convolutional Code, Narrowband Filtering, Pilot Tone, Power

  1. A tone-aided dual vestigial sideband system for digital communications on fading channels

    NASA Technical Reports Server (NTRS)

    Hladik, Stephen M.; Saulnier, Gary J.; Rafferty, William

    1989-01-01

    A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receiver's ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application.

  2. A tone-aided dual vestigial sideband system for digital communications on fading channels

    NASA Technical Reports Server (NTRS)

    Hladik, Stephen M.; Saulnier, Gary J.; Rafferty, William

    1989-01-01

    A spectrally efficient tone-aided dual vestigial sideband (TA/DVSB) system for digital data communications on fading channels is presented and described analytically. This PSK (phase-shift-keying) system incorporates a feed-forward, tone-aided demodulation technique to compensate for Doppler frequency shift and channel- induced, multipath fading. In contrast to other tone-in-band-type systems, receiver synchronization is derived from the complete data VSBs. Simulation results for the Rician fading channel are presented. These results demonstrate the receiver's ability to mitigate performance degradation due to fading and to obtain proper data carrier synchronization, suggesting that the proposed TA/DVSB system has promise for this application. Simulated BER (bit-error rate) data indicate that the TA/DVSB system effectively alleviates the channel distortions of the land mobile satellite application.

  3. Power and Rate Adaptation Based on Imperfect Channel Estimation over MIMO Fading Channels

    NASA Astrophysics Data System (ADS)

    Kobravi, Alireza; Shikh-Bahaei, Mohammad

    We derive the optimum power and rate adaptation for maximizing the spectral efficiency of Multilevel Quadrature Amplitude Modulation (MQAM) over Multiple-Input Multiple-Output (MIMO) fading channels based on imperfect channel estimation. We use Pilot Symbol Assisted Modulation (PSAM)-based Minimum Mean Square Error (MMSE) channel estimator, and show that the optimum power adaptation on each sub-channel is a generalization of water-filling. We also show that the conventional water-filling (with bias) strategy for power adaptation is a suboptimum solution of the general optimization problem and it tends to the optimal solution as the correlation coefficients between eigenvalues of the true channel matrix and its estimate tend to one.

  4. A novel scheme to aid coherent detection of GMSK signals in fast Rayleigh fading channels

    NASA Technical Reports Server (NTRS)

    Leung, Patrick S. K.; Feher, Kamilo

    1990-01-01

    A novel scheme to insert carrier pilot to Gaussian Minimum Shift Keying (GMSK) signal using Binary Block Code (BBC) and a highpass filter in baseband is proposed. This allows the signal to be coherently demodulated even in a fast Rayleigh fading environment. As an illustrative example, the scheme is applied to a 16 kb/s GMSK signal, and its performance over a fast Rayleigh fading channel is investigated using computer simulation. This modem's 'irreducible error rate' is found to be Pe = 5.5 x 10(exp -5) which is more than that of differential detection. The modem's performance in Rician fading channel is currently under investigation.

  5. A Peak to Peak Frame Synchronization Algorithm for Data Frames Transmitted Asynchronously over Fading Channels

    DTIC Science & Technology

    2011-04-12

    will examine the performance of a frame synchronization algorithm suitable for the system shown in Fig. 1. Section II discusses the communications...provides the conclusions. II . CHANNEL MODEL A block diagram of the communication channels shown in Fig.l is provided in Fig. 2. These conununication...channel 10 -lsL---~~--~--~--~--~--~--~--~--- 0 :Z 3 4 5 6 7 II !I 10 Sample x10’ Figure 4: Channel Fading B. Summary of Channel Induced Framing Errors

  6. Performance of FH/BFSK with generalized fading in worst case partial-band Gaussian interference

    NASA Astrophysics Data System (ADS)

    Crepeau, Paul J.

    1990-06-01

    For frequency-hopped (noncoherent) binary frequency shift keying (FH/BFSK) on a worst-case partial-band Gaussian interference channel, the bit error probability results are well known for the extreme cases where the signal is either nonfading or Rayleigh fading. In this work, the region between these extremes is filled in by considering the general Nakagami-m fading model. The worst-case partial-band Gaussian interference results are given by a one-parameter family which for m goes to infinity gives the Viterbi-Jacobs nonfading result, and for m = 1 gives the Rayleigh fading result. In the latter case, a broadband interference strategy is optimal. Thus, the Nakagami-m results provide a smooth one-parameter bridge between the Viterbi-Jacobs channel and the Rayleigh fading channel. The results show that the worst-case interference fraction rho increases as the fading variance increases, up to Rayleigh fading. Any fading less severe than Rayleigh, however slight the departure from Rayleigh, requires a partial-band strategy for sufficiently large Eb/NI.

  7. Channel fading for mobile satellite communications using spread spectrum signaling and TDRSS

    NASA Technical Reports Server (NTRS)

    Jenkins, Jeffrey D.; Fan, Yiping; Osborne, William P.

    1995-01-01

    This paper will present some preliminary results from a propagation experiment which employed NASA's TDRSS and an 8 MHz chip rate spread spectrum signal. Channel fade statistics were measured and analyzed in 21 representative geographical locations covering urban/suburban, open plain, and forested areas. Cumulative distribution Functions (CDF's) of 12 individual locations are presented and classified based on location. Representative CDF's from each of these three types of terrain are summarized. These results are discussed, and the fade depths exceeded 10 percent of the time in three types of environments are tabulated. The spread spectrum fade statistics for tree-lined roads are compared with the Empirical Roadside Shadowing Model.

  8. Fading losses on the LCRD free-space optical link due to channel turbulence

    NASA Astrophysics Data System (ADS)

    Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon

    2013-03-01

    The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Optical turbulence over the communication paths will cause random uctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by optical turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.

  9. Fading Losses on the LCRD Free-Space Optical Link Due to Channel Turbulence

    NASA Technical Reports Server (NTRS)

    Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon

    2013-01-01

    The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Clear air turbulence over the communication paths will cause random fluctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by clear air turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.

  10. Fading Losses on the LCRD Free-Space Optical Link Due to Channel Turbulence

    NASA Technical Reports Server (NTRS)

    Moision, Bruce; Piazzolla, Sabino; Hamkins, Jon

    2013-01-01

    The Laser Communications Relay Demonstration (LCRD) will implement an optical communications link between a pair of Earth terminals via an Earth-orbiting satellite relay. Clear air turbulence over the communication paths will cause random fluctuations, or fading, in the received signal irradiance. In this paper we characterize losses due to fading caused by clear air turbulence. We illustrate the performance of a representative relay link, utilizing a channel interleaver and error-correction-code to mitigate fading, and provide a method to quickly determine the link performance.

  11. Performance of quasi-optimum digital FM demodulators for fading channels

    NASA Technical Reports Server (NTRS)

    Dharamsi, M. T.; Gupta, S. C.

    1975-01-01

    This paper deals with the problem of digital demodulation of FM signals transmitted over Rayleigh and Rician fading channels. The Rayleigh and Rician fading channels are represented by two quadrature multiplicative nonzero mean white Gaussian processes in addition to an additive zero-mean white Gaussian noise. Quasi-optimum digital baseband demodulation algorithms using various nonlinear estimation techniques are derived. The digital demodulator structures are then simulated on a digital computer for an FM system with first order message spectrum for various values of the parameters for Rayleigh and Rician channels.

  12. Communications by vocoder on a mobile satellite fading channel

    NASA Astrophysics Data System (ADS)

    dal Degan, N.; Perosino, F.; Rusina, F.

    The performance of a LPC vocoder system is analyzed under various bit rate and fading errors. The error generation model developed to estimate error probability, and length of error bursts and distributions is described. Two algorithms that will improve burst are proposed. The evaluation of the spectral distance measures of the voice coding system is examined. The intelligibility, quality, and acceptability of the system are assessed using the mean opinion scores method.

  13. Performance of convolutional codes on fading channels typical of planetary entry missions

    NASA Technical Reports Server (NTRS)

    Modestino, J. W.; Mui, S. Y.; Reale, T. J.

    1974-01-01

    The performance of convolutional codes in fading channels typical of the planetary entry channel is examined in detail. The signal fading is due primarily to turbulent atmospheric scattering of the RF signal transmitted from an entry probe through a planetary atmosphere. Short constraint length convolutional codes are considered in conjunction with binary phase-shift keyed modulation and Viterbi maximum likelihood decoding, and for longer constraint length codes sequential decoding utilizing both the Fano and Zigangirov-Jelinek (ZJ) algorithms are considered. Careful consideration is given to the modeling of the channel in terms of a few meaningful parameters which can be correlated closely with theoretical propagation studies. For short constraint length codes the bit error probability performance was investigated as a function of E sub b/N sub o parameterized by the fading channel parameters. For longer constraint length codes the effect was examined of the fading channel parameters on the computational requirements of both the Fano and ZJ algorithms. The effects of simple block interleaving in combatting the memory of the channel is explored, using the analytic approach or digital computer simulation.

  14. Performance analysis of digital FM demodulators for fading channels in the threshold region

    NASA Technical Reports Server (NTRS)

    Dharamsi, M. T.; Gupta, S. C.

    1976-01-01

    The quasi-optimum digital FM demodulators for fading channels reported earlier (1975) reflected the system performance accurately under high signal to noise ratio conditions. In this paper, the prediction of the system performance for low SNR values is considered. A new set of error variance algorithms is developed from the filter algorithm assuming a Gaussian distribution for the state estimation errors and taking the effect of high frequency terms into consideration. Simulation analysis for an FM system with Rician fading channel shows that these algorithms predict the system performance accurately in the threshold region.

  15. Trellis coded modulation for 4800-9600 bps transmission over a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Divsalar, D.; Simon, M. K.

    1986-01-01

    The combination of trellis coding and multiple phase-shift-keyed (MPSK) signalling with the addition of asymmetry to the signal set is discussed with regard to its suitability as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in the paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, results will reflect only the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.

  16. Adaptive Channel-Tracking Method and Equalization for MC-CDMA Systems over Rapidly Fading Channel under Colored Noise

    NASA Astrophysics Data System (ADS)

    Yang, Chang-Yi; Chen, Bor-Sen

    2010-12-01

    A recursive maximum-likelihood (RML) algorithm for channel estimation under rapidly fading channel and colored noise in a multicarrier code-division multiple-access (MC-CDMA) system is proposed in this paper. A moving-average model with exogenous input (MAX) is given to describe the transmission channel and colored noise. Based on the pseudoregression method, the proposed RML algorithm can simultaneously estimate the parameters of channel and colored noise. Following the estimation results, these parameters can be used to enhance the minimum mean-square error (MMSE) equalizer. Considering high-speed mobile stations, a one-step linear trend predictor is added to improve symbol detection. Simulation results indicate that the proposed RML estimator can track the channel more precisely than the conventional estimator. Meanwhile, the performance of the proposed enhanced MMSE equalizer is robust to the rapidly Rayleigh fading channel under colored noise in the MC-CDMA systems.

  17. Error Performance of Direct Sequence Spread Spectrum Systems on Nonselective Generalized rayleigh Fading Channel.

    DTIC Science & Technology

    1980-04-01

    Nakagami Nakagami (mlo;m2,0) 1 ( m t = cm1 2 /(m1 2 m2 Q )] m1 Nakagami Rayleigh ( m ,O;1,0) [m1 2 /(l+m1 2 ) Nakagami Gaussian (m1,0;/2,0) It(m1,1...2) , t = [2m, 2 /( Q +2m 1 Q )] Rayleigh Rician (1,0;1,62) 1 - [0l/(Ql+02)] exp-62/(Ql+Q2 )] Rayleigh Nakagami (1, m ;22,) 1 - Rayleigh Rayleigh (1,0;1,0...Q2/(a + Q Rayleigh *Gaussian (1,0;1/2,0) 1 - [Q1/(Q1 252)]1/2 Gaussian Nakagami

  18. A free-space optical terminal for fading channels

    NASA Astrophysics Data System (ADS)

    Williams, T.; Murphy, R. J.; Walther, F.; Volpicelli, A.; Wilcox, B.; Crucioli, D.

    2009-08-01

    This paper describes a lasercom terminal using spatial diversity to mitigate fading caused by atmospheric scintillation. Multiple receive apertures are separated sufficiently to capture statistically independent samples of the incoming beam. The received optical signals are tracked individually, photo-detected, and summed electrically, with measured diversity gain. The terminal consists of COTS components. It was used in successful demonstrations over a 5.4km ground-ground link from June through September 2008, during which it experienced a wide temperature range. Design overview and hardware realization are presented. This work was sponsored by the Department of Defense, RRCO DDR&E, under Air Force Contract FA8721-05-C-0002. Opinions, interpretations, conclusions and recommendations are those of the authors and are not necessarily endorsed by the United States Government.

  19. Design of a robust underwater acoustic communication system over multipath fading channels

    NASA Astrophysics Data System (ADS)

    Kim, Jangeun; Shim, Taebo

    2012-11-01

    Due to the surface and bottom constraints of the underwater acoustic channel (UAC) in shallow waters, multipath fading occurs and causes degradation of the signal for the UAC system. To overcome these problems, a robust underwater acoustic communication system was designed over multipath fading channels by employing both decision feedback equalization with the RLS algorithm and convolutional coding with interleaving+shuffling block data sequence. The dual use of these two methods simultaneously can reduce the intersymbol interference (ISI) and the adjacent bit and burst errors. The system will retransmit the same signal if the system fails to estimate the channel due to severe multipath fading. To verify the performance of the system, the transmission of an image was tested using a 524,288bit gray-scaled image through the multipath fading channel. The test results showed that the number of bit errors was reduced from 86,824 to 5,106 when the reference SNR was 12 dB.

  20. Performance Analysis of Variable Code Rate Signals Transmitted over Frequency-Nonselective, Slowly Fading Channels in a Pulse-Interference Environment

    DTIC Science & Technology

    2005-09-01

    is examined. The amplitude of the signal power 2ca is modeled as a random variable, and the channel is modeled as either Rayleigh fading or Ricean...Decoding, Soft Decision Decoding, FEC, Convolutional Code, Rayleigh Fading, Ricean Fading, Pulse-Noise Interference, Noise-Normalization 16. PRICE CODE...channel is modeled as either Rayleigh fading or Ricean fading, depending on the modulation under consideration

  1. Demodulation of OFDM Signals in the Presence of Deep Fading Channels and Signal Clipping

    DTIC Science & Technology

    2012-06-01

    FFT) operation zero padded to twice the data length allows for the recovery of subcarriers located next to a deep faded (at low signal-to-noise ratio...signals transmitted over fading channels. We show that the use of a zero prefix (ZP) along with a fast Fourier transform (FFT) operation zero padded to...refer to two widely used standards: IEEE 802.11 for local area networks (LAN) and WiFi and IEEE 802.16 for wide area networks (WAN) and WiMax. The two

  2. Approximate Minimum Bit Error Rate Equalization for Fading Channels

    NASA Astrophysics Data System (ADS)

    Kovacs, Lorant; Levendovszky, Janos; Olah, Andras; Treplan, Gergely

    2010-12-01

    A novel channel equalizer algorithm is introduced for wireless communication systems to combat channel distortions resulting from multipath propagation. The novel algorithm is based on minimizing the bit error rate (BER) using a fast approximation of its gradient with respect to the equalizer coefficients. This approximation is obtained by estimating the exponential summation in the gradient with only some carefully chosen dominant terms. The paper derives an algorithm to calculate these dominant terms in real-time. Summing only these dominant terms provides a highly accurate approximation of the true gradient. Combined with a fast adaptive channel state estimator, the new equalization algorithm yields better performance than the traditional zero forcing (ZF) or minimum mean square error (MMSE) equalizers. The performance of the new method is tested by simulations performed on standard wireless channels. From the performance analysis one can infer that the new equalizer is capable of efficient channel equalization and maintaining a relatively low bit error probability in the case of channels corrupted by frequency selectivity. Hence, the new algorithm can contribute to ensuring QoS communication over highly distorted channels.

  3. Receiver diversity combining using evolutionary algorithms in Rayleigh fading channel.

    PubMed

    Akbari, Mohsen; Manesh, Mohsen Riahi; El-Saleh, Ayman A; Reza, Ahmed Wasif

    2014-01-01

    In diversity combining at the receiver, the output signal-to-noise ratio (SNR) is often maximized by using the maximal ratio combining (MRC) provided that the channel is perfectly estimated at the receiver. However, channel estimation is rarely perfect in practice, which results in deteriorating the system performance. In this paper, an imperialistic competitive algorithm (ICA) is proposed and compared with two other evolutionary based algorithms, namely, particle swarm optimization (PSO) and genetic algorithm (GA), for diversity combining of signals travelling across the imperfect channels. The proposed algorithm adjusts the combiner weights of the received signal components in such a way that maximizes the SNR and minimizes the bit error rate (BER). The results indicate that the proposed method eliminates the need of channel estimation and can outperform the conventional diversity combining methods.

  4. Receiver Diversity Combining Using Evolutionary Algorithms in Rayleigh Fading Channel

    PubMed Central

    Akbari, Mohsen; Manesh, Mohsen Riahi

    2014-01-01

    In diversity combining at the receiver, the output signal-to-noise ratio (SNR) is often maximized by using the maximal ratio combining (MRC) provided that the channel is perfectly estimated at the receiver. However, channel estimation is rarely perfect in practice, which results in deteriorating the system performance. In this paper, an imperialistic competitive algorithm (ICA) is proposed and compared with two other evolutionary based algorithms, namely, particle swarm optimization (PSO) and genetic algorithm (GA), for diversity combining of signals travelling across the imperfect channels. The proposed algorithm adjusts the combiner weights of the received signal components in such a way that maximizes the SNR and minimizes the bit error rate (BER). The results indicate that the proposed method eliminates the need of channel estimation and can outperform the conventional diversity combining methods. PMID:25045725

  5. Fading probability density function of free-space optical communication channels with pointing error

    NASA Astrophysics Data System (ADS)

    Zhao, Zhijun; Liao, Rui

    2011-06-01

    The turbulent atmosphere causes wavefront distortion, beam wander, and beam broadening of a laser beam. These effects result in average power loss and instantaneous power fading at the receiver aperture and thus degrade performance of a free-space optical (FSO) communication system. In addition to the atmospheric turbulence, a FSO communication system may also suffer from laser beam pointing error. The pointing error causes excessive power loss and power fading. This paper proposes and studies an analytical method for calculating the FSO channel fading probability density function (pdf) induced by both atmospheric turbulence and pointing error. This method is based on the fast-tracked laser beam fading profile and the joint effects of beam wander and pointing error. In order to evaluate the proposed analytical method, large-scale numerical wave-optics simulations are conducted. Three types of pointing errors are studied , namely, the Gaussian random pointing error, the residual tracking error, and the sinusoidal sway pointing error. The FSO system employs a collimated Gaussian laser beam propagating along a horizontal path. The propagation distances range from 0.25 miles to 2.5 miles. The refractive index structure parameter is chosen to be Cn2 = 5×10-15m-2/3 and Cn2 = 5×10-13m-2/3. The studied cases cover from weak to strong fluctuations. The fading pdf curves of channels with pointing error calculated using the analytical method match accurately the corresponding pdf curves obtained directly from large-scale wave-optics simulations. They also give accurate average bit-error-rate (BER) curves and outage probabilities. Both the lognormal and the best-fit gamma-gamma fading pdf curves deviate from those of corresponding simulation curves, and they produce overoptimistic average BER curves and outage probabilities.

  6. Robustness of predictive sensor network routing in fading channels

    NASA Astrophysics Data System (ADS)

    Muraleedharan, Rajani; Osadciw, Lisa A.

    2005-06-01

    Sensors have varied constraints, which make the network challenging for communicating with peers. In this paper, an extension, to the physical layer of the previous predictive sensor network model using the ant system is proposed. The tiny and low-cost sensor nodes are made of RF wireless links, where the states of the nodes vary with respect to time and environment. The ant system is a learning algorithm, that can be used to solve any NP hard communication problem and possesses characteristics such as robustness and versatility. The ant system possesses unique features that keep the network functional by detecting weak links and re-routing the agents. The swarm agents are distributed along the network, where the agent communicates with its neighbors (agents) by means of pheromone deposition and tabu list. The transition probability in the ant system includes an objective function, which is influenced by the poset weights. The poset weights on each of the orthogonal communication parameters greatly affects the decisions made by ant system. The agents carry updated information of its previous nodes, which helps in monitoring the strength of the communication links. Through simulation, comparison between DSSS-BPSK and Bluetooth-GFSK signals are shown. This paper demonstrates the robustness of the model under slow/fast fading, and energy loss at node during transmission. Implementation of this algorithm should be able to handle hostile environmental conditions and human tampering of data. The performance of the network is evaluated based on accuracy and response time of the agents within the network.

  7. Blind Equalization and Fading Channel Signal Recovery of OFDM Modulation

    DTIC Science & Technology

    2011-03-01

    of WiMAX. San Francisco, CA: Prentice Hall, 2007. [2] P. P. Vaidyanathan and B. Vrcelj, “A frequency domain approach for blind identification with...filter bank precoders,” in Proc. 2004 Int. Symp. Circuits and Systems, pp. III- 349–52, 2004. [3] P. P. Vaidyanathan and B. Su, “Remarks on certain...OBJECTIVES AND METHODOLOGY The goal of this thesis was to further investigate the method of blind channel equalization proposed by P. P. Vaidyanathan , et al

  8. Multiple trellis coded modulation (MTCM) performance on a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Simon, Marvin K.; Divsalar, Dariush

    1987-01-01

    The author recently introduced the notion of multiple trellis coding, in which more than one channel symbol per trellis branch is transmitted. He showed that on the ideal additive white Gaussian noise (AWGN) channel, the combination of multiple trellis coding with M-ary modulation yields a performance gain with symmetric signal sets comparable to and in some cases better than that previously achieved only with signal constellation asymmetry. The combination of conventional trellis coding with multiple phase-shift-keyed (MPSK) signaling has recently been shown by the author to be a well-suited modulation/coding scheme for transmission over the fading mobile satellite channel. In particular, a rate 2/3 coded 8-PSK scheme operating at 4800 b/s is currently under development for use in NASA's Mobile Satellite Experiment (MSAT-X). The author applies the multiple trellis-coded modulation technique in the same fading mobile satellite environment, extending the analysis results previously found for its performance over the AWGN channel to the MSAT-X channel.

  9. Capacity of Cognitive Radio with Partial Channel Distribution Information in Rayleigh Fading Environments

    NASA Astrophysics Data System (ADS)

    Xu, D.; Li, Q.

    2015-11-01

    This paper investigates the capacity of the secondary user (SU) in a cognitive radio (CR) network in Rayleigh fading environments. Different from existing works where perfect channel state information (CSI) or channel distribution information (CDI) of the interference link from the SU to the primary user (PU) is assumed to be available, this paper assumes that only partial CDI is available. Specifically, we assume the distribution parameter is unknown and estimated from a set of channel gain samples. With such partial CDI, closed-form expressions for the ergodic and outage capacities of the SU are obtained under the transmit power and the interference outage constraints. It is shown that the capacity with partial CDI is not degraded compared to that with perfect CDI if the interference outage constraint is loose. It is also shown that the capacity can be significantly improved by increasing the number of channel gain samples.

  10. Performance analysis for mixed FSO/RF Nakagami-m and Exponentiated Weibull dual-hop airborne systems

    NASA Astrophysics Data System (ADS)

    Jing, Zhao; Shang-hong, Zhao; Wei-hu, Zhao; Ke-fan, Chen

    2017-06-01

    In this paper, the performances of mixed free-space optical (FSO)/radio frequency (RF) systems are presented based on the decode-and-forward relaying. The Exponentiated Weibull fading channel with pointing error effect is adopted for the atmospheric fluctuation of FSO channel and the RF link undergoes the Nakagami-m fading. We derived the analytical expression for cumulative distribution function (CDF) of equivalent signal-to-noise ratio (SNR). The novel mathematical presentations of outage probability and average bit-error-rate (BER) are developed based on the Meijer's G function. The analytical results show an accurately match to the Monte-Carlo simulation results. The outage and BER performance for the mixed system by decode-and-forward relay are investigated considering atmospheric turbulence and pointing error condition. The effect of aperture averaging is evaluated in all atmospheric turbulence conditions as well.

  11. Methods and Apparatuses for Signaling with Geometric Constellations in a Raleigh Fading Channel

    NASA Technical Reports Server (NTRS)

    Barsoum, Maged F. (Inventor); Jones, Christopher R. (Inventor)

    2017-01-01

    Communication systems are described that use signal constellations, which have unequally spaced (i.e. `geometrically` shaped) points. In many embodiments, the communication systems use specific geometric constellations that are capacity optimized at a specific SNR, over the Raleigh fading channel. In addition, ranges within which the constellation points of a capacity optimized constellation can be perturbed and are still likely to achieve a given percentage of the optimal capacity increase compared to a constellation that maximizes d.sub.min, are also described. Capacity measures that are used in the selection of the location of constellation points include, but are not limited to, parallel decode (PD) capacity and joint capacity.

  12. Efficiency of MIMO configuration and adaptive optics corrections in free space optical fading channels

    NASA Astrophysics Data System (ADS)

    Hajjarian, Zeinab; Kavehrad, Mohsen; Fadlullah, Jarir

    2010-01-01

    Free Space Optical (FSO) communications is the only practical candidate for realizing universal network coverage between ground and airborne nodes, satellites, and even moon and other nearby planets. When atmosphere (be it the earth or Mars) is a part of the optical channel, attributes of scattering and turbulence bring about amplitude attenuation, and scintillation, as well as beam wander and phase aberrations at the receiving aperture. Phase screens are usually used in order to simulate the atmospheric fading channel and phase fluctuations. In this paper, different methods of generating phase screens are compared based on their accuracy and computational complexity, as in most computer simulations, a large ensemble of phase screens are required for averaging purposes. To combat the focal plane intensity fading, caused by amplitude and phase variations in the received wave-front, it is possible to replace the Single Input-Single Output (SISO) communications system with its Multiple Input Multiple Output (MIMO) equivalent, which has the same total transmit power and receiving aperture area. Another alternative is to equip the receiver with a state of the art Adaptive Optics (AO) correction system. Using average Bit Error Rate (BER), as a performance metric, effectiveness of these two approaches are compared and it is shown that while a MIMO configuration outperforms a basic AO system capable of only tilt corrections, an ideal AO system, which is able to remove higher orders of Zernike modes can asymptotically perform as well as an equivalent MIMO configuration.

  13. Upper and lower bounds for the ergodic capacity of MIMO Jacobi fading channels.

    PubMed

    Nafkha, Amor; Bonnefoi, Rémi

    2017-05-29

    In multi-(core/mode) optical fiber communication, the transmission channel can be modeled as a complex sub-matrix of the Haar-distributed unitary matrix (complex Jacobi unitary ensemble). In this letter, we present new analytical expressions of the upper and lower bounds for the ergodic capacity of multiple-input multiple-output Jacobi-fading channels. Recent results on the determinant of the Jacobi unitary ensemble are employed to derive a tight lower bound on the ergodic capacity. We use Jensen's inequality to provide an analytical closed-form upper bound to the ergodic capacity at any signal-to-noise ratio (SNR). Closed-form expressions of the ergodic capacity, at low and high SNR regimes, are also derived. Simulation results are presented to validate the accuracy of the derived expressions.

  14. A Differential MIMO SC-FDE Transceiver Design over Multipath Fast Fading Channels

    NASA Astrophysics Data System (ADS)

    Deng, Juinn-Horng; Hwang, Jeng-Kuang

    In this paper, we propose a new differential MIMO single-carrier system with frequency-domain equalization (SC-FDE) aided by the insertion of cyclic prefix. This block transmission system not only inherits all the merits of the SISO SC-FDE system, but is also equipped with a differential space-time block coding (DSTBC) such as to combat the fast-changing frequency selective fading channels without the needs to estimate and then compensate the channel effects. Hence, for practical applications, it has the additional merits of decoding simplicity and robustness against high mobility transmission environments. Computer simulations show that the proposed system can provide diversity benefit as the non-differential system does, while greatly reducing the receiver complexity.

  15. Use of Bigaussian approximation to describe fading in scattering communications channel

    NASA Astrophysics Data System (ADS)

    Sushkova, L. T.; Marchenko, Y. Y.; Bryksin, V. V.

    1985-01-01

    An algorithm is presented for the analytical description of the statistical properties of fading in a scattering radio channel. Two Gaussian random processes W1 (x) and W2 (x) with parameters a1, delta 1, a2, delta 2, respectively where a1; delta 1- mathematical expectation, as the expression approximating the arbitrary probability density W*(x) of the composition are considered. A graph analytical method is proposed for estimating the parameters a sub 1, a sub 2, delta and lambda from the known estimates of the moments of the empirical distribution described. The proposed method is used to describe the real statistics of signal level variation in a troposcatter radio channel as an example.

  16. On fading probability density functions of fast-tracked and untracked free-space optical communication channels

    NASA Astrophysics Data System (ADS)

    Zhao, Zhijun; Liao, Rui

    2011-03-01

    Free-space optical (FSO) communication systems suffer from average power loss and instantaneous power fading due to the atmospheric turbulence. The channel fading probability density function (pdf) is of critical importance for FSO communication system design and evaluation. The performance and reliability of FSO communication systems can be greatly enhanced if fast-tacking devices are employed at the transmitter in order to compensate laser beam wander at the receiver aperture. The fast-tracking method is especially effective when communication distance is long. This paper studies the fading probability density functions of both fast-tracked and untracked FSO communication channels. Large-scale wave-optics simulations are conducted for both tracked and untracked lasers. In the simulations, the Kolmogorov spectrum is adopted, and it is assumed that the outer scale is infinitely large and the inner scale is negligibly small. The fading pdfs of both fast-tracked and untracked FSO channels are obtained from the simulations. Results show that the fast-tracked channel fading can be accurately modeled as gamma-distributed if receiver aperture size is smaller than the coherence radius. An analytical method is given for calculating the untracked fading pdfs of both point-like and finite-size receiver apertures from the fast-tracked fading pdf. For point-like apertures, the analytical method gives pdfs close to the well-known gamma-gamma pdfs if off-axis effects are omitted in the formulation. When off-axis effects are taken into consideration, the untracked pdfs obtained using the analytical method fit the simulation pdfs better than gamma-gamma distributions for point-like apertures, and closely fit the simulation pdfs for finite-size apertures where gamma-gamma pdfs deviate from those of the simulations significantly.

  17. Trellis coded modulation for 4800-9600 bits/s transmission over a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Divsalar, Dariush; Simon, Marvin K.

    1987-01-01

    The combination of trellis coding and multiple phase-shift-keyed (MPSK) signaling with the addition of asymmetry to the signal set is discussed with regard to its suitability as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in the paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, results will reflect only the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.

  18. Trellis coded modulation for 4800-9600 bits/s transmission over a fading mobile satellite channel

    NASA Technical Reports Server (NTRS)

    Divsalar, Dariush; Simon, Marvin K.

    1987-01-01

    The combination of trellis coding and multiple phase-shift-keyed (MPSK) signaling with the addition of asymmetry to the signal set is discussed with regard to its suitability as a modulation/coding scheme for the fading mobile satellite channel. For MPSK, introducing nonuniformity (asymmetry) into the spacing between signal points in the constellation buys a further improvement in performance over that achievable with trellis coded symmetric MPSK, all this without increasing average or peak power, or changing the bandwidth constraints imposed on the system. Whereas previous contributions have considered the performance of trellis coded modulation transmitted over an additive white Gaussian noise (AWGN) channel, the emphasis in the paper is on the performance of trellis coded MPSK in the fading environment. The results will be obtained by using a combination of analysis and simulation. It will be assumed that the effect of the fading on the phase of the received signal is fully compensated for either by tracking it with some form of phase-locked loop or with pilot tone calibration techniques. Thus, results will reflect only the degradation due to the effect of the fading on the amplitude of the received signal. Also, we shall consider only the case where interleaving/deinterleaving is employed to further combat the fading. This allows for considerable simplification of the analysis and is of great practical interest. Finally, the impact of the availability of channel state information on average bit error probability performance is assessed.

  19. Frequency Tracking Performance Using a Hyperbolic Digital-Phase Locked Loop for Ka-Band Communication in Rain Fading Channels

    NASA Astrophysics Data System (ADS)

    Sithamparanathan, Kandeepan; Piesiewicz, Radoslaw

    In this paper we study and present some results on the performances of frequency tracking for Ka-band satellite communications in rain fading channels. The carrier frequency is tracked using a 2nd order hyperbolic phase detector based digital-phase locked loop (D-PLL). The hyperbolic D-PLL has the capability of extending the tracking range compared to the other D-PLL and hence can be designed such that to achieve low phase jitter performance for improved carrier tracking. We present the design and analysis of the D-PLL and show some simulation results on the frequency tracking performance for Ka-band rain fading channel. The results are compared with the non-fading noise only case and comparative analyses are made.

  20. Performance of MIMO E-SDM Systems Using Channel Prediction in Actual Time-Varying Indoor Fading Environments

    NASA Astrophysics Data System (ADS)

    Bui, Huu Phu; Nishimoto, Hiroshi; Nishimura, Toshihiko; Ohgane, Takeo; Ogawa, Yasutaka

    In time-varying fading environments, the performance of multiple-input multiple-output (MIMO) systems applying an eigenbeam-space division multiplexing (E-SDM) technique may be degraded due to a channel change during the time interval between the transmit weight matrix determination and the actual data transmission. To compensate for the channel change, we have proposed some channel prediction methods. Simulation results based on computer-generated channel data showed that better performance can be obtained when using the prediction methods in Rayleigh fading environments assuming the Jakes model with rich scatterers. However, actual MIMO systems may be used in line-of-sight (LOS) environments, and even in a non-LOS case, scatterers may not be uniformly distributed around a receiver and/or a transmitter. In addition, mutual coupling between antennas at both the transmitter and the receiver cannot be ignored as it affects the system performance in actual implementation. We conducted MIMO channel measurement campaigns at a 5.2GHz frequency band to evaluate the channel prediction techniques. In this paper, we present the experiment and simulation results using the measured channel data. The results show that robust bit-error rate performance is obtained when using the channel prediction methods and that the methods can be used in both Rayleigh and Rician fading environments, and do not need to know the maximum Doppler frequency.

  1. Acoustic echo cancellation for full-duplex voice transmission on fading channels

    NASA Technical Reports Server (NTRS)

    Park, Sangil; Messer, Dion D.

    1990-01-01

    This paper discusses the implementation of an adaptive acoustic echo canceler for a hands-free cellular phone operating on a fading channel. The adaptive lattice structure, which is particularly known for faster convergence relative to the conventional tapped-delay-line (TDL) structure, is used in the initialization stage. After convergence, the lattice coefficients are converted into the coefficients for the TDL structure which can accommodate a larger number of taps in real-time operation due to its computational simplicity. The conversion method of the TDL coefficients from the lattice coefficients is derived and the DSP56001 assembly code for the lattice and TDL structure is included, as well as simulation results and the schematic diagram for the hardware implementation.

  2. SER performance analysis of MPPM FSO system with three decision thresholds over exponentiated Weibull fading channels

    NASA Astrophysics Data System (ADS)

    Wang, Ping; Yang, Bensheng; Guo, Lixin; Shang, Tao

    2015-11-01

    In this work, the symbol error rate (SER) performance of the multiple pulse position modulation (MPPM) based free-space optical communication (FSO) system with three different decision thresholds, fixed decision threshold (FDT), optimized decision threshold (ODT) and dynamic decision threshold (DDT) over exponentiated Weibull (EW) fading channels has been investigated in detail. The effects of aperture averaging on each decision threshold under weak-to-strong turbulence conditions are further studied and compared. The closed-form SER expressions for three thresholds derived with the help of generalized Gauss-Laguerre quadrature rule are verified by the Monte Carlo simulations. This work is helpful for the design of receivers for FSO communication systems.

  3. Atmospheric turbulence-induced fading channel model for space-to-ground laser communications links.

    PubMed

    Toyoshima, Morio; Takenaka, Hideki; Takayama, Yoshihisa

    2011-08-15

    The fading channel model for generating a random time-varying signal based on the atmospheric turbulence spectrum for space-to-ground laser links is discussed. The temporal frequency characteristics of the downlink are theoretically derived based on the von Karman spectrum. The rms wind speed based on the Bufton wind model is used as the transverse wind velocity, which makes the simulation simple. The time-varying signal is generated as functions of the receiver aperture diameter and the rms wind speed. The simulated result of the time-varying signal is presented and compared with the gamma-gamma distribution based on the scintillation theory in a moderate-to-strong-turbulence regime. © 2011 Optical Society of America

  4. Atmospheric turbulence-induced fading channel model for space-to-ground laser communications links

    NASA Astrophysics Data System (ADS)

    Toyoshima, Morio; Takenaka, Hideki; Takayama, Yoshihisa

    2011-08-01

    The fading channel model for generating a random time-varying signal based on the atmospheric turbulence spectrum for space-to-ground laser links is discussed. The temporal frequency characteristics of the downlink are theoretically derived based on the von Karman spectrum. The rms wind speed based on the Bufton wind model is used as the transverse wind velocity, which makes the simulation simple. The time-varying signal is generated as functions of the receiver aperture diameter and the rms wind speed. The simulated result of the time-varying signal is presented and compared with the gamma-gamma distribution based on the scintillation theory in a moderate-to-strong-turbulence regime.

  5. Distributed Inference for Relay-Assisted Sensor Networks With Intermittent Measurements Over Fading Channels

    NASA Astrophysics Data System (ADS)

    Zhu, Shanying; Soh, Yeng Chai; Xie, Lihua

    2016-02-01

    In this paper, we consider a general distributed estimation problem in relay-assisted sensor networks by taking into account time-varying asymmetric communications, fading channels and intermittent measurements. Motivated by centralized filtering algorithms, we propose a distributed innovation-based estimation algorithm by combining the measurement innovation (assimilation of new measurement) and local data innovation (incorporation of neighboring data). Our algorithm is fully distributed which does not need a fusion center. We establish theoretical results regarding asymptotic unbiasedness and consistency of the proposed algorithm. Specifically, in order to cope with time-varying asymmetric communications, we utilize an ordering technique and the generalized Perron complement to manipulate the first and second moment analyses in a tractable framework. Furthermore, we present a performance-oriented design of the proposed algorithm for energy-constrained networks based on the theoretical results. Simulation results corroborate the theoretical findings, thus demonstrating the effectiveness of the proposed algorithm.

  6. Multilevel Concatenated Block Modulation Codes for the Frequency Non-selective Rayleigh Fading Channel

    NASA Technical Reports Server (NTRS)

    Lin, Shu; Rhee, Dojun

    1996-01-01

    This paper is concerned with construction of multilevel concatenated block modulation codes using a multi-level concatenation scheme for the frequency non-selective Rayleigh fading channel. In the construction of multilevel concatenated modulation code, block modulation codes are used as the inner codes. Various types of codes (block or convolutional, binary or nonbinary) are being considered as the outer codes. In particular, we focus on the special case for which Reed-Solomon (RS) codes are used as the outer codes. For this special case, a systematic algebraic technique for constructing q-level concatenated block modulation codes is proposed. Codes have been constructed for certain specific values of q and compared with the single-level concatenated block modulation codes using the same inner codes. A multilevel closest coset decoding scheme for these codes is proposed.

  7. A Power-Efficient Clustering Protocol for Coal Mine Face Monitoring with Wireless Sensor Networks Under Channel Fading Conditions.

    PubMed

    Ren, Peng; Qian, Jiansheng

    2016-06-07

    This study proposes a novel power-efficient and anti-fading clustering based on a cross-layer that is specific to the time-varying fading characteristics of channels in the monitoring of coal mine faces with wireless sensor networks. The number of active sensor nodes and a sliding window are set up such that the optimal number of cluster heads (CHs) is selected in each round. Based on a stable expected number of CHs, we explore the channel efficiency between nodes and the base station by using a probe frame and the joint surplus energy in assessing the CH selection. Moreover, the sending power of a node in different periods is regulated by the signal fade margin method. The simulation results demonstrate that compared with several common algorithms, the power-efficient and fading-aware clustering with a cross-layer (PEAFC-CL) protocol features a stable network topology and adaptability under signal time-varying fading, which effectively prolongs the lifetime of the network and reduces network packet loss, thus making it more applicable to the complex and variable environment characteristic of a coal mine face.

  8. A Power-Efficient Clustering Protocol for Coal Mine Face Monitoring with Wireless Sensor Networks Under Channel Fading Conditions

    PubMed Central

    Ren, Peng; Qian, Jiansheng

    2016-01-01

    This study proposes a novel power-efficient and anti-fading clustering based on a cross-layer that is specific to the time-varying fading characteristics of channels in the monitoring of coal mine faces with wireless sensor networks. The number of active sensor nodes and a sliding window are set up such that the optimal number of cluster heads (CHs) is selected in each round. Based on a stable expected number of CHs, we explore the channel efficiency between nodes and the base station by using a probe frame and the joint surplus energy in assessing the CH selection. Moreover, the sending power of a node in different periods is regulated by the signal fade margin method. The simulation results demonstrate that compared with several common algorithms, the power-efficient and fading-aware clustering with a cross-layer (PEAFC-CL) protocol features a stable network topology and adaptability under signal time-varying fading, which effectively prolongs the lifetime of the network and reduces network packet loss, thus making it more applicable to the complex and variable environment characteristic of a coal mine face. PMID:27338380

  9. Improving the performance of continuous variable quantum key distribution using fading effects of free-space channel

    NASA Astrophysics Data System (ADS)

    Zhang, Zeyu; Zhu, Chengrui; He, Guangqiang

    2015-08-01

    Quantum key distribution can be used to share secret keys with information-theoretic security between two legitimate partners for secure communication. In the case of satellite communication, free-space channel is the only way to transmit information, thus research on its properties is of great significance to quantum cryptographic communication. In this paper, we thoroughly analyze the influence of free-space channel fading effects on continuous variable quantum key distribution and for the first time prove that random distribution (such as Rayleigh distribution, Rice distribution and et al.) of free-space channel fading coefficients can be used to increase secret information rates and improve system stability against excess noises. Our results offer academic reference for practical applications of ground-space and space-space quantum communication and global quantum communication network.

  10. Finite-Time Distributed State Estimation Over Sensor Networks With Round-Robin Protocol and Fading Channels.

    PubMed

    Xu, Yong; Lu, Renquan; Shi, Peng; Li, Hongyi; Xie, Shengli

    2016-12-15

    This paper considers finite-time distributed state estimation for discrete-time nonlinear systems over sensor networks. The Round-Robin protocol is introduced to overcome the channel capacity constraint among sensor nodes, and the multiplicative noise is employed to model the channel fading. In order to improve the performance of the estimator under the situation, where the transmission resources are limited, fading channels with different stochastic properties are used in each round by allocating the resources. Sufficient conditions of the average stochastic finite-time boundedness and the average stochastic finite-time stability for the estimation error system are derived on the basis of the periodic system analysis method and Lyapunov approach, respectively. According to the linear matrix inequality approach, the estimator gains are designed. Finally, the effectiveness of the developed results are illustrated by a numerical example.

  11. Outage performance of MIMO FSO links over strong turbulence and misalignment fading channels.

    PubMed

    García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2011-07-04

    Atmospheric turbulence produces fluctuations in the irradiance of the transmitted optical beam, which is known as atmospheric scintillation, severely degrading the performance over free-space optical (FSO) links. Additionally, since FSO systems are usually installed on high buildings, building sway causes vibrations in the transmitted beam, leading to an unsuitable alignment between transmitter and receiver and, hence, a greater deterioration in performance. In this paper, the outage probability as a performance measure for multiple-input/multiple-output (MIMO) FSO communication systems with intensity modulation and direct detection (IM/DD) over strong atmospheric turbulence channels with pointing errors is analyzed. Novel closed-form expressions for the outage probability as well as their corresponding asymptotic expressions are presented when the irradiance of the transmitted optical beam is susceptible to either strong turbulence conditions, following a negative exponential distribution, and pointing error effects, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. Obtained results show that the diversity order is independent of the pointing error when the equivalent beam radius at the receiver is at least twice the value of the pointing error displacement standard deviation at the receiver. Simulation results are further demonstrated to confirm the analytical results. Additionally, since proper FSO transmission requires transmitters with accurate control of their beamwidth, asymptotic expressions here obtained for different diversity techniques are used to find the optimum beamwidth that minimizes the outage performance.

  12. On the capacity of MISO FSO systems over gamma-gamma and misalignment fading channels.

    PubMed

    Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Beatriz; Castillo-Vázquez, Carmen

    2015-08-24

    In this work, the ergodic capacity performance for multiple-input/single-output (MISO) free-space optical (FSO) communications system with equal gain combining (EGC) reception is analyzed over gamma-gamma and misalignment fading channels, which are modeled as statistically independent, but not necessarily identically distributed (i.n.i.d.). Novel and analytical closed-form ergodic capacity expression is obtained in terms of H-Fox function by using the well-known inequality between arithmetic and geometric mean of positive random variables (RV) in order to obtain an approximate closed-form expression of the distribution of the sum of M gamma-gamma with pointing errors variates. In addition, we present an asymptotic ergodic capacity expression at high signal-to-noise ratio (SNR) for the ergodic capacity of MISO FSO systems. It can be concluded that the use of MISO technique can significantly reduce the effect of the atmospheric turbulence as well as pointing errors and, hence, provide significant capacity gain over the direct path link (DL). The impact of pointing errors on the MISO FSO system is also analyzed, which only depends on the number of laser sources and pointing error parameters. Moreover, it can be also concluded that the ergodic capacity performance is dramatically reduced as a consequence of the severity of pointing error effects. Simulation results are further demonstrated to confirm the analytical results.

  13. Improved GOB synchronization for robust transmission of H.263 video over slow-fading channels

    NASA Astrophysics Data System (ADS)

    Abrardo, Andrea; Barni, Mauro; Garzelli, Andrea

    2001-10-01

    Among the techniques to limit the effect of error propagation in low bitrate video coding, the best performance is achieved through the joint use of forward error correction (FEC) and automatic repeat request strategies. However, retransmission of corrupted data introduces additional delay which may be critical in some practical applications. In such cases, only a FEC strategy is feasible at the expense of a significant increase of the overall transmission bit rate. In this paper, a strategy is proposed which instead of protecting the whole H.263 video stream, uses all the redundancy to protect the most important parts of the bit stream, i.e., group-of-block (GOB) start codes. More specifically, the 22-bit long start code used in the H.263 standard is replaced with longer Gold sequences which ensure a higher protection against noise. A different sequence is used for each GOB so that additional information can be obtained which can be used to improve the quality of the decoded sequence. The new technique is derived by assuming a slow-fading channel such as those encountered in pedestrian applications. Simulation results prove the effectiveness of the proposed technique with respect to classical FEC schemes in terms of PSNR and overall bit rate.

  14. Multidimensional Trellis Coded Phase Modulation Using a Multilevel Concatenation Approach. Part 2; Codes for AWGN and Fading Channels

    NASA Technical Reports Server (NTRS)

    Rajpal, Sandeep; Rhee, DoJun; Lin, Shu

    1997-01-01

    In this paper, we will use the construction technique proposed in to construct multidimensional trellis coded modulation (TCM) codes for both the additive white Gaussian noise (AWGN) and the fading channels. Analytical performance bounds and simulation results show that these codes perform very well and achieve significant coding gains over uncoded reference modulation systems. In addition, the proposed technique can be used to construct codes which have a performance/decoding complexity advantage over the codes listed in literature.

  15. H∞ state estimation for discrete-time neural networks with distributed delays and randomly occurring uncertainties through Fading channels.

    PubMed

    Hou, Nan; Dong, Hongli; Wang, Zidong; Ren, Weijian; Alsaadi, Fuad E

    2017-05-01

    In this paper, the H∞ state estimation problem is investigated for a class of uncertain discrete-time neural networks subject to infinitely distributed delays and fading channels. Randomly occurring uncertainties (ROUs) are introduced to reflect the random nature of the network condition fluctuations, and the channel fading phenomenon is considered to account for the possibly unreliable network medium on which the measurement signal is transmitted. A set of Bernoulli-distributed white sequences are employed to govern the ROUs and the L-th Rice fading model is utilized where channel coefficients are mutually independent random variables with certain probability density function on [0,1]. We aim to design a state estimator such that the dynamics of the estimation error is asymptotically stable while satisfying the prescribed H∞ performance constraint. By adopting the Lyapunov-Krasovskii functional and the stochastic analysis theory, sufficient conditions are established to ensure the existence of the desired state estimators and the explicit expression of such estimators is acquired. A simulation example is provided to verify the usefulness of the proposed approach. Copyright © 2016 Elsevier Ltd. All rights reserved.

  16. Comparative analysis of H.263 resilience techniques for H.223-based video transmission over slow-fading channels

    NASA Astrophysics Data System (ADS)

    Garzelli, Andrea; Abrardo, Andrea; Barni, Mauro; Marotta, D.

    2000-11-01

    The objective of this work is to analyze and compare H.263 resilience techniques for H.223-based real-time video transmission over narrow-band slow-fading channels. These channel conditions, which are typical for pedestrian video communications, are very critical, because they require Forward Error Correction (FEC), since data retransmission is not feasible, due to high network delay, and they reduce the effectiveness of FEC techniques- due to the bursty nature of the channel. In this work, two different strategies for H.263 video protection against channel errors are considered and compared. The strategies are tested over a slow-fading wireless channel, over which the H.263 video streams, organized and multiplexed by the H.223 Multiplex Protocol, are transmitted. Both standard FEC techniques considered by the H.223 recommendation for equal error protection of the video stream, and unequal error protection (UEP) through GOB synchronization are tested. The experimental results of this comparative analysis prove the superiority of the UEP technique for H.223-based video transmission.

  17. Outage Capacity of Spectrum Sharing Cognitive Radio with Channel Estimation Errors and Feedback Delay in Rayleigh Fading Environments

    NASA Astrophysics Data System (ADS)

    Xu, D.; Feng, Z.; Zhang, P.

    2013-04-01

    This paper considers a spectrum sharing cognitive radio (CR) network consisting of one secondary user (SU) and one primary user (PU) in Rayleigh fading environments. The channel state information (CSI) between the secondary transmitter (STx) and the primary receiver (PRx) is assumed to be imperfect. Particularly, this CSI is assumed to be not only having channel estimation errors but also outdated due to feedback delay, which is different from existing work. We derive the closed-form expression for the outage capacity of the SU with this imperfect CSI under the average interference power constraint at the PU. Analytical results confirmed by simulations are presented to show the effect of the imperfect CSI. Particularly, it is shown that the outage capacity of the SU is robust to the channel estimation errors and feedback delay for low outage probability and high channel estimation errors and feedback delay.

  18. Wavelength-diversity transmission for fading mitigation in the atmospheric optical communication channel

    NASA Astrophysics Data System (ADS)

    Giggenbach, Dirk; Wilkerson, Brandon L.; Henniger, Hennes; Perlot, Nicolas

    2006-08-01

    Mitigation of index of refraction turbulence (IRT) effects is crucial in long-range atmospheric communication links. Diversity-transmission is one favorable way for fading compensation. One of several different diversity concepts is the exploitation of the wavelength-dependent index of refraction of the atmosphere, which leads to ideal stochastically independent fading at different wavelengths, depending on the scenario. This concept is here named wavelength-diversity (WLD). Theoretical analysis and numerical simulation for the strength of this effect are given and verified by experimental tests.

  19. BER Analysis of Dual-Hop Amplify-and-Forward MIMO Relaying with Best Antenna Selection in Rayleigh Fading Channels

    NASA Astrophysics Data System (ADS)

    Kim, Jung-Bin; Kim, Dongwoo

    Combining relaying and multi-input multi-output (MIMO) transmission is a generic way to overcome the channel-fading impairments. Best antenna selection is a simple but efficient MIMO method that achieves the full diversity and also serves as a lower bound reference of MIMO performance. For a dual-hop MIMO system with an ideal amplify-and-forward (AF) relaying gain and best antenna selection, we provide a probability density function (PDF) of received signal-to-noise ratio (SNR) and an analytic BER equation when using M-ary PSK in Rayleigh fading channels. The analytic result is shown to exactly match with simulated one. Furthermore, the effect of link unbalance between the first hop and the second hop, due to differences in the number of antennas deployed in both hops as well as in the average power of channel coefficients, on the BER performance is numerically investigated and the results show that the links with better balance give better performance.

  20. Bit error rate performance of pi/4-DQPSK in a frequency-selective fast Rayleigh fading channel

    NASA Technical Reports Server (NTRS)

    Liu, Chia-Liang; Feher, Kamilo

    1991-01-01

    The bit error rate (BER) performance of pi/4-differential quadrature phase shift keying (DQPSK) modems in cellular mobile communication systems is derived and analyzed. The system is modeled as a frequency-selective fast Rayleigh fading channel corrupted by additive white Gaussian noise (AWGN) and co-channel interference (CCI). The probability density function of the phase difference between two consecutive symbols of M-ary differential phase shift keying (DPSK) signals is first derived. In M-ary DPSK systems, the information is completely contained in this phase difference. For pi/4-DQPSK, the BER is derived in a closed form and calculated directly. Numerical results show that for the 24 kBd (48 kb/s) pi/4-DQPSK operated at a carrier frequency of 850 MHz and C/I less than 20 dB, the BER will be dominated by CCI if the vehicular speed is below 100 mi/h. In this derivation, frequency-selective fading is modeled by two independent Rayleigh signal paths. Only one co-channel is assumed in this derivation. The results obtained are also shown to be valid for discriminator detection of M-ary DPSK signals.

  1. Performance of single and dual-polarized optically preamplified M-ary PPM systems with finite extinction ratios over FSO fading channels

    NASA Astrophysics Data System (ADS)

    Landolsi, Taha; Elrefaie, Aly F.

    2016-05-01

    M-ary pulse position modulation (PPM) systems have been considered in free-space optical (FSO) communications, optical fiber links, and passive optical networks. In this paper, we study the error performance of direct-detection optically preamplified M-ary PPM systems over slowly fading FSO channels. The study considers the combined effects on the probability of bit error, Pb, of channel fading with a given scintillation index, σp2, the transmitter finite extinction ratio, r, and the preamplifier spontaneous emission (ASE) noise. We provide results for both single and dual-polarized systems with symbol sizes M ∈ { 2, 4, …, 1024 } at Pb =10-4 and Pb =10-9. The fading models considered in this study are the exponential, log-normal, and gamma-gamma channels. For single-polarized systems with infinite extinction ratios, we provide closed-form expressions for the bit error probabilities for the three channel models. For the dual-polarized systems we compute them numerically. The results indicate that gamma-gamma fading imposes a more severe penalty than the log-normal case. In this study, the power penalty at Pb =10-9 ranges between 1.8 and 14 dB for the log-normal channel, whereas it ranges between 2.2 and 30.7 dB for the gamma-gamma channel. The study also demonstrates that the power penalty due to the combined effects of transmitter finite r and channel fading is the sum of the penalty due to fading alone and the penalty due to a finite r alone, and that the power penalty for dual-polarized systems is about 0.4 dB larger than single-polarized ones.

  2. Effect of filtering on the synchronization and performance of chaos-based secure communication over Rayleigh fading channel

    NASA Astrophysics Data System (ADS)

    Al-Hussaibi, Walid

    2015-09-01

    Chaos synchronization is one of the main challenging issues involved in the development of wireless chaos-based secure communication (CBSC) due its crucial influence on the error performance and system reliability. This paper is concerned with the effect of filtering chaotic signals on the synchronization and error performance of CBSC schemes due to the finite bandwidth of realistic fading channel and/or signal detection necessities. The double scroll chaotic attractor is employed at the transmit and receive terminals as in a drive-response configuration with identical synchronization and a low pass filter model is utilized in this investigation. The upper bound of bit error probability considering Rayleigh fading channel and synchronization mean squared error is derived and evaluated for different values of filter parameter. Theoretical analysis and simulation results show that as the filter cut-off frequency decreased lower than the chaotic signal bandwidth, the synchronization error is considerably increased due to high distortion in the normal geometrical configuration of the attractor. As a result, the average bit-error-rate performance is degraded significantly with high possibility of link failure. Therefore, careful system design should be made to mitigate the filtering effects and achieve the essential synchronization of promising CBSC systems.

  3. SER Performance of Enhanced Spatial Multiplexing Codes with ZF/MRC Receiver in Time-Varying Rayleigh Fading Channels

    PubMed Central

    Lee, In-Ho

    2014-01-01

    We propose enhanced spatial multiplexing codes (E-SMCs) to enable various encoding rates. The symbol error rate (SER) performance of the E-SMC is investigated when zero-forcing (ZF) and maximal-ratio combining (MRC) techniques are used at a receiver. The proposed E-SMC allows a transmitted symbol to be repeated over time to achieve further diversity gain at the cost of the encoding rate. With the spatial correlation between transmit antennas, SER equations for M-ary QAM and PSK constellations are derived by using a moment generating function (MGF) approximation of a signal-to-noise ratio (SNR), based on the assumption of independent zero-forced SNRs. Analytic and simulated results are compared for time-varying and spatially correlated Rayleigh fading channels that are modelled as first-order Markovian channels. Furthermore, we can find an optimal block length for the E-SMC that meets a required SER. PMID:25114969

  4. Combined coding and delay-throughput analysis for fading channels of mobile satellite communications

    NASA Technical Reports Server (NTRS)

    Wang, C. C.; Yan, Tsun-Yee

    1986-01-01

    This paper presents the analysis of using the punctured convolutional code with Viterbi decoding to improve communications reliability. The punctured code rate is optimized so that the average delay is minimized. The coding gain in terms of the message delay is also defined. Since using punctured convolutional code with interleaving is still inadequate to combat the severe fading for short packets, the use of multiple copies of assignment and acknowledgment packets is suggested. The performance on the average end-to-end delay of this protocol is analyzed. It is shown that a replication of three copies for both assignment packets and acknowledgment packets is optimum for the cases considered.

  5. Adaptive selective relaying in cooperative free-space optical systems over atmospheric turbulence and misalignment fading channels.

    PubMed

    Boluda-Ruiz, Rubén; García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2014-06-30

    In this paper, a novel adaptive cooperative protocol with multiple relays using detect-and-forward (DF) over atmospheric turbulence channels with pointing errors is proposed. The adaptive DF cooperative protocol here analyzed is based on the selection of the optical path, source-destination or different source-relay links, with a greater value of fading gain or irradiance, maintaining a high diversity order. Closed-form asymptotic bit error-rate (BER) expressions are obtained for a cooperative free-space optical (FSO) communication system with Nr relays, when the irradiance of the transmitted optical beam is susceptible to either a wide range of turbulence conditions, following a gamma-gamma distribution of parameters α and β, or pointing errors, following a misalignment fading model where the effect of beam width, detector size and jitter variance is considered. A greater robustness for different link distances and pointing errors is corroborated by the obtained results if compared with similar cooperative schemes or equivalent multiple-input multiple-output (MIMO) systems. Simulation results are further demonstrated to confirm the accuracy and usefulness of the derived results.

  6. Performance Improvement in Spatially Multiplexed MIMO Systems over Weibull-Gamma Fading Channel

    NASA Astrophysics Data System (ADS)

    Tiwari, Keerti; Saini, Davinder S.; Bhooshan, Sunil V.

    2016-11-01

    In multiple-input multiple-output (MIMO) systems, spatial demultiplexing at the receiver has its own significance. Thus, several detection techniques have been investigated. There is a tradeoff between computational complexity and optimal performance in most of the detection techniques. One of the detection techniques which gives improved performance and acceptable level of complexity is ordered successive interference cancellation (OSIC) with minimum mean square error (MMSE). However, optimal performance can be achieved by maximum likelihood (ML) detection but at a higher complexity level. Therefore, MMSE-OSIC with candidates (OSIC2) detection is recommended as a solution. In this paper, spatial multiplexed (SM) MIMO systems are considered to evaluate error performance with different detection techniques such as MMSE-OSIC, ML and MMSE-OSIC2 in a composite fading i. e. Weibull-gamma (WG) fading environment. In WG distribution, Weibull and gamma distribution represent multipath and shadowing effects, respectively. Simulation results illustrate that MMSE-OSIC2 detection technique gives the improved symbol error rate (SER) performance which is similar to ML performance and its complexity level approaches to MMSE-OSIC.

  7. Delay and throughput characteristics of TH, CDMA, TDMA, and hybrid networks for multipath faded data transmission channels

    NASA Astrophysics Data System (ADS)

    Elhakeem, Ahmed K.; Digirolamo, Rocco; Bdira, Ilyess B.; Talla, M.

    1994-05-01

    The new concepts of adaptive time hopping and variable frame Code Division (CDMA) Multiple Access are introduced. By a unified analysis, the probabilities of bit and packet errors in multipath fading environment for five Time Division (TDMA), Code Division, and Time Hopping (TH) related multiaccess networks are obtained; namely, TDMA, CDMA, CDMA/TDMA, Adaptive CDMA/TH, and variable frame CDMA/TDMA networks. The delay and useful throughputs of the five systems are also evaluated for data and voice traffic. All systems compared have the same channel power and bandwidth and support the same traffic. Though implementation issues are not covered, CDMA systems are put at a disadvantage (compared to cellular-type FDMA networks, for example) by ignoring such inherent advantages as voice silence utilizations and automatic frequency reuse. Nonetheless, two CDMA systems outperform TDMA systems at low and medium input traffics.

  8. Performance of concatenated Reed-Solomon trellis-coded modulation over Rician fading channels

    NASA Technical Reports Server (NTRS)

    Moher, Michael L.; Lodge, John H.

    1990-01-01

    A concatenated coding scheme for providing very reliable data over mobile-satellite channels at power levels similar to those used for vocoded speech is described. The outer code is a shorter Reed-Solomon code which provides error detection as well as error correction capabilities. The inner code is a 1-D 8-state trellis code applied independently to both the inphase and quadrature channels. To achieve the full error correction potential of this inner code, the code symbols are multiplexed with a pilot sequence which is used to provide dynamic channel estimation and coherent detection. The implementation structure of this scheme is discussed and its performance is estimated.

  9. On Frequency Offset Estimation Using the iNET Preamble in Frequency Selective Fading Channels

    DTIC Science & Technology

    2014-03-01

    ASM fields; (bottom) the relationship between the indexes of the received samples r(n), the signal samples s(n), the preamble samples p (n) and the short...frequency offset estimators for SOQPSK-TG equipped with the iNET preamble and operating in ISI channels. Four of the five estimators exam - ined here are...sync marker ( ASM ), and data bits (an LDPC codeword). The availability of a preamble introduces the possibility of data-aided synchro- nization in

  10. Unequal error protection codes for wavelet video transmission over W-CDMA, AWGN, and Rayleigh fading channels

    NASA Astrophysics Data System (ADS)

    Le, Minh Hung; Liyana-Pathirana, Ranjith

    2003-06-01

    The unequal error protection (UEP) codes with wavelet-based algorithm for video compression over wide-band code division multiple access (W-CDMA), additive white Gaussian noise (AWGN) and Rayleigh fading channels are analysed. The utilization of Wavelets has come out to be a powerful method for compress video sequence. The wavelet transform compression technique has shown to be more appropriate to high quality video applications, producing better quality output for the compressed frames of video. A spatially scalable video coding framework of MPEG2 in which motion correspondences between successive video frames are exploited in the wavelet transform domain. The basic motivation for our coder is that motion fields are typically smooth that can be efficiently captured through a multiresolutional framework. Wavelet decomposition is applied to video frames and the coefficients at each level are predicted from the coarser level through backward motion compensation. The proposed algorithms of the embedded zero-tree wavelet (EZW) coder and the 2-D wavelet packet transform (2-D WPT) are investigated.

  11. Outage Performance Analysis of Relay Selection Schemes in Wireless Energy Harvesting Cooperative Networks over Non-Identical Rayleigh Fading Channels.

    PubMed

    Do, Nhu Tri; Bao, Vo Nguyen Quoc; An, Beongku

    2016-02-26

    In this paper, we study relay selection in decode-and-forward wireless energy harvesting cooperative networks. In contrast to conventional cooperative networks, the relays harvest energy from the source's radio-frequency radiation and then use that energy to forward the source information. Considering power splitting receiver architecture used at relays to harvest energy, we are concerned with the performance of two popular relay selection schemes, namely, partial relay selection (PRS) scheme and optimal relay selection (ORS) scheme. In particular, we analyze the system performance in terms of outage probability (OP) over independent and non-identical (i.n.i.d.) Rayleigh fading channels. We derive the closed-form approximations for the system outage probabilities of both schemes and validate the analysis by the Monte-Carlo simulation. The numerical results provide comprehensive performance comparison between the PRS and ORS schemes and reveal the effect of wireless energy harvesting on the outage performances of both schemes. Additionally, we also show the advantages and drawbacks of the wireless energy harvesting cooperative networks and compare to the conventional cooperative networks.

  12. Improved BDF Relaying Scheme Using Time Diversity over Atmospheric Turbulence and Misalignment Fading Channels

    PubMed Central

    García-Zambrana, Antonio; Castillo-Vázquez, Carmen; Castillo-Vázquez, Beatriz

    2014-01-01

    A novel bit-detect-and-forward (BDF) relaying scheme based on repetition coding with the relay is proposed, significantly improving the robustness to impairments proper to free-space optical (FSO) communications such as unsuitable alignment between transmitter and receiver as well as fluctuations in the irradiance of the transmitted optical beam due to the atmospheric turbulence. Closed-form asymptotic bit-error-rate (BER) expressions are derived for a 3-way FSO communication setup. Fully exploiting the potential time-diversity available in the relay turbulent channel, a relevant better performance is achieved, showing a greater robustness to the relay location since a high diversity gain is provided regardless of the source-destination link distance. PMID:24587711

  13. Antenna Switching Schemes for Downlink Time Switched Transmit Diversity with ARQ in Rayleigh Fading Channels

    NASA Astrophysics Data System (ADS)

    Jeon, Cha-Eul; Hwang, Seung-Hoon

    For automatic repeat request (ARQ)-aided TSTD (Time Switched Transmit Diversity) system, a receiver sends the acknowledgement signal (ACK or NACK) to a transmitter in order to predict the condition of the channel. In this paper, two antenna switching schemes, in which the NACK trigger the transmit antenna switching in the proposed antenna switching patterns, are proposed for the TSTD with the ARQ in WCDMA LCR-TDD systems. In addition, the system performances are investigated. Simulation results demonstrate that the performances of the TSTD systems can be improved by applying the ARQ scheme. Furthermore, the performances of ARQ-aided TSTD systems may be significantly improved by applying the proposed antenna switching schemes, especially when the mobile's speed is low.

  14. Characterization of time delayed diversity to mitigate fading in atmospheric turbulence channels

    NASA Astrophysics Data System (ADS)

    Trisno, Sugianto; Smolyaninov, Igor I.; Milner, Stuart D.; Davis, Christopher C.

    2005-08-01

    Atmospheric turbulence is caused by inhomogeneities in the temperature and pressure of the atmosphere, resulting in random variations of the refractive index. A laser beam propagating through such turbulences experiences random amplitude and phase fluctuations, which can severely degrade the performance of free space optical (FSO) communication systems. In our time delayed diversity (TDD) technique, we transmit twice and take advantage of the fact that propagation along an atmospheric path is statistically uncorrelated with an earlier-time path for a time interval greater than the atmospheric turbulence correlation time. Communications performance is improved because the joint probability of error is less than the probability of error from individual channels. In this paper, we describe the theoretical and experimental analyses of FSO systems implementing this novel scheme in various performance scenarios. Theoretical models and performance of TDD systems are derived and characterized. The experimental performance results obtained under weak turbulence conditions are shown to be in good agreement with the theory. Related system design and implementation issues, such as: atmospheric turbulence statistics, laser beam depolarization, and diversity receiver architecture are also discussed.

  15. Fuzzy [Formula: see text] output-feedback control for the discrete-time system with channel fadings, sector nonlinearities, and randomly occurring interval delays and nonlinearities.

    PubMed

    Fan, Xiaozheng; Wang, Yan; Hu, Manfeng

    2016-01-01

    In this paper, the fuzzy [Formula: see text] output-feedback control problem is investigated for a class of discrete-time T-S fuzzy systems with channel fadings, sector nonlinearities, randomly occurring interval delays (ROIDs) and randomly occurring nonlinearities (RONs). A series of variables of the randomly occurring phenomena obeying the Bernoulli distribution is used to govern ROIDs and RONs. Meanwhile, the measurement outputs are subject to the sector nonlinearities (i.e. the sensor saturations) and we assume the system output is [Formula: see text], [Formula: see text]. The Lth-order Rice model is utilized to describe the phenomenon of channel fadings by setting different values of the channel coefficients. The aim of this work is to deal with the problem of designing a full-order dynamic fuzzy [Formula: see text] output-feedback controller such that the fuzzy closed-loop system is exponentially mean-square stable and the [Formula: see text] performance constraint is satisfied, by means of a combination of Lyapunov stability theory and stochastic analysis along with LMI methods. The proposed fuzzy controller parameters are derived by solving a convex optimization problem via the semidefinite programming technique. Finally, a numerical simulation is given to illustrate the feasibility and effectiveness of the proposed design technique.

  16. An error protection protocol for user-transparent bridging of Fast Ethernet data transmission over the optical fading channel in an aeronautical environment

    NASA Astrophysics Data System (ADS)

    Epple, Bernhard; Henniger, Hennes; Serrano Solsona, Clara

    2008-02-01

    This paper presents an extensive insight into error protection techniques for free space optical links, focusing in particular in aeronautic stratospherically applications. The long distances present in these scenarios along with challenging atmospherically conditions present significant obstacles that degrade link performance. Thus it is imperative to apply highly efficient error protection scheme to avoid unacceptably high loss rates. The goal was to design a point-to-point data link layer error protection protocol that allows user-transparent bridging of Fast Ethernet data transmission over the optical fading channel in an high altitude inter platform link environment.

  17. Multi-pair two-way massive MIMO AF relaying with ZFR/ZFT beamforming and imperfect CSI over ricean fading channels

    NASA Astrophysics Data System (ADS)

    Xu, Kui; Sun, Xiaoli; Zhang, Dongmei

    2016-10-01

    This paper investigates the spectral and energy efficiencies of a multi-pair two-way amplify-and-forward (AF) relay system over Ricean fading channels, where multiple user-pairs exchange information within pair through a relay with very large number of antennas, while each user equipped with a single antenna. Firstly, beamforming matrixe of zero-forcing reception/zero-forcing transmission (ZFR/ZFT) with imperfect channel state information (CSI) at the relay is given. Then, the unified asymptotic signal-to-interference-plus-noise ratio (SINR) expressions with imperfect CSI are obtained analytically. Finally, two power scaling schemes are proposed and the asymptotic spectral and energy efficiencies based on the proposed power scaling schemes are derived and verified by the Monte-Carlo simulations. Theoretical analyses and simulation results show that with imperfect CSI, if the number of relay antennas grows asymptotically large, we need cut down the transmit power of each user and relay to different proportion when the Ricean K-factor is non-zero and zero (Rayleigh fading) in order to maintain a desirable rate.

  18. Fading Skies

    ERIC Educational Resources Information Center

    Sio, Betsy Menson

    2009-01-01

    A sky fading from blue to white to red at the horizon, and water darkening from light to midnight blue. Strong diagonals slashing through the image, drawing a viewer's eyes deeper into the picture, and delicate trees poised to convey a sense of beauty. These are the fascinating strengths of the ukiyo-e woodblock prints of Japanese artist Ando…

  19. Fading In

    ERIC Educational Resources Information Center

    Nader, Karim; Wang, Szu-Han

    2006-01-01

    Patient H.M. can form new memories and maintain them for a few seconds before they fade away. From a neurobiological perspective, this amnesia is usually attributed to the absence of memory consolidation, that is, memory storage. An alternative view holds that this impairment reflects that the memory is present but cannot be retrieved. This debate…

  20. Fading Skies

    ERIC Educational Resources Information Center

    Sio, Betsy Menson

    2009-01-01

    A sky fading from blue to white to red at the horizon, and water darkening from light to midnight blue. Strong diagonals slashing through the image, drawing a viewer's eyes deeper into the picture, and delicate trees poised to convey a sense of beauty. These are the fascinating strengths of the ukiyo-e woodblock prints of Japanese artist Ando…

  1. Fading In

    ERIC Educational Resources Information Center

    Nader, Karim; Wang, Szu-Han

    2006-01-01

    Patient H.M. can form new memories and maintain them for a few seconds before they fade away. From a neurobiological perspective, this amnesia is usually attributed to the absence of memory consolidation, that is, memory storage. An alternative view holds that this impairment reflects that the memory is present but cannot be retrieved. This debate…

  2. Statistical analysis on the optical fading in free space optical channel for RoFSO link design

    NASA Astrophysics Data System (ADS)

    Kim, Kyung-Hwan; Higashino, Takeshi; Tsukamoto, Katsutoshi; Komaki, Shozo; Kazaura, Kamugisha; Matsumoto, Mitsuji

    2010-01-01

    This paper presents empirical probability density functions (p.d.fs) of variance and fluctuation speed of scintillation, through analyzing a number of experimental data measured in Japan by a statistical model. The model enables us to treat scintillation speed by one parameter of cut-off frequency in the power spectral density (PDS). By using the model and based on the two p.d.fs, we also present simulation results on the level crossing rate (LCR) and average fade duration (AFD). Combined the two results, an outage probabilities corresponding to a threshold optical intensity can be derived.

  3. Window-modulated compounding Nakagami imaging for ultrasound tissue characterization.

    PubMed

    Tsui, Po-Hsiang; Ma, Hsiang-Yang; Zhou, Zhuhuang; Ho, Ming-Chih; Lee, Yu-Hsin

    2014-08-01

    Ultrasound Nakagami parametric imaging is a useful tool for tissue characterization. Previous literature has suggested using a square with side lengths corresponding to 3 times the transducer pulse length as the minimum window for constructing the Nakagami image. This criterion does not produce sufficiently smooth images for the Nakagami image to characterize homogeneous tissues. To improve image smoothness, we proposed window-modulated compounding (WMC) Nakagami imaging based on summing and averaging the Nakagami images formed using sliding windows with varying window side lengths from 1 to N times the transducer pulse length in 1 pulse length step. Simulations (the number densities of scatterers: 2-16 scatterers/mm(2)) and experiments on fully developed speckle phantoms (the scatterer diameters: 20-106 μm) were conducted to suggest an appropriate number of frames N and to evaluate the image smoothness and resolution by analyzing the full width at half maximum (FWHM) of the parameter distribution and the widths of the image autocorrelation function (ACF), respectively. In vivo ultrasound measurements on rat livers without and with cirrhosis were performed to validate the practical performance of the WMC Nakagami image in tissue characterization. The simulation results showed that using a range of N from 7 to 10 as the number of frames for image compounding reduces the estimation error to less than 5%. Based on this criterion, the Nakagami parameter obtained from the WMC Nakagami image increased from 0.45 to 0.95 after increasing the number densities of scatterers from 2 to 16 scatterers/mm(2). The FWHM of the parameter distribution (bins=40) was 13.5±1.4 for the Nakagami image and 9.1±1.43 for the WMC Nakagami image, respectively (p-value<.05). The widths of the ACF for the Nakagami and WMC Nakagami images were 454±5.36 and 458±4.33, respectively (p-value>.05). In the phantom experiments, we also found that the FWHM of the parameter distribution for the WMC

  4. Performance of multi-hop parallel free-space optical communication over gamma-gamma fading channel with pointing errors.

    PubMed

    Gao, Zhengguang; Liu, Hongzhan; Ma, Xiaoping; Lu, Wei

    2016-11-10

    Multi-hop parallel relaying is considered in a free-space optical (FSO) communication system deploying binary phase-shift keying (BPSK) modulation under the combined effects of a gamma-gamma (GG) distribution and misalignment fading. Based on the best path selection criterion, the cumulative distribution function (CDF) of this cooperative random variable is derived. Then the performance of this optical mesh network is analyzed in detail. A Monte Carlo simulation is also conducted to demonstrate the effectiveness of the results for the average bit error rate (ABER) and outage probability. The numerical result proves that it needs a smaller average transmitted optical power to achieve the same ABER and outage probability when using the multi-hop parallel network in FSO links. Furthermore, the system use of more number of hops and cooperative paths can improve the quality of the communication.

  5. Three-dimensional ultrasonic Nakagami imaging for tissue characterization

    NASA Astrophysics Data System (ADS)

    Tsui, Po-Hsiang; Hsu, Cheng-Wei; Ho, Ming-Chih; Chen, Yung-Sheng; Lin, Jen-Jen; Chang, Chien-Cheng; Chu, Chin-Chou

    2010-10-01

    The two-dimensional (2D) Nakagami image complements the ultrasound B-scan image when attempting to visualize the scatterer properties of tissues. The resolution of the Nakagami image is lower than that of the B-scan image, since the former is produced by processing the raw envelope data using a 2D sliding window with side lengths typically corresponding to three times the pulse length of the incident ultrasound. This paper proposes using three-dimensional (3D) Nakagami imaging for improving the resolution of the obtained Nakagami image and providing more complete information of scatterers for a better tissue characterization. The 3D Nakagami image is based on a voxel array composed of the Nakagami parameters constructed using a 3D sliding cube to process the 3D backscattered raw data. Experiments on phantoms with different scatterer concentrations were carried out to determine the optimal size of the sliding cube for a stable estimation of the Nakagami parameter. Tissue measurements on rat livers without and with fibrosis formation were further used to explore the practical feasibility of 3D Nakagami imaging. The results indicated that the side length of the cube used to construct the 3D Nakagami image must be at least two times the pulse length, which improved the resolution for each Nakagami image frame in the 3D Nakagami image. The results further demonstrated that the 3D Nakagami image is better than the conventional 2D Nakagami image for complementing the B-scan in detecting spatial variations in the scatterer concentration and classifying normal and fibrotic livers. This study suggests that 3D Nakagami imaging has the potential to become a new 3D quantitative imaging approach.

  6. Three-dimensional ultrasonic Nakagami imaging for tissue characterization.

    PubMed

    Tsui, Po-Hsiang; Hsu, Cheng-Wei; Ho, Ming-Chih; Chen, Yung-Sheng; Lin, Jen-Jen; Chang, Chien-Cheng; Chu, Chin-Chou

    2010-10-07

    The two-dimensional (2D) Nakagami image complements the ultrasound B-scan image when attempting to visualize the scatterer properties of tissues. The resolution of the Nakagami image is lower than that of the B-scan image, since the former is produced by processing the raw envelope data using a 2D sliding window with side lengths typically corresponding to three times the pulse length of the incident ultrasound. This paper proposes using three-dimensional (3D) Nakagami imaging for improving the resolution of the obtained Nakagami image and providing more complete information of scatterers for a better tissue characterization. The 3D Nakagami image is based on a voxel array composed of the Nakagami parameters constructed using a 3D sliding cube to process the 3D backscattered raw data. Experiments on phantoms with different scatterer concentrations were carried out to determine the optimal size of the sliding cube for a stable estimation of the Nakagami parameter. Tissue measurements on rat livers without and with fibrosis formation were further used to explore the practical feasibility of 3D Nakagami imaging. The results indicated that the side length of the cube used to construct the 3D Nakagami image must be at least two times the pulse length, which improved the resolution for each Nakagami image frame in the 3D Nakagami image. The results further demonstrated that the 3D Nakagami image is better than the conventional 2D Nakagami image for complementing the B-scan in detecting spatial variations in the scatterer concentration and classifying normal and fibrotic livers. This study suggests that 3D Nakagami imaging has the potential to become a new 3D quantitative imaging approach.

  7. Modeling, Real-Time Estimation, and Identification of UWB Indoor Wireless Channels

    DOE PAGES

    Olama, Mohammed M.; Djouadi, Seddik M.; Li, Yanyan; ...

    2013-01-01

    Stochastic differential equations (SDEs) are used to model ultrawideband (UWB) indoor wireless channels. We show that the impulse responses for time-varying indoor wireless channels can be approximated in a mean-square sense as close as desired by impulse responses that can be realized by SDEs. The state variables represent the inphase and quadrature components of the UWB channel. The expected maximization and extended Kalman filter are employed to recursively identify and estimate the channel parameters and states, respectively, from online received signal strength measured data. Both resolvable and nonresolvable multipath received signals are considered and represented as small-scaled Nakagami fading. Themore » proposed models together with the estimation algorithm are tested using UWB indoor measurement data demonstrating the method’s viability and the results are presented.« less

  8. Modeling, Real-Time Estimation, and Identification of UWB Indoor Wireless Channels

    SciTech Connect

    Olama, Mohammed M; Djouadi, Seddik M; Li, Yanyan; Fathy, Aly

    2013-01-01

    In this paper, stochastic differential equations (SDEs) are used to model ultrawideband (UWB) indoor wireless channels. We show that the impulse responses for time-varying indoor wireless channels can be approximated in a mean square sense as close as desired by impulse responses that can be realized by SDEs. The state variables represent the inphase and quadrature components of the UWB channel. The expected maximization and extended Kalman filter are employed to recursively identify and estimate the channel parameters and states, respectively, from online received signal strength measured data. Both resolvable and non-resolvable multipath received signals are considered and represented as small-scaled Nakagami fading. The proposed models together with the estimation algorithm are tested using UWB indoor measurement data demonstrating the method s viability and the results are presented.

  9. ACTS Rain Fade Compensation

    NASA Technical Reports Server (NTRS)

    Coney, Thom A.

    1996-01-01

    Performance status of the Adaptive Rain Fade Compensation includes: (1) The rain fade protocol is functional detecting fades, providing an additional 10 dB of margin and seamless transitions to and from coded operation; (2) The stabilization of the link margins and the optimization of rain fade decision thresholds has resulted in improved BER performance; (3) Characterization of the fade compensation algorithm is ongoing.

  10. ACTS Rain Fade Compensation

    NASA Technical Reports Server (NTRS)

    Coney, Thom A.

    1996-01-01

    Performance status of the Adaptive Rain Fade Compensation includes: (1) The rain fade protocol is functional detecting fades, providing an additional 10 dB of margin and seamless transitions to and from coded operation; (2) The stabilization of the link margins and the optimization of rain fade decision thresholds has resulted in improved BER performance; (3) Characterization of the fade compensation algorithm is ongoing.

  11. Impact of nonzero boresight pointing errors on the performance of a relay-assisted free-space optical communication system over exponentiated Weibull fading channels.

    PubMed

    Wang, Ping; Liu, Xiaoxia; Cao, Tian; Fu, Huihua; Wang, Ranran; Guo, Lixin

    2016-09-20

    The impact of nonzero boresight pointing errors on the system performance of decode-and-forward protocol-based multihop parallel optical wireless communication systems is studied. For the aggregated fading channel, the atmospheric turbulence is simulated by an exponentiated Weibull model, and pointing errors are described by one recently proposed statistical model including both boresight and jitter. The binary phase-shift keying subcarrier intensity modulation-based analytical average bit error rate (ABER) and outage probability expressions are achieved for a nonidentically and independently distributed system. The ABER and outage probability are then analyzed with different turbulence strengths, receiving aperture sizes, structure parameters (P and Q), jitter variances, and boresight displacements. The results show that aperture averaging offers almost the same system performance improvement with boresight included or not, despite the values of P and Q. The performance enhancement owing to the increase of cooperative path (P) is more evident with nonzero boresight than that with zero boresight (jitter only), whereas the performance deterioration because of the increasing hops (Q) with nonzero boresight is almost the same as that with zero boresight. Monte Carlo simulation is offered to verify the validity of ABER and outage probability expressions.

  12. Outage Performance Analysis of Relay Selection Schemes in Wireless Energy Harvesting Cooperative Networks over Non-Identical Rayleigh Fading Channels

    PubMed Central

    Do, Nhu Tri; Bao, Vo Nguyen Quoc; An, Beongku

    2016-01-01

    In this paper, we study relay selection in decode-and-forward wireless energy harvesting cooperative networks. In contrast to conventional cooperative networks, the relays harvest energy from the source’s radio-frequency radiation and then use that energy to forward the source information. Considering power splitting receiver architecture used at relays to harvest energy, we are concerned with the performance of two popular relay selection schemes, namely, partial relay selection (PRS) scheme and optimal relay selection (ORS) scheme. In particular, we analyze the system performance in terms of outage probability (OP) over independent and non-identical (i.n.i.d.) Rayleigh fading channels. We derive the closed-form approximations for the system outage probabilities of both schemes and validate the analysis by the Monte-Carlo simulation. The numerical results provide comprehensive performance comparison between the PRS and ORS schemes and reveal the effect of wireless energy harvesting on the outage performances of both schemes. Additionally, we also show the advantages and drawbacks of the wireless energy harvesting cooperative networks and compare to the conventional cooperative networks. PMID:26927119

  13. Indoor radio channel modeling and mitigation of fading effects using linear and circular polarized antennas in combination for smart home system at 868 MHz

    NASA Astrophysics Data System (ADS)

    Wunderlich, S.; Welpot, M.; Gaspard, I.

    2014-11-01

    The markets for smart home products and services are expected to grow over the next years, driven by the increasing demands of homeowners considering energy monitoring, management, environmental controls and security. Many of these new systems will be installed in existing homes and offices and therefore using radio based systems for cost reduction. A drawback of radio based systems in indoor environments are fading effects which lead to a high variance of the received signal strength and thereby to a difficult predictability of the encountered path loss of the various communication links. For that reason it is necessary to derive a statistical path loss model which can be used to plan a reliable and cost effective radio network. This paper presents the results of a measurement campaign, which was performed in six buildings to deduce realistic radio channel models for a high variety of indoor radio propagation scenarios in the short range devices (SRD) band at 868 MHz. Furthermore, a potential concept to reduce the variance of the received signal strength using a circular polarized (CP) patch antenna in combination with a linear polarized antenna in an one-to-one communication link is presented.

  14. Beamforming effects on generalized Nakagami imaging.

    PubMed

    Yu, Xue; Guo, Yuexin; Huang, Sheng-Min; Li, Meng-Lin; Lee, Wei-Ning

    2015-10-07

    Ultrasound tissue characterization is crucial for the detection of tissue abnormalities. Since the statistics of the backscattered ultrasound signals strongly depend on density and spatial arrangement of local scatterers, appropriate modeling of the backscattered signals may be capable of providing unique physiological information on local tissue properties. Among various techniques, the Nakagami imaging, realized in a window-based estimation scheme, has a good performance in assessing different scatterer statistics in tissues. However, inconsistent m values have been reported in literature and obtained only from a local tissue region, abating the reliability of Nakagami imaging in tissue characterization. The discrepancies in m values in relevant literature may stem from the nonuniformity of the ultrasound image resolution, which is often neglected. We therefore hypothesized that window-based Nakagami m estimation was highly associated with the regional spatial resolution of ultrasound imaging. To test this hypothesis, our study investigated the effect of beamforming methods, including synthetic aperture (SA), coherent plane wave compounding (CPWC), multi-focusing (MF), and single-focusing (SF), on window-based m parameter estimation from the perspective of the resolution cell. The statistics of m parameter distribution as a function of imaging depth were characterized by their mean, variance, and skewness. The phantom with a low scatterer density (16 scatterers mm(-3)) had significantly lower m values compared to the ones with high scatterer densities (32 and 64 scatterers mm(-3)). Results from the homogeneous phantom with 64 scatterers mm(-3) showed that SA, MF, and CPWC had relatively uniform lateral resolutions compared to SF and thus relatively constant m estimates at different imaging depths. Our findings suggest that an ultrasound imaging regime exhibiting invariant spatial resolution throughout the entire imaging field of view would be the most appropriate

  15. Beamforming effects on generalized Nakagami imaging

    NASA Astrophysics Data System (ADS)

    Yu, Xue; Guo, Yuexin; Huang, Sheng-Min; Li, Meng-Lin; Lee, Wei-Ning

    2015-10-01

    Ultrasound tissue characterization is crucial for the detection of tissue abnormalities. Since the statistics of the backscattered ultrasound signals strongly depend on density and spatial arrangement of local scatterers, appropriate modeling of the backscattered signals may be capable of providing unique physiological information on local tissue properties. Among various techniques, the Nakagami imaging, realized in a window-based estimation scheme, has a good performance in assessing different scatterer statistics in tissues. However, inconsistent m values have been reported in literature and obtained only from a local tissue region, abating the reliability of Nakagami imaging in tissue characterization. The discrepancies in m values in relevant literature may stem from the nonuniformity of the ultrasound image resolution, which is often neglected. We therefore hypothesized that window-based Nakagami m estimation was highly associated with the regional spatial resolution of ultrasound imaging. To test this hypothesis, our study investigated the effect of beamforming methods, including synthetic aperture (SA), coherent plane wave compounding (CPWC), multi-focusing (MF), and single-focusing (SF), on window-based m parameter estimation from the perspective of the resolution cell. The statistics of m parameter distribution as a function of imaging depth were characterized by their mean, variance, and skewness. The phantom with a low scatterer density (16 scatterers mm-3) had significantly lower m values compared to the ones with high scatterer densities (32 and 64 scatterers mm-3). Results from the homogeneous phantom with 64 scatterers mm-3 showed that SA, MF, and CPWC had relatively uniform lateral resolutions compared to SF and thus relatively constant m estimates at different imaging depths. Our findings suggest that an ultrasound imaging regime exhibiting invariant spatial resolution throughout the entire imaging field of view would be the most appropriate for

  16. Performance Analysis of IEEE 802.11g Receivers With Erasure Decoding to Mitigate the Effects of Pulse-Noise Interference

    DTIC Science & Technology

    2006-12-01

    alternative statistical model is the Nakagami - m distribution which is a flexible model for the fading channel since it includes the Rayleigh fading...with r=1/2 convolutional source coding and HDD for a Nakagami fading channel ( m =1) ( 0 15dBbE N...BPSK/QPSK in AWGN and PNI with r=3/4 convolutional source coding and HDD for a Nakagami fading channel ( m =1) ( 0 24dBbE N

  17. Digital Communications Over Fading Channels

    DTIC Science & Technology

    2007-11-02

    46 22 Exact and approximate performance of BPSK with continuous narrowband...1) M−1∑ n=1 (−1)n+1 n + 1 ( M − 1 n ) exp (−nγs n+ 1 ) ( 46 ) Substituting (14) and ( 46 ) into (10), we obtain Pb = M 2(M − 1) ∫ ∞ 0 M−1∑ n=1 (−1)n+1 n...average transmitted power is the same whether coded or uncoded bits are transmitted: EbcRbc = EbRb (60) Hence, Ebc = rEb (61) Since r < 1, the average

  18. Performance analysis of generalized QAM modulation under η-μ and κ-μ fading

    NASA Astrophysics Data System (ADS)

    L Queiroz, Wamberto J.; Madeiro, Francisco; A Lopes, Waslon T.; Alencar, Marcelo S.

    2013-12-01

    This paper presents new closed-form expressions for the symbol error probability (SEP) of θ-QAM modulation with maximum ratio combining (MRC) receiver under η- μ and κ- μ fading. The SEP formulae, obtained from the definite integrals of the moment generating function (MGF) of the signal-to-noise ratio (SNR) at the input of the MRC receiver, are written in terms of Lauricella functions. The numerical evaluation of the expressions is carried out for the η- μ distribution, which includes important distributions as special cases, such as Hoyt, Nakagami- m, Rayleigh, and one-sided Gaussian, as well as for the κ- μ distribution, which includes Rice, Nakagami- m, Rayleigh, and one-sided Gaussian as special cases.

  19. Performance evaluation of ultrasonic Nakagami image in tissue characterization.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Chang, Chien-Cheng; Chen, Wen-Shiang

    2008-04-01

    Conventional ultrasonic B-mode images qualitatively describe tissue structures but are unsuitable for quantitative analyses of scatterer properties. We have recently developed an ultrasonic parametric imaging technique based on the Nakagami statistical distribution that is able to quantify scatterer concentrations. The aim of the present study is to further explore both the behavior of a Nakagami image in characterizing different scatterer structures at different signal-to-noise ratios (SNRs) and the feasibility of Nakagami imaging using a general commercial ultrasound scanner for tissue examinations. Simulations, experiments on a tissue-mimicking phantom and in vitro measurements on a muscle tissue before and after microwave treatment were carried out. The SNR and contrast-to-noise ratio (CNR) were estimated to quantify image performance. The results demonstrate that a Nakagami image can differentiate different scatterer concentrations for single, hypoechoic and hyperechoic targets. Also, a Nakagami image, when combined with an ultrasound scanner, can complement the B-scan to characterize tissue and to identify the region of interest with a larger CNR. However, the noise effect can degrade the performance of a Nakagami image. When the signal SNR decreased to 15 dB in simulations and to 8 dB in experiments, the CNR of the hyperechoic Nakagami image decreased by 4% and 27%, respectively, and that of the hypoechoic one decreased by 42% and 80%, respectively. These results indicate that a Nakagami image behaves well in identifying regions with high scatterer concentrations but does not perform well when both the scatterer concentration and SNR are low.

  20. Imaging local scatterer concentrations by the Nakagami statistical model.

    PubMed

    Tsui, Po-Hsiang; Chang, Chien-Cheng

    2007-04-01

    The ultrasonic B-mode image is an important clinical tool used to examine the internal structures of the biological tissue. Due to the fact that the conventional B-scans cannot fully reflect the nature of the tissue, some useful quantitative parameters have been applied to quantify the properties of the tissue. Among various possibilities, the Nakagami parameter was demonstrated to have an outstanding ability to detect the variation of the scatterer concentration. This study is aimed to develop a scatterer concentration image based on the Nakagami parameter map to assist in the B-mode image for tissue characterization. In particular, computer simulations are carried out to generate phantoms of different scatterer concentrations and echogenicity coefficients and their B-mode and Nakagami parametric images are compared to evaluate the performance of the Nakagami image in differentiating the properties of the scatterers. The simulated results show that the B-mode image would be affected by the system settings and user operations, whereas the Nakagami parametric image provides a comparatively consistent image result when different diagnosticians use different dynamic ranges and system gains. This is largely because the Nakagami image formation is only based on the backscattered statistics of the ultrasonic signals in local tissues. Such an imaging principle allows the Nakagami image to quantify the local scatterer concentrations in the tissue and to extract the backscattering information from the regions of the weaker echoes that may be lost in the B-mode image. These findings suggest that the Nakagami image can be combined with the use of the B-mode image simultaneously to visualize the tissue structures and the scatterer properties for a better medical diagnosis.

  1. MODTEQ (Modulation Techniques), AN/FRC-170(V), Equalization, and Channel Medium Simulations.

    DTIC Science & Technology

    1986-01-01

    been enhanced to include the ability to model a Nakagami -Rice fading characteristic. The Nakagami -Rice characteristic is similar to the Rayleigh fading...8217’ PRDFFRNTA Figure 3-5 16 and 64 LEVEL Q AMI 3.4 MODTEI BASIC MODULES Figure 3-6 depicts the basic modules in block form utilized in the M ODTEQ...to hadwr cmlxty rati wa improve great.l. by SYM STM SY M SYM SYM S M STM_.’ v: ~ ~~Figure 5-2 UNDISTORTED Q PR EYE PATTERN.-’-2 5"-.’.’l . -. 5.1.4

  2. Ultrasound window-modulated compounding Nakagami imaging: Resolution improvement and computational acceleration for liver characterization.

    PubMed

    Ma, Hsiang-Yang; Lin, Ying-Hsiu; Wang, Chiao-Yin; Chen, Chiung-Nien; Ho, Ming-Chih; Tsui, Po-Hsiang

    2016-08-01

    Ultrasound Nakagami imaging is an attractive method for visualizing changes in envelope statistics. Window-modulated compounding (WMC) Nakagami imaging was reported to improve image smoothness. The sliding window technique is typically used for constructing ultrasound parametric and Nakagami images. Using a large window overlap ratio may improve the WMC Nakagami image resolution but reduces computational efficiency. Therefore, the objectives of this study include: (i) exploring the effects of the window overlap ratio on the resolution and smoothness of WMC Nakagami images; (ii) proposing a fast algorithm that is based on the convolution operator (FACO) to accelerate WMC Nakagami imaging. Computer simulations and preliminary clinical tests on liver fibrosis samples (n=48) were performed to validate the FACO-based WMC Nakagami imaging. The results demonstrated that the width of the autocorrelation function and the parameter distribution of the WMC Nakagami image reduce with the increase in the window overlap ratio. One-pixel shifting (i.e., sliding the window on the image data in steps of one pixel for parametric imaging) as the maximum overlap ratio significantly improves the WMC Nakagami image quality. Concurrently, the proposed FACO method combined with a computational platform that optimizes the matrix computation can accelerate WMC Nakagami imaging, allowing the detection of liver fibrosis-induced changes in envelope statistics. FACO-accelerated WMC Nakagami imaging is a new-generation Nakagami imaging technique with an improved image quality and fast computation.

  3. Measurement of satellite PCS fading using GPS

    NASA Astrophysics Data System (ADS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1995-08-01

    A six-channel commercial GPS receiver with a custom-made 40 deg tilted, rotating antenna has been assembled to make fade measurements for personal satellite communications. The system can measure up to two times per minute fades of up to 15 dB in the direction of each tracked satellite from 10 to 90 deg elevation. Photographic fisheye lens images were used to categorize the fade data obtained in several test locations according to fade states of clear, shadowed, or blocked. Multipath effects in the form of annular rings can be observed when most of the sky is clear. Tree fading by a Pecan exceeding 3.5 dB and 12 dB at 50 to 10 percent probability, respectively, compared with median fades of 7.5 dB measured earlier and the discrepancy is attributed to the change in ratio when measuring over an area as opposed to along a line. Data acquired inside buildings revealed 'rf-leaky' ceilings. Satellite diversity gain in a shadowed environment exceeded 6 dB at the 10 percent probability.

  4. Measurement of satellite PCS fading using GPS

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1995-01-01

    A six-channel commercial GPS receiver with a custom-made 40 deg tilted, rotating antenna has been assembled to make fade measurements for personal satellite communications. The system can measure up to two times per minute fades of up to 15 dB in the direction of each tracked satellite from 10 to 90 deg elevation. Photographic fisheye lens images were used to categorize the fade data obtained in several test locations according to fade states of clear, shadowed, or blocked. Multipath effects in the form of annular rings can be observed when most of the sky is clear. Tree fading by a Pecan exceeding 3.5 dB and 12 dB at 50 to 10 percent probability, respectively, compared with median fades of 7.5 dB measured earlier and the discrepancy is attributed to the change in ratio when measuring over an area as opposed to along a line. Data acquired inside buildings revealed 'rf-leaky' ceilings. Satellite diversity gain in a shadowed environment exceeded 6 dB at the 10 percent probability.

  5. Statistics of Sampled Rician Fading

    DTIC Science & Technology

    1993-02-01

    Equation 2.3. When R is zero, corresponding to full Rayleigh fading, i; il uces to the well-known form. 1 (PsE.) = 2( 1 + "y (Rayleigha Channel...t+ T)) = 20T2 p(r) Il where Eo = r cos +ir sin . There are two limiting forms for the correlation function p(,,). Under strongly disturbed scattering...f*1 , " I I Il I 1 I I’ I "i I I 1 1 I 1 I I I ’ 0 5 10.5.0.5.3.3.4 where ro, the decorrelation time of the electric field, is defined as the e

  6. Using ultrasound Nakagami imaging to assess liver fibrosis in rats.

    PubMed

    Ho, Ming-Chih; Lin, Jen-Jen; Shu, Yu-Chen; Chen, Chiung-Nien; Chang, King-Jen; Chang, Chien-Cheng; Tsui, Po-Hsiang

    2012-02-01

    This study explored the feasibility of using the ultrasound Nakagami image to assess the degree of liver fibrosis in rats. The rat has been widely used as a model in investigations of liver fibrosis. Ultrasound grayscale imaging makes it possible to observe fibrotic rat livers in real time. Statistical analysis of the envelopes of signals backscattered from rat livers may provide useful clues about the degree of liver fibrosis. The Nakagami-model-based image has been shown to be useful for characterizing scatterers in tissues by reflecting the echo statistics, and hence the Nakagami image may serve as a functional imaging tool for quantifying rat liver fibrosis. To validate this idea, fibrosis was induced in each rat liver (n=21) by an intraperitoneal injection of 0.5% dimethylnitrosamine. Livers were excised from rats for in vitro ultrasound scanning using a single-element transducer. The backscattered-signal envelopes of the acquired raw ultrasound signals were used for Nakagami imaging. The Metavir score determined by a pathologist was used to histologically quantify the degree of liver fibrosis. It was found that the Nakagami image could be used to distinguish different degrees of liver fibrosis in rats, since the average Nakagami parameter increased from 0.55 to 0.83 as the fibrosis score increased from 0 (i.e., normal) to 4. This correlation may be due to liver fibrosis in rats involving an increase in the concentration of local scatterers and the appearance of the periodic structures or clustering of scatterers that would change the backscattering statistics. The current findings indicate that the ultrasound Nakagami image has great potential as a functional imaging tool to complement the use of the conventional B-scan in animal studies of liver fibrosis.

  7. Completion Time Minimization and Robust Power Control in Wireless Packet Networks

    DTIC Science & Technology

    2008-12-18

    independent Rayleigh, Nakagami , or log-normal fading. I. INTRODUCTION Power control plays a crucial role in the operation of a wireless network, as it...concave in exponentiated channel power gains; e.g., when each user is under independent Rayleigh, Nakagami , or log-normal fading. 15. SUBJECT TERMS...probability constraint. We show that for a wide class of commonly used channel fading distributions, e.g., Rayleigh, Nakagami , and log-normal, robust

  8. Effect of adaptive threshold filtering on ultrasonic nakagami parameter to detect variation in scatterer concentration.

    PubMed

    Tsui, Po-Hsiang; Wan, Yung-Liang; Huang, Chih-Chung; Wang, Ming-Chen

    2010-10-01

    The Nakagami parameter is associated with the Nakagami distribution estimated from ultrasonic backscattered signals and closely reflects the scatterer concentrations in tissues. There is an interest in exploring the possibility of enhancing the ability of the Nakagami parameter to characterize tissues. In this paper, we explore the effect of adaptive thresholdfiltering based on the noise-assisted empirical mode decomposition of the ultrasonic backscattered signals on the Nakagami parameter as a function of scatterer concentration for improving the Nakagami parameter performance. We carried out phantom experiments using 5 MHz focused and nonfocused transducers. Before filtering, the dynamic ranges of the Nakagami parameter, estimated using focused and nonfocused transducers between the scatterer concentrations of 2 and 32 scatterers/mm3, were 0.44 and 0.1, respectively. After filtering, the dynamic ranges of the Nakagami parameter, using the focused and nonfocused transducers, were 0.71 and 0.79, respectively. The experimental results showed that the adaptive threshold filter makes the Nakagami parameter measured by a focused transducer more sensitive to the variation in the scatterer concentration. The proposed method also endows the Nakagami parameter measured by a nonfocused transducer with the ability to differentiate various scatterer concentrations. However, the Nakagami parameters estimated by focused and nonfocused transducers after adaptive threshold filtering have different physical meanings: the former represents the statistics of signals backscattered from unresolvable scatterers while the latter is associated with stronger resolvable scatterers or local inhomogeneity due to scatterer aggregation.

  9. Performance analysis of relay-aided free-space optical communication system over gamma-gamma fading channels with pointing errors

    NASA Astrophysics Data System (ADS)

    Fu, Hui-hua; Wang, Ping; Wang, Ran-ran; Liu, Xiao-xia; Guo, Li-xin; Yang, Yin-tang

    2016-07-01

    The average bit error rate ( ABER) performance of a decode-and-forward (DF) based relay-assisted free-space optical (FSO) communication system over gamma-gamma distribution channels considering the pointing errors is studied. With the help of Meijer's G-function, the probability density function (PDF) and cumulative distribution function (CDF) of the aggregated channel model are derived on the basis of the best path selection scheme. The analytical ABER expression is achieved and the system performance is then investigated with the influence of pointing errors, turbulence strengths and structure parameters. Monte Carlo (MC) simulation is also provided to confirm the analytical ABER expression.

  10. Ultrasonic backscattering in tissue: characterization through Nakagami-generalized inverse Gaussian distribution.

    PubMed

    Agrawal, Rajeev; Karmeshu

    2007-02-01

    Ultrasonic tissue characterization through composite probability distributions such as Nakagami-lognormal, Nakagami-gamma, Nakagami-inverse Gaussian has been found to be useful. Such a probabilistic description also depicts heavy tails which arise from multiple scattering in tissue besides local and global variations in scattering cross-sections. A new composite probability distribution, viz. Nakagami-generalized inverse Gaussian distribution (NGIGD) with four parameters is proposed which under different limiting conditions results in approximating the known distributions. A salient aspect of the new distribution is that the probability density function (pdf) of NGIGD variate is available in closed form and is analytically tractable.

  11. Acoustic structure quantification by using ultrasound Nakagami imaging for assessing liver fibrosis

    PubMed Central

    Tsui, Po-Hsiang; Ho, Ming-Chih; Tai, Dar-In; Lin, Ying-Hsiu; Wang, Chiao-Yin; Ma, Hsiang-Yang

    2016-01-01

    Acoustic structure quantification (ASQ) is a recently developed technique widely used for detecting liver fibrosis. Ultrasound Nakagami parametric imaging based on the Nakagami distribution has been widely used to model echo amplitude distribution for tissue characterization. We explored the feasibility of using ultrasound Nakagami imaging as a model-based ASQ technique for assessing liver fibrosis. Standard ultrasound examinations were performed on 19 healthy volunteers and 91 patients with chronic hepatitis B and C (n = 110). Liver biopsy and ultrasound Nakagami imaging analysis were conducted to compare the METAVIR score and Nakagami parameter. The diagnostic value of ultrasound Nakagami imaging was evaluated using receiver operating characteristic (ROC) curves. The Nakagami parameter obtained through ultrasound Nakagami imaging decreased with an increase in the METAVIR score (p < 0.0001), representing an increase in the extent of pre-Rayleigh statistics for echo amplitude distribution. The area under the ROC curve (AUROC) was 0.88 for the diagnosis of any degree of fibrosis (≥F1), whereas it was 0.84, 0.69, and 0.67 for ≥F2, ≥F3, and ≥F4, respectively. Ultrasound Nakagami imaging is a model-based ASQ technique that can be beneficial for the clinical diagnosis of early liver fibrosis. PMID:27605260

  12. Acoustic structure quantification by using ultrasound Nakagami imaging for assessing liver fibrosis.

    PubMed

    Tsui, Po-Hsiang; Ho, Ming-Chih; Tai, Dar-In; Lin, Ying-Hsiu; Wang, Chiao-Yin; Ma, Hsiang-Yang

    2016-09-08

    Acoustic structure quantification (ASQ) is a recently developed technique widely used for detecting liver fibrosis. Ultrasound Nakagami parametric imaging based on the Nakagami distribution has been widely used to model echo amplitude distribution for tissue characterization. We explored the feasibility of using ultrasound Nakagami imaging as a model-based ASQ technique for assessing liver fibrosis. Standard ultrasound examinations were performed on 19 healthy volunteers and 91 patients with chronic hepatitis B and C (n = 110). Liver biopsy and ultrasound Nakagami imaging analysis were conducted to compare the METAVIR score and Nakagami parameter. The diagnostic value of ultrasound Nakagami imaging was evaluated using receiver operating characteristic (ROC) curves. The Nakagami parameter obtained through ultrasound Nakagami imaging decreased with an increase in the METAVIR score (p < 0.0001), representing an increase in the extent of pre-Rayleigh statistics for echo amplitude distribution. The area under the ROC curve (AUROC) was 0.88 for the diagnosis of any degree of fibrosis (≥F1), whereas it was 0.84, 0.69, and 0.67 for ≥F2, ≥F3, and ≥F4, respectively. Ultrasound Nakagami imaging is a model-based ASQ technique that can be beneficial for the clinical diagnosis of early liver fibrosis.

  13. Characteristics of deep GPS signal fading due to ionospheric scintillation for aviation receiver design

    NASA Astrophysics Data System (ADS)

    Seo, Jiwon; Walter, Todd; Chiou, Tsung-Yu; Enge, Per

    2009-02-01

    Deep and frequent fading of Global Positioning System (GPS) signals caused by ionospheric scintillation is a major concern for aircraft navigation using GPS in the equatorial region during solar maximum. Aviation receivers use both code and carrier measurements to calculate position solutions. Deep signal fading can break a receiver's carrier tracking lock to a satellite channel. The lost channel cannot be used for position calculation until the receiver reacquires the channel and reestablishes tracking. A solar maximum data set analyzed in this paper demonstrates frequent deep signal fading of almost all satellites in view. This could significantly reduce the number of simultaneous tracked satellites and consequently decrease navigation availability. Forty-five minutes of strong scintillation, which was the worst scintillation period of a 9 day campaign at Ascension Island in 2001, are analyzed in this paper. The importance of short reacquisition time of the receiver is described. In order to design an aviation receiver with short reacquisition time under frequent deep signal fading, the characteristics of signal fading should be well understood. Fading duration and the time between deep fades are two important characteristics for GPS navigation. This paper presents a fading duration model based on real scintillation data. The time between deep fades observed in this data shows very frequent deep fades which can significantly reduce benefit of carrier smoothing filters of aviation receivers.

  14. Microvascular flow estimation by microbubble-assisted Nakagami imaging.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Chang, Chien-Cheng

    2009-04-01

    The destruction and replenishment of microbubbles has been previously applied to estimating blood flow in the microcirculation. The rate of increase of the time-intensity curve (TIC) due to microbubbles flowing into the region-of-interest (ROI) as measured from the conventional B-mode images reflects the flow velocity. In this study, we monitored microbubble replenishment using a new proposed approach called the time-Nakagami-parameter curve (TNC) obtained from the parametric image based on the Nakagami statistical parameter for quantifying the microvascular flow velocity. The Nakagami parameter is estimated from signal envelope to reflect the backscattered statistics. The feasibility of using the TNC to estimate the microvascular flow was explored by carrying out phantom measurements and in vivo animal experiments. The rates of increase of the TIC and TNC were quantified as the rate constants beta(I) and beta(N) of monoexponential fitted curves, respectively. The experimental results showed that beta(N) behaves similarly to the conventional beta(I) in quantifying the flow velocity. Moreover, the tolerance to the effects of clutter is greater for the TNC than for the TIC, which makes it possible to use beta(N) to differentiate various flow velocities even when the ROI contains nonperfused areas. This finding suggests that the TNC-based technique can be used as a complementary tool for the conventional TIC to improve measurement of blood flow in the microcirculation.

  15. Use of nakagami statistics and empirical mode decomposition for ultrasound tissue characterization by a nonfocused transducer.

    PubMed

    Tsui, Po-Hsiang; Chang, Chien-Cheng; Ho, Ming-Chih; Lee, Yu-Hsin; Chen, Yung-Sheng; Chang, Chien-Chung; Huang, Norden E; Wu, Zhao-Hua; Chang, King-Jen

    2009-12-01

    The Nakagami parameter associated with the Nakagami distribution estimated from ultrasonic backscattered signals reflects the scatterer concentration in a tissue. A nonfocused transducer does not allow tissue characterization based on the Nakagami parameter. This paper proposes a new method called the noise-assisted Nakagami parameter based on empirical mode decomposition of noisy backscattered echoes to allow quantification of the scatterer concentration based on data obtained using a nonfocused transducer. To explore the practical feasibility of the proposed method, the current study performed experiments on phantoms and measurements on rat livers in vitro with and without fibrosis induction. The results show that using a nonfocused transducer makes it possible to use the noise-assisted Nakagami parameter to classify phantoms with different scatterer concentrations and different stages of liver fibrosis in rats more accurately than when using techniques based on the echo intensity and the conventional Nakagami parameter. However, the conventional Nakagami parameter and the noise-assisted Nakagami parameter have different meanings: the former represents the statistics of signals backscattered from unresolvable scatterers, whereas the latter is associated with stronger resolvable scatterers or local inhomogeneity caused by scatterer aggregation.

  16. Modeling of errors in Nakagami imaging: illustration on breast mass characterization.

    PubMed

    Larrue, Aymeric; Noble, J Alison

    2014-05-01

    Nakagami imaging is an attractive tissue characterization method, as the parameter estimated at each location is related to properties of the tissues. The application to clinical ultrasound images is problematic, as the estimation of the parameters is disturbed by the presence of complex structures. We propose to consider separately the different aspects potentially affecting the value of the Nakagami parameters and quantify their effects on the estimation. This framework is applied to the classification of breast masses. Quantitative parameters are computed on two groups of ultrasound images of benign and malignant tumors. A statistical analysis of the result indicated that the previously observed difference between average values of the Nakagami parameters is explained mostly by estimation errors. In the future, new methods for reliable computation of Nakagami parameters need to be developed, and factors of error should be considered in studies using Nakagami parameters.

  17. Noise-assisted correlation algorithm for suppressing noise-induced artifacts in ultrasonic Nakagami images.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Huang, Chih-Chung

    2012-05-01

    Ultrasonic Nakagami images can complement conventional B-mode images for scatterer characterization. White noise in anechoic areas leads to artifacts that affect the Nakagami image to characterize tissues. Artifact removal requires rejection of the white noise without deforming the backscattered waveform. This study proposes a noise-assisted correlation algorithm (NCA) and carries out simulations, phantom experiments, and clinical measurements to validate its feasibility and practicality. The simulation results show that the NCA can reject white noise in an anechoic area without any deformation of the backscattered waveforms. The results obtained from phantoms and tissues further demonstrate that the proposed NCA can suppress a Nakagami image artifact without changing the texture of the Nakagami image of the scattering background. The NCA is an essential algorithm to construct artifact-free Nakagami image for correctly reflecting scatterer properties of biological tissues.

  18. Development of a heterogeneous microwave network fade simulation tool applicable to networks that span Europe

    NASA Astrophysics Data System (ADS)

    Paulson, Kevin S.; Basarudin, Hafiz

    2011-08-01

    Several research groups in Europe are developing joint channel simulators for arbitrarily complex networks of terrestrial and slant path, microwave telecommunications links. Currently, the Hull Rain Fade Network Simulator (HRFNS) developed at University of Hull can simulate rain fade on arbitrary terrestrial networks in the southern United Kingdom, producing joint rain fade time series with a 10 s integration time. This paper reports on work to broaden the function of the existing HRFNS to include slant paths such as Earth-space links and communications to high altitude platforms and unmanned airborne systems. The area of application of the new simulation tool is being extended to the whole of Europe, and other fade mechanisms are being included. Nimrod/OPERA has been chosen as the input meteorological data sets for the new system to simulate rain fade. Zero-degree isotherm heights taken from NCEP/NCAR Reanalysis Data are used in conjunction with the Eden-Bacon sleet (wet snow) model to introduce melting layer effects. Other fading mechanisms, including cloud fade, scintillation and absorption losses by atmospheric gasses, can be added to the simulator. The simulator is tested against ITU-R models for rain fade distribution experienced by terrestrial and Earth-space links in the southern United Kingdom. Statistics of fade dynamics, i.e., fade slope and fade duration, for a simulated Earth-space link are compared to International Telecommunication Union models.

  19. Quantitative Ultrasonic Nakagami Imaging of Neck Fibrosis After Head and Neck Radiation Therapy.

    PubMed

    Yang, Xiaofeng; Yoshida, Emi; Cassidy, Richard J; Beitler, Jonathan J; Yu, David S; Curran, Walter J; Liu, Tian

    2015-06-01

    To investigate the feasibility of ultrasound Nakagami imaging to quantitatively assess radiation-induced neck fibrosis, a common sequela of radiation therapy (RT) to the head and neck. In a pilot study, 40 study participants were enrolled and classified into 3 subgroups: (1) a control group of 12 healthy volunteers; (2) an asymptomatic group of 11 patients who had received intensity modulated RT for head and neck cancer and had experienced no neck fibrosis; and (3) a symptomatic group of 17 post-RT patients with neck fibrosis. Each study participant underwent 1 ultrasound study in which scans were performed in the longitudinal orientation of the bilateral neck. Three Nakagami parameters were calculated to quantify radiation-induced tissue injury: Nakagami probability distribution function, shape, and scaling parameters. Physician-based assessments of the neck fibrosis were performed according to the Radiation Therapy Oncology Group late morbidity scoring scheme, and patient-based fibrosis assessments were rated based on symptoms such as pain and stiffness. Major discrepancies existed between physician-based and patient-based assessments of radiation-induced fibrosis. Significant differences in all Nakagami parameters were observed between the control group and 2 post-RT groups. Moreover, significant differences in Nakagami shape and scaling parameters were observed among asymptomatic and symptomatic groups. Compared with the control group, the average Nakagami shape parameter value increased by 32.1% (P<.001), and the average Nakagami scaling parameter increased by 55.7% (P<.001) for the asymptomatic group, whereas the Nakagami shape parameter increased by 74.1% (P<.001) and the Nakagami scaling parameter increased by 83.5% (P<.001) for the symptomatic group. Ultrasonic Nakagami imaging is a potential quantitative tool to characterize radiation-induced asymptomatic and symptomatic neck fibrosis. Copyright © 2015 Elsevier Inc. All rights reserved.

  20. Quantitative Ultrasonic Nakagami Imaging of Neck Fibrosis After Head and Neck Radiation Therapy

    SciTech Connect

    Yang, Xiaofeng; Yoshida, Emi; Cassidy, Richard J.; Beitler, Jonathan J.; Yu, David S.; Curran, Walter J.; Liu, Tian

    2015-06-01

    Purpose: To investigate the feasibility of ultrasound Nakagami imaging to quantitatively assess radiation-induced neck fibrosis, a common sequela of radiation therapy (RT) to the head and neck. Methods and Materials: In a pilot study, 40 study participants were enrolled and classified into 3 subgroups: (1) a control group of 12 healthy volunteers; (2) an asymptomatic group of 11 patients who had received intensity modulated RT for head and neck cancer and had experienced no neck fibrosis; and (3) a symptomatic group of 17 post-RT patients with neck fibrosis. Each study participant underwent 1 ultrasound study in which scans were performed in the longitudinal orientation of the bilateral neck. Three Nakagami parameters were calculated to quantify radiation-induced tissue injury: Nakagami probability distribution function, shape, and scaling parameters. Physician-based assessments of the neck fibrosis were performed according to the Radiation Therapy Oncology Group late morbidity scoring scheme, and patient-based fibrosis assessments were rated based on symptoms such as pain and stiffness. Results: Major discrepancies existed between physician-based and patient-based assessments of radiation-induced fibrosis. Significant differences in all Nakagami parameters were observed between the control group and 2 post-RT groups. Moreover, significant differences in Nakagami shape and scaling parameters were observed among asymptomatic and symptomatic groups. Compared with the control group, the average Nakagami shape parameter value increased by 32.1% (P<.001), and the average Nakagami scaling parameter increased by 55.7% (P<.001) for the asymptomatic group, whereas the Nakagami shape parameter increased by 74.1% (P<.001) and the Nakagami scaling parameter increased by 83.5% (P<.001) for the symptomatic group. Conclusions: Ultrasonic Nakagami imaging is a potential quantitative tool to characterize radiation-induced asymptomatic and symptomatic neck fibrosis.

  1. Feasibility of using Nakagami distribution in evaluating the formation of ultrasound-induced thermal lesions.

    PubMed

    Zhang, Siyuan; Zhou, Fanyu; Wan, Mingxi; Wei, Min; Fu, Quanyou; Wang, Xing; Wang, Supin

    2012-06-01

    The acoustic posterior shadowing effects of bubbles influence the accuracy for defining the location and range of ablated thermal lesions during focused ultrasound surgery when using ultrasonic monitoring imaging. This paper explored the feasibility of using Nakagami distribution to evaluate the ablated region induced by focused ultrasound exposures at different acoustic power levels in transparent tissue-mimicking phantoms. The mean value of the Nakagami parameter m was about 0.5 in the cavitation region and increased to around 1 in the ablated region. Nakagami images were not subject to significant shadowing effects of bubbles. Ultrasound-induced thermal lesions observed in the photos and Nakagami images were overshadowed by bubbles in the B-mode images. The lesion size predicted in the Nakagami images was smaller than that predicted in the photos due to the sub resolvable effect of Nakagami imaging at the interface. This preliminary study on tissue-mimicking phantom suggested that the Nakagami parameter m may have the potential use in evaluating the formation of ultrasound-induced thermal lesion when the shadowing effect of bubbles is strong while the thermal lesion was small. Further studies in vivo and in vitro will be needed to evaluate the potential application.

  2. Ultrasonic Nakagami imaging: a strategy to visualize the scatterer properties of benign and malignant breast tumors.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Liao, Yin-Yin; Chang, Chien-Cheng; Kuo, Wen-Hung; Chang, King-Jen; Chen, Chiung-Nien

    2010-02-01

    Previous studies have demonstrated the usefulness of the Nakagami parameter in characterizing breast tumors by ultrasound. However, physicians or radiologists may need imaging tools in a clinical setting to visually identify the properties of breast tumors. This study proposed the ultrasonic Nakagami image to visualize the scatterer properties of breast tumors and then explored its clinical performance in classifying benign and malignant tumors. Raw data of ultrasonic backscattered signals were collected from 100 patients (50 benign and 50 malignant cases) using a commercial ultrasound scanner with a 7.5 MHz linear array transducer. The backscattered signals were used to form the B-scan and the Nakagami images of breast tumors. For each tumor, the average Nakagami parameter was calculated from the pixel values in the region-of-interest in the Nakagami image. The receiver operating characteristic (ROC) curve was used to evaluate the clinical performance of the Nakagami image. The results showed that the Nakagami image shadings in benign tumors were different from those in malignant cases. The average Nakagami parameters for benign and malignant tumors were 0.69 +/- 0.12 and 0.55 +/- 0.12, respectively. This means that the backscattered signals received from malignant tumors tend to be more pre-Rayleigh distributed than those from benign tumors, corresponding to a more complex scatterer arrangement or composition. The ROC analysis showed that the area under the ROC curve was 0.81 +/- 0.04 and the diagnostic accuracy was 82%, sensitivity was 92% and specificity was 72%. The results showed that the Nakagami image is useful to distinguishing between benign and malignant breast tumors. 2010 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. All rights reserved.

  3. Tissue Characterization on Ultrasound Harmonic Signals using Nakagami Statistics

    NASA Astrophysics Data System (ADS)

    Lin, Fanglue; Cristea, Anca; Cachard, Christian; Basset, Olivier

    Quantitative ultrasound (QUS) imaging provides a way to characterize biological tissue. The QUS estimates can be obtained from the envelope statistics. Previous studies are mainly based on the whole backscattered signals analysis. However, the ultrasound propagation is a nonlinear process and the harmonic signals can therefore reveal the nonlinear nature of a biological medium. The present study investigates the statistics of harmonic signal envelopes to relate the distribution parameters to the nonlinear coefficients. The main results demonstrate that the distributions exhibit a different behavior for fundamental and harmonic signals and that media with different nonlinearities can be distinguished, when using Nakagami statistics on the harmonic signal envelopes.

  4. Study of ultrasonic echo envelope based on Nakagami-inverse Gaussian distribution.

    PubMed

    Karmeshu; Agrawal, Rajeev

    2006-03-01

    A new probability density function (pdf) to describe the envelope of the backscattered echoes from tissues is proposed. The combined effect of multiple scattering and randomness arising from local and global variations in scattering cross-section is captured through Nakagami-inverse Gaussian distribution (NIGD). The proposed distribution has the advantage that it has a closed form unlike the realistic Nakagami-lognormal distribution (NLD). The degree of closeness, as measured in terms of Kullback-Leibler (KL) distance between two probability distributions is computed. It is shown that NIGD much more closely approximates NLD compared to Nakagami-gamma distribution (NGD) used to model such problems.

  5. Digital Communications in Fading Channels: COMLINK Validation

    DTIC Science & Technology

    2000-09-01

    U.S. Customary to metric (SI) units of measurement MULTIPLY "- BY D- TOGET TOGET N-o BY -- DIVIDE angstrom 1.000000 x E -10 meters (m) atmosphere...normal) 1.01325 x E +2 kilo pascal (kPa) bar 1.000000 x E +2 kilo pascal (kPa) barn 1.000000 x E -28 meter2 (m2 ) British thermal unit (thermochemical...1.054350 x E +3 joule (J) calorie (thermochemical) 4.184000 joule (J) cal (thermochemical) /cm2’ 4.184000 x E -2 mega joule/m2 (MJ/m 2) curie 3.700000

  6. Locally adaptive Nakagami-based ultrasound similarity measures.

    PubMed

    Wachinger, Christian; Klein, Tassilo; Navab, Nassir

    2012-04-01

    The derivation of statistically optimal similarity measures for intensity-based registration is possible by modeling the underlying image noise distribution. The parameters of these distributions are, however, commonly set heuristically across all images. In this article, we show that the estimation of the parameters on the present images largely improves the registration, which is a consequence of the more accurate characterization of the image noise. More precisely, instead of having constant parameters over the entire image domain, we estimate them on patches, leading to a local adaptation of the similarity measure. While this basic idea of creating locally adaptive metrics is interesting for various fields of application, we present the derivation for ultrasound imaging. The domain of ultrasound is particularly appealing for this approach, due to the inherent contamination with speckle noise. Furthermore, there exist detailed analyses of suitable noise distributions in the literature. We present experiments for applying a bivariate Nakagami distribution that facilitates modeling of several scattering scenarios prominent in medical ultrasound. Depending on the number of scatterers per resolution cell and the presence of coherent structures, different Nakagami parameters are required to obtain a valid approximation of the intensity statistics and to account for distributional locality. Our registration results on radio-frequency ultrasound data confirm the theoretical necessity for a spatial adaptation of similarity metrics.

  7. Classification of breast masses by ultrasonic Nakagami imaging: a feasibility study

    NASA Astrophysics Data System (ADS)

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Chang, Chien-Cheng; Liao, Yin-Yin

    2008-11-01

    Ultrasound is an important clinical tool in noninvasive diagnoses of breast cancer. The Nakagami statistical parameter estimated from the ultrasonic backscattered envelope has been demonstrated to be useful in complementing conventional B-mode scans when classifying breast masses. However, the shadowing effect caused by certain high-attenuation tumors in the B-mode image makes the tumor contour unclear, and thus it is more difficult to choose an appropriate region of interest from which to collect tumor data for estimating the Nakagami parameter. This study explored the feasibility of using the Nakagami parametric image to overcome the shadowing effect for visualizing the properties of breast masses. Experiments were performed on a breast-mimicking phantom and on some typical clinical cases for cysts, fat and tumors (fibroadenoma) (n = 18) in order to explore the performance of the Nakagami image under ideal and practical conditions. The experimental results showed that the Nakagami image pixels (i.e. the local Nakagami parameter) in the cyst, tumor and fat are 0.21 ± 0.01, 0.65 ± 0.05 and 0.98 ± 0.07, respectively, for six independent phantom measurements, and 0.14 ± 0.03, 0.67 ± 0.11 and 0.89 ± 0.08, respectively, for clinical experiments. This suggests that the Nakagami image is able to classify various breast masses (p < 0.005) although the clinical results from tumors of different cases have a larger variance that may be caused by the complexity of real breast tissues. In particular, unlike the B-mode image, the Nakagami image is not subject to significant shadowing effects, making it useful to complement the B-mode image to describe the tumor contour for identifying the tumor-related region when the shadowing effect is stronger or a low system gain is used.

  8. Classification of breast masses by ultrasonic Nakagami imaging: a feasibility study.

    PubMed

    Tsui, Po-Hsiang; Yeh, Chih-Kuang; Chang, Chien-Cheng; Liao, Yin-Yin

    2008-11-07

    Ultrasound is an important clinical tool in noninvasive diagnoses of breast cancer. The Nakagami statistical parameter estimated from the ultrasonic backscattered envelope has been demonstrated to be useful in complementing conventional B-mode scans when classifying breast masses. However, the shadowing effect caused by certain high-attenuation tumors in the B-mode image makes the tumor contour unclear, and thus it is more difficult to choose an appropriate region of interest from which to collect tumor data for estimating the Nakagami parameter. This study explored the feasibility of using the Nakagami parametric image to overcome the shadowing effect for visualizing the properties of breast masses. Experiments were performed on a breast-mimicking phantom and on some typical clinical cases for cysts, fat and tumors (fibroadenoma) (n = 18) in order to explore the performance of the Nakagami image under ideal and practical conditions. The experimental results showed that the Nakagami image pixels (i.e. the local Nakagami parameter) in the cyst, tumor and fat are 0.21 +/- 0.01, 0.65 +/- 0.05 and 0.98 +/- 0.07, respectively, for six independent phantom measurements, and 0.14 +/- 0.03, 0.67 +/- 0.11 and 0.89 +/- 0.08, respectively, for clinical experiments. This suggests that the Nakagami image is able to classify various breast masses (p < 0.005) although the clinical results from tumors of different cases have a larger variance that may be caused by the complexity of real breast tissues. In particular, unlike the B-mode image, the Nakagami image is not subject to significant shadowing effects, making it useful to complement the B-mode image to describe the tumor contour for identifying the tumor-related region when the shadowing effect is stronger or a low system gain is used.

  9. Nakagami imaging for detecting thermal lesions induced by high-intensity focused ultrasound in tissue.

    PubMed

    Rangraz, Parisa; Behnam, Hamid; Tavakkoli, Jahan

    2014-01-01

    High-intensity focused ultrasound induces focalized tissue coagulation by increasing the tissue temperature in a tight focal region. Several methods have been proposed to monitor high-intensity focused ultrasound-induced thermal lesions. Currently, ultrasound imaging techniques that are clinically used for monitoring high-intensity focused ultrasound treatment are standard pulse-echo B-mode ultrasound imaging, ultrasound temperature estimation, and elastography-based methods. On the contrary, the efficacy of two-dimensional Nakagami parametric imaging based on the distribution of the ultrasound backscattered signals to quantify properties of soft tissue has recently been evaluated. In this study, ultrasound radio frequency echo signals from ex vivo tissue samples were acquired before and after high-intensity focused ultrasound exposures and then their Nakagami parameter and scaling parameter of Nakagami distribution were estimated. These parameters were used to detect high-intensity focused ultrasound-induced thermal lesions. Also, the effects of changing the acoustic power of the high-intensity focused ultrasound transducer on the Nakagami parameters were studied. The results obtained suggest that the Nakagami distribution's scaling and Nakagami parameters can effectively be used to detect high-intensity focused ultrasound-induced thermal lesions in tissue ex vivo. These parameters can also be used to understand the degree of change in tissue caused by high-intensity focused ultrasound exposures, which could be interpreted as a measure of degree of variability in scatterer concentration in various parts of the high-intensity focused ultrasound lesion.

  10. Earth-Space Links and Fade-Duration Statistics

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz

    1996-01-01

    In recent years, fade-duration statistics have been the subject of several experimental investigations. A good knowledge of the fade-duration distribution is important for the assessment of a satellite communication system's channel dynamics: What is a typical link outage duration? How often do link outages exceeding a given duration occur? Unfortunately there is yet no model that can universally answer the above questions. The available field measurements mainly come from temperate climatic zones and only from a few sites. Furthermore, the available statistics are also limited in the choice of frequency and path elevation angle. Yet, much can be learned from the available information. For example, we now know that the fade-duration distribution is approximately lognormal. Under certain conditions, we can even determine the median and other percentiles of the distribution. This paper reviews the available data obtained by several experimenters in different parts of the world. Areas of emphasis are mobile and fixed satellite links. Fades in mobile links are due to roadside-tree shadowing, whereas fades in fixed links are due to rain attenuation.

  11. Earth-space links and fade-duration statistics

    NASA Technical Reports Server (NTRS)

    Davarian, Faramaz

    1995-01-01

    In recent years, fade-duration statistics have been the subject of several experimental investigations. A good knowledge of the fade-duration distribution is important for the assessment of a satellite communication system's channel dynamics: What is a typical link outage duration? How often do link outages exceeding a given duration occur? Unfortunately there is yet no model that can universally answer the above questions. The available field measurements mainly come from temperate climatic zones and only from a few sites. Furthermore, the available statistics are also limited in the choice of frequency and path elevation angle. Yet, much can be learned from the available information. For example, we now know that the fade-duration distribution is approximately lognormal. Under certain conditions, we can even determine the median and other percentiles of the distribution. This paper reviews the available data obtained by several experimenters in different parts of the world. Areas of emphasis are mobile and fixed satellite links. Fades in mobile links are due to roadside-tree shadowing, whereas fades in fixed links are due to rain attenuation.

  12. Phase and frequency coherency in fading environment in tracking and data relay satellites

    NASA Astrophysics Data System (ADS)

    Varanasi, S.; Gupta, S. C.

    Communication systems employing relay satellites require strict maintaining of frequency and phase coherence. In this paper, the tracking performance of a Digital Fading Phase Locked Loop (DFPLL) is presented considering that the transmitted signal passes through a Rician fading communication channel and also an Additive White Gaussian Noise (AWGN) channel. The stochastic difference equations governing the loop operation considering both phase-step and frequency-step inputs for a first order DFPLL is derived and also mathematical modeling of the Rician fading communication channel. Approximate analytic expressions for the steady state phase error process probability density function (pdf) and phase error variance, which characterize the tracking performance of the loop are presented by solving the corresponding Chapman-Kolmogorov (C-K) equations for both types of inputs considered. Numerical and simulation results are provided that confirm the analytical results for various signal to noise ratios and for various values of the fading parameter.

  13. Differential Space-Time Modulation for Wideband Wireless Networks

    DTIC Science & Technology

    2006-09-30

    modulation for wireless relay networks in Nakagami -m channels,” in Proceedings of the 2006 IEEE International Conference on Acoustic, Speech, and Signal... Nakagami -m fading channels," in Proceedings of the 6th IEEE International Workshop on Signal Processing Advances for Wireless Communications (SPAWC

  14. A review of fade detection techniques

    NASA Technical Reports Server (NTRS)

    Pergal, F. J.

    1990-01-01

    Several proposed propagation fade detection techniques are reviewed in light of general requirements presented for beacon fade characterization. The discussion includes an analysis of phase lock versus frequency lock beacon tracking loops and of excess noise injection type radiometers. The Advanced Communications Technology Satellite (ACTS) beacon fade detection schemes proposed by the Communications Satellite Corporation and the Jet Propulsion Laboratory are examined along with the fade detection technique used by Harris in the Advanced Communications Technology Satellite (ACTS) low burst rate (LBR) terminal.

  15. Perceptual Fading without Retinal Adaptation

    ERIC Educational Resources Information Center

    Hsieh, Po-Jang; Colas, Jaron T.

    2012-01-01

    A retinally stabilized object readily undergoes perceptual fading and disappears from consciousness. This startling phenomenon is commonly believed to arise from local bottom-up sensory adaptation to edge information that occurs early in the visual pathway, such as in the lateral geniculate nucleus of the thalamus or retinal ganglion cells. Here…

  16. Perceptual Fading without Retinal Adaptation

    ERIC Educational Resources Information Center

    Hsieh, Po-Jang; Colas, Jaron T.

    2012-01-01

    A retinally stabilized object readily undergoes perceptual fading and disappears from consciousness. This startling phenomenon is commonly believed to arise from local bottom-up sensory adaptation to edge information that occurs early in the visual pathway, such as in the lateral geniculate nucleus of the thalamus or retinal ganglion cells. Here…

  17. 3D ultrasound Nakagami imaging for radiation-induced vaginal fibrosis

    NASA Astrophysics Data System (ADS)

    Yang, Xiaofeng; Rossi, Peter; Shelton, Joseph; Bruner, Debrorah; Tridandapani, Srini; Liu, Tian

    2014-03-01

    Radiation-induced vaginal fibrosis is a debilitating side-effect affecting up to 80% of women receiving radiotherapy for their gynecological (GYN) malignancies. Despite the significant incidence and severity, little research has been conducted to identify the pathophysiologic changes of vaginal toxicity. In a previous study, we have demonstrated that ultrasound Nakagami shape and PDF parameters can be used to quantify radiation-induced vaginal toxicity. These Nakagami parameters are derived from the statistics of ultrasound backscattered signals to capture the physical properties (e.g., arrangement and distribution) of the biological tissues. In this paper, we propose to expand this Nakagami imaging concept from 2D to 3D to fully characterize radiation-induced changes to the vaginal wall within the radiation treatment field. A pilot study with 5 post-radiotherapy GYN patients was conducted using a clinical ultrasound scanner (6 MHz) with a mechanical stepper. A serial of 2D ultrasound images, with radio-frequency (RF) signals, were acquired at 1 mm step size. The 2D Nakagami shape and PDF parameters were calculated from the RF signal envelope with a sliding window, and then 3D Nakagami parameter images were generated from the parallel 2D images. This imaging method may be useful as we try to monitor radiation-induced vaginal injury, and address vaginal toxicities and sexual dysfunction in women after radiotherapy for GYN malignancies.

  18. 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

  19. Feasibility of Using Ultrasonic Nakagami Imaging for Monitoring Microwave-Induced Thermal Lesion in Ex Vivo Porcine Liver.

    PubMed

    Zhang, Siyuan; Han, Yuqiang; Zhu, Xingguang; Shang, Shaoqiang; Huang, Guojing; Zhang, Lei; Niu, Gang; Wang, Supin; He, Xijing; Wan, Mingxi

    2017-02-01

    The feasibility of using ultrasonic Nakagami imaging to evaluate thermal lesions induced by microwave ablation (MWA) in ex vivo porcine liver was explored. Dynamic changes in echo amplitudes and Nakagami parameters in the region of the MWA-induced thermal lesion, as well as the contrast-to-noise ratio (CNR) between the MWA-induced thermal lesion and the surrounding normal tissue, were calculated simultaneously during the MWA procedure. After MWA exposure, a bright hyper-echoic region appeared in ultrasonic B-mode and Nakagami parameter images as an indicator of the thermal lesion. Mean values of the Nakagami parameter in the thermal lesion region increased to 0.58, 0.71 and 0.91 after 1, 3 and 5 min of MVA. There were no significant differences in envelope amplitudes in the thermal lesion region among ultrasonic B-mode images obtained after different durations of MWA. Unlike ultrasonic B-mode images, Nakagami images were less affected by the shadow effect in monitoring of MWA exposure, and a fairly complete hyper-echoic region was observed in the Nakagami image. The mean value of the Nakagami parameter increased from approximately 0.47 to 0.82 during MWA exposure. At the end of the postablation stage, the mean value of the Nakagami parameter decreased to 0.55 and was higher than that before MWA exposure. CNR values calculated for Nakagami parameter images increased from 0.13 to approximately 0.61 during MWA and then decreased to 0.26 at the end of the post-ablation stage. The corresponding CNR values calculated for ultrasonic B-mode images were 0.24, 0.42 and 0.17. This preliminary study on ex vivo porcine liver suggested that Nakagami imaging have potential use in evaluating the formation of MWA-induced thermal lesions. Further in vivo studies are needed to evaluate the potential application.

  20. Fading testbed for free-space optical communications

    NASA Astrophysics Data System (ADS)

    Shrestha, Amita; Giggenbach, Dirk; Mustafa, Ahmad; Pacheco-Labrador, Jorge; Ramirez, Julio; Rein, Fabian

    2016-10-01

    Free-space optical (FSO) communication is a very attractive technology offering very high throughput without spectral regulation constraints, yet allowing small antennas (telescopes) and tap-proof communication. However, the transmitted signal has to travel through the atmosphere where it gets influenced by atmospheric turbulence, causing scintillation of the received signal. In addition, climatic effects like fogs, clouds and rain also affect the signal significantly. Moreover, FSO being a line of sight communication requires precise pointing and tracking of the telescopes, which otherwise also causes fading. To achieve error-free transmission, various mitigation techniques like aperture averaging, adaptive optics, transmitter diversity, sophisticated coding and modulation schemes are being investigated and implemented. Evaluating the performance of such systems under controlled conditions is very difficult in field trials since the atmospheric situation constantly changes, and the target scenario (e.g. on aircraft or satellites) is not easily accessible for test purposes. Therefore, with the motivation to be able to test and verify a system under laboratory conditions, DLR has developed a fading testbed that can emulate most realistic channel conditions. The main principle of the fading testbed is to control the input current of a variable optical attenuator such that it attenuates the incoming signal according to the loaded power vector. The sampling frequency and mean power of the vector can be optionally changed according to requirements. This paper provides a brief introduction to software and hardware development of the fading testbed and measurement results showing its accuracy and application scenarios.

  1. Linear and nonlinear characterization of microbubbles and tissue using the Nakagami statistical model.

    PubMed

    Bahbah, N; Novell, A; Bouakaz, A; Djelouah, H

    2017-04-01

    The goal of this work is to exploit the statistical signatures for discrimination between biological tissues and contrast microbubbles in order to develop new strategies for contrast imaging and tissue characterization. For this purpose, the efficiency of the Nakagami statistical model, for describing the ultrasonic echoes of both contrast microbubbles and tissues, was investigated. Experimental measurements have been performed using a linear array probe connected to an open research platform. A commercially available in vitro phantom was used to mimic biological tissue in which SonoVue contrast microbubbles were flowing. Experimental ultrasound echoes have been filtered around the transmitted frequency (fundamental at 2.5MHz) and around twice the transmitted frequency (at 5MHz) for 2nd harmonic analysis, and a logarithmic compression was applied. The signals have been analyzed in order to evaluate the Nakagami parameter m, the scaling parameter Ω and the probability density function at both frequencies. Parametric images based on the Nakagami parameters map (Nakagami-mode images) were reconstructed and compared to B-mode images. Contrary to the B-mode image which is influenced by the system settings and user operations, the Nakagami parametric image is only based on the backscattered statistics of the ultrasonic signals in a local phantom. Such an imaging principle allows the Nakagami image to quantify the local scatterer concentrations in the phantom and to extract the backscattering information from the regions of the weakest echoes that may be lost in the conventional B-mode image. Results show that the tissue and microbubbles characterization is more sensitive in the 2nd harmonic mode when a logarithmic transform is used. These results would be useful for improving the ultrasound image quality and contrast detection in nonlinear mode. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. Detecting changes in ultrasound backscattered statistics by using Nakagami parameters: Comparisons of moment-based and maximum likelihood estimators.

    PubMed

    Lin, Jen-Jen; Cheng, Jung-Yu; Huang, Li-Fei; Lin, Ying-Hsiu; Wan, Yung-Liang; Tsui, Po-Hsiang

    2017-05-01

    The Nakagami distribution is an approximation useful to the statistics of ultrasound backscattered signals for tissue characterization. Various estimators may affect the Nakagami parameter in the detection of changes in backscattered statistics. In particular, the moment-based estimator (MBE) and maximum likelihood estimator (MLE) are two primary methods used to estimate the Nakagami parameters of ultrasound signals. This study explored the effects of the MBE and different MLE approximations on Nakagami parameter estimations. Ultrasound backscattered signals of different scatterer number densities were generated using a simulation model, and phantom experiments and measurements of human liver tissues were also conducted to acquire real backscattered echoes. Envelope signals were employed to estimate the Nakagami parameters by using the MBE, first- and second-order approximations of MLE (MLE1 and MLE2, respectively), and Greenwood approximation (MLEgw) for comparisons. The simulation results demonstrated that, compared with the MBE and MLE1, the MLE2 and MLEgw enabled more stable parameter estimations with small sample sizes. Notably, the required data length of the envelope signal was 3.6 times the pulse length. The phantom and tissue measurement results also showed that the Nakagami parameters estimated using the MLE2 and MLEgw could simultaneously differentiate various scatterer concentrations with lower standard deviations and reliably reflect physical meanings associated with the backscattered statistics. Therefore, the MLE2 and MLEgw are suggested as estimators for the development of Nakagami-based methodologies for ultrasound tissue characterization.

  3. Monitoring radiofrequency ablation using real-time ultrasound Nakagami imaging combined with frequency and temporal compounding techniques.

    PubMed

    Zhou, Zhuhuang; Wu, Shuicai; Wang, Chiao-Yin; Ma, Hsiang-Yang; Lin, Chung-Chih; Tsui, Po-Hsiang

    2015-01-01

    Gas bubbles induced during the radiofrequency ablation (RFA) of tissues can affect the detection of ablation zones (necrosis zone or thermal lesion) during ultrasound elastography. To resolve this problem, our previous study proposed ultrasound Nakagami imaging for detecting thermal-induced bubble formation to evaluate ablation zones. To prepare for future applications, this study (i) created a novel algorithmic scheme based on the frequency and temporal compounding of Nakagami imaging for enhanced ablation zone visualization, (ii) integrated the proposed algorithm into a clinical scanner to develop a real-time Nakagami imaging system for monitoring RFA, and (iii) investigated the applicability of Nakagami imaging to various types of tissues. The performance of the real-time Nakagami imaging system in visualizing RFA-induced ablation zones was validated by measuring porcine liver (n = 18) and muscle tissues (n = 6). The experimental results showed that the proposed algorithm can operate on a standard clinical ultrasound scanner to monitor RFA in real time. The Nakagami imaging system effectively monitors RFA-induced ablation zones in liver tissues. However, because tissue properties differ, the system cannot visualize ablation zones in muscle fibers. In the future, real-time Nakagami imaging should be focused on the RFA of the liver and is suggested as an alternative monitoring tool when advanced elastography is unavailable or substantial bubbles exist in the ablation zone.

  4. Monitoring Radiofrequency Ablation Using Real-Time Ultrasound Nakagami Imaging Combined with Frequency and Temporal Compounding Techniques

    PubMed Central

    Zhou, Zhuhuang; Wu, Shuicai; Wang, Chiao-Yin; Ma, Hsiang-Yang; Lin, Chung-Chih; Tsui, Po-Hsiang

    2015-01-01

    Gas bubbles induced during the radiofrequency ablation (RFA) of tissues can affect the detection of ablation zones (necrosis zone or thermal lesion) during ultrasound elastography. To resolve this problem, our previous study proposed ultrasound Nakagami imaging for detecting thermal-induced bubble formation to evaluate ablation zones. To prepare for future applications, this study (i) created a novel algorithmic scheme based on the frequency and temporal compounding of Nakagami imaging for enhanced ablation zone visualization, (ii) integrated the proposed algorithm into a clinical scanner to develop a real-time Nakagami imaging system for monitoring RFA, and (iii) investigated the applicability of Nakagami imaging to various types of tissues. The performance of the real-time Nakagami imaging system in visualizing RFA-induced ablation zones was validated by measuring porcine liver (n = 18) and muscle tissues (n = 6). The experimental results showed that the proposed algorithm can operate on a standard clinical ultrasound scanner to monitor RFA in real time. The Nakagami imaging system effectively monitors RFA-induced ablation zones in liver tissues. However, because tissue properties differ, the system cannot visualize ablation zones in muscle fibers. In the future, real-time Nakagami imaging should be focused on the RFA of the liver and is suggested as an alternative monitoring tool when advanced elastography is unavailable or substantial bubbles exist in the ablation zone. PMID:25658424

  5. Channels

    NASA Image and Video Library

    2014-04-29

    Two channels are visible in this image from NASA 2001 Mars Odyssey spacecraft . The smaller one near the bottom did not carve as deeply as the larger channel at the top. The channel near the top of the image is near the origin of Mamers Valles.

  6. Minimum requirement of artificial noise level for using noise-assisted correlation algorithm to suppress artifacts in ultrasonic Nakagami images.

    PubMed

    Tsui, Po-Hsiang

    2012-04-01

    The Nakagami image is a complementary imaging mode for pulse-echo ultrasound B-scan to characterize tissues. White noise in anechoic areas induces artifacts in the Nakagami image. Recently, we proposed a noise-assisted correlation algorithm (NCA) for suppressing the Nakagami artifact. In the NCA, artificial white noise is intentionally added twice to backscattered signals to produce two noisy data, which are used to establish a correlation profile for rejecting noise. This study explored the effects of artificial noise level on the NCA to suppress the artifact of the Nakagami image. Simulations were conducted to produce B-mode images of anechoic regions under signal-to-noise ratios (SNRs) of 20, 10 and 5 dB. Various artificial noise levels ranging from 0.1- to 1-fold of the intrinsic noise amplitude were used in the NCA for constructing the Nakagami images. Phantom experiments were conducted to validate the performance of using the optimal artificial noise level suggested by the simulation results to suppress the Nakagami artifacts by the NCA. The simulation results indicated that the artifacts of the Nakagami image in the anechoic regions can be gradually suppressed by increasing the artificial noise level used in the NCA to improve the image contrast-to-noise ratio (CNR). The CNR of the Nakagami image reached 20 dB when the artificial noise level was 0.7-fold of the intrinsic noise amplitude. This criterion was demonstrated by the phantom results to provide the NCA with an excellent ability to obtain artifact-free Nakagami images.

  7. Antifade sonar employs acoustic field diversity to recover signals from multipath fading

    SciTech Connect

    Lubman, D.

    1996-04-01

    Co-located pressure and particle motion (PM) hydrophones together with four-channel diversity combiners may be used to recover signals from multipath fading. Multipath fading is important in both shallow and deep water propagation and can be an important source of signal loss. The acoustic field diversity concept arises from the notion of conservation of signal energy and the observation that in rooms at least, the total acoustic energy density is the sum of potential energy (scalar field-sound pressure) and kinetic energy (vector field-sound PM) portions. One pressure hydrophone determines acoustic potential energy density at a point. In principle, three PM sensors (displacement, velocity, or acceleration) directed along orthogonal axes describe the kinetic energy density at a point. For a single plane wave, the time-averaged potential and kinetic field energies are identical everywhere. In multipath interference, however, potential and kinetic field energies at a point are partitioned unequally, depending mainly on relative signal phases. Thus, when pressure signals are in deep fade, abundant kinetic field signal energy may be available at that location. Performance benefits require a degree of uncorrelated fading between channels. The expectation of nearly uncorrelated fading is motivated from room theory. Performance benefits for sonar limited by independent Rayleigh fading are suggested by analogy to antifade radio. Average SNR can be improved by several decibels, holding time on target is multiplied manifold, and the bit error rate for data communication is reduced substantially. {copyright} {ital 1996 American Institute of Physics.}

  8. Tight Bounds on the Ergodic Capacity of Cooperative Analog Relaying with Adaptive Source Transmission Techniques

    DTIC Science & Technology

    2010-05-01

    limited to Rayleigh fading. But in an airborne platform, it is much more reasonable to model the channel gain of each link as a Nakagami -m or a Rice...link SNR, and 2 2 , , , ,(1/ 1/ ) 2 (1/ 1/ )s i i d s i i ds sΔ = Ω − Ω + Ω + Ω + Moreover, the MGF of iγ for a Nakagami channel...8) 2 If a closed-form expression for iγ is not available (e.g., Nakagami -m channel with i.n.d fading statistics), but does exist for

  9. Strain-compounding technique with ultrasound Nakagami imaging for distinguishing between benign and malignant breast tumors.

    PubMed

    Liao, Yin-Yin; Li, Chia-Hui; Tsui, Po-Hsiang; Chang, Chien-Cheng; Kuo, Wen-Hung; Chang, King-Jen; Yeh, Chih-Kuang

    2012-05-01

    The scatterer properties of breast tissues are related to the presence of collagen structures, while the elasticity properties of breast tissues depend on their structural organization; these two characteristics are functionally complementary in ultrasound-based tissue characterizations. This study investigated the use of a strain-compounding technique with Nakagami imaging to provide information associated with the scatterer and elasticity characteristics of tissues when attempting to identify benign and malignant breast tumors. The efficacy of the proposed method was tested by collecting raw data of ultrasound backscattered signals from 50 clinical cases (25 benign tumors and 25 malignant tumors, as verified by histology biopsies). The different strain conditions were created by applying manual compression. For each region in which breast tumors were suspected, estimates of the full width at half maximum (FWHM) from the Gaussian fitting curve for the Nakagami-parameter histogram in the strain-compounding Nakagami images were divided by those of the corresponding reference Nakagami images (uncompressed images); this parameter was denoted as the FWHM ratio. Receiver operating characteristic (ROC) curve analysis was adopted to assess the diagnostic performance. The results demonstrated that the difference in scatterer distributions between before and after compounding was greater for benign tumors than for malignant tumors. The FWHM ratio estimates for benign and malignant tumors were 0.76 ± 0.14 and 0.96 ± 0.06 (mean ± standard deviation), respectively (p < 0.01). The mean area under the ROC curve using the FWHM ratio estimates was 0.92, with a 95% confidence interval of 0.83-1.00. These findings indicate that the strain-compounding Nakagami imaging method based on the acquisition of multiple frames under different strain states could provide objective information that would improve the ability to classify benign and malignant breast tumors.

  10. Effect of ultrasound frequency on the Nakagami statistics of human liver tissues.

    PubMed

    Tsui, Po-Hsiang; Zhou, Zhuhuang; Lin, Ying-Hsiu; Hung, Chieh-Ming; Chung, Shih-Jou; Wan, Yung-Liang

    2017-01-01

    The analysis of the backscattered statistics using the Nakagami parameter is an emerging ultrasound technique for assessing hepatic steatosis and fibrosis. Previous studies indicated that the echo amplitude distribution of a normal liver follows the Rayleigh distribution (the Nakagami parameter m is close to 1). However, using different frequencies may change the backscattered statistics of normal livers. This study explored the frequency dependence of the backscattered statistics in human livers and then discussed the sources of ultrasound scattering in the liver. A total of 30 healthy participants were enrolled to undergo a standard care ultrasound examination on the liver, which is a natural model containing diffuse and coherent scatterers. The liver of each volunteer was scanned from the right intercostal view to obtain image raw data at different central frequencies ranging from 2 to 3.5 MHz. Phantoms with diffuse scatterers only were also made to perform ultrasound scanning using the same protocol for comparisons with clinical data. The Nakagami parameter-frequency correlation was evaluated using Pearson correlation analysis. The median and interquartile range of the Nakagami parameter obtained from livers was 1.00 (0.98-1.05) for 2 MHz, 0.93 (0.89-0.98) for 2.3 MHz, 0.87 (0.84-0.92) for 2.5 MHz, 0.82 (0.77-0.88) for 3.3 MHz, and 0.81 (0.76-0.88) for 3.5 MHz. The Nakagami parameter decreased with the increasing central frequency (r = -0.67, p < 0.0001). However, the effect of ultrasound frequency on the statistical distribution of the backscattered envelopes was not found in the phantom results (r = -0.147, p = 0.0727). The current results demonstrated that the backscattered statistics of normal livers is frequency-dependent. Moreover, the coherent scatterers may be the primary factor to dominate the frequency dependence of the backscattered statistics in a liver.

  11. Feasibility study of using high-frequency ultrasonic Nakagami imaging for characterizing the cataract lens in vitro.

    PubMed

    Tsui, Po-Hsiang; Huang, Chih-Chung; Chang, Chien-Cheng; Wang, Shyh-Hau; Shung, K Kirk

    2007-11-07

    A cataract is a clouding of the crystalline lens that reduces the amount of incoming light and impairs visual perception. Phacoemulsification is the most common surgical method for treating advanced cataracts, and determining the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the feasibility of using an ultrasonic parametric image based on the Nakagami distribution to quantify the lens hardness. Young's modulus was measured in porcine lenses in which cataracts had been artificially induced. High-frequency ultrasound at 35 MHz was used to obtain the B-mode and Nakagami images of the cataract lenses. The averaged integrated backscatter and Nakagami parameters were also estimated in the region of interest. The experimental results show that the conventional B-scan and integrated backscatter are inadequate for quantifying the lens hardness, whereas Nakagami imaging allows different degrees of lens hardening to be distinguished both globally and locally based on the concentration of fiber coemption therein.

  12. Feasibility study of using high-frequency ultrasonic Nakagami imaging for characterizing the cataract lens in vitro

    NASA Astrophysics Data System (ADS)

    Tsui, Po-Hsiang; Huang, Chih-Chung; Chang, Chien-Cheng; Wang, Shyh-Hau; Shung, K. Kirk

    2007-11-01

    A cataract is a clouding of the crystalline lens that reduces the amount of incoming light and impairs visual perception. Phacoemulsification is the most common surgical method for treating advanced cataracts, and determining the optimal phacoemulsification energy is dependent on measuring the hardness of the lens. This study explored the feasibility of using an ultrasonic parametric image based on the Nakagami distribution to quantify the lens hardness. Young's modulus was measured in porcine lenses in which cataracts had been artificially induced. High-frequency ultrasound at 35 MHz was used to obtain the B-mode and Nakagami images of the cataract lenses. The averaged integrated backscatter and Nakagami parameters were also estimated in the region of interest. The experimental results show that the conventional B-scan and integrated backscatter are inadequate for quantifying the lens hardness, whereas Nakagami imaging allows different degrees of lens hardening to be distinguished both globally and locally based on the concentration of fiber coemption therein.

  13. Artifact reduction of ultrasound Nakagami imaging by combining multifocus image reconstruction and the noise-assisted correlation algorithm.

    PubMed

    Tsui, Po-Hsiang; Tsai, Yu-Wei

    2015-01-01

    Several studies have investigated Nakagami imaging to complement the B-scan in tissue characterization. The noise-induced artifact and the parameter ambiguity effect can affect performance of Nakagami imaging in the detection of variations in scatterer concentration. This study combined multifocus image reconstruction and the noise-assisted correlation algorithm (NCA) into the algorithm of Nakagami imaging to suppress the artifacts. A single-element imaging system equipped with a 5 MHz transducer was used to perform the brightness/depth (B/D) scanning of agar phantoms with scatterer concentrations ranging from 2 to 32 scatterers/mm(3). Experiments were also carried out on a mass with some strong point reflectors in a breast phantom using a commercial scanner with a 7.5 MHz linear array transducer operated at multifocus mode. The multifocus radiofrequency (RF) signals after the NCA process were used for Nakagami imaging. In the experiments on agar phantoms, an increasing scatterer concentration from 2 to 32 scatterers/mm(3) led to backscattered statistics ranging from pre-Rayleigh to Rayleigh distributions, corresponding to the increase in the Nakagami parameter measured in the focal zone from 0.1 to 0.8. However, the artifacts in the far field resulted in the Nakagami parameters of various scatterer concentrations to be close to 1 (Rayleigh distribution), making Nakagami imaging difficult to characterize scatterers. In the same scatterer concentration range, multifocus Nakagami imaging with the NCA simultaneously suppressed two types of artifacts, making the Nakagami parameter increase from 0.1 to 0.8 in the focal zone and from 0.18 to 0.7 in the far field, respectively. In the breast phantom experiments, the backscattered statistics of the mass corresponded to a high degree of pre-Rayleigh distribution. The Nakagami parameter of the mass before and after artifact reduction was 0.7 and 0.37, respectively. The results demonstrated that the proposed method for

  14. Performance Analysis of Dual-hop MIMO Relay Systems with MRT&RAS in the Presence of Co-channel Interference

    NASA Astrophysics Data System (ADS)

    Xu, Xiaoming; Cai, Yueming; Yang, Weiwei

    2013-09-01

    This paper focuses on the downlink dual-hop multiple-input multiple-output (MIMO) amplify-and-forward (AF) relay systems that employ the maximal-ratio transmission and receive antenna selection scheme (MRT&RAS) for use in each hop. The system under consideration is equipped with arbitrary NS, NR, and ND antennas at the base station (BS), relay station (RS), and mobile station (MS), respectively. The system performance has been investigated over Nakagami-m fading in presence of independent but not necessarily identically distributed co-channel interferences (CCIs) at both the RS and MS. First, we derive an accurate closed-form approximate expression for the outage probability and a single-integral expression for the average symbol error rate (SER), respectively. Besides, to render direct insights into the combined effect of multiple-antenna and interference on the system performance, the asymptotic expressions for the outage probability and the average SER are also presented. Furthermore, we determine the optimal power allocation (OPA) by using the exact and asymptotic methods, respectively, such that the outage probability is minimized. Finally, numerical results validate the correctness of the derived expressions and show that OPA offers superior performance over uniform power allocation. Our analysis and results provide insights on investigating and optimizing the performance of the downlink MIMO relay transmission in practical interference-limited wireless networks.

  15. When Does Fading Enhance Perceptual Category Learning?

    ERIC Educational Resources Information Center

    Pashler, Harold; Mozer, Michael C.

    2013-01-01

    Training that uses exaggerated versions of a stimulus discrimination (fading) has sometimes been found to enhance category learning, mostly in studies involving animals and impaired populations. However, little is known about whether and when fading facilitates learning for typical individuals. This issue was explored in 7 experiments. In…

  16. When Does Fading Enhance Perceptual Category Learning?

    ERIC Educational Resources Information Center

    Pashler, Harold; Mozer, Michael C.

    2013-01-01

    Training that uses exaggerated versions of a stimulus discrimination (fading) has sometimes been found to enhance category learning, mostly in studies involving animals and impaired populations. However, little is known about whether and when fading facilitates learning for typical individuals. This issue was explored in 7 experiments. In…

  17. The effect of transducer characteristics on the estimation of Nakagami paramater as a function of scatterer concentration.

    PubMed

    Tsui, Po-Hsiang; Wang, Shyh-Hau

    2004-10-01

    The effect of transducer characteristics on the sensitivity of the Nakagami parameter to detect the variation of scatterer concentrations was studied. The rationale for this study stems from our pilot results which showed that the Nakagami parameters, estimated using a nonfocused transducer were not as sensitive as those of measurements using a commercial ultrasonic scanner in previous reports. This discrepancy may be attributed to the effects of transducer characteristics relative to the size of the resolution cell as verified by measurements of phantoms and 2-D computer simulations. The Nakagami parameter as a function of scatterer concentration was calculated using backscattered signals acquired from the scattering medium of different scatterer concentrations ranging from 2 to 32 scatterers/mm(3) using both 5 MHz nonfocused and focused transducers. Experimental and simulation results obtained from the nonfocused transducer represent that their respective Nakagami parameters increased from 1.17 to 1.31 and from 0.82 to 1.01 corresponding to the increase of scatterer concentrations. For the results obtained from the focused transducer, their average Nakagami parameters increased from 0.27 to 0.72 and from 0.33 to 0.81. These consistent results demonstrated that Nakagami parameter estimated using a focused transducer tends to be more sensitive than that by a nonfocused transducer to detect the variation of low scatterer concentration. This difference is fully due to the effect of transducer characteristics associated with the effective number of scatterers in the resolution cell.

  18. Fade-resistant forward error correction method for free-space optical communications systems

    DOEpatents

    Johnson, Gary W.; Dowla, Farid U.; Ruggiero, Anthony J.

    2007-10-02

    Free-space optical (FSO) laser communication systems offer exceptionally wide-bandwidth, secure connections between platforms that cannot other wise be connected via physical means such as optical fiber or cable. However, FSO links are subject to strong channel fading due to atmospheric turbulence and beam pointing errors, limiting practical performance and reliability. We have developed a fade-tolerant architecture based on forward error correcting codes (FECs) combined with delayed, redundant, sub-channels. This redundancy is made feasible though dense wavelength division multiplexing (WDM) and/or high-order M-ary modulation. Experiments and simulations show that error-free communications is feasible even when faced with fades that are tens of milliseconds long. We describe plans for practical implementation of a complete system operating at 2.5 Gbps.

  19. Outage Probability for ARQ Decode-and-Forward Relaying under Packet-Rate Fading

    NASA Astrophysics Data System (ADS)

    Lee, Sangkook; Su, Weifeng; Batalama, Stella; Matyjas, John D.

    In this paper, a new analytical approach is developed for the evaluation of the outage probability of decode-and-forward (DF) automatic-repeat-request (ARQ) relaying under packet-rate fading (fast fading) channels. Based on this approach, a closed-form asymptotically tight (as SNR → ∞) approximation of the outage probability is derived, and the diversity order of the DF cooperative ARQ relay scheme is shown to be equal to 2L - 1, where L is the maximum number of ARQ retransmissions. The closed-form expression clearly shows that the achieved diversity is partially due to the DF cooperative relaying and partially due to the fast fading nature of the channels (temporal diversity). Numerical and simulation studies illustrate the theoretical developments.

  20. Differential reinforcement with and without instructional fading.

    PubMed Central

    Ringdahl, Joel E; Kitsukawa, Kana; Andelman, Marc S; Call, Nathan; Winborn, Lisa; Barretto, Anjali; Reed, Gregory K

    2002-01-01

    We evaluated a differential-reinforcement-based treatment package for the reduction of problem behavior during instructional situations. Differential reinforcement of alternative behavior (DRA; compliance) was implemented across two conditions. During one condition, instructions were presented approximately once every other minute. This condition was considered the terminal goal for treatment. During the second condition, the rate of instructions was gradually increased (beginning at zero and ending when instruction rate was similar to the first condition). Results indicated that DRA with instructional fading resulted in less problem behavior than DRA without instructional fading. These results are similar to previous studies regarding the utility of instructional fading. PMID:12365743

  1. Channels

    NASA Image and Video Library

    2015-11-20

    Today's VIS image shows a number of unnamed channels located on the northeastern margin of Terra Sabaea. Orbit Number: 61049 Latitude: 33.5036 Longitude: 58.6967 Instrument: VIS Captured: 2015-09-18 12:54 http://photojournal.jpl.nasa.gov/catalog/PIA20097

  2. The Parametric Images of Microbubbles and Tissue Mimicking Phantoms Based on the Nakagami Parameters Map

    NASA Astrophysics Data System (ADS)

    Nardjess, Bahbah; Hakim, Djelouah; Bouakaz, A.

    The ultrasonic B-mode imaging is an important clinical tool used to examine internal structures of biological tissue and contrast microbubbles. To overcome the drawbacks of conventional B-scans which cannot fully reflect the nature of the tissue, other imaging methods based on stochastic models are proposed. Among these models, the Nakagami statistical model was chosen, because it is more general and simpler to apply than other statistical models (Rayleigh and K models), to generate parametric images based on the Nakagami parameters. Experiments were performed using a 2.5 MHz linear array connected to an open research platform. A commercially phantom was used to mimic tissue and microbubbles backscatters. For several regions of interest and for different microbubbles dilutions, the RF signals have been generated at 3 and 5 transmit cycles. The Nakagami image can be combined with the use of the B-mode image simultaneously to visualize the tissue and the contrast microbubbles structures for a better medical diagnosis.

  3. Nakagami-based total variation method for speckle reduction in thyroid ultrasound images.

    PubMed

    Koundal, Deepika; Gupta, Savita; Singh, Sukhwinder

    2016-02-01

    A good statistical model is necessary for the reduction in speckle noise. The Nakagami model is more general than the Rayleigh distribution for statistical modeling of speckle in ultrasound images. In this article, the Nakagami-based noise removal method is presented to enhance thyroid ultrasound images and to improve clinical diagnosis. The statistics of log-compressed image are derived from the Nakagami distribution following a maximum a posteriori estimation framework. The minimization problem is solved by optimizing an augmented Lagrange and Chambolle's projection method. The proposed method is evaluated on both artificial speckle-simulated and real ultrasound images. The experimental findings reveal the superiority of the proposed method both quantitatively and qualitatively in comparison with other speckle reduction methods reported in the literature. The proposed method yields an average signal-to-noise ratio gain of more than 2.16 dB over the non-convex regularizer-based speckle noise removal method, 3.83 dB over the Aubert-Aujol model, 1.71 dB over the Shi-Osher model and 3.21 dB over the Rudin-Lions-Osher model on speckle-simulated synthetic images. Furthermore, visual evaluation of the despeckled images shows that the proposed method suppresses speckle noise well while preserving the textures and fine details.

  4. Fade-durations derived from land-mobile-satellite measurements in Australia

    NASA Technical Reports Server (NTRS)

    Hase, Yoshihiro; Vogel, Wolfhard J.; Goldhirsh, Julius

    1991-01-01

    Transmissions from the Japanese ETS-V geostationary satellite were measured at L band (1.5 GHz) in a vehicle driving on roads of southeastern Australia. The measurements were part of a program designed to characterize propagation effects due to roadside trees and terrain for mobile satellite service. It is shown that the cumulative distributions of fade and nonfade durations follow a lognormal and power law, respectively. At 1 percent probability, fades last 2-8 m, and nonfades 10-100 m, depending on the degree of shadowing. Phase fluctuations are generally small, allowing the channel characteristics to be estimated from levels only.

  5. Fade-durations derived from land-mobile-satellite measurements in Australia

    NASA Technical Reports Server (NTRS)

    Hase, Yoshihiro; Vogel, Wolfhard J.; Goldhirsh, Julius

    1991-01-01

    Transmissions from the Japanese ETS-V geostationary satellite were measured at L band (1.5 GHz) in a vehicle driving on roads of southeastern Australia. The measurements were part of a program designed to characterize propagation effects due to roadside trees and terrain for mobile satellite service. It is shown that the cumulative distributions of fade and nonfade durations follow a lognormal and power law, respectively. At 1 percent probability, fades last 2-8 m, and nonfades 10-100 m, depending on the degree of shadowing. Phase fluctuations are generally small, allowing the channel characteristics to be estimated from levels only.

  6. Ultrasonic Nakagami-parameter characterization of parotid-gland injury following head-and-neck radiotherapy: A feasibility study of late toxicity

    SciTech Connect

    Yang, Xiaofeng; Wu, Ning; Wang, Yuefeng; Tridandapani, Srini; Beitler, Jonathan J.; Yu, David S.; Curran, Walter J.; Liu, Tian; Bruner, Deborah W.

    2014-02-15

    Purpose: The study aims to investigate whether Nakagami parameters—estimated from the statistical distribution of the backscattered ultrasound radio-frequency (RF) signals—could provide a means for quantitative characterization of parotid-gland injury resulting from head-and-neck radiotherapy. Methods: A preliminary clinical study was conducted with 12 postradiotherapy patients and 12 healthy volunteers. Each participant underwent one ultrasound study in which ultrasound scans were performed in the longitudinal, i.e., vertical orientation on the bilateral parotids. For the 12 patients, the mean radiation dose to the parotid glands was 37.7 ± 9.5 Gy, and the mean follow-up time was 16.3 ± 4.8 months. All enrolled patients experienced grade 1 or 2 late salivary-gland toxicity (RTOG/EORTC morbidity scale). The normal parotid glands served as the control group. The Nakagami-scaling and Nakagami-shape parameters were computed from the RF data to quantify radiation-induced parotid-gland changes. Results: Significant differences in Nakagami parameters were observed between the normal and postradiotherapy parotid glands. Compared with the control group, the Nakagami-scaling parameter of the postradiotherapy group decreased by 25.8% (p < 0.001), and the Nakagami-shape parameter decreased by 31.3% (p < 0.001). The area under the receiver operating characteristic curve was 0.85 for the Nakagami-scaling parameter and was 0.95 for the Nakagami-shape parameter, which further demonstrated the diagnostic efficiency of the Nakagami parameters. Conclusions: Nakagami parameters could be used to quantitatively measure parotid-gland injury following head-and-neck radiotherapy. Moreover, the clinical feasibility was demonstrated and this study provides meaningful preliminary data for future clinical investigation.

  7. Effects of Estimators on Ultrasound Nakagami Imaging in Visualizing the Change in the Backscattered Statistics from a Rayleigh Distribution to a Pre-Rayleigh Distribution.

    PubMed

    Tsui, Po-Hsiang; Wan, Yung-Liang; Tai, Dar-In; Shu, Yu-Chen

    2015-08-01

    Ultrasound Nakagami imaging has recently attracted interest as an imaging technique for analyzing envelope statistics. Because the presence of structures has a strong effect on estimation of the Nakagami parameter, previous studies have indicated that Nakagami imaging should be used specifically for characterization of soft tissues with fewer structures, such as liver tissues. Typically, changes in the properties of the liver parenchyma cause the backscattered statistics to transform from a Rayleigh distribution to a pre-Rayleigh distribution, and this transformation can be visualized using a Nakagami imaging technique. However, different estimators result in different estimated values; thus, the performance of a Nakagami image may depend on the type of estimator used. This study explored the effects of various estimators on ultrasound Nakagami imaging to describe the backscattered statistics as they change from a Rayleigh distribution to a pre-Rayleigh distribution. Simulations and clinical measurements involving patients with liver fibrosis (n = 85) yielded image data that were used to construct B-mode and conventional Nakagami images based on the moment estimator (denoted as mINV images) and maximum-likelihood estimator (denoted as mML images). In addition, novel window-modulated compounding Nakagami images based on the moment estimator (denoted as mWMC images) were also obtained. The means and standard deviations of the Nakagami parameters were examined as a function of the backscattered statistics. The experimental results indicate that the mINV, mML and mWMC images enabled quantitative visualization of the change in backscattered statistics from a Rayleigh distribution to a pre-Rayleigh distribution. Importantly, the mWMC image is superior to both mINV and mML images because it simultaneously realizes sensitive detection of the backscattered statistics and a reduction of estimation variance for image smoothness improvement. We therefore recommend using m

  8. Effects of fading and interference in narrowband land-mobile networks

    NASA Astrophysics Data System (ADS)

    Linnartz, Johan Paul Marie Gerard

    1991-05-01

    The performance of mobile radio systems with narrowband radio channels is studied. Several results of previous research are included. In particular, the effects of multipath and shadow 'fading' and of mutual 'interference' between mobile users is investigated. To this end, initially the relevant propagation mechanisms are addressed, focusing on statistical channel models. For the planning of real systems, the suitability of some propagation models using terrain data is empirically evaluated. The statistical channel description is used to compute the performance of mobile radio links. Expressions are given for the outage probability and for the average duration of fades, taking account of mutual interference between users. A simplified model for the bit error rate in digital transmission is proposed. Numerical results are given for mobile telephone networks.

  9. [On NAKAGAMI Kinkei's Seiseido Rogosetsu (a commentary on Rongo): bibliography, philology, and philosophy of medicine].

    PubMed

    Tateno, Masami

    2006-12-01

    NAKAGAMI, Kinkei's Seiseido Rogosetsu is one of his main works. It has been handed down merely as a manuscript copy. It conveys the contents regarding Kinkei's own understanding of the phrases in the Rongo, his inquiry on those sentences based on the shapes of characters, and his will for revolution. He wrote this volume because he was influenced by OGYU Sorai's commentary and he wanted to clarify his own profound medical view based on the idea that Confucianism and medicine were derived from one common origin. Accordingly, his understanding of the Rongo is above the level of a mere commentary and it has a profound philosophy of medicine.

  10. Early detection of liver fibrosis in rats using 3-D ultrasound Nakagami imaging: a feasibility evaluation.

    PubMed

    Ho, Ming-Chih; Tsui, Po-Hsiang; Lee, Yu-Hsin; Chen, Yung-Sheng; Chen, Chiung-Nien; Lin, Jen-Jen; Chang, Chien-Cheng

    2014-09-01

    We investigated the feasibility of using 3-D ultrasound Nakagami imaging to detect the early stages of liver fibrosis in rats. Fibrosis was induced in livers of rats (n = 60) by intraperitoneal injection of 0.5% dimethylnitrosamine (DMN). Group 1 was the control group, and rats in groups 2-6 received DMN injections for 1-5 weeks, respectively. Each rat was sacrificed to perform 3-D ultrasound scanning of the liver in vitro using a single-element transducer of 6.5 MHz. The 3-D raw data acquired at a sampling rate of 50 MHz were used to construct 3-D Nakagami images. The liver specimen was further used for histologic analysis with hematoxylin and eosin and Masson staining to score the degree of liver fibrosis. The results indicate that the Metavir scores of the hematoxylin and eosin-stained sections in Groups 1-4 were 0 (defined as early liver fibrosis in this study), and those in groups 5 and 6 ranged from 1 to 2 and 2 to 3, respectively. To quantify the degree of early liver fibrosis, the histologic sections with Masson stain were analyzed to calculate the number of fiber-related blue pixels. The number of blue pixels increased from (2.36 ± 0.79) × 10(4) (group 1) to (7.68 ± 2.62) × 10(4) (group 4) after DMN injections for 3 weeks, indicating that early stages of liver fibrosis were successfully induced in rats. The Nakagami parameter increased from 0.36 ± 0.02 (group 1) to 0.55 ± 0.03 (group 4), with increasing numbers of blue pixels in the Masson-stained sections (p-value < 0.05, t-test). We concluded that 3-D Nakagami imaging has potential in the early detection of liver fibrosis in rats and may serve as an image-based pathologic model to visually track fibrosis formation and growth.

  11. Evaluate thermal lesion using Nakagami imaging for monitoring of high-intensity focused ultrasound

    NASA Astrophysics Data System (ADS)

    Zhang, Siyuan; Li, Chong; Zhou, Fanyu; Wang, Supin; Wan, Mingxi

    2017-03-01

    High-intensity focused ultrasound (HIFU) is currently being developed as a noninvasive technique for the treatment of cancer located in various tissues. Cavitation microbubbles (MBs) have been potential to aid treatment while the acoustic posterior shadowing effects of MBs influence the accuracy for defining the location and range of ablated thermal lesions during focused ultrasound surgery when using ultrasonic monitoring imaging. This work explored the feasibility of using ultrasonic Nakagami imaging to evaluate the ablated region induced by focused ultrasound exposures at different acoustic power levels in transparent tissue-mimicking phantoms.

  12. "Concreteness Fading" Promotes Transfer of Mathematical Knowledge

    ERIC Educational Resources Information Center

    McNeil, Nicole M.; Fyfe, Emily R.

    2012-01-01

    Recent studies have suggested that educators should avoid concrete instantiations when the goal is to promote transfer. However, concrete instantiations may benefit transfer in the long run, particularly if they are "faded" into more abstract instantiations. Undergraduates were randomly assigned to learn a mathematical concept in one of three…

  13. "Concreteness Fading" Promotes Transfer of Mathematical Knowledge

    ERIC Educational Resources Information Center

    McNeil, Nicole M.; Fyfe, Emily R.

    2012-01-01

    Recent studies have suggested that educators should avoid concrete instantiations when the goal is to promote transfer. However, concrete instantiations may benefit transfer in the long run, particularly if they are "faded" into more abstract instantiations. Undergraduates were randomly assigned to learn a mathematical concept in one of three…

  14. Improved maximum likelihood detection for mitigating fading estimation error in free space optical communication

    NASA Astrophysics Data System (ADS)

    Zhang, Lu; Wu, Zhiyong; Zhang, Yaoyu; Detian, Huang

    2013-01-01

    To mitigate the impact of the error between the estimated channel fading coefficient and the perfect fading coefficient on the bit error rate (BER), a priori conditional probability density function averaging the estimation error is proposed. Then, an improved maximum-likelihood (ML) symbol-by-symbol detection is derived for the free-space optical communication systems, which implement pilot symbol assisted modulation. To reduce complexity, a closed-form suboptimal improved ML detection is deduced using distribution approximation. Numerical results confirm that BER performance improvement can be reached by the improved ML detection, and that its suboptimal version performs as well as it does. Therefore, they both outperform classical ML detection, which doses not consider channel estimation error.

  15. Enhanced lesion-to-bubble ratio on ultrasonic Nakagami imaging for monitoring of high-intensity focused ultrasound.

    PubMed

    Zhang, Siyuan; Li, Chong; Zhou, Fanyu; Wan, Mingxi; Wang, Supin

    2014-06-01

    This work explored the feasibility of using ultrasonic Nakagami imaging to enhance the contrast between thermal lesions and bubbles induced by high-intensity focused ultrasound (US) in a transparent tissue-mimicking phantom at different acoustic power levels. The term "lesion-to-bubble ratio" was proposed and defined as the ratio of the scattered power from the thermal lesion to the scattered power from the bubbles calculated in the various monitoring of images for high-intensity focused US. Two-dimensional radiofrequency data backscattered from the exposed region were captured by a modified diagnostic US scanner to estimate the Nakagami statistical parameter, m, and reconstruct the ultrasonic B-mode images and Nakagami parameter images. The dynamic changes in the lesion-to-bubble ratio over the US exposure procedure were calculated simultaneously and compared among video photos, B-mode images, and Nakagami images for monitoring of high-intensity focused US. After a small thermal lesion was induced by high-intensity focused US in the phantom, the lesion-to-bubble ratio values corresponding to the video photo, B-mode image, and Nakagami image were 5.3, 1, and 9.8 dB, respectively. When a large thermal lesion appeared in the phantom, the ratio values increased to 7.2, 3, and 14 dB. During US exposure, the ratio values calculated for the video photo, B-mode image, and Nakagami image began to increase gradually and rose to peak values of 8.3, 2.9, and 14.8 dB at the end of the US exposure. This preliminary study on a tissue-mimicking phantom suggests that Nakagami imaging may have a potential use in enhancing the lesion-to-bubble ratio for monitoring high-intensity focused US. Further studies in vivo and in vitro will be needed to evaluate the potential applications for high-intensity focused US. © 2014 by the American Institute of Ultrasound in Medicine.

  16. Performance optimization of partially coherent CPM on multipath fading channel

    NASA Astrophysics Data System (ADS)

    Norris, James A.

    2012-05-01

    Constant Envelope, Continuous Phase Modulation (CPM) is highly desirable for low-power, battery-operated systems as well as for small-profile vehicular and aircraft systems where large amplifiers won't fit. In the past, CPM was noted for increased demodulator complexity (over simple PSK or FSK receivers) but with modern computational power it is possible to continue to improve the power efficiency of CPM modulation at the receiver. In the specific case of multipath, there are several known methods (Rake Receiver is one example) to resolve and correct for inter-symbol interference and phase distortion. This paper develops a standard CPM demodulation and compares the optimal coherent performance with a partially coherent receiver. Several methods are developed to compensate and correct for ISI due to various types of multipath and the power efficiency is compared to the original, coherent demodulation.

  17. Signal Classification in Fading Channels Using Cyclic Spectral Analysis

    DTIC Science & Technology

    2009-07-01

    efficient algorithms to detect and classify an OFDM signal based on its cyclic prefix through the use of a simple autocorrelation procedure [21–23...we focus on the case of an OFDM signal transmitted with no cyclic prefix. Therefore, an intermediate stage is needed between the SOF- based ...classifications and the HOCS- based classifications. A simple yet effective method to distinguish OFDM signals from the single carrier signals in question is

  18. Noninvasive evaluation of vaginal fibrosis following radiotherapy for gynecologic malignancies: A feasibility study with ultrasound B-mode and Nakagami parameter imaging

    PubMed Central

    Yang, Xiaofeng; Rossi, Peter; Bruner, Deborah Watkins; Tridandapani, Srini; Shelton, Joseph; Liu, Tian

    2013-01-01

    Purpose: This study's purpose is to develop a quantitative ultrasound technology to evaluate radiation-induced vaginal fibrosis. Radiation therapy (RT) is an important treatment modality for most gynecologic (GYN) malignancies. However, vaginal fibrosis is a common chronic side-effect, affecting 80% of women post vaginal or pelvic RT. Vaginal fibrosis leads to pain, sexual dysfunction, and poor quality of life. Methods: The authors propose a novel ultrasound approach that combines conventional B-mode imaging with Nakagami parameter imaging to quantitatively evaluate post-RT vaginal injury. From the B-mode image, vaginal wall thickness and echo intensity were calculated to capture the anatomy and echogenicity of the vaginal wall. From Nakagami imaging, two statistical parameters, Nakagami probability density function (PDF) and Nakagami shape, were computed to measure the concentration and arrangement of vaginal tissue microstructures. This novel ultrasound imaging concept was investigated in a pilot study of 12 patients, who were previously diagnosed and treated for endometrial cancer. The 12 participants were stratified into two groups: (1) the control group consisted of 6 patients who received surgery (hysterectomy) alone and (2) the post-RT group consisted of 6 patients who received surgery plus radiotherapy, with a follow-up time of 12–38 months. Each participant underwent one transvaginal ultrasound study (6 MHz). Three transverse images of the anterior vaginal wall were acquired in a 2 cm step from the apex (vaginal cuff) to the introitus (vagina opening). The vaginal wall thickness, echo intensity, Nakagami PDF, and Nakagami parameter were calculated to evaluate radiation-induced vaginal fibrosis. Results: Both B-mode and Nakagami methods showed significant differences in parameters between the post-RT and nonirradiated vaginal walls. Compared with the control group, the vaginal wall thickness of the post-RT group increased by 153.2% (p = 0.002), the echo

  19. Noninvasive evaluation of vaginal fibrosis following radiotherapy for gynecologic malignancies: a feasibility study with ultrasound B-mode and Nakagami parameter imaging.

    PubMed

    Yang, Xiaofeng; Rossi, Peter; Bruner, Deborah Watkins; Tridandapani, Srini; Shelton, Joseph; Liu, Tian

    2013-02-01

    This study's purpose is to develop a quantitative ultrasound technology to evaluate radiation-induced vaginal fibrosis. Radiation therapy (RT) is an important treatment modality for most gynecologic (GYN) malignancies. However, vaginal fibrosis is a common chronic side-effect, affecting 80% of women post vaginal or pelvic RT. Vaginal fibrosis leads to pain, sexual dysfunction, and poor quality of life. The authors propose a novel ultrasound approach that combines conventional B-mode imaging with Nakagami parameter imaging to quantitatively evaluate post-RT vaginal injury. From the B-mode image, vaginal wall thickness and echo intensity were calculated to capture the anatomy and echogenicity of the vaginal wall. From Nakagami imaging, two statistical parameters, Nakagami probability density function (PDF) and Nakagami shape, were computed to measure the concentration and arrangement of vaginal tissue microstructures. This novel ultrasound imaging concept was investigated in a pilot study of 12 patients, who were previously diagnosed and treated for endometrial cancer. The 12 participants were stratified into two groups: (1) the control group consisted of 6 patients who received surgery (hysterectomy) alone and (2) the post-RT group consisted of 6 patients who received surgery plus radiotherapy, with a follow-up time of 12-38 months. Each participant underwent one transvaginal ultrasound study (6 MHz). Three transverse images of the anterior vaginal wall were acquired in a 2 cm step from the apex (vaginal cuff) to the introitus (vagina opening). The vaginal wall thickness, echo intensity, Nakagami PDF, and Nakagami parameter were calculated to evaluate radiation-induced vaginal fibrosis. Both B-mode and Nakagami methods showed significant differences in parameters between the post-RT and nonirradiated vaginal walls. Compared with the control group, the vaginal wall thickness of the post-RT group increased by 153.2% (p = 0.002), the echo intensity increased by 11

  20. Optical scintillations and fade statistics for a satellite-communication system.

    PubMed

    Andrews, L C; Phillips, R L; Yu, P T

    1995-11-20

    Estimates of the scintillation index, fractional fade time, expected number of fades, and mean duration of fade time associated with a propagating Gaussian-beam wave are developed for uplink and downlink laser satellite-communication channels. Estimates for the spot size of the beam at the satellite or the ground or airborne receiver are also provided. Weak-fluctuation theory based on the log-normal model is applicable for intensity fluctuations near the optical axis of the beam provided that the zenith angle is not too large, generally not exceeding 60°. However, there is an increase in scintillations that occurs with increasing pointing error at any zenith angle, particularly for uplink channels. Large off-axis scintillations are of particular significance because they imply that small pointing errors can cause serious degradation in the communication-channel reliability. Off-axis scintillations increase more rapidly for larger-diameter beams and, in some cases, can lead to a radial saturation effect for pointing errors less than 1 µrad off the optical beam axis.

  1. Fade durations in satellite-path mobile radio propagation

    NASA Technical Reports Server (NTRS)

    Schmier, Robert G.; Bostian, Charles W.

    1986-01-01

    Fades on satellite to land mobile radio links are caused by several factors, the most important of which are multipath propagation and vegetative shadowing. Designers of vehicular satellite communications systems require information about the statistics of fade durations in order to overcome or compensate for the fades. Except for a few limiting cases, only the mean fade duration can be determined analytically, and all other statistics must be obtained experimentally or via simulation. This report describes and presents results from a computer program developed at Virginia Tech to simulate satellite path propagation of a mobile station in a rural area. It generates rapidly-fading and slowly-fading signals by separate processes that yield correct cumulative signal distributions and then combines these to simulate the overall signal. This is then analyzed to yield the statistics of fade duration.

  2. Monocular depth effects on perceptual fading.

    PubMed

    Hsu, Li-Chuan; Kramer, Peter; Yeh, Su-Ling

    2010-08-06

    After prolonged viewing, a static target among moving non-targets is perceived to repeatedly disappear and reappear. An uncrossed stereoscopic disparity of the target facilitates this Motion-Induced Blindness (MIB). Here we test whether monocular depth cues can affect MIB too, and whether they can also affect perceptual fading in static displays. Experiment 1 reveals an effect of interposition: more MIB when the target appears partially covered by, than when it appears to cover, its surroundings. Experiment 2 shows that the effect is indeed due to interposition and not to the target's contours. Experiment 3 induces depth with the watercolor illusion and replicates Experiment 1. Experiments 4 and 5 replicate Experiments 1 and 3 without the use of motion. Since almost any stimulus contains a monocular depth cue, we conclude that perceived depth affects perceptual fading in almost any stimulus, whether dynamic or static. Copyright 2010 Elsevier Ltd. All rights reserved.

  3. Observations of auroral fading before breakup

    NASA Technical Reports Server (NTRS)

    Pellinen, R. J.; Heikkila, W. J.

    1978-01-01

    The onset of auroral breakup was studied by using a variety of instruments with time resolution of some tens of second. Rapid sequences of all-sky photographs, and fast meridian scans by photometers, show that breakup is usually preceded by moderate brightening, followed by fading of the auroral brightness lasting one or two minutes, before the actual breakup itself. This optical activity is closely correlated with the development of auroral radar echoes. Data from a magnetometer network provide some indication of a correlated response by the local auroral and ionospheric currents. Riometer recordings show a slow decrease in ionspheric radio wave absorption over a period of about ten minutes prior to breakup, with the largest decrease essentially to quiet-time values in the region of auroral fading and subsequent breakup.

  4. Backwards Fading to Speed Task Learning

    DTIC Science & Technology

    2013-09-01

    Schaefer: 14. ABSTRACT (Maximum 200 words): In Backwards Fading (BF), a learner is provided with an initial, complete demonstration of a multi ...promise for effective/efficient training, but the utility of BF in Army settings and with Army tasks needs to be empirically evaluated. To that end...accelerated BF resulted in poorer performance than gradual BF (Experiment 2). Recommendations for utilizing BF in Army settings are provided. 15

  5. Optimal Power Assignment for Minimizing the Average Total Transmission Power in Hybrid-ARQ Rayleigh Fading Links

    DTIC Science & Technology

    2011-07-01

    in Hybrid- ARQ Rayleigh Fading Links 5a. CONTRACT NUMBER FA8750-08-1-0063 5b. GRANT NUMBER N/A 5c. PROGRAM ELEMENT NUMBER N/A 6. AUTHOR(S...sequence for hybrid automatic-repeat- request (H- ARQ ) communications over quasistatic Rayleigh fading channels. For any targeted H- ARQ link outage...reveals that conventional equal-power H- ARQ assignment is far from optimal. For example, for targeted outage probability of 10e−3 with a maximum of two

  6. Comparison of hybrid FDMA/CDMA systems in frequency selective Rayleigh fading

    NASA Astrophysics Data System (ADS)

    Eng, Thomas; Milstein, Laurence B.

    1994-06-01

    A hybrid FDMA/CDMA scheme operating over a frequency selective Rayleigh fading channel is described and analyzed. The performance of the hybrid system is then compared with that of a wideband CDMA system occupying the same total bandwidth. Both coherent and noncoherent modulation formats are investigated; it is found that, for coherent modulation with a RAKE receiver, wideband CDMA has greater capacity than does the hybrid. However, for the noncoherent modulation formats (either DPSK or square-law detected orthogonal signaling), a hybrid system can have a greater capacity if a high channel error rate can be tolerated. Otherwise, a wideband noncoherent system remains optimal.

  7. Improvements to a UHF rebroadcast television link suffering tidal fading: Countisbury UHF relay station

    NASA Astrophysics Data System (ADS)

    Moore, J. H.

    1987-09-01

    The Countisbury UHF relay station serves the localities of Lynmouth and Lynton in North Devon. For some time, the problems of co-channel interference and tidal fading have on occasion been evident . Results obtained utilizing a new Rebroadcast LINK (RBL) antenna array are given. The RBL has improved considerably the quality of signals received at this relay station. Details are also given of apparatus which enables sampled television picture sequences to be recorded on a VHS video cassette recorder. The channel identification, date and time are derived from the teletext signal and superimposed at the top of the picture.

  8. Capacity fade of Sony 18650 cells cycled at elevated temperatures. Part II. Capacity fade analysis

    NASA Astrophysics Data System (ADS)

    Ramadass, P.; Haran, Bala; White, Ralph; Popov, Branko N.

    A complete capacity fade analysis was carried out for Sony 18650 cells cycled at elevated temperatures. The major causes of capacity loss were identified and a complete capacity fade balance was carried out to account for the total capacity loss of Li-ion battery as a function of cycle number and temperature. The three most significant parameters that cause capacity loss were loss of secondary active material (LiCoO 2/carbon) and primary active material (Li +) and the rate capability losses. Intrinsic capacity measurements for both positive and negative electrode has been used to estimate the capacity loss due to secondary active material and a charge balance gives the capacity lost due to primary active material (Li +). Capacity fade has been quantified with secondary active material loss dominating the other losses.

  9. Using ultrasound backscattering signals and Nakagami statistical distribution to assess regional cataract hardness.

    PubMed

    Caixinha, Miguel; Jesus, Danilo A; Velte, Elena; Santos, Mário J; Santos, Jaime B

    2014-12-01

    This study aims to analyze the protein aggregates spatial distribution for different cataract degrees, and correlate this information with the lens acoustical parameters and by this way, assess the cataract regional hardness. Different cataract degrees were induced ex vivo in porcine lenses. A 25 MHz ultrasonic transducer was used to obtain the acoustical parameters (velocity, attenuation, and backscattering signals). B-scan and Nakagami images were constructed. Also, lenses with different cataract degrees were sliced in two regions (nucleus and cortex), for fibers and collagen detection. A significant increase with cataract formation was found for the velocity, attenuation, and brightness intensity of the B-scan images and Nakagami m parameter ( ). The acoustical parameters showed a good to moderate correlation with the m parameter for the different stages of cataract formation. A strong correlation was found between the protein aggregates in the cortex and the m parameter. Lenses without cataract are characterized using a classification and regression tree, by a mean brightness intensity ≤0.351, a variance of the B-scan brightness intensity ≤0.070, a velocity ≤1625 m/s, and an attenuation ≤0.415 dB/mm·MHz (sensitivity: 100% and specificity: 72.6%). To characterize different cataract degrees, the m parameter should be considered. Initial stages of cataract are characterized by a mean brightness intensity >0.351 and a variance of the m parameter >0.110. Advanced stages of cataract are characterized by a mean brightness intensity >0.351, a variance of the m parameter ≤0.110, and a mean m parameter >0.374. For initial and advanced stages of cataract, a sensitivity of 78.4% and a specificity of 86.5% are obtained.

  10. Capacity fade in nickel cadmium and nickel hydrogen cells

    NASA Technical Reports Server (NTRS)

    Edgar, Tim; Hayden, Jeff; Pickett, David F.; Abrams-Blakemore, Bruce; Liptak, ED

    1993-01-01

    Research and operational experience with capacity fade in nickel cadmium and nickel hydrogen cells are summarized in outline form. The theoretical causes of capacity fade are reviewed and the role of cell storage, positive electrodes, and cobalt additives are addressed. Three examples of observed capacity fade are discussed: INTELSAT 5, INTELSAT 6, and an Explorer platform. Finally, prevention and recovery methods are addressed and the current status of Eagle Picher/Hughes research is discussed.

  11. Design of an anti-Rician-fading modem for mobile satellite communication systems

    NASA Technical Reports Server (NTRS)

    Kojima, Toshiharu; Ishizu, Fumio; Miyake, Makoto; Murakami, Keishi; Fujino, Tadashi

    1995-01-01

    To design a demodulator applicable to mobile satellite communication systems using differential phase shift keying modulation, we have developed key technologies including an anti-Rician-fading demodulation scheme, an initial acquisition scheme, automatic gain control (AGC), automatic frequency control (AFC), and bit timing recovery (BTR). Using these technologies, we have developed one-chip digital signal processor (DSP) modem for mobile terminal, which is compact, of light weight, and of low power consumption. Results of performance test show that the developed DSP modem achieves good performance in terms of bit error ratio in mobile satellite communication environment, i.e., Rician fading channel. It is also shown that the initial acquisition scheme acquires received signal rapidly even if the carrier-to-noise power ratio (CNR) of the received signal is considerably low.

  12. Design of an anti-Rician-fading modem for mobile satellite communication systems

    NASA Technical Reports Server (NTRS)

    Kojima, Toshiharu; Ishizu, Fumio; Miyake, Makoto; Murakami, Keishi; Fujino, Tadashi

    1995-01-01

    To design a demodulator applicable to mobile satellite communication systems using differential phase shift keying modulation, we have developed key technologies including an anti-Rician-fading demodulation scheme, an initial acquisition scheme, automatic gain control (AGC), automatic frequency control (AFC), and bit timing recovery (BTR). Using these technologies, we have developed one-chip digital signal processor (DSP) modem for mobile terminal, which is compact, of light weight, and of low power consumption. Results of performance test show that the developed DSP modem achieves good performance in terms of bit error ratio in mobile satellite communication environment, i.e., Rician fading channel. It is also shown that the initial acquisition scheme acquires received signal rapidly even if the carrier-to-noise power ratio (CNR) of the received signal is considerably low.

  13. Fading correlation and analytical performance evaluation of the space-diversity free-space optical communications system

    NASA Astrophysics Data System (ADS)

    Yang, G.; Khalighi, M. A.; Bourennane, S.; Ghassemlooy, Z.

    2014-03-01

    This paper investigates fading correlation in space-diversity free-space optical (FSO) communication systems and its effect on the link performance. We firstly evaluate the fading correlation in multiple-aperture FSO systems using wave-optics simulations. The influence of different system parameters including the link distance and aperture spacing is illustrated under realistic beam propagation conditions. In particular, we show that, at relatively large link distances where the scattering disk is much larger than the receiver aperture size, the fading correlation coefficient is almost independent of the apertures’ diameter and depends only on the apertures’ edge separation. To investigate the impact of fading correlation on the system’s performance, we propose an analytical approach to evaluate the performance of the space-diversity FSO system over a correlated Gamma-Gamma (ΓΓ) fading channel. Our approach is based on approximating the sum of arbitrarily correlated ΓΓ random variables by an α-μ distribution. To validate the accuracy of this method, we evaluate the average bit-error-rate (BER) performance for the case of a multiple-aperture FSO system and compare it with the BER results obtained via Monte Carlo simulations.

  14. Overview of techniques for mitigation of fading and shadowing in the direct broadcast satellite radio environment

    NASA Technical Reports Server (NTRS)

    Bell, David; Gevargiz, John; Vaisnys, Arvydas; Julian, David

    1995-01-01

    The DBS radio propagation environment is divided into three sub-environments, indoor, rural-suburban mobile and urban mobile. Indoor propagation effects are in a large part determined by construction material. Non-metallic materials afford direct, albeit attenuated penetration of the satellite signal with a minimum of multipath signal scattering. Signal penetration into structures using significant metallic materials is often indirect, through openings such as doors and windows and propagation will involve significant multipath components. Even so, delay spread in many situations is on the order of 10's of nanoseconds resulting in relatively flat fading. Thus frequency diversity techniques such as Orthogonal Frequency Division Multiplex (OFDM) and Code Division Multiple Access (CDMA) or equalization techniques do not realize their intended performance enhancement. Antenna diversity, directivity and placement are key mitigation techniques for the indoor environment. In the Rural-Suburban mobile environment with elevation angles greater than 20 deg, multipath components from the satellite signal are 15-20 dB below the line-of-sight signal level and often originate from nearby reflectors. Thus shadowing is the dominant signal impairment and fading effects are again found to be relatively flat for a large fading margin. Because receiver motion induces rapid variations in the signal level, temporal diversity techniques such as interleaving, channel coding and retransmission can be used to combat short intermittent fading events. Antenna diversity and directivity techniques are again useful in this environment. Finally, in the Urban mobile environment, slower vehicle speeds and blockage by buildings causes signal fades that are too long and too deep to combat with signal margin or time diversity. Land-based signal boosters are needed to fill in the coverage gaps of the satellite only broadcast scheme. On frequency boosters are suggested to conserve bandwidth yet these

  15. Classification of scattering media within benign and malignant breast tumors based on ultrasound texture-feature-based and Nakagami-parameter images.

    PubMed

    Liao, Yin-Yin; Tsui, Po-Hsiang; Li, Chia-Hui; Chang, King-Jen; Kuo, Wen-Hung; Chang, Chien-Cheng; Yeh, Chih-Kuang

    2011-04-01

    Benign and malignant tumors can be classified by using texture analysis of the ultrasound B-scan image to describe the variation in the echogenicity of scatterers. The recently proposed ultrasonic Nakagami parametric image has also been used to detect the concentrations and arrangements of scatterers for tumor characterization applications. B-scan-based texture analysis and the Nakagami parametric image are functionally complementary in ultrasonic tissue characterizations and this study aimed to combine these methods in order to improve the ability to characterize breast tumors. To validate this concept, radio-frequency data obtained from 130 clinical cases were used to construct the texture-feature parametric image and the Nakagami parametric image. Four texture-feature parameters based on a gray-level co-occurrence matrix (homogeneity, contrast, energy, and variance) and the Nakagami parameters of the benign and malignant tumors were calculated. The usefulness of an individual parameter was determined and scatter graphs indicated the relationship between two selected texture-feature parameters. Fisher's linear discriminant analysis was used to combine the selected texture-feature parameters with the Nakagami parameter. The performance in classifying tumors was evaluated based on the receiver operating characteristic curve. The results indicated that there is a trade-off between sensitivity and specificity when using an individual texture-feature parameter or when combining two such correlated parameters to discriminate benign and malignant cases. However, the best performance was obtained when combining selected texture-feature parameters with the Nakagami parameter. The study findings suggest that combining B-scan-based texture analysis and the Nakagami parametric image could improve the ability to classify benign and malignant breast tumors.

  16. Teaching braille line tracking using stimulus fading.

    PubMed

    Scheithauer, Mindy C; Tiger, Jeffrey H

    2014-01-01

    Line tracking is a prerequisite skill for braille literacy that involves moving one's finger horizontally across a line of braille text and identifying when a line ends so the reader may reset his or her finger on the subsequent line. Current procedures for teaching line tracking are incomplete, because they focus on tracking lines with only small gaps between characters. The current study extended previous line-tracking instruction using stimulus fading to teach tracking across larger gaps. After instruction, all participants showed improvement in line tracking, and 2 of 3 participants met mastery criteria for tracking across extended spaces.

  17. Channel simulation for optical communication systems

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.

    1974-01-01

    A technique is reported for simulating the signal fading that will be experienced by typical optical communication systems. The desired irradiance or amplitude fading statistics can be simulated by incorporating a linearized optical modulator subsystem between the transmitter and receiver. This technique has been implemented in the design and construction of a laboratory channel simulator. The design of the processing electronics is discussed along with the results of tests performed for each mode of operation.

  18. Why does consciousness fade in early sleep?

    PubMed

    Tononi, Giulio; Massimini, Marcello

    2008-01-01

    Consciousness fades during deep nonrapid eye movement (NREM) sleep early in the night, yet cortical neurons remain active, keep receiving sensory inputs, and can display patterns of synchronous activity. Why then does consciousness fade? According to the integrated information theory of consciousness, what is critical for consciousness is not firing rates, sensory input, or synchronization per se, but rather the ability of a system to integrate information. If consciousness is the capacity to integrate information, then the brain should be able to generate consciousness to the extent that it has a large repertoire of available states (information), yet it cannot be decomposed into a collection of causally independent subsystems (integration). A key prediction stemming from this hypothesis is that such ability should be greatly reduced in deep NREM sleep; the dreamless brain either breaks down into causally independent modules, shrinks its repertoire of possible responses, or both. In this article, we report the results of a series of experiments in which we employed a combination of transcranial magnetic stimulation and high-density electroencephalography (TMS/hd-EEG) to directly test this prediction in humans. Altogether, TMS/hdEEG measurements suggest that the sleeping brain, despite being active and reactive, loses its ability of entering states that are both integrated and differentiated; it either breaks down in causally independent modules, responding to TMS with a short and local activation, or it bursts into an explosive and aspecific response, producing a full-fledged slow wave.

  19. T1 VSAT Fade Compensation Statistical Results

    NASA Technical Reports Server (NTRS)

    Johnson, Sandra K.; Acosta, Roberto; Ugweje, Oke

    2000-01-01

    New satellite communication systems are steadily seeking to use higher frequency bands to accommodate the requirements for additional capacity. At these higher frequencies, propagation impairments that did not significantly affect the signal at lower frequencies begin to have considerable impact. In Ka-band. the next logical commercial frequency band to be used for satellite communication, attenuation of the signal due to rain is a primary concern. An experimental satellite built by NASA, the Advanced Communication Technology Satellite (ACTS). launched in September 1993, is the first U.S. communication satellite operating in the Ka-band. In addition to higher carrier frequencies, a number of other new technologies, including on-board baseband processing. multiple beam antennas, and rain fade detection and compensation techniques, were designed into the ACTS. Verification experiments have been conducted since the launch to characterize the new technologies. The focus of this paper is to characterize the method used by the ACTS TI Very Small Aperture Terminal (TI VSAT) ground stations in detecting the presence of fade in the communication signal and to adaptively compensate for it by the addition of burst rate reduction and forward error correction. Measured data obtained from the ACTS program was used to validate the compensation technique. A software process was developed and demonstrated to statistically characterize the increased availability achieved by the compensation techniques in terms of the bit error rate time enhancement factor. Several improvements to the ACTS technique are discussed and possible implementations for future Ka band system are offered.

  20. Multipath fading analysis of telemetry signals power fluctuations from Universitetsky microsatellite

    NASA Astrophysics Data System (ADS)

    Shakhparonov, Vladimir; Millán Adán, Espinoza; Vicente Vivas, Esaú

    2012-03-01

    The article deals with the results of the fading fluctuations analysis for telemetry signals in the 2 m and 70 cm bands from the first Moscow State University microsatellite better known as "Universitetsky". Radio telemetry signals were received from the microsatellite for around 2 years, collecting and recording the power signal data of almost 7500 satellite overpasses. The received signals from about 2300 satellite overpasses had a very low signal to noise ratio (SNR) that caused high transmission losses. The rest of the signals had a SNR high enough to complete the transmission without losses. The main objective of this paper was to find the fading fluctuations caused both by diffusion and by the presence of Gaussian and non Gaussian noise in telemetry signal power data. The purpose was both to characterize the communication channel as well as to elaborate solutions both to improve the communication quality as well as to identify no homogeneous zones in the ionosphere environment. The signal power analysis was based in the observation of statistical characteristics from different power signal components, in particular the components influenced by diffusion and non Gaussian noise. The employed methodology follows the next steps: removing the power signal envelope; taking away the Gaussian noise; obtaining the statistical characteristics from non Gaussian noise, Gaussian noise and envelope; finally identifying the LOS and NLOS signal fading components. For this purpose, the wavelet technique was used to perform the signal decomposition. In particular, the discrete wavelet transform DWT was utilized to carry out the signal de-noising. Then, the results were statistically treated in order to obtain a diffusion index for Rician fading, which are associated with fading in atmosphere and ionosphere layers. In this way the communications channel among satellite and ground station was characterized and a BER parameter was obtained for every satellite overpass, which

  1. Restoration Of Faded Color Photographs By Digital Image Processing

    NASA Astrophysics Data System (ADS)

    Gschwind, Rudolf

    1989-10-01

    Color photographs possess a poor stability towards light, chemicals heat and humidity. As a consequence, the colors of photographs deteriorate with time. Because of the complexity of processes that cause the dyes to fade, it is impossible to restore the images by chemical means. It is therefore attempted to restore faded color films by means of digital image processing.

  2. Fading characteristics of panchromatic radar backscatter from selected agricultural targets

    NASA Technical Reports Server (NTRS)

    Bush, T. F.; Ulaby, F. T.

    1973-01-01

    An experiment was performed to empirically determine the fading characteristics of backscattered radar signals from four agricultural targets at 9 GHz. After a short review of the statistics of Rayleigh fading backscatter, the data processing method and results of the data are analyzed. Comparison with theory shows adequate agreement with the experimental results, provided of course, the targets are modeled in a correct manner.

  3. Autonomous detection of ISO fade point with color laser printers

    NASA Astrophysics Data System (ADS)

    Yan, Ni; Maggard, Eric; Fothergill, Roberta; Jessome, Renee J.; Allebach, Jan P.

    2015-01-01

    Image quality assessment is a very important field in image processing. Human observation is slow and subjective, it also requires strict environment setup for the psychological test 1. Thus developing algorithms to match desired human experiments is always in need. Many studies have focused on detecting the fading phenomenon after the materials are printed, that is to monitor the persistence of the color ink 2-4. However, fading is also a common artifact produced by printing systems when the cartridges run low. We want to develop an automatic system to monitor cartridge life and report fading defects when they appear. In this paper, we first describe a psychological experiment that studies the human perspective on printed fading pages. Then we propose an algorithm based on Color Space Projection and K-means clustering to predict the visibility of fading defects. At last, we integrate the psychological experiment result with our algorithm to give a machine learning tool that monitors cartridge life.

  4. Beam-tracking in FSO links impaired by correlated fading

    NASA Astrophysics Data System (ADS)

    Kiasaleh, Kamran

    2006-08-01

    In this paper, the performance of quad-APD spatial tracking loop (STL)in the presence of scintillation is studied for a frozen atmosphere turbulent model for free-space communications (FSO). The atmospheric turbulence responsible for the beam scintillation is assumed to follow the weak turbulence model, described by Rytov approximation, which in turn suggests log-normal statistics for the received optical signal intensity. It is assumed that pointing error in large part is due to atmospheric wander and that the correlation time of the beam wander is comparable to the correlation time of the amplitude variations due to amplitude scintillation. Provided recently reported estimation strategies, a new model for spatial tracking is proposed where estimates of channel coefficient are used to adjust the gain of the tracking loop, enabling an adaptive bandwidth adjustment in the presence of correlated fading. The performance of the proposed loop as well as that of the standard tracking loop are assessed and compared via simulation in terms of the mean square tracking error (MSTE).

  5. A laboratory system for the investigation of rain fade compensation techniques for Ka-band satellites

    NASA Technical Reports Server (NTRS)

    Svoboda, James S.; Kachmar, Brian A.

    1993-01-01

    The design and performance of a rain fade simulation/counteraction system on a laboratory simulated 30/20 GHz, time division multiple access (TDMA) satellite communications testbed is evaluated. Severe rain attenuation of electromagnetic radiation at 30/20 GHz occurs due to the carrier wavelength approaching the water droplet size. Rain in the downlink path lowers the signal power present at the receiver, resulting in a higher number of bit errors induced in the digital ground terminal. The laboratory simulation performed at NASA Lewis Research Center uses a programmable PIN diode attenuator to simulate 20 GHz satellite downlink geographic rain fade profiles. A computer based network control system monitors the downlink power and informs the network of any power threshold violations, which then prompts the network to issue commands that temporarily increase the gain of the satellite based traveling wave tube (TWT) amplifier. After the rain subsides, the network returns the TWT to the normal energy conserving power mode. Bit error rate (BER) data taken at the receiving ground terminal serves as a measure of the severity of rain degradation, and also evaluates the extent to which the network can improve the faded channel.

  6. Cross-Sectional Nakagami Images in Passive Stretches Reveal Damage of Injured Muscles.

    PubMed

    Lin, Shih-Ping; Lin, Yi-Hsun; Fan, Shih-Chen; Huang, Bu-Miin; Lin, Wei-Yin; Wang, Shyh-Hau; Shung, K Kirk; Su, Fong-Chin; Wu, Chia-Ching

    2016-01-01

    Muscle strain is still awanting a noninvasive quantitatively diagnosis tool. High frequency ultrasound (HFU) improves image resolution for monitoring changes of tissue structures, but the biomechanical factors may influence ultrasonography during injury detection. We aim to illustrate the ultrasonic parameters to present the histological damage of overstretched muscle with the consideration of biomechanical factors. Gastrocnemius muscles from mice were assembled and ex vivo passive stretching was performed before or after injury. After injury, the muscle significantly decreased mechanical strength. Ultrasonic images were obtained by HFU at different deformations to scan in cross and longitudinal orientations of muscle. The ultrasonography was quantified by echogenicity and Nakagami parameters (NP) for structural evaluation and correlated with histological results. The injured muscle at its original length exhibited decreased echogenicity and NP from HFU images. Cross-sectional ultrasonography revealed a loss of correlation between NP and passive muscle stretching that suggested a special scatterer pattern in the cross section of injured muscle. The independence of NP during passive stretching of injured muscle was confirmed by histological findings in ruptured collagen fibers, decreased muscle density, and increased intermuscular fiber space. Thus, HFU analysis of NP in cross section represents muscle injury that may benefit the clinical diagnosis.

  7. Cross-Sectional Nakagami Images in Passive Stretches Reveal Damage of Injured Muscles

    PubMed Central

    Lin, Shih-Ping; Lin, Yi-Hsun; Fan, Shih-Chen; Huang, Bu-Miin; Lin, Wei-Yin; Wang, Shyh-Hau; Shung, K. Kirk; Su, Fong-Chin; Wu, Chia-Ching

    2016-01-01

    Muscle strain is still awanting a noninvasive quantitatively diagnosis tool. High frequency ultrasound (HFU) improves image resolution for monitoring changes of tissue structures, but the biomechanical factors may influence ultrasonography during injury detection. We aim to illustrate the ultrasonic parameters to present the histological damage of overstretched muscle with the consideration of biomechanical factors. Gastrocnemius muscles from mice were assembled and ex vivo passive stretching was performed before or after injury. After injury, the muscle significantly decreased mechanical strength. Ultrasonic images were obtained by HFU at different deformations to scan in cross and longitudinal orientations of muscle. The ultrasonography was quantified by echogenicity and Nakagami parameters (NP) for structural evaluation and correlated with histological results. The injured muscle at its original length exhibited decreased echogenicity and NP from HFU images. Cross-sectional ultrasonography revealed a loss of correlation between NP and passive muscle stretching that suggested a special scatterer pattern in the cross section of injured muscle. The independence of NP during passive stretching of injured muscle was confirmed by histological findings in ruptured collagen fibers, decreased muscle density, and increased intermuscular fiber space. Thus, HFU analysis of NP in cross section represents muscle injury that may benefit the clinical diagnosis. PMID:27034946

  8. Flow quantification with nakagami parametric imaging for suppressing contrast microbubbles attenuation.

    PubMed

    Gu, Xiaolin; Wei, Min; Zong, Yujin; Jiang, Hujie; Wan, Mingxi

    2013-04-01

    Flow quantification with contrast-enhanced ultrasound is still limited by the effects of contrast microbubble attenuation. Nakagami parametric imaging (NPI) based on the m parameter, which is related to the statistical property of echo envelope, is implemented to suppress contrast attenuation. Flow velocity (FV) and volumetric flow rate (VFR) are estimated through the least square fitting of burst depletion kinetic model to time m parameter curves (TMCs). A non-recirculating flow phantom is imaged as contrast microbubbles are infused at 10, 15, 20, 25, and 30 mL/min. Contrast microbubbles with two different concentrations are used to generate variations of contrast microbubble attenuation. The results suggest that 4 × 4 mm(2) is the optimal size of a sliding window of NPI for flow quantification under current experiment condition. At a lower microbubble concentration, the FV calculated from TMCs correlates strongly with actual FV in both unattenuated (R(2) = 0.97; p < 0.01) and attenuated regions (R(2) = 0.92; p < 0.01) within phantom. And there is a strong correlation (R(2) = 0.98; p < 0.01; slope = 0.96; intercept = 0.68) between VFR calculated from TMCs and actual VFR within the whole phantom. Similar results are obtained at higher microbubble concentrations. Compared with conventional ultrasound imaging that is intensity dependent, NPI achieves better performance on flow quantification in the presence of contrast microbubble attenuation.

  9. On the Fading of the STIS Ultraviolet Calibration Lamps

    NASA Astrophysics Data System (ADS)

    Peeples, Molly S.

    2017-09-01

    The Space Telescope Imaging Spectrograph (STIS) has been in orbit for over 20 years, so its calibration lamps are fading, risking the precision of future science opportunities. The report documents analysis on the fading of these lamps in the ultraviolet and suggests possible mitigation strategies. A discussion of the strategy of alternating years to obtain deep NUV and FUV flats appears to have slowed the fading of these lamps, but the modes in which the flat fields are taken may have to be changed again in future cycles to obtain enough counts for robust flat fields.

  10. Fade detector for the FODA-TDMA access scheme

    NASA Astrophysics Data System (ADS)

    Celandroni, Nedo; Ferro, Erina; Marzoli, Antonio

    1989-05-01

    The First in first out Ordered Demand Assignment-Time Division Multiple Access (FODA-TDMA) satellite access scheme designed for simultaneous transmissions of real time data, like packetized voice and slow-scan images (stream traffic) and data coming from standard EDP applications, such as bulk data tansfer, interactive computer access, mailing, data base enquiry and updating (datagram traffic) is described. When deep fades are experienced due to rain attenuation, the system is able to counter the fade. Techniques to detect the fade are presented.

  11. A PSAM-based estimator of noise and fading statistics for optimum receivers of free space optics signals

    NASA Astrophysics Data System (ADS)

    Moradi, Hassan; Refai, Hazem H.; LoPresti, Peter G.; Atiquzzaman, Mohammed

    2010-02-01

    Incoherent receivers of Free Space Optical (FSO) signals have no knowledge of instantaneous channel state. Thus, the receiver requires some information about the noise and fading statistics for a maximum likelihood (ML)-based optimal detection. Using pilot-aided symbols, we develop a simple multi slot averaging (MSA) estimation technique to approximate the values of parameters required at the incoherent detector. No channel state information (CSI) is available at the receiver side and this work will not be also trying to estimate it. But the estimation of noise and fading statistics will be practically investigated. We evaluate the bit error rate (BER) performance of FSO links with MSA estimation over both Gaussian and lognormal atmospheric turbulence fading (scintillation) channels. Numerical simulation will be completed to evaluate the estimation error of the MSA estimator. We will see that at signal to noise ratio (SNR)=13dB, the performance loss of the Gaussian estimator improves from 3dB to 0.4dB when we increase the number of pilot symbols from 16 to 64. This paper also presents the hardware design of the estimator using Xilinx system generator.

  12. Radar prediction of absolute rain fade distributions for earth-satellite paths and general methods for extrapolation of fade statistics to other locations

    NASA Technical Reports Server (NTRS)

    Goldhirsh, J.

    1982-01-01

    The first absolute rain fade distribution method described establishes absolute fade statistics at a given site by means of a sampled radar data base. The second method extrapolates absolute fade statistics from one location to another, given simultaneously measured fade and rain rate statistics at the former. Both methods employ similar conditional fade statistic concepts and long term rain rate distributions. Probability deviations in the 2-19% range, with an 11% average, were obtained upon comparison of measured and predicted levels at given attenuations. The extrapolation of fade distributions to other locations at 28 GHz showed very good agreement with measured data at three sites located in the continental temperate region.

  13. NiH2 capacity fade during early cycling

    NASA Technical Reports Server (NTRS)

    Zagrodnik, Jeffrey P.

    1993-01-01

    Tests were conducted on nickel hydrogen batteries to determine the charge efficiency of the nickel electrode as a function of rate and temperature, cell discharge capacity, and capacity fade. Test procedures and results are presented in outline and graphic form.

  14. An examination of ham colour fading using optical fibre methods

    NASA Astrophysics Data System (ADS)

    Sheridan, Cormac; O'Farrell, Marion; Lewis, Elfed; Flanagan, Colin; Kerry, John F.; Jackman, Nick

    2006-10-01

    Sliced ham products undergo significant discolouration and fading when placed in retail display cabinets. This is due to factors such as illumination of the display cabinet, packaging, i.e. low OTR (Oxygen Transmission Rate) or very low OTR packaging, product to headspace ratio and percentage of residual oxygen. This paper presents initial investigations into the development of a sensor to measure rate of colour fading in cured ham, in order to predict an optimum colour sell-by-date. An investigation has been carried out that shows that spectral reflections offer more reproducibility than CIE L*a*b* readings, which are, at present, most often used to measure meat colour. Self-Organising Maps were then used to classify the data into five colour fading stages, from very pink to grey. The results presented here show that this classifier could prove an effective system for determining the rate of colour fading in ham.

  15. Kinetics of the Fading of Phenolphthalein in Alkaline Solution.

    ERIC Educational Resources Information Center

    Nicholson, Lois

    1989-01-01

    Described is an experiment which illustrates pseudo-first-order kinetics in the fading of a common indicator in an alkaline solution. Included are background information, details of materials used, laboratory procedures, and sample results. (CW)

  16. Motion fading is driven by perceived, not actual angular velocity.

    PubMed

    Kohler, P J; Caplovitz, G P; Hsieh, P-J; Sun, J; Tse, P U

    2010-06-01

    After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. Here we examine the relationship between such 'motion fading' and perceived angular velocity. Using several different dot patterns that generate emergent virtual contours, we demonstrate that whenever there is a difference in the perceived angular velocity of two patterns of dots that are in fact rotating at the same angular velocity, there is also a difference in the time to undergo motion fading for those two patterns. Conversely, whenever two patterns show no difference in perceived angular velocity, even if in fact rotating at different angular velocities, we find no difference in the time to undergo motion fading. Thus, motion fading is driven by the perceived rather than actual angular velocity of a rotating stimulus.

  17. OVERVIEW OF SPILLWAY FROM SOUTH BANK OF RIVER; FADING NORTHNORTHEAST ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    OVERVIEW OF SPILLWAY FROM SOUTH BANK OF RIVER; FADING NORTH-NORTHEAST - Shoshone Falls Hydroelectric Project, Reservoir and Dam Complex, North Bank of Snake River, extreme Eastern end of the Shoshone Falls Hydroelectric Project, Tipperary Corner, Jerome County, ID

  18. Fading of Jupiter's South Equatorial Belt

    NASA Technical Reports Server (NTRS)

    Sola, Michael A.; Orton, Glenn; Baines, Kevin; Yanamandra-Fisher, Padma

    2011-01-01

    One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.

  19. Fading of Jupiter's South Equatorial Belt

    NASA Technical Reports Server (NTRS)

    Sola, Michael A.; Orton, Glenn; Baines, Kevin; Yanamandra-Fisher, Padma

    2011-01-01

    One of Jupiter's most dominant features, the South Equatorial Belt, has historically gone through a "fading" cycle. The usual dark, brownish clouds turn white, and after a period of time, the region returns to its normal color. Understanding this phenomenon, the latest occurring in 2010, will increase our knowledge of planetary atmospheres. Using the near infrared camera, NSFCAM2, at NASA's Infrared Telescope Facility in Hawaii, images were taken of Jupiter accompanied by data describing the circumstances of each observation. These images are then processed and reduced through an IDL program. By scanning the central meridian of the planet, graphs were produced plotting the average values across the central meridian, which are used to find variations in the region of interest. Calculations using Albert4, a FORTRAN program that calculates the upwelling reflected sunlight from a designated cloud model, can be used to determine the effects of a model atmosphere due to various absorption, scattering, and emission processes. Spectra that were produced show ammonia bands in the South Equatorial Belt. So far, we can deduce from this information that an upwelling of ammonia particles caused a cloud layer to cover up the region. Further investigations using Albert4 and other models will help us to constrain better the chemical make up of the cloud and its location in the atmosphere.

  20. Optically derived elevation angle dependence of fading for satellite PCS

    NASA Technical Reports Server (NTRS)

    Akturan, R.; Vogel, Wolf J.

    1995-01-01

    Images of urban Japan taken vertically through a 180 deg fisheye lens were analyzed to derive, as a function of elevation the fraction of sky that is clear, shadowed by trees, or blocked by buildings. At 32 deg elevation, results match those derived from satellite measurements fit to a 3-state fade model. Using the same model, for the first time the elevation angle dependence of mobile satellite fading is predicted.

  1. Statistical Space-Time-Frequency Characterization of MIMO Shallow Water Acoustic Channels

    DTIC Science & Technology

    2010-06-01

    multiple - input multiple - output ( MIMO ) SWA communication systems. By taking into account...20375 USA Abstract—This paper proposes a geometry-based statistical model for multiple - input multiple - output shallow water acous- tic multipath fading...statistical model for multiple - input multiple - output shallow water acoustic multipath fading channels. From the reference model, the corresponding

  2. Theoretical study of a dynamic simulator of selective fading for digital, wireless beam microwave links

    NASA Astrophysics Data System (ADS)

    Bouidene, A.; Vandamme, P.

    1984-10-01

    A channel simulator for line-of-sight digital radio systems is presented. The basic principle is to reproduce channel transfer functions measured in the field during multipath propagation activity, by driving a complex linear transversal filter with precomputed data. The criterion used for calculating the values of the filter taps for each transfer function is the minimum mean square error criterion. It is shown that a thirteen-taps complex transversal filter with a period of 70 MHz in the frequency domain leads to accurate simulations of selective fading transfer functions in a 50 MHz bandwidth. Technological features are investigated. Effects of the accuracy in the delays implementation and of the tap-weight quantification are particularly analyzed.

  3. Performance evaluation of land mobile satellite system under fading and interference using multiple TCM by Monte-Carlo simulation

    NASA Technical Reports Server (NTRS)

    Kwa, S. C.; Vanderaar, Mark J.; Kim, Junghwan; Stevens, Grady H.

    1991-01-01

    The performance of the land mobile satellite system (LMSS) was evaluated by using two trellis coded modulation (TCM) schemes under multipath fading and interference. The results were also compared with uncoded QPSK. The trellis coding formats included a trellis code designed for optimum performance on the fading channel that typifies satellite to mobile communications, as well as one designed for optimum performance in the additive white Gaussian noise (AWGN) channel. The results show that, in Rayleigh fading, the TCM code designed for optimum performance in such an environment performs 4 dB better than the TCM code designed for optimum performance in AWGN, and 10 dB better than the uncoded format, at a bit error rate (BER) of 10 exp -4. Additional results on the performance degradation due to the nonlinearities in the satellite transponder and the adjacent and cochannel interference show that the TCM system is more sensitive than the uncoded system to the phase distortion caused by these impairments.

  4. Performance evaluation of land mobile satellite system under fading and interference using multiple TCM by Monte-Carlo simulation

    NASA Technical Reports Server (NTRS)

    Kwa, S. C.; Vanderaar, Mark J.; Kim, Junghwan; Stevens, Grady H.

    1991-01-01

    The performance of the land mobile satellite system (LMSS) was evaluated by using two trellis coded modulation (TCM) schemes under multipath fading and interference. The results were also compared with uncoded QPSK. The trellis coding formats included a trellis code designed for optimum performance on the fading channel that typifies satellite to mobile communications, as well as one designed for optimum performance in the additive white Gaussian noise (AWGN) channel. The results show that, in Rayleigh fading, the TCM code designed for optimum performance in such an environment performs 4 dB better than the TCM code designed for optimum performance in AWGN, and 10 dB better than the uncoded format, at a bit error rate (BER) of 10 exp -4. Additional results on the performance degradation due to the nonlinearities in the satellite transponder and the adjacent and cochannel interference show that the TCM system is more sensitive than the uncoded system to the phase distortion caused by these impairments.

  5. Digital data communications over microwave radio channels

    NASA Astrophysics Data System (ADS)

    Salz, J.

    1984-10-01

    A major contribution to system outage in a terrestrial digital radio channel is deep fading of the frequency transfer characteristic, which in addition to causing a precipitous drop in received signal-to-noise ratio also causes signal dispersion that can result in severe intersymbol interference. Because the temporal variation of the channel is slow compared to the signaling rate, the information theoretic channel capacity and the efficiency index in bits/cycle can be viewed as random processes. Based on an established mathematical model for fading channels, the probability distribution of channel capacity and the distribution of efficiency indices for different communications techniques are estimated. A crucial obstacle to achieving these rates is the nonlinear distortion introduced by power amplifiers. A method for coping with this nonlinear distortion is also described.

  6. Communication Channel Estimation and Waveform Design: Time Delay Estimation on Parallel, Flat Fading Channels

    DTIC Science & Technology

    2010-02-01

    JCR (τ̂ ) = T 2π ∫ ∞ −∞ ω2 SNR(ω) dω, (8) where SNR(ω) is defined as SNR(ω) = (S(ω)/N1(ω)) (S(ω)/N2(ω)) 1 + (S(ω)/N1(ω)) + (S(ω)/N2(ω)) (9) and the...expression with a linear array is given in (9). 5 and the Fisher information in equation 8 evaluates to JCR (τ̂ ) = 2ω 2 c ( TB 2π )[ 1 + 1 12 ( B ωc )2] SNR

  7. Autonomous detection of text fade point with color laser printers

    NASA Astrophysics Data System (ADS)

    Ju, Yanling; Maggard, Eric; Jessome, Renee; Allebach, Jan

    2015-01-01

    Fading is one of the issues of most critical concern for print quality degradation with color laser electro- photographic printers. Fading occurs when the cartridge is depleted. ISO/IEC 19798:2007(E) specifies a process for determining the cartridge page yield for a given color electro-photographic printer model. It is based on repeatedly printing a suite of test pages, followed by visual examination of the sequence of printed diagnostic pages. But this method is a very costly process since it involves visual examination of a large number of pages. And also the final decision is based on the visual examination of a specially designed diagnostic page, which is different than typical office document pages, since it consists of color bars, and contains no text. In this paper, we propose a new method to autonomously detect the text fading in prints from home or office color printers using a typical office document page instead of a specially designed diagnostic page. In our method, we scan and analyze the printed pages to predict where expert observers would judge fading to have occurred in the print sequence. Our approach is based on a machine-learning framework in which features derived from image analysis are mapped to a fade point prediction.

  8. Rain Fade Compensation for Ka-Band Communications Satellites

    NASA Technical Reports Server (NTRS)

    Mitchell, W. Carl; Nguyen, Lan; Dissanayake, Asoka; Markey, Brian; Le, Anh

    1997-01-01

    This report provides a review and evaluation of rain fade measurement and compensation techniques for Ka-band satellite systems. This report includes a description of and cost estimates for performing three rain fade measurement and compensation experiments. The first experiment deals with rain fade measurement techniques while the second one covers the rain fade compensation techniques. The third experiment addresses a feedback flow control technique for the ABR service (for ATM-based traffic). The following conclusions were observed in this report; a sufficient system signal margin should be allocated for all carriers in a network, that is a fixed clear-sky margin should be typically in the range of 4-5 dB and should be more like 15 dB in the up link for moderate and heavy rain zones; to obtain a higher system margin it is desirable to combine the uplink power control technique with the technique that implements the source information rate and FEC code rate changes resulting in a 4-5 dB increase in the dynamic part of the system margin. The experiments would assess the feasibility of the fade measurements and compensation techniques, and ABR feedback control technique.

  9. Measurement of multipath delay profile in land mobile satellite channels

    NASA Technical Reports Server (NTRS)

    Ikegami, Tetsushi; Arakaki, Yoshiya; Wakana, Hiromitsu; Suzuki, Ryutaro

    1993-01-01

    Mobile satellite communication channel has been evaluated mainly with fading statistics of signal. When bandwidth of transmitting signal becomes wider, frequency selectivity of fading becomes a significant factor of the channel. Channel characteristics, not only signal variation but multipath delay spread should be evaluated. A multipath measurement system is proposed and developed for mobile satellite applications. With this system and ETS-V satellite, multipath delay profiles are measured in various environments including Tokyo metropolis and Sapporo city at 1.5 GHz. Results show that the maximum excess delay is within 1 microsec and the maximum delay spread is 0.2 microsecs at elevation angles of 40 to 47 degrees. In wideband signal transmission of about 1 MHz and more, designers should consider the effect of selective fading due to the multipath of land mobile satellite channel.

  10. Stochastic Wireless Channel Modeling, Estimation and Identification from Measurements

    SciTech Connect

    Olama, Mohammed M; Djouadi, Seddik M; Li, Yanyan

    2008-07-01

    This paper is concerned with stochastic modeling of wireless fading channels, parameter estimation, and system identification from measurement data. Wireless channels are represented by stochastic state-space form, whose parameters and state variables are estimated using the expectation maximization algorithm and Kalman filtering, respectively. The latter are carried out solely from received signal measurements. These algorithms estimate the channel inphase and quadrature components and identify the channel parameters recursively. The proposed algorithm is tested using measurement data, and the results are presented.

  11. An Analysis of Vocal Stereotypy and Therapist Fading

    PubMed Central

    Athens, Elizabeth S; Vollmer, Timothy R; Sloman, Kimberly N; St. Peter Pipkin, Claire

    2008-01-01

    A functional analysis for a boy with Down syndrome and autism suggested that vocal stereotypy was maintained by automatic reinforcement. The analysis also showed that instructions and noncontingent attention suppressed vocal stereotypy. A treatment package consisting of noncontingent attention, contingent demands, and response cost effectively reduced vocal stereotypy. The treatment package remained effective even when noncontingent attention was removed, making the procedure easier to implement. Also, the presence of the therapist in the room with the participant was faded systematically. After completion of fading, vocal stereotypy remained low during conditions similar to the no-consequence phase of the functional analysis. PMID:18595296

  12. Fast Faraday fading of long range satellite signals.

    NASA Technical Reports Server (NTRS)

    Heron, M. L.

    1972-01-01

    20 MHz radio signals have been received during the day from satellite Beacon-B when it was below the optical horizon by using a bank of narrow filters to improve the signal to noise ratio. The Faraday fading rate becomes constant, under these conditions, at a level determined by the plasma frequency just below the F-layer peak. Variations in the Faraday fading rate reveal fluctuations in the electron density near the peak, while the rate of attaining the constant level depends on the shape of the electron density profile.

  13. An analysis of vocal stereotypy and therapist fading.

    PubMed

    Athens, Elizabeth S; Vollmer, Timothy R; Sloman, Kimberly N; St Peter Pipkin, Claire

    2008-01-01

    A functional analysis for a boy with Down syndrome and autism suggested that vocal stereotypy was maintained by automatic reinforcement. The analysis also showed that instructions and noncontingent attention suppressed vocal stereotypy. A treatment package consisting of noncontingent attention, contingent demands, and response cost effectively reduced vocal stereotypy. The treatment package remained effective even when noncontingent attention was removed, making the procedure easier to implement. Also, the presence of the therapist in the room with the participant was faded systematically. After completion of fading, vocal stereotypy remained low during conditions similar to the no-consequence phase of the functional analysis.

  14. Different fixational eye movements mediate the prevention and the reversal of visual fading

    PubMed Central

    McCamy, Michael B; Macknik, Stephen L; Martinez-Conde, Susana

    2014-01-01

    Fixational eye movements (FEMs; including microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different FEM types influence this process is a matter of debate. Attempts to answer this question have been hampered by the failure to distinguish between the prevention of fading (where fading is blocked before it happens in the first place) and the reversal of fading (where vision is restored after fading has already occurred). Because fading during fixation is a detriment to clear vision, the prevention of fading, which avoids visual degradation before it happens, is a more desirable scenario than improving visibility after fading has occurred. Yet previous studies have not examined the role of FEMs in the prevention of fading, but have focused on visual restoration instead. Here we set out to determine the differential contributions and efficacies of microsaccades and drift to preventing fading in human vision. Our results indicate that both microsaccades and drift mediate the prevention of visual fading. We also found that drift is a potentially larger contributor to preventing fading than microsaccades, although microsaccades are more effective than drift. Microsaccades moreover prevented foveal and peripheral fading in an equivalent fashion, and their efficacy was independent of their size, number, and direction. Our data also suggest that faster drift may prevent fading better than slower drift. These findings may help to reconcile the long-standing controversy concerning the comparative roles of microsaccades and drift in visibility during fixation. PMID:25128571

  15. Transmission over EHF mobile satellite channels

    NASA Technical Reports Server (NTRS)

    Zhuang, W.; Chouinard, J.-Y.; Yongacoglu, A.

    1993-01-01

    Land mobile satellite communications at Ka-band (30/20 GHz) are attracting an increasing interest among researchers because of the frequency band availability and the possibility of small earth station designs. However, communications at the Ka-band pose significant challenges in the system designs due to severe channel impairments. Because only very limited experimental data for mobile applications at Ka-band is available, this paper studies the channel characteristics based on experimental data at L-band (1.6/1.5 GHz) and the use of frequency scaling. The land mobile satellite communication channel at Ka-band is modelled as log-normal Rayleigh fading channel. The first and second-order statistics of the fading channel are studied. The performance of a coherent BPSK system over the fading channel at L-band and K-band is evaluated theoretically and validated by computer simulations. Conclusions on the communication channel characteristics and system performance at L-band and Ka-band are presented.

  16. Combining Stimulus Fading, Reinforcement, and Extinction To Treat Food Refusal.

    ERIC Educational Resources Information Center

    Freeman, Kurt A.; Piazza, Cathleen C.

    1998-01-01

    The food refusal of a 6-year-old girl with autism and destructive behavior was treated using stimulus fading, reinforcement, and escape extinction. Intake increased, and compliance with prompting procedures remained relatively stable despite the increased consumption requirement. (Author/CR)

  17. The Landmark Decision that Faded into Historical Obscurity

    ERIC Educational Resources Information Center

    Nance, Molly

    2007-01-01

    This article takes a look at the Mendez v. Westminster School District, a landmark case that faded into historical obscurity. In the 1940s, Gonzalo and Felicita Mendez wanted their three children to attend the school nearest their farm, which was the 17th Street Elementary School in Westminster. But in the Westminster, Orange County, El Medina,…

  18. Fade Measurements into Buildings from 500 to 3000 MHz

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1996-01-01

    Slant-path fade measurements from 500 to 3000 MHz were made into six different buildings employing a vector network analyzer, a tower-mounted transmitting antenna and an automatically positioned receiving antenna. The objective of the measurements was to provide information for satellite audio broadcasting and personal communications satellite design on the correlation of fading inside buildings. Fades were measured with 5 cm spatial separation and every 0.2% of the frequency. Median fades ranged from 10 to 20 dB in woodframe houses with metal roofs and walls without and with an aluminum heatshield, respectively. The median decorrelation distance was from 0.5 to 1.1 m and was independent of frequency. The attenuation into the buildings increased only moderately with frequency in most of the buildings with a median slope of about 1 to 3 dB/GHz, but increased fastest in the least attenuating building with a slope of 5 dB/GHz. The median decorrelation bandwidth ranged from 1.2 to 3.8% of frequency in five of the buildings, and was largest in the least attenuating building, with 20.2% of frequency.

  19. Fade Measurements into Buildings from 500 to 3000 MHz

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.

    1996-01-01

    Slant-path fade measurements from 500 to 3000 MHz were made into six different buildings employing a vector network analyzer, a tower-mounted transmitting antenna and an automatically positioned receiving antenna. The objective of the measurements was to provide information for satellite audio broadcasting and personal communications satellite design on the correlation of fading inside buildings. Fades were measured with 5 cm spatial separation and every 0.2 percent of the frequency. Median fades ranged from 10 to 20 dB in woodframe houses with metal roofs and walls without and with an aluminum heat shield, respectively. The median decorrelation distance was from 0.5 to 1.1. m and was independent of frequency. The attenuation into the buildings increased only moderately with frequency in most of the buildings with a median slope of about 1 to 3 db/GHz, but increased fastest in the least attenuating building with a slope of 5 dB/GHz. The median decorrelation bandwidth ranged from 1.2 to 3.8 percent of frequency in five of the buildings, and was largest in the least attenuating building, with 20.2 percent of frequency.

  20. Use of Texture Fading in the Treatment of Food Selectivity.

    ERIC Educational Resources Information Center

    Shore, Bridget A.; Babbitt, Roberta L.; Williams, Keith E.; Coe, David A.; Snyder, Angela

    1998-01-01

    A study investigated the efficacy of texture fading in the treatment of food selectivity displayed by four children (ages 2-5). Successful treatment involved the gradual addition of higher textures based on results of periodic probes. Food acceptance and swallowing were reinforced, while food refusal and expulsion were placed on extinction.…

  1. Treating Total Liquid Refusal with Backward Chaining and Fading.

    ERIC Educational Resources Information Center

    Hagopian, Louis P.; And Others

    1996-01-01

    In this study of a 12-year-old boy with autism, mental retardation, and a history of severe gastrointestinal problems, who refused liquids and food, backward chaining was used to shape drinking from a cup and a fading procedure was used to increase the water he was required to drink. (Author/CR)

  2. 77 FR 22381 - Odorant Fade in Railroad Tank Cars

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-13

    ... Federal Railroad Administration Odorant Fade in Railroad Tank Cars AGENCY: Federal Railroad Administration... Safety Advisory 2012-01 to remind shippers and consignees of railroad tank cars containing odorized... United States by railroad tank car is from bulk suppliers to either industrial end-users or to...

  3. A Probe Intermix Procedure for Fading Response Prompts.

    ERIC Educational Resources Information Center

    Billingsley, Felix F.

    1987-01-01

    A prompt fading method was employed to teach an eight-year-old student with severe behavior disorders the self-paced use of a functional behavior (requesting rather than grabbing food items). Initial pairing of prompts and natural cues was followed by a mix of prompted and probe (unprompted) trials. (Author/JW)

  4. A Probe Intermix Procedure for Fading Response Prompts.

    ERIC Educational Resources Information Center

    Billingsley, Felix F.

    1987-01-01

    A prompt fading method was employed to teach an eight-year-old student with severe behavior disorders the self-paced use of a functional behavior (requesting rather than grabbing food items). Initial pairing of prompts and natural cues was followed by a mix of prompted and probe (unprompted) trials. (Author/JW)

  5. The Landmark Decision that Faded into Historical Obscurity

    ERIC Educational Resources Information Center

    Nance, Molly

    2007-01-01

    This article takes a look at the Mendez v. Westminster School District, a landmark case that faded into historical obscurity. In the 1940s, Gonzalo and Felicita Mendez wanted their three children to attend the school nearest their farm, which was the 17th Street Elementary School in Westminster. But in the Westminster, Orange County, El Medina,…

  6. Enuresis Control through Fading, Escape, and Avoidance Training.

    ERIC Educational Resources Information Center

    Hansen, Gordon D.

    1979-01-01

    A twin signal device that provides both escape and avoidance conditioning in enuresis control was documented with case studies of two enuretic children (eight and nine years old). In addition, a technique of fading as an adjunct to the process was utilized with one subject. (Author/SBH)

  7. A new fading event is underway in FO Aqr

    NASA Astrophysics Data System (ADS)

    Littlefield, Colin; Myers, Gordon; Sabo, Richard; Garnavich, Peter; Kennedy, Mark

    2017-09-01

    The intermediate polar FO Aqr, which in 2016 underwent the first low state in its observational history (Littlefield et al. 2016, ApJ, 833, 93), has faded by nearly 0.7 mag since 2017 August 10, implying a decrease in the system's accretion rate.

  8. Power fade and capacity fade resulting from cycle-life testing of Advanced Technology Development Program lithium-ion batteries

    NASA Astrophysics Data System (ADS)

    Wright, R. B.; Christophersen, J. P.; Motloch, C. G.; Belt, J. R.; Ho, C. D.; Battaglia, V. S.; Barnes, J. A.; Duong, T. Q.; Sutula, R. A.

    This paper presents the test results and analysis of the power and capacity fade resulting from the cycle-life testing using PNGV (now referred to as FreedomCAR) test protocols at 25 and 45 °C of 18650-size Li-ion batteries developed by the US Department of Energy sponsored Advanced Technology Development (ATD) Program. Two cell chemistries were studied, a Baseline chemistry that had a cathode composition of LiNi 0.8Co 0.15Al 0.05O 2 with binders, that was cycle-life tested at 25 and 45 °C, and a Variant C chemistry with a cathode composition of LiNi 0.8Co 0.10Al 0.10O 2 with binders, that was tested only at 45 °C. The 300 Wh power, and % power fade were determined as a function of test time, i.e. the number of test cycles for up to 44 weeks (369,600 test cycles) for the Baseline cells, and for 24 weeks (201,600 test cycles) for the Variant C cells. The C/1 and C/25 discharge capacity and capacity fade were also determined during the course of these studies. The results of this study indicate that the 300 Wh power for the Baseline cells tested at 25 °C (up to 44 weeks of testing) decreased as a linear function of test time. The % power fade for these cells increased as a linear function of test time. The Baseline cells tested at 45 °C (up to 44 weeks of testing) displayed a decrease in their power proportional to the square root of the test time, with a faster rate of decrease of the power occurring at ˜28 weeks of testing. The % power fade for these cells also increased as the square root of the test time, and exhibited an increase in the % power fade rate at ˜28 weeks of testing. The 45 °C tested Baseline cells' power decreased, and their % power fade increased at a greater rate than the 25 °C tested Baseline cells. The power fade was greater for the Variant C cells. The power of the Variant C cells (tested at 45 °C) decreased as the square root of the test time, and their % power fade was also found to be a function of the square root of the test time

  9. GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties

    NASA Technical Reports Server (NTRS)

    Kavak, Adnan; Xu, Guang-Han; Vogel, Wolfhard J.

    1996-01-01

    In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, GPS receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.

  10. GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties

    NASA Technical Reports Server (NTRS)

    Kavak, Adnan; Xu, Guanghan; Vogel, W. J.

    1996-01-01

    In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, global positioning system (GPS) receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.

  11. GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties

    NASA Technical Reports Server (NTRS)

    Kavak, Adnan; Xu, Guanghan; Vogel, W. J.

    1996-01-01

    In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, global positioning system (GPS) receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.

  12. GPS Multipath Fade Measurements to Determine L-Band Ground Reflectivity Properties

    NASA Technical Reports Server (NTRS)

    Kavak, Adnan; Xu, Guang-Han; Vogel, Wolfhard J.

    1996-01-01

    In personal satellite communications, especially when the line-of-sight is clear, ground specular reflected signals along with direct signals are received by low gain, almost omni-directional subscriber antennas. A six-channel, C/A code processing, GPS receiver with an almost omni-directional patch antenna was used to take measurements over three types of ground to characterize 1.575 GHz specular ground reflections and ground dielectric properties. Fade measurements were taken over grass, asphalt, and lake water surfaces by placing the antenna in a vertical position at a fixed height from the ground. Electrical characteristics (conductivity and dielectric constant) of these surfaces (grass, asphalt, lake water) were obtained by matching computer simulations to the experimental results.

  13. Intelligibility Performance of the LPC-10 and APC/SQ Speech Algorithms in a Fading Environment.

    DTIC Science & Technology

    1985-02-26

    Conditions ----------------------------- 26 3 INTELLIGIBILITY TEST RESULTS --------------------- 29 3.1 Overview ------------------------------------ 29 3.2...ideal conditions , this study needed to use a new approach to more characteristically describe the algorithms’ performance in a fading environment. As...evaluating the performance in fading environments. 3. Conducting a series of intelligibility tests in a variety of noise and fading conditions . For LPC-10

  14. Comparative study on the performance of power and bandwidth efficient modulations in LMSS under fading and interference

    NASA Technical Reports Server (NTRS)

    Liu, Jian; Kim, Junghwan; Kwatra, S. C.; Stevens, Grady H.

    1991-01-01

    Aspects of error performance of various power and bandwidth efficient modulations for the land mobile satellite systems (LMSS) were investigated under multipath fading and interferences by using Monte-Carlo simulation. A differential detection for 16QAM (quadrature amplitude modulation) was proposed to cope with Ricean fading and Doppler shift. Computer simulation results show that the performance of 16QAM with differential detection is as good as that of 16PSK with coherent detection and 3 dB better than that of 16PSK with differential detection, although it degrades by about 4.5 dB as compared to 16QAM with coherent detection under an additive white Gaussian noise (AWGN) channel. For the nonlinear channels, 16QAM with modified signal constellations is introduced and analyzed. The simulation results show that the modified 16QAM exhibits a gain of 2.5 dB over 16PSK under traveling-wave tube nonlinearity, and about 4 dB gain over 16PSK at the bit error rate of 10 exp -5 under AWGN. Computer simulation results for modified 16 QAM under cochannel interference and adjacent-channel interference are also presented.

  15. Channel Estimation in DCT-Based OFDM

    PubMed Central

    Wang, Yulin; Zhang, Gengxin; Xie, Zhidong; Hu, Jing

    2014-01-01

    This paper derives the channel estimation of a discrete cosine transform- (DCT-) based orthogonal frequency-division multiplexing (OFDM) system over a frequency-selective multipath fading channel. Channel estimation has been proved to improve system throughput and performance by allowing for coherent demodulation. Pilot-aided methods are traditionally used to learn the channel response. Least square (LS) and mean square error estimators (MMSE) are investigated. We also study a compressed sensing (CS) based channel estimation, which takes the sparse property of wireless channel into account. Simulation results have shown that the CS based channel estimation is expected to have better performance than LS. However MMSE can achieve optimal performance because of prior knowledge of the channel statistic. PMID:24757439

  16. Spoon distance fading with and without escape extinction as treatment for food refusal.

    PubMed

    Rivas, Kristi D; Piazza, Cathleen C; Patel, Meeta R; Bachmeyer, Melanie H

    2010-01-01

    Little is known about the characteristics of meals that serve as motivating operations (MOs) for escape behavior. In the current investigation, we showed that the distance at which a therapist held a spoon from a child's lips served as an MO for escape behavior. Based on these results, we implemented spoon distance fading, compared fading with and without escape extinction (EE), and compared fading plus EE to EE alone. Initially, inappropriate mealtime behavior decreased during fading, but this effect was not maintained as fading progressed. Inappropriate mealtime behavior was lower initially when we combined fading and EE relative to EE alone, but acceptance increased more rapidly with EE than with fading plus EE. These results suggest that a number of mealtime characteristics might function as MOs for escape behavior and that analyses of MOs may be useful for developing treatments for food refusal.

  17. An Approach to the Development of Software for Computer-Aided Design of Satellite Communications Receivers for Operation in Scintillating Channels

    DTIC Science & Technology

    1989-04-28

    coherent BPSK and for coherent offset quaternary PSK ( OQPSK ). The different curves in these figures show the effect of different channel decorrelation...77=-- --- - - 7 ~ To/Tcb - TO/Tcb =10 05101202303 1012 7 _ 7---7 7-77 COHERENT OQPSK -BLTcb)= V30 RAYLEIGH FADING f-4 FADING SpECTRUM - roTcb =30

  18. Effectiveness of Convolutional Code in Multipath Underwater Acoustic Channel

    NASA Astrophysics Data System (ADS)

    Park, Jihyun; Seo, Chulwon; Park, Kyu-Chil; Yoon, Jong Rak

    2013-07-01

    The forward error correction (FEC) is achieved by increasing redundancy of information. Convolutional coding with Viterbi decoding is a typical FEC technique in channel corrupted by additive white gaussian noise. But the FEC effectiveness of convolutional code is questioned in multipath frequency selective fading channel. In this paper, how convolutional code works in multipath channel in underwater, is examined. Bit error rates (BER) with and without 1/2 convolutional code are analyzed based on channel bandwidth which is frequency selectivity parameter. It is found that convolution code performance is well matched in non selective channel and also effective in selective channel.

  19. Use of texture fading in the treatment of food selectivity.

    PubMed

    Shore, B A; Babbitt, R L; Williams, K E; Coe, D A; Snyder, A

    1998-01-01

    Children with feeding disorders often display severe food selectivity. For many of these children, consuming highly textured foods may be aversive or potentially dangerous because of frequent gagging. The purpose of this study was to demonstrate the efficacy of texture fading in the treatment of food selectivity displayed by 4 children. Treatment involved the gradual addition of higher textures based on the results of periodic probes. In addition, food acceptance and swallowing were reinforced, while food refusal and food expulsion were placed on extinction. Results showed that all participants successfully advanced to consumption of age-appropriate texture and volume. The results suggest that texture fading with intermittent probes at higher textures may be an effective method for the treatment of food selectivity by texture.

  20. Motor learning with fading and growing haptic guidance.

    PubMed

    Heuer, Herbert; Lüttgen, Jenna

    2014-07-01

    Haptic guidance has been shown to have both facilitatory and interfering effects on motor learning. Interfering effects have been hypothesized to result from the particular dynamic environment, which supports a passive role of the learner, and they should be attenuated by fading guidance. Facilitatory effects, in particular for dynamic movement characteristics, have been hypothesized to result from the high-quality information provided by haptic demonstration. If haptic demonstration provides particularly precise information about target movements, the motor system's need for such information should more likely increase in the course of motor learning, in which case growing guidance should be more beneficial for learning. We contrasted fading and growing guidance in the course of learning a spatio-temporal motor pattern. To stimulate an active role of the learner, practice trials consisted of three phases, a visual demonstration of the target movement, a guided reproduction, and a reproduction without haptic guidance. Performance was assessed in terms of variable duration errors, relative-timing errors, variable path-length errors, and shape errors. Motor learning with growing and fading guidance turned out to be largely equivalent, so that the notion of an increasing optimal precision of haptic demonstrations, which matches a demand of increasingly precise information on the target movement, found no support. Duration errors declined only with fading, but not with growing guidance. Relative timing revealed a benefit of immediately preceding haptic demonstration, but learning was not different between the two practice protocols. This contrast between absolute and relative timing adds to other evidence according to which acquisition of these two aspects of motor timing involves different learning mechanisms. Whereas relative timing gained from immediately preceding haptic demonstration, but revealed no practice-related improvement in the presence of haptic guidance

  1. Optical communication system performance with tracking error induced signal fading.

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.; Premo, D. A.

    1973-01-01

    System performance is determined for an optical communication system using noncoherent detection in the presence of tracking error induced signal fading assuming (1) binary on-off modulation (OOK) with both fixed and adaptive threshold receivers, and (2) binary polarization modulation (BPM). BPM is shown to maintain its inherent 2- to 3-dB advantage over OOK when adaptive thresholding is used, and to have a substantially greater advantage when the OOK system is restricted to a fixed decision threshold.

  2. On the nature of rapidly fading Type II supernovae

    NASA Astrophysics Data System (ADS)

    Moriya, Takashi J.; Pruzhinskaya, Maria V.; Ergon, Mattias; Blinnikov, Sergei I.

    2016-01-01

    It has been suggested that Type II supernovae with rapidly fading light curves (a.k.a. Type IIL supernovae) are explosions of progenitors with low-mass hydrogen-rich envelopes which are of the order of 1 M⊙. We investigate light-curve properties of supernovae from such progenitors. We confirm that such progenitors lead to rapidly fading Type II supernovae. We find that the luminosity of supernovae from such progenitors with the canonical explosion energy of 1051 erg and 56Ni mass of 0.05 M⊙ can increase temporarily shortly before all the hydrogen in the envelope recombines. As a result, a bump appears in their light curves. The bump appears because the heating from the nuclear decay of 56Ni can keep the bottom of hydrogen-rich layers in the ejecta ionized, and thus the photosphere can stay there for a while. We find that the light-curve bump becomes less significant when we make explosion energy larger (≳2 × 1051 erg), 56Ni mass smaller (≲0.01 M⊙), 56Ni mixed in the ejecta, or the progenitor radius larger. Helium mixing in hydrogen-rich layers makes the light-curve decline rates large but does not help reducing the light-curve bump. Because the light-curve bump we found in our light-curve models has not been observed in rapidly fading Type II supernovae, they may be characterized by not only low-mass hydrogen-rich envelopes but also higher explosion energy, larger degrees of 56Ni mixing, and/or larger progenitor radii than slowly fading Type II supernovae, so that the light-curve bump does not become significant.

  3. Optical communication system performance with tracking error induced signal fading.

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.; Premo, D. A.

    1973-01-01

    System performance is determined for an optical communication system using noncoherent detection in the presence of tracking error induced signal fading assuming (1) binary on-off modulation (OOK) with both fixed and adaptive threshold receivers, and (2) binary polarization modulation (BPM). BPM is shown to maintain its inherent 2- to 3-dB advantage over OOK when adaptive thresholding is used, and to have a substantially greater advantage when the OOK system is restricted to a fixed decision threshold.

  4. Land-mobile-satellite fade measurements in Australia

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Goldhirsh, Julius; Hase, Yoshihiro

    1992-01-01

    Attenuation measurements were implemented at L-band (1.5 GHz) in southeastern Australia during an 11-day period in October 1988 as part of a continuing examination of the propagation effects due to roadside trees and terrain for mobile-satellite service. Beacon transmissions from the geostationary ETS-V and IPORS satellites were observed. The Australian campaign expanded to another continent our Mobile Satellite Service data base of measurements executed in the eastern and southwestern United States regions. An empirical fade distribution model based on U.S. data predicted the Australian results with errors generally less than 1 dB in the 1-20 percent probability region. Directive antennas are shown to suffer deeper fades under severe shadowing conditions (3 dB excess at 4 percent), the equal-probability isolation between co- and cross-polarized transmissions deteriorated to 10 dB at the 5 dB fade level, and antenna diversity reception may reduce unavailability of the system by a factor of 2-8.

  5. Rain Fade Compensation Alternatives for Ka Band Communication Satellites

    NASA Technical Reports Server (NTRS)

    Acosta, Roberto J.

    1997-01-01

    Future satellite communications systems operating in Ka-band frequency band are subject to degradation produced by the troposphere which is much more severe than those found at lower frequency bands. These impairments include signal absorption by rain, clouds and gases, and amplitude scintillation's arising from refractive index irregularities. For example, rain attenuation at 20 GHz is almost three times that at 11 GHz. Although some of these impairments can be overcome by oversizing the ground station antennas and high power amplifiers, the current trend is using small (less than 20 inches apertures), low-cost ground stations (less than $1000) that can be easily deployed at user premises. As a consequence, most Ka-band systems are expected to employ different forms of fade mitigation that can be implemented relatively easily and at modest cost. The rain fade mitigation approaches are defined by three types of Ka-band communications systems - a low service rate (less than 1.5 Mb/s), a moderate service rate (1.5 to 6 Mb/s) system and a high service rate (greater than 43 Mb/s) system. The ACTS VSAT network, which includes an adaptive rain fade technique, is an example of a moderate service rate.

  6. DISK-RELATED BURSTS AND FADES IN YOUNG STARS

    SciTech Connect

    Findeisen, Krzysztof; Hillenbrand, Lynne; Levitan, David; Sesar, Branimir; Ofek, Eran; Laher, Russ; Surace, Jason E-mail: lah@astro.caltech.edu

    2013-05-01

    We present first results from a new, multiyear, time domain survey of young stars in the North America Nebula complex using the Palomar Transient Factory. Our survey is providing an unprecedented view of aperiodic variability in young stars on timescales of days to years. The analyzed sample covers R{sub PTF} Almost-Equal-To 13.5-18 and spans a range of mid-infrared color, with larger-amplitude optical variables (exceeding 0.4 mag root mean squared) more likely to have mid-infrared evidence for circumstellar material. This paper characterizes infrared excess stars with distinct bursts above or fades below a baseline of lower-level variability, identifying 41 examples. The light curves exhibit a remarkable diversity of amplitudes, timescales, and morphologies, with a continuum of behaviors that cannot be classified into distinct groups. Among the bursters, we identify three particularly promising sources that may represent theoretically predicted short-timescale accretion instabilities. Finally, we find that fading behavior is approximately twice as common as bursting behavior on timescales of days to years, although the bursting and fading duty cycle for individual objects often varies from year to year.

  7. Land-mobile-satellite fade measurements in Australia

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Goldhirsh, Julius; Hase, Yoshihiro

    1992-01-01

    Attenuation measurements were implemented at L-band (1.5 GHz) in southeastern Australia during an 11-day period in October 1988 as part of a continuing examination of the propagation effects due to roadside trees and terrain for mobile-satellite service. Beacon transmissions from the geostationary ETS-V and IPORS satellites were observed. The Australian campaign expanded to another continent our Mobile Satellite Service data base of measurements executed in the eastern and southwestern United States regions. An empirical fade distribution model based on U.S. data predicted the Australian results with errors generally less than 1 dB in the 1-20 percent probability region. Directive antennas are shown to suffer deeper fades under severe shadowing conditions (3 dB excess at 4 percent), the equal-probability isolation between co- and cross-polarized transmissions deteriorated to 10 dB at the 5 dB fade level, and antenna diversity reception may reduce unavailability of the system by a factor of 2-8.

  8. Into building fading at L- and S-band for satellite PCS

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.; Lin, Hsin Piao'

    1995-01-01

    Selected results from L- and S-Band slant-path fade measurements into six different buildings employing a tower-mounted transmitter and dual-frequency receiver are presented. The objective of the measurements was to provide information for personal communications satellite design on the correlation of fading inside buildings between frequencies near 1620 and 2500 MHz. Fades were measured along horizontal directions with 5 cm spacing. Fade differences between L- and S-Band exhibited a normal distribution with means usually near 0 dB and standard deviations from 7.2 to 8.2 dB. After spatial averaging over a few wavelengths, the correlation between L- and S-Band was significantly improved. Simultaneous swept measurements over 160 MHz spans showed that the standard deviation of the power levels as function of frequency increased linearly with average fade depth from a minimum of about 1.3 dB and increased by .2 dB per 1 dB of fade. Fade slopes were also a function of fade level, with LMSS-Band averages in the range of 1 to 2 dB/MHz for 10 dB fades and increasing to about 3 to 4 dB/MHz at a 30 dB fade.

  9. Into building fading at L- and S-band for satellite PCS

    NASA Astrophysics Data System (ADS)

    Vogel, Wolfhard J.; Torrence, Geoffrey W.; Lin, Hsin Piao'

    1995-08-01

    Selected results from L- and S-Band slant-path fade measurements into six different buildings employing a tower-mounted transmitter and dual-frequency receiver are presented. The objective of the measurements was to provide information for personal communications satellite design on the correlation of fading inside buildings between frequencies near 1620 and 2500 MHz. Fades were measured along horizontal directions with 5 cm spacing. Fade differences between L- and S-Band exhibited a normal distribution with means usually near 0 dB and standard deviations from 7.2 to 8.2 dB. After spatial averaging over a few wavelengths, the correlation between L- and S-Band was significantly improved. Simultaneous swept measurements over 160 MHz spans showed that the standard deviation of the power levels as function of frequency increased linearly with average fade depth from a minimum of about 1.3 dB and increased by .2 dB per 1 dB of fade. Fade slopes were also a function of fade level, with LMSS-Band averages in the range of 1 to 2 dB/MHz for 10 dB fades and increasing to about 3 to 4 dB/MHz at a 30 dB fade.

  10. Different fixational eye movements mediate the prevention and the reversal of visual fading.

    PubMed

    McCamy, Michael B; Macknik, Stephen L; Martinez-Conde, Susana

    2014-10-01

    Fixational eye movements (FEMs; including microsaccades, drift and tremor) are thought to improve visibility during fixation by thwarting neural adaptation to unchanging stimuli, but how the different FEM types influence this process is a matter of debate. Attempts to answer this question have been hampered by the failure to distinguish between the prevention of fading (where fading is blocked before it happens in the first place) and the reversal of fading (where vision is restored after fading has already occurred). Because fading during fixation is a detriment to clear vision, the prevention of fading, which avoids visual degradation before it happens, is a more desirable scenario than improving visibility after fading has occurred. Yet previous studies have not examined the role of FEMs in the prevention of fading, but have focused on visual restoration instead. Here we set out to determine the differential contributions and efficacies of microsaccades and drift to preventing fading in human vision. Our results indicate that both microsaccades and drift mediate the prevention of visual fading. We also found that drift is a potentially larger contributor to preventing fading than microsaccades, although microsaccades are more effective than drift. Microsaccades moreover prevented foveal and peripheral fading in an equivalent fashion, and their efficacy was independent of their size, number, and direction. Our data also suggest that faster drift may prevent fading better than slower drift. These findings may help to reconcile the long-standing controversy concerning the comparative roles of microsaccades and drift in visibility during fixation. © 2014 The Authors. The Journal of Physiology © 2014 The Physiological Society.

  11. Rain-fade simulation and power augmentation for satellite communication systems

    NASA Technical Reports Server (NTRS)

    Shalkhauser, Kurt A.; Nagy, Lawrence A.; Svoboda, James S.

    1990-01-01

    The design and implementation of an automated rain-fade simulation and power augmentation system is presented. The system experimentally simulates and measures the effects of radiofrequency power fade on a 20 GHz communication link using a multimode travelling wave tube amplifier for loss compensation. Precision, computer-controlled attenuators are used in the fade simulation. Test plans for analog and digital testing are discussed.

  12. A recursive solution for a fading memory filter derived from Kalman filter theory

    NASA Technical Reports Server (NTRS)

    Statman, J. I.

    1986-01-01

    A simple recursive solution for a class of fading memory tracking filters is presented. A fading memory filter provides estimates of filter states based on past measurements, similar to a traditional Kalman filter. Unlike a Kalman filter, an exponentially decaying weight is applied to older measurements, discounting their effect on present state estimates. It is shown that Kalman filters and fading memory filters are closely related solutions to a general least squares estimator problem. Closed form filter transfer functions are derived for a time invariant, steady state, fading memory filter. These can be applied in loop filter implementation of the Deep Space Network (DSN) Advanced Receiver carrier phase locked loop (PLL).

  13. A Stackelberg Game Approach to Cognitive Radio Network with Anti-Jamming Capability

    DTIC Science & Technology

    2012-10-10

    Rayleigh , Nakagami , and Rician fading channels were presented. In [5] Distribution Statement A: Approved for public release; distribution is unlimited...Without loss of generality, it is assumed that there are M independent communication channels available for data transmission from B to A, with...transmitter to the receiver. It is assumed that the jammer has sufficient processing capability to simultaneously monitor all the M communication

  14. Dye fading test for mission control operator console displays

    NASA Technical Reports Server (NTRS)

    Lockwood, H. E.

    1975-01-01

    A dye fading test of 40 days duration was conducted to determine the effect of mission control operator console and ambient lighting effects on a series of photographic products under consideration for use in mission console operator consoles. Six different display samples, each containing 36 windows of several different colors, were prepared and placed in the mission control consoles for testing. No significant changes were recorded during the testing period. All changes were attributed to a mechanical problem with the densitometer. Detailed results are given in graphs.

  15. Modeling capacity fade in lithium-ion cells.

    SciTech Connect

    Liaw, Bor Yann; Doughty, Daniel Harvey; Nagasubramanian, Ganesan; Jungst, Rudolph George

    2003-09-01

    Battery life is an important, yet technically challenging, issue for battery development and application. Adequately estimating battery life requires a significant amount of testing and modeling effort to validate the results. Integrated battery testing and modeling is quite feasible today to simulate battery performance, and therefore applicable to predict its life. A relatively simple equivalent-circuit model (ECM) is used in this work to show that such an integrated approach can actually lead to a high-fidelity simulation of a lithium-ion cell's performance and life. The methodology to model the cell's capacity fade during thermal aging is described to illustrate its applicability to battery calendar life prediction.

  16. Fade duration statistics for Ku-band satellite links

    NASA Astrophysics Data System (ADS)

    Mandeep, J. S.

    2013-08-01

    Fade duration database was built to enhance the study of propagation characterises in the Equatorial region. The data was measured via a beacon receiver Ku-band whereby the antenna was directed to a SUPERBIRD-C2 satellite at 12.255 GHz. The performance of the measured data has been compared with ITU-R model, Kormanyos et al. and Paulson-Gibbins. The results show that the Paulson-Gibbins fits well with measured data with a low RMS error of 0.2 dB. The number of statistics available for the equatorial is small and the periods of measurement are short compared to those for temperate regions.

  17. Channel simulation for direct-detection optical communication systems

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.

    1974-01-01

    A technique is described for simulating the random modulation imposed by atmospheric scintillation and transmitter pointing jitter on a direct-detection optical communication system. The system is capable of providing signal fading statistics which obey log-normal, beta, Rayleigh, Ricean, or chi-square density functions. Experimental tests of the performance of the channel simulator are presented.

  18. Channel simulation for direct detection optical communication systems

    NASA Technical Reports Server (NTRS)

    Tycz, M.; Fitzmaurice, M. W.

    1974-01-01

    A technique is described for simulating the random modulation imposed by atmospheric scintillation and transmitter pointing jitter on a direct detection optical communication system. The system is capable of providing signal fading statistics which obey log normal, beta, Rayleigh, Ricean or chi-squared density functions. Experimental tests of the performance of the Channel Simulator are presented.

  19. Distributed Space-Time Coding for Cooperative Networks

    DTIC Science & Technology

    2006-12-05

    log2 M . (10) We assume that the channels are Rayleigh fading, so that |h|2 is an exponential random variable with expected value σ2h = 1/r α, where r is...analysis to Nakagami - m -fading channels and we showed that the advantage decreases as the index m increases, i.e. as the channel tends to be less and less...symbols over two successive time periods, so that TSR2D = 2Ts and TS2R = 2 log2( M )Ts/ log2( Q ). The sequence transmitted by the source-relay pair is

  20. Color transplant for reverse ageing of faded artworks

    NASA Astrophysics Data System (ADS)

    Del Mastio, A.; Piva, A.; Barni, M.; Cappellini, V.; Stefanini, L.

    2008-02-01

    Nowadays, photographs are one of the most used media for communication. Images are used for the representation of documents, Cultural goods, and so on: they are used to pass on a wedge of historical memory of the society. Since its origin, the photographic technique has got several improvements; nevertheless, photos are liable to several damages, both concerning the physical support and concerning the colors and figures which are depicted in it: for example, think about scratches or rips happened to a photo, or think about the fading or red (or yellow) toning concerning the colors of a photo. In this paper, we propose a novel method which is able to assess the original beauty of digital reproductions of aged photos, as well as digital reproductions of faded goods. The method is based on the comparison of the degraded image with a not-degraded one showing similar contents; thus, the colors of the not-degraded image can be transplanted in the degraded one. The key idea is a dualism between the analytical mechanics and the color theory: for each of the degraded and not-degraded images we compute first a scatter plot of the x and y normalized coordinates of their colors; these scatter diagrams can be regarded as a system of point masses, thus provided of inertia axes and an inertia ellipsoid. Moving the scatter diagram of the degraded image over the one belonging to the not-degraded image, the colors of the degraded image can be restored.

  1. Fading AGN Candidates: AGN Histories and Outflow Signatures

    NASA Astrophysics Data System (ADS)

    Keel, William C.; Lintott, Chris J.; Maksym, W. Peter; Bennert, Vardha N.; Chojnowski, S. Drew; Moiseev, Alexei; Smirnova, Aleksandrina; Schawinski, Kevin; Sartori, Lia F.; Urry, C. Megan; Pancoast, Anna; Schirmer, Mischa; Scott, Bryan; Showley, Charles; Flatland, Kelsi

    2017-02-01

    We consider the energy budgets and radiative history of eight fading active galactic nuclei (AGNs), identified from an energy shortfall between the requirements to ionize very extended (radius > 10 kpc) ionized clouds and the luminosity of the nucleus as we view it directly. All show evidence of significant fading on timescales of ≈50,000 yr. We explore the use of minimum ionizing luminosity Qion derived from photoionization balance in the brightest pixels in Hα at each projected radius. Tests using presumably constant Palomar-Green QSOs, and one of our targets with detailed photoionization modeling, suggest that we can derive useful histories of individual AGNs, with the caveat that the minimum ionizing luminosity is always an underestimate and subject to uncertainties about fine structure in the ionized material. These consistency tests suggest that the degree of underestimation from the upper envelope of reconstructed Qion values is roughly constant for a given object and therefore does not prevent such derivation. The AGNs in our sample show a range of behaviors, with rapid drops and standstills; the common feature is a rapid drop in the last ≈2 × 104 yr before the direct view of the nucleus. The e-folding timescales for ionizing luminosity are mostly in the thousands of years, with a few episodes as short as 400 yr. In the limit of largely obscured AGNs, we find additional evidence for fading from the shortfall between even the lower limits from recombination balance and the maximum luminosities derived from far-infrared fluxes. We compare these long-term light curves, and the occurrence of these fading objects among all optically identified AGNs, to simulations of AGN accretion; the strongest variations over these timespans are seen in models with strong and local (parsec-scale) feedback. We present Gemini integral-field optical spectroscopy, which shows a very limited role for outflows in these ionized structures. While rings and loops of emission

  2. The FADE mass-stat: a technique for inserting or deleting particles in molecular dynamics simulations.

    PubMed

    Borg, Matthew K; Lockerby, Duncan A; Reese, Jason M

    2014-02-21

    The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually "fades-in" (inserts) or "fades-out" (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C60 Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors.

  3. Examining the Impact of Adaptively Faded Worked Examples on Student Learning Outcomes

    ERIC Educational Resources Information Center

    Flores, Raymond; Inan, Fethi

    2014-01-01

    The purpose of this study was to explore effective ways to design guided practices within a web-based mathematics problem solving tutorial. Specifically, this study examined student learning outcome differences between two support designs (e.g. adaptively faded and fixed). In the adaptively faded design, students were presented with problems in…

  4. The Impact of Reading Material's Lexical Accessibility on Text Fading Effects in Children's Reading Performance

    ERIC Educational Resources Information Center

    Nagler, Telse; Lonnemann, Jan; Linkersdörfer, Janosch; Hasselhorn, Marcus; Lindberg, Sven

    2014-01-01

    The "acceleration phenomenon" (AP) is defined by improvements in reading speed and reading comprehension, induced by an artificial text fading procedure corresponding to the previously determined fastest individual reading rate. Recent results, however, indicated that fading that is slower than the self-paced reading rate can produce…

  5. The Impact of Reading Material's Lexical Accessibility on Text Fading Effects in Children's Reading Performance

    ERIC Educational Resources Information Center

    Nagler, Telse; Lonnemann, Jan; Linkersdörfer, Janosch; Hasselhorn, Marcus; Lindberg, Sven

    2014-01-01

    The "acceleration phenomenon" (AP) is defined by improvements in reading speed and reading comprehension, induced by an artificial text fading procedure corresponding to the previously determined fastest individual reading rate. Recent results, however, indicated that fading that is slower than the self-paced reading rate can produce…

  6. Beam evolutions of solitons in strongly nonlocal media with fading optical lattices

    NASA Astrophysics Data System (ADS)

    Dai, Zhi-Ping; Lu, Shi-Zhuan; You, Kai-Ming

    2013-01-01

    We address the impact of imprinted fading optical lattices on the beam evolution of solitons in strongly nonlocal nonlinear media. The results show that the width of the soliton experiences a change with the increasing propagation distance, the critical power for the soliton varies with the lattice fading away, and the soliton breathing is affected by the initial lattice depth and the nonlocality degree.

  7. Using Video Prompting with Different Fading Procedures to Teach Daily Living Skills: A Preliminary Examination

    ERIC Educational Resources Information Center

    Wu, Pei-Fang; Cannella-Malone, Helen I.; Wheaton, Joe E.; Tullis, Chris A.

    2016-01-01

    Two students with developmental disabilities were taught two daily living skills using video prompting with error correction presented on an iPod Touch, and two different fading procedures were implemented. In one fading procedure, individual video clips were merged into multiple larger clips following acquisition of the entire skill. In the…

  8. The FADE mass-stat: A technique for inserting or deleting particles in molecular dynamics simulations

    SciTech Connect

    Borg, Matthew K.; Lockerby, Duncan A.; Reese, Jason M.

    2014-02-21

    The emergence of new applications of molecular dynamics (MD) simulation calls for the development of mass-statting procedures that insert or delete particles on-the-fly. In this paper we present a new mass-stat which we term FADE, because it gradually “fades-in” (inserts) or “fades-out” (deletes) molecules over a short relaxation period within a MD simulation. FADE applies a time-weighted relaxation to the intermolecular pair forces between the inserting/deleting molecule and any neighbouring molecules. The weighting function we propose in this paper is a piece-wise polynomial that can be described entirely by two parameters: the relaxation time scale and the order of the polynomial. FADE inherently conserves overall system momentum independent of the form of the weighting function. We demonstrate various simulations of insertions of atomic argon, polyatomic TIP4P water, polymer strands, and C{sub 60} Buckminsterfullerene molecules. We propose FADE parameters and a maximum density variation per insertion-instance that restricts spurious potential energy changes entering the system within desired tolerances. We also demonstrate in this paper that FADE compares very well to an existing insertion algorithm called USHER, in terms of accuracy, insertion rate (in dense fluids), and computational efficiency. The USHER algorithm is applicable to monatomic and water molecules only, but we demonstrate that FADE can be generally applied to various forms and sizes of molecules, such as polymeric molecules of long aspect ratio, and spherical carbon fullerenes with hollow interiors.

  9. Spoon Distance Fading with and without Escape Extinction as Treatment for Food Refusal

    ERIC Educational Resources Information Center

    Rivas, Kristi D.; Piazza, Cathleen C.; Patel, Meeta R.; Bachmeyer, Melanie H.

    2010-01-01

    Little is known about the characteristics of meals that serve as motivating operations (MOs) for escape behavior. In the current investigation, we showed that the distance at which a therapist held a spoon from a child's lips served as an MO for escape behavior. Based on these results, we implemented spoon distance fading, compared fading with and…

  10. Using Stimulus Fading without Escape Extinction to Increase Compliance with Toothbrushing in Children with Autism

    ERIC Educational Resources Information Center

    Bishop, Michele R.; Kenzer, Amy L.; Coffman, Christine M.; Tarbox, Courtney M.; Tarbox, Jonathan; Lanagan, Taira M.

    2013-01-01

    Routine toothbrushing is an essential part of good oral hygiene. This study investigated the use of stimulus fading without escape extinction to increase compliance with toothbrushing with three children with autism spectrum disorder (ASD). A 30-step stimulus fading hierarchy was implemented; gradually increasing the proximity of the toothbrush to…

  11. Using Script Fading to Promote Natural Environment Stimulus Control of Verbal Interactions among Youths with Autism

    ERIC Educational Resources Information Center

    Brown, John L.; Krantz, Patricia J.; McClannahan, Lynn E.; Poulson, Claire L.

    2008-01-01

    Script fading was used to teach three youths with autism to initiate and sustain verbal interactions under stimulus control consistent with the natural environment. The youths learned to engage in verbal interactions during simulated shopping trips and during visits to community stores. The effectiveness of script fading was examined using a…

  12. Grouping Inhibits Motion Fading by Giving Rise to Virtual Trackable Features

    ERIC Educational Resources Information Center

    Hsieh, P. -J.; Tse, P. U.

    2007-01-01

    After prolonged viewing of a slowly drifting or rotating pattern under strict fixation, the pattern appears to slow down and then momentarily stop. The authors show that grouping can slow down the process of "motion fading," suggesting that cortical configural form analysis interacts with the computation of motion signals during motion fading. The…

  13. Using Video Prompting with Different Fading Procedures to Teach Daily Living Skills: A Preliminary Examination

    ERIC Educational Resources Information Center

    Wu, Pei-Fang; Cannella-Malone, Helen I.; Wheaton, Joe E.; Tullis, Chris A.

    2016-01-01

    Two students with developmental disabilities were taught two daily living skills using video prompting with error correction presented on an iPod Touch, and two different fading procedures were implemented. In one fading procedure, individual video clips were merged into multiple larger clips following acquisition of the entire skill. In the…

  14. Using Stimulus Fading without Escape Extinction to Increase Compliance with Toothbrushing in Children with Autism

    ERIC Educational Resources Information Center

    Bishop, Michele R.; Kenzer, Amy L.; Coffman, Christine M.; Tarbox, Courtney M.; Tarbox, Jonathan; Lanagan, Taira M.

    2013-01-01

    Routine toothbrushing is an essential part of good oral hygiene. This study investigated the use of stimulus fading without escape extinction to increase compliance with toothbrushing with three children with autism spectrum disorder (ASD). A 30-step stimulus fading hierarchy was implemented; gradually increasing the proximity of the toothbrush to…

  15. Using Script Fading to Promote Natural Environment Stimulus Control of Verbal Interactions among Youths with Autism

    ERIC Educational Resources Information Center

    Brown, John L.; Krantz, Patricia J.; McClannahan, Lynn E.; Poulson, Claire L.

    2008-01-01

    Script fading was used to teach three youths with autism to initiate and sustain verbal interactions under stimulus control consistent with the natural environment. The youths learned to engage in verbal interactions during simulated shopping trips and during visits to community stores. The effectiveness of script fading was examined using a…

  16. Stimulus Fading and Differential Reinforcement for the Treatment of Needle Phobia in a Youth with Autism

    ERIC Educational Resources Information Center

    Shabani, Daniel B.; Fisher, Wayne W.

    2006-01-01

    Stimulus fading in the form of gradually increased exposure to a fear-evoking stimulus, often combined with differential reinforcement, has been used to treat phobias in children who are otherwise normal and in children with autism. In this investigation, we applied stimulus fading plus differential reinforcement with an adolescent with autism and…

  17. Fading of artificial hair color and its prevention by photofilters.

    PubMed

    Locke, B; Jachowicz, J

    2005-01-01

    Fading of artificial hair color has been investigated by simulating actual usage conditions through exposure to artificial radiation in a weatherometer, with 0.35 mW/(m(2) nm) at 340 nm, for 16 to 48 hours, and by periodical washing. Hair color was produced by using commercial two-part, permanent hair dyes with light auburn, medium auburn, and dark auburn shades. Formulations based on red couplers, such as 4-amino-2-hydroxytoluene and 1-naphtol, as well as primary intermediates, such as 1-hydroxyethyl-4,5-diamino pyrazole sulfate, were employed. Results indicate that the extent of fading, as measured by the total color change parameter, dE, is greatest for colored hair subjected to both irradiation and shampooing, and significantly smaller for hair undergoing only irradiation or washing. Color loss has been also found to be dependent upon the hair type employed, with colored natural white and bleached hair undergoing much greater change than colored brown hair. It has been also shown that hair color based on pyrazole intermediates displayed the deepest fading as a result of shampooing (dE approximately 4-6 after ten shampooings) and irradiation/shampooing (dE approximately 14-16 after 32 hours of light exposure and four shampooings). The contribution of UV light (UVB + UVA) to the artificial hair-color loss was found experimentally to be dependent upon the irradiation dose and varied from 63% at 16 hours of irradiation time to 27% at 48 hours of light exposure. The theoretical extent of photoprotection by a formulation was assessed by calculating the percentage of UV light it attenuates in the wavelength range from 290 nm to 400 nm. The results indicate that UVB photofilters, such as octyl methoxy cinnamate, absorb less than 25% of the total UV irradiation at concentrations as high as 30 mg/(g hair). UVA absorbers were found to be more effective, with benzophenone-3 and benzophenone-4 absorbing about 40% of UV at the same concentration. Corresponding experimental

  18. Ultrasonic simulation of MSBLS multipath fading for orbiter landing configuration

    NASA Technical Reports Server (NTRS)

    Hayre, H. S.

    1978-01-01

    The on-shuttle antenna pattern of the MSBLS receiver, and the azimuth and elevation beamwidths were simulated by their corresponding ultrasonic transducer beams. The scanning rate for the azimuth and elevation beams was 1.75 degrees/second. The results were adjusted for full-scale maximum sinusoidal scan rates of 691 and 377 deg/sec for AZ and EL respectively. The rain drops were simulated by air bubbles, with a similar size distribution, in water. The rain volume was created along a part of the propagation path, and not on the runway, because it was found difficult to avoid an accumulation of bubbles on the runway surface and surroundings simulated by the model surface. Multipath fading from the ground, and its possible degrading effect on the orbiter received beam shape and the associated landing guidance parameters is discussed.

  19. Quantum illumination for enhanced detection of Rayleigh-fading targets

    NASA Astrophysics Data System (ADS)

    Zhuang, Quntao; Zhang, Zheshen; Shapiro, Jeffrey H.

    2017-08-01

    Quantum illumination (QI) is an entanglement-enhanced sensing system whose performance advantage over a comparable classical system survives its usage in an entanglement-breaking scenario plagued by loss and noise. In particular, QI's error-probability exponent for discriminating between equally likely hypotheses of target absence or presence is 6 dB higher than that of the optimum classical system using the same transmitted power. This performance advantage, however, presumes that the target return, when present, has known amplitude and phase, a situation that seldom occurs in light detection and ranging (lidar) applications. At lidar wavelengths, most target surfaces are sufficiently rough that their returns are speckled, i.e., they have Rayleigh-distributed amplitudes and uniformly distributed phases. QI's optical parametric amplifier receiver—which affords a 3 dB better-than-classical error-probability exponent for a return with known amplitude and phase—fails to offer any performance gain for Rayleigh-fading targets. We show that the sum-frequency generation receiver [Zhuang et al., Phys. Rev. Lett. 118, 040801 (2017), 10.1103/PhysRevLett.118.040801]—whose error-probability exponent for a nonfading target achieves QI's full 6 dB advantage over optimum classical operation—outperforms the classical system for Rayleigh-fading targets. In this case, QI's advantage is subexponential: its error probability is lower than the classical system's by a factor of 1 /ln(M κ ¯NS/NB) , when M κ ¯NS/NB≫1 , with M ≫1 being the QI transmitter's time-bandwidth product, NS≪1 its brightness, κ ¯ the target return's average intensity, and NB the background light's brightness.

  20. Fading memory and kernel properties of generic cortical microcircuit models.

    PubMed

    Maass, Wolfgang; Natschläger, Thomas; Markram, Henry

    2004-01-01

    It is quite difficult to construct circuits of spiking neurons that can carry out complex computational tasks. On the other hand even randomly connected circuits of spiking neurons can in principle be used for complex computational tasks such as time-warp invariant speech recognition. This is possible because such circuits have an inherent tendency to integrate incoming information in such a way that simple linear readouts can be trained to transform the current circuit activity into the target output for a very large number of computational tasks. Consequently we propose to analyze circuits of spiking neurons in terms of their roles as analog fading memory and non-linear kernels, rather than as implementations of specific computational operations and algorithms. This article is a sequel to [W. Maass, T. Natschläger, H. Markram, Real-time computing without stable states: a new framework for neural computation based on perturbations, Neural Comput. 14 (11) (2002) 2531-2560, Online available as #130 from: ], and contains new results about the performance of generic neural microcircuit models for the recognition of speech that is subject to linear and non-linear time-warps, as well as for computations on time-varying firing rates. These computations rely, apart from general properties of generic neural microcircuit models, just on capabilities of simple linear readouts trained by linear regression. This article also provides detailed data on the fading memory property of generic neural microcircuit models, and a quick review of other new results on the computational power of such circuits of spiking neurons.

  1. Peer-Monitoring vs. Micro-Script Fading for Enhancing Knowledge Acquisition when Learning in Computer-Supported Argumentation Environments

    ERIC Educational Resources Information Center

    Bouyias, Yannis; Demetriadis, Stavros

    2012-01-01

    Research on computer-supported collaborative learning (CSCL) has strongly emphasized the value of providing student support with micro-scripts, which should withdraw (fade-out) allowing students to practice the acquired skills. However, research on fading shows conflicting results and some researchers suggest that the impact of fading is enhanced…

  2. MIMO System with Relative Phase Difference Time-Shift Modulation for Rician Fading Environment

    NASA Astrophysics Data System (ADS)

    Kobayashi, Kenichi; Someya, Takao; Ohtsuki, Tomoaki; Jarot, Sigit P. W.; Kashima, Tsuyoshi

    Multiple-Input Multiple-Output (MIMO) systems that realize high-speed data transmission with multiple antennas at both transmitter and receiver are drawing much attention. In line-of sight (LOS) environments, the performance of MIMO systems depends largely on the difference of the phase difference of direct paths from transmit antennas to each receive antenna. When the phase difference of direct paths are close to each other, the spatial division multiplexing (SDM) channels are not orthogonal to each other so signal detection becomes difficult. In this paper, we propose a MIMO system with relative phase difference time-shift modulation (RPDTM) in Rician fading environments. The proposed scheme transmits independent signals from each antenna at each time slot where the relative phase difference between signal constellations used by transmit antennas varies in a pre-determined pattern. This transmission virtually changes the phase difference of direct paths from transmit antennas to each receive antenna without lowering data rate and without knowledge of the channels. In addition, forward error correction coding (ECC) is applied to exploit the time slots where the receiver can detect the signals easily to improve the detection performance. If there are time slots where the receiver can separate the received signal, the receiver can decode the data by using the time slots and the correlation between data. From the results of computer simulation, we show that MIMO system with RPDTM can achieve the better bit error rate (BER) than the conventional MIMO system. We also show that the MIMO system with RPDTM is effective by about Rician factor K=10dB.

  3. Methods and Apparatuses for Signaling with Geometric Constellations in a Raleigh Fading Channel

    NASA Technical Reports Server (NTRS)

    Barsoum, Maged F. (Inventor); Jones, Christopher R. (Inventor)

    2015-01-01

    Communication systems are described that use signal constellations, which have unequally spaced (i.e., `geometrically` shaped) points. In many embodiments, the communication systems use specific geometric constellations that are capacity optimized at a specific SNR (signal to noise ratio). In addition, ranges within which the constellation points of a capacity optimized constellation can be perturbed and are still likely to achieve a given percentage of the optimal capacity increase compared to a constellation that maximizes d (sub min) (i.e. minimum distance between constellations) are also described. Capacity measures that are used in the selection of the location of constellation points include, but are not limited to, parallel decode (PD) capacity and joint capacity.

  4. Performance Analysis of Direct-Sequence Spread-Spectrum Multiple-Access Communication via Fading Channels.

    DTIC Science & Technology

    1980-04-01

    of solving this set of equations is to use a Fibonacci search ([Aoki, 1971], [Wilde, 19643) to search over z while holding zI fixed, where we are...Georgia. Mr. Borth is co-author of the papers "O i. D. E. Borth and C. A. Cain, "The generation of acoustic signals in materials irradiated with...Illinois, p. 103, June 3-5, 1975. 183 3. D. E. Borth and C. A. Cain, "Theoretical analysis of acoustic signal generation in materials irradiated with

  5. The Multipath and Fading Profile of the High Latitude Meteor Burst Communication Channel.

    DTIC Science & Technology

    1986-10-01

    APPROVED: j~ ~ e. c ALLAN C. SCHELL Chief, Electromagnetic Sciences Division FOR THE COMMANDER: [ JOHN A. RITZ - Plans and Programs Division *, If your...multipath measurement VHF propagation / 19 ABSTRACT (Continue on reverse ,f necessary and identify by block number) ------ ------ .. tion High...latitude propagation phenomenon such as scatter from the aurora and sporadic-E propagation can alter the communication characteristics of the high latitude

  6. An implementation of a reference symbol approach to generic modulation in fading channels

    NASA Technical Reports Server (NTRS)

    Young, R. J.; Lodge, J. H.; Pacola, L. C.

    1990-01-01

    As mobile satellite communications systems evolve over the next decade, they will have to adapt to a changing tradeoff between bandwidth and power. This paper presents a flexible approach to digital modulation and coding that will accommodate both wideband and narrowband schemes. This architecture could be the basis for a family of modems, each satisfying a specific power and bandwidth constraint, yet all having a large number of common signal processing blocks. The implementation of this generic approach, with general purpose digital processors for transmission of 4.8 kilobits per sec. digitally encoded speech, is described.

  7. Optimal throughput for cognitive radio with energy harvesting in fading wireless channel.

    PubMed

    Vu-Van, Hiep; Koo, Insoo

    2014-01-01

    Energy resource management is a crucial problem of a device with a finite capacity battery. In this paper, cognitive radio is considered to be a device with an energy harvester that can harvest energy from a non-RF energy resource while performing other actions of cognitive radio. Harvested energy will be stored in a finite capacity battery. At the start of the time slot of cognitive radio, the radio needs to determine if it should remain silent or carry out spectrum sensing based on the idle probability of the primary user and the remaining energy in order to maximize the throughput of the cognitive radio system. In addition, optimal sensing energy and adaptive transmission power control are also investigated in this paper to effectively utilize the limited energy of cognitive radio. Finding an optimal approach is formulated as a partially observable Markov decision process. The simulation results show that the proposed optimal decision scheme outperforms the myopic scheme in which current throughput is only considered when making a decision.

  8. Optimal Throughput for Cognitive Radio with Energy Harvesting in Fading Wireless Channel

    PubMed Central

    Vu-Van, Hiep; Koo, Insoo

    2014-01-01

    Energy resource management is a crucial problem of a device with a finite capacity battery. In this paper, cognitive radio is considered to be a device with an energy harvester that can harvest energy from a non-RF energy resource while performing other actions of cognitive radio. Harvested energy will be stored in a finite capacity battery. At the start of the time slot of cognitive radio, the radio needs to determine if it should remain silent or carry out spectrum sensing based on the idle probability of the primary user and the remaining energy in order to maximize the throughput of the cognitive radio system. In addition, optimal sensing energy and adaptive transmission power control are also investigated in this paper to effectively utilize the limited energy of cognitive radio. Finding an optimal approach is formulated as a partially observable Markov decision process. The simulation results show that the proposed optimal decision scheme outperforms the myopic scheme in which current throughput is only considered when making a decision. PMID:24574885

  9. Modeling of twitch fade based on slow interaction of nondepolarizing muscle relaxants with the presynaptic receptors.

    PubMed

    Bhatt, Shashi B; Amann, Anton; Nigrovic, Vladimir

    2006-08-01

    Nondepolarizing muscle relaxants (MRs) diminish the indirectly evoked single twitch due to their binding to the postsynaptic receptors. Additionally, the MRs produce progressive diminution of successive twitches upon repetitive stimulation (fade). Our study addresses the generation of fade as observed under clinical situation. The study was conducted in two phases. In the clinical part, we have evaluated the time course of twitch depression and fade following the administration of several doses of three MRs (rocuronium, pancuronium, and cisatracurium). In the second part, we have modified our model of neuromuscular transmission to simulate the time course of twitch depression and fade. The MR was assumed to bind to a single site on the presynaptic receptor to produce fade. The rates of interaction with the presynaptic receptors were characterized in terms of the arbitrarily assigned equilibrium dissociation constant and the half-life for dissociation of the presynaptic complex. A method was developed to relate the release of acetylcholine to the occupancy of the presynaptic receptors. The strength of the first and the fourth twitch was calculated from the peak concentration of the activated postsynaptic receptors, i.e., of those receptors with both sites occupied by acetylcholine. Our results indicate that, while the affinity of the MR for the presynaptic receptor plays little role in the time course of fade, the rate of dissociation of the complex between the presynaptic receptors and the muscle relaxant may be critical in determining the time course of fade. Tentative estimates of this parameter are offered.

  10. Text-fading based training leads to transfer effects on children's sentence reading fluency

    PubMed Central

    Nagler, Telse; Korinth, Sebastian P.; Linkersdörfer, Janosch; Lonnemann, Jan; Rump, Björn; Hasselhorn, Marcus; Lindberg, Sven

    2015-01-01

    Previous studies used a text-fading procedure as a training tool with the goal to increase silent reading fluency (i.e., proficient reading rate and comprehension). In recently published studies, this procedure resulted in lasting reading enhancements for adult and adolescent research samples. However, studies working with children reported mixed results. While reading rate improvements were observable for Dutch reading children in a text-fading training study, reading fluency improvements in standardized reading tests post-training attributable to the fading manipulation were not detectable. These results raise the question of whether text-fading training is not effective for children or whether research design issues have concealed possible transfer effects. Hence, the present study sought to investigate possible transfer effects resulting from a text-fading based reading training program, using a modified research design. Over a period of 3 weeks, two groups of German third-graders read sentences either with an adaptive text-fading procedure or at their self-paced reading rate. A standardized test measuring reading fluency at the word, sentence, and text level was conducted pre- and post-training. Text level reading fluency improved for both groups equally. Post-training gains at the word level were found for the text-fading group, however, no significant interaction between groups was revealed for word reading fluency. Sentence level reading fluency gains were found for the text-fading group, which significantly differed from the group of children reading at their self-paced reading routine. These findings provide evidence for the efficacy of text-fading as a training method for sentence reading fluency improvement also for children. PMID:25713554

  11. Text-fading based training leads to transfer effects on children's sentence reading fluency.

    PubMed

    Nagler, Telse; Korinth, Sebastian P; Linkersdörfer, Janosch; Lonnemann, Jan; Rump, Björn; Hasselhorn, Marcus; Lindberg, Sven

    2015-01-01

    Previous studies used a text-fading procedure as a training tool with the goal to increase silent reading fluency (i.e., proficient reading rate and comprehension). In recently published studies, this procedure resulted in lasting reading enhancements for adult and adolescent research samples. However, studies working with children reported mixed results. While reading rate improvements were observable for Dutch reading children in a text-fading training study, reading fluency improvements in standardized reading tests post-training attributable to the fading manipulation were not detectable. These results raise the question of whether text-fading training is not effective for children or whether research design issues have concealed possible transfer effects. Hence, the present study sought to investigate possible transfer effects resulting from a text-fading based reading training program, using a modified research design. Over a period of 3 weeks, two groups of German third-graders read sentences either with an adaptive text-fading procedure or at their self-paced reading rate. A standardized test measuring reading fluency at the word, sentence, and text level was conducted pre- and post-training. Text level reading fluency improved for both groups equally. Post-training gains at the word level were found for the text-fading group, however, no significant interaction between groups was revealed for word reading fluency. Sentence level reading fluency gains were found for the text-fading group, which significantly differed from the group of children reading at their self-paced reading routine. These findings provide evidence for the efficacy of text-fading as a training method for sentence reading fluency improvement also for children.

  12. Analysis of rain fade duration models for Earth-to-satellite path based on data measured in Malaysia

    NASA Astrophysics Data System (ADS)

    Dao, Hassan; Rafiqul, Islam Md; Al-Khateeb, Khalid A. S.

    2013-12-01

    Statistical analysis of rain fade duration is crucial information for system engineer to design and plan a fade mitigation technique (FMT) for the satellite communication system. An investigation is carried out based on data measured of one year period in Kuala Lumpur, Malaysia from satellite path of MEASAT3. This paper presents statistical analysis of measured fade duration on high elevation angle (77.4°) in Ku-band compared to three prediction models of fade duration. It is found that none of the models could predict measured fade duration distribution accurately.

  13. Atmospheric turbulence-induced signal fades on optical heterodyne communication links

    NASA Astrophysics Data System (ADS)

    Winick, K. A.

    1986-06-01

    The three basic atmospheric propagation effects, absorption, scattering, and turbulence, are reviewed. A simulation approach is then developed to determine signal fade probability distributions on heterodyne-detected satellite links which operate through naturally occurring atmospheric turbulence. The calculations are performed on both angle-tracked and nonangle-tracked downlinks, and on uplinks, with and without adaptive optics. Turbulence-induced degradations in communication performance are determined using signal fade probability distributions, and it is shown that the average signal fade can be a poor measure of the performance degradation.

  14. Simultaneous L-band and VHF ionospheric fading effects at the geomagnetic equator

    NASA Technical Reports Server (NTRS)

    Sessions, W. B.; Golden, T. S.

    1972-01-01

    Simultaneous observations of ionspheric fading of 1550 MHz and 136 MHz radio waves from the ATS-5 spacecraft were recorded on the geomagnetic equator at Ancon, Peru. The observations were made during a period around the 1971 spring equinox; they show fades as great as 27 db at 136 MHz, and 6 db at 1550 MHz. The general characteristics of the scintillation signatures at the two frequencies are discussed with emphasis on comparison of the two frequencies with respect to rates and depths of fades. Typical statistical distributions of signal levels are also presented from which time availabilities of the signals relative to the median levels can be derived.

  15. Channel Characterization and Robust Tracking for Diversity Reception over Time-Variant Off-Body Wireless Communication Channels

    NASA Astrophysics Data System (ADS)

    Van Torre, Patrick; Vallozzi, Luigi; Rogier, Hendrik; Moeneclaey, Marc; Verhaevert, Jo

    2010-12-01

    In the 2.45 GHz band, indoor wireless off-body data communication by a moving person can be problematic due to time-variant signal fading and the consequent variation in channel parameters. Off-body communication specifically suffers from the combined effects of fading, shadowing, and path loss due to time-variant multipath propagation in combination with shadowing by the human body. Measurements are performed to analyze the autocorrelation, coherence time, and power spectral density for a person equipped with a wearable receive system moving at different speeds for different configurations and antenna positions. Diversity reception with multiple textile antennas integrated in the clothing provides a means of improving the reliability of the link. For the dynamic channel estimation, a scheme using hard decision feedback after MRC with adaptive low-pass filtering is demonstrated to be successful in providing robust data detection for long data bursts, in the presence of dramatic channel variation.

  16. Stochastic Representation of the Marcum Q-Function and Associated Radar Detection Probabilities

    DTIC Science & Technology

    2005-12-01

    coherent detection of digital modulation over Nakagami fading channels. In radar signal processing, the Q -Function appears as a detection probability...Simon, M . K. (1998), A New Twist on the Marcum Q -Function and its Application. IEEE Comms. Lett., 2, 39—41. 29. Simon, M . K. and Alouini, M .-S. (2000...48, 359—366. 30. Simon, M . K. and Alouini, M .-S. (2003), Some New Results for Integrals Involving the Generalised Marcum Q Function and Their

  17. Capacity and power fading mechanism identification from a commercial cell evaluation

    NASA Astrophysics Data System (ADS)

    Dubarry, Matthieu; Svoboda, Vojtech; Hwu, Ruey; Liaw, Bor Yann

    An 18650 lithium ion cell was evaluated using dynamic stress test (DST) protocol for cycle life study. Reference performance tests were applied every 60 DST cycles to quantify capacity fade and peak power capability (PPC) degradation with cycles to the end of life. A quantitative incremental capacity analysis (ICA) was applied to identify extrinsic and intrinsic contributions to capacity fading, whereas the open circuit voltage (OCV) measurements were utilized to determine the correct state of charge (SOC) in order to accurately correlate the capacity fade with SOC. The analysis also helps us identify that cell polarization resistance change in the cycles is the primary culprit that bifurcates to both extrinsic and intrinsic origins in capacity fade and PPC degradation. This analysis allows us to develop better understanding in predicting battery performance and life in the rechargeable lithium batteries.

  18. Internal tides and deep diel fades in acoustic intensity.

    PubMed

    White, Andrew W; Henyey, Frank S; Andrew, Rex K; Mercer, James A; Worcester, Peter F; Dzieciuch, Matthew A; Colosi, John A

    2016-11-01

    A mechanism is presented by which the observed acoustic intensity is made to vary due to changes in the acoustic path that are caused by internal-tide vertical fluid displacements. The position in range and depth of large-scale caustic structure is determined by the background sound-speed profile. Internal tides cause a deformation of the background profile, changing the positions of the caustic structures-which can introduce intensity changes at a distant receiver. Gradual fades in the acoustic intensity occurring over timescales similar to those of the tides were measured during a low-frequency (284-Hz) acoustic scattering experiment in the Philippine Sea in 2009 [White et al., J. Acoust. Soc. Am. 134(4), 3347-3358 (2013)]. Parabolic equation and Hamiltonian ray-tracing calculations of acoustic propagation through a plane-wave internal tide environmental model employing sound-speed profiles taken during the experiment indicate that internal tides could cause significant gradual changes in the received intensity. Furthermore, the calculations demonstrate how large-scale perturbations to the index of refraction can result in variation in the received intensity.

  19. Neutron Fading Characteristics of Copper Doped Lithium Fluoride (LiF: MCP) Thermoluminescent Dosimeters (TLDs)

    DTIC Science & Technology

    2008-05-21

    Fading Characteristics of Copper-Doped Lithium Fluoride (LiF: MCP) Thermoluminescent Dosimeters (TLDs)" Name of Candidate: L T Jeffrey A. Delzer Master...Lithium Fluoride Thermoluminescent Dosimeters beyond brief excerpts is with the permission of the copyright owner, and will save and hold harmless...Thesis: Author: Thesis directed by: ABSTRACT "Neutron Fading Characteristics of Copper-Doped Lithium Fluoride (LiF: MCP) Thermoluminescent

  20. MIMO FSO communication using subcarrier intensity modulation over double generalized gamma fading

    NASA Astrophysics Data System (ADS)

    Yi, Xiang; Yao, Mingwu; Wang, Xiaoyang

    2017-01-01

    Atmospheric turbulence-induced fading is known to have a serious detrimental effect on the performance of free-space optical (FSO) communication. The involvement of multiple lasers and photodetectors in FSO systems offers an effective way to overcome fading. Very recently, a new generic fading model, called double-generalized gamma (double GG), is developed for accurately describing irradiance fading over a wide range of turbulence conditions. Therefore, for a general and exact study of the multiple-input multiple-output (MIMO) FSO system, the double GG fading model is adopted in this paper. We investigate the MIMO FSO systems using subcarrier intensity modulation. Two typical transmit diversity schemes, repetition code (RC) and orthogonal space-time block code (OSTBC), are considered. We first propose a new power series expression for the probability density function of the double GG fading. Then we derive the average error rate expressions for both schemes in terms of double power series. The truncated forms of the derived power series enable the rapid and accurate numerical computation of the error rates. Furthermore, we present the asymptotic error rate analyses at high electrical signal-to-noise ratio (SNR) for both schemes. Closed-form diversity order and coding gain for both schemes are also obtained. Our numerical results, verified by simulation, confirm that RC outperforms OSTBC for MIMO FSO systems with subcarrier intensity modulation in double GG fading. The asymptotic coding gain of the RC scheme over the OSTBC scheme is analytically quantified for varying degrees of the fading strength.

  1. Transcriptome Analysis Reveals Candidate Genes Related to Color Fading of 'Red Bartlett' (Pyrus communis L.).

    PubMed

    Wang, Zhigang; Du, Hong; Zhai, Rui; Song, Linyan; Ma, Fengwang; Xu, Lingfei

    2017-01-01

    The red color of fruit is an attractive plant trait for consumers. Plants with color-faded fruit have a lower commercial value, such as 'Red Bartlett' pears (Pyrus communis L.) that have dark-red fruit in the early stages of fruit development that subsequently fade to red-green at maturity. To identify the reason for color fading, we first analyzed the anthocyanin content of peel from 'Red Bartlett,' which displays the color fading phenomenon, and 'Starkrimson,' which has no color fading. Results showed that the anthocyanin content of 'Red Bartlett' peel decreased significantly late in fruit development, while in 'Starkrimson' there was no significant decrease. Next, RNA-Sequencing was used to identify 947 differentially expressed genes (DEGs) between 'Red Bartlett' and 'Starkrimson.' Among them, 471 genes were upregulated and 476 genes were downregulated in 'Red Bartlett' at the late development stage relative to 'Starkrimson.' During 'Red Bartlett' color fading, the structural gene LDOX and six GST family genes were downregulated, while FLS, LAC, POD, and five light-responding genes were significantly upregulated. Additionally, 45 genes encoding transcription factors MYB, bHLH, WRKY, NAC, ERF, and zinc finger were identified among 947 DEGs. Changes in the expression of these genes may be responsible for the decrease in anthocyanin accumulation in 'Red Bartlett' fruit. Taken together, this study demonstrated that color fading of 'Red Bartlett' was closely linked to reduced anthocyanin biosynthesis, increased anthocyanin degradation and suppression of anthocyanin transport. It also provided novel evidence for the involvement of light signals in the color fading of red-skinned pears.

  2. Spoon-to-Cup Fading as Treatment for Cup Drinking in a Child with Intestinal Failure

    ERIC Educational Resources Information Center

    Groff, Rebecca A.; Piazza, Cathleen C.; Zeleny, Jason R.; Dempsey, Jack R.

    2011-01-01

    We treated a child with intestinal failure who consumed solids on a spoon but not liquids from a cup. We used spoon-to-cup fading, which consisted of taping a spoon to a cup and then gradually moving the bowl of the spoon closer to the edge of the cup. Spoon-to-cup fading was effective for increasing consumption of liquids from a cup. (Contains 2…

  3. Fade measurements at L-band and UHF in mountainous terrain for land mobile satellite systems

    NASA Technical Reports Server (NTRS)

    Vogel, Wolfhard J.; Goldhirsh, Julius

    1988-01-01

    Fading results related to land mobile satellite communications at L-band (1502 MHz) and UHF (870 MHz) are described. These results were derived from an experiment performed in a series of canyon passes in the Boulder, Colorado region of the US. The experimental configuration involved a helicopter as the source platform, which maintained a relatively fixed geometry with a mobile van containing the receiver and data-acquisition system. An unobstructed line of sight between the radiating sources and the receiving van was, for the most part, also maintained. In this configuration, the dominant mechanism causing signal fading (or enhancement) is a result of multipath. The resulting fade distributions demonstrated that at the 1 percent and 5 percent levels, 5.5- and 2.6-dB fades were on the average exceeded at L-band and 4.8- and 2.4-dB at UHF, respectively, for a path elevation angle of 45 deg. The canyon results as compared with previous roadside-tree-shadowing results demonstrate that the deciding factor dictating fade margin for future land mobile satellite systems is tree shadowing rather than fades caused by multipath.

  4. Dynamic propagation channel characterization and modeling for human body communication.

    PubMed

    Nie, Zedong; Ma, Jingjing; Li, Zhicheng; Chen, Hong; Wang, Lei

    2012-12-18

    This paper presents the first characterization and modeling of dynamic propagation channels for human body communication (HBC). In-situ experiments were performed using customized transceivers in an anechoic chamber. Three HBC propagation channels, i.e., from right leg to left leg, from right hand to left hand and from right hand to left leg, were investigated under thirty-three motion scenarios. Snapshots of data (2,800,000) were acquired from five volunteers. Various path gains caused by different locations and movements were quantified and the statistical distributions were estimated. In general, for a given reference threshold è = -10 dB, the maximum average level crossing rate of the HBC was approximately 1.99 Hz, the maximum average fade time was 59.4 ms, and the percentage of bad channel duration time was less than 4.16%. The HBC exhibited a fade depth of -4 dB at 90% complementary cumulative probability. The statistical parameters were observed to be centered for each propagation channel. Subsequently a Fritchman model was implemented to estimate the burst characteristics of the on-body fading. It was concluded that the HBC is motion-insensitive, which is sufficient for reliable communication link during motions, and therefore it has great potential for body sensor/area networks.

  5. Measurement and Modeling of Narrowband Channels for Ultrasonic Underwater Communications

    PubMed Central

    Cañete, Francisco J.; López-Fernández, Jesús; García-Corrales, Celia; Sánchez, Antonio; Robles, Encarnación; Rodrigo, Francisco J.; Paris, José F.

    2016-01-01

    Underwater acoustic sensor networks are a promising technology that allow real-time data collection in seas and oceans for a wide variety of applications. Smaller size and weight sensors can be achieved with working frequencies shifted from audio to the ultrasonic band. At these frequencies, the fading phenomena has a significant presence in the channel behavior, and the design of a reliable communication link between the network sensors will require a precise characterization of it. Fading in underwater channels has been previously measured and modeled in the audio band. However, there have been few attempts to study it at ultrasonic frequencies. In this paper, a campaign of measurements of ultrasonic underwater acoustic channels in Mediterranean shallow waters conducted by the authors is presented. These measurements are used to determine the parameters of the so-called κ-μ shadowed distribution, a fading model with a direct connection to the underlying physical mechanisms. The model is then used to evaluate the capacity of the measured channels with a closed-form expression. PMID:26907281

  6. Measurement and Modeling of Narrowband Channels for Ultrasonic Underwater Communications.

    PubMed

    Cañete, Francisco J; López-Fernández, Jesús; García-Corrales, Celia; Sánchez, Antonio; Robles, Encarnación; Rodrigo, Francisco J; Paris, José F

    2016-02-19

    Underwater acoustic sensor networks are a promising technology that allow real-time data collection in seas and oceans for a wide variety of applications. Smaller size and weight sensors can be achieved with working frequencies shifted from audio to the ultrasonic band. At these frequencies, the fading phenomena has a significant presence in the channel behavior, and the design of a reliable communication link between the network sensors will require a precise characterization of it. Fading in underwater channels has been previously measured and modeled in the audio band. However, there have been few attempts to study it at ultrasonic frequencies. In this paper, a campaign of measurements of ultrasonic underwater acoustic channels in Mediterranean shallow waters conducted by the authors is presented. These measurements are used to determine the parameters of the so-called κ-μ shadowed distribution, a fading model with a direct connection to the underlying physical mechanisms. The model is then used to evaluate the capacity of the measured channels with a closed-form expression.

  7. Dynamic Propagation Channel Characterization and Modeling for Human Body Communication

    PubMed Central

    Nie, Zedong; Ma, Jingjing; Li, Zhicheng; Chen, Hong; Wang, Lei

    2012-01-01

    This paper presents the first characterization and modeling of dynamic propagation channels for human body communication (HBC). In-situ experiments were performed using customized transceivers in an anechoic chamber. Three HBC propagation channels, i.e., from right leg to left leg, from right hand to left hand and from right hand to left leg, were investigated under thirty-three motion scenarios. Snapshots of data (2,800,000) were acquired from five volunteers. Various path gains caused by different locations and movements were quantified and the statistical distributions were estimated. In general, for a given reference threshold è = −10 dB, the maximum average level crossing rate of the HBC was approximately 1.99 Hz, the maximum average fade time was 59.4 ms, and the percentage of bad channel duration time was less than 4.16%. The HBC exhibited a fade depth of −4 dB at 90% complementary cumulative probability. The statistical parameters were observed to be centered for each propagation channel. Subsequently a Fritchman model was implemented to estimate the burst characteristics of the on-body fading. It was concluded that the HBC is motion-insensitive, which is sufficient for reliable communication link during motions, and therefore it has great potential for body sensor/area networks. PMID:23250278

  8. Impact of a Backwards Faded Scaffolding Approach to Learning Astronomy

    NASA Astrophysics Data System (ADS)

    Slater, Stephanie

    2010-01-01

    The Boyer Commission Report, "Reinventing Undergraduate Education" eloquently argues that all undergraduate coursework would benefit greatly by being framed as authentic research experiences where students create and defend knowledge. Yet, our experience in guiding students to do research projects using astronomical databases has demonstrated time and time again that the most difficult aspect of engaging in scientific research is helping students identify and frame a fruitful research question itself. To scaffold students' learning experiences to help them ask better research questions, we have adopted a backwards faded scaffolding approach where students do multiple inquiry experiences, rather than a single protracted one. In this approach, we first carefully guide students through an entire astronomical inquiry sequence, from giving them the targeted research question through an accurate scientific conclusion tightly matched to the research question. Then, for their second inquiry experience, students generate their conclusions independently, with the previous experience set out as a guide. Students are required to make sense of data that has been purposefully planned, collected, and analyzed with instructor guidance. They construct and defend conclusions based upon data that is, effectively, given to them. By the time students reach their third inquiry they have been exposed to two experiences in which they were guided through the. During this third inquiry data collection and analysis becomes an independent task. By the fourth inquiry, students have received explicit instruction on the connection between the research questions and the procedure undertaken to address them three times. They are prepared to take responsibility for creating a plausible method for collecting data given a research prompt. By the fifth inquiry, students have now seen four examples of quality research questions/hypotheses, and their relationship to procedures, data collection and

  9. A Novel 2-D OFDM-DS-CDMA Receiver with Frequency-Time Spreading

    NASA Astrophysics Data System (ADS)

    Chen, Joy Iong-Zong

    This paper presents a novel 2-D (2-dimension) receiver that adopts the reception scheme to promote OFDM-DS-CDMA (orthogonal frequency division multiplexing multi-carrier coded-division multiple-access) system performance. The system model includes spread coding and a system block diagram of the 2-D receiver shown graphically with 3-D (three dimensions) plots. The analytical calculation of system performance for an OFDM-DS-CDMA system combined with the proposed receiver equipment is investigated. To evaluate the results from the channel fading effect is considered over the correlated fading environments. The correlated-Nakagami-m statistical distribution is taken into account in the evaluation. The results show that the number of users, the number of subcarriers and the fading channel correlation generally affect OFDM-DS-CDMA systems. The system is also influenced by the Doppler shift and the signal propagation environment (fading parameter).

  10. Cognitive Jointly Optimal Code-Division Channelization and Routing Over Cooperative Links

    DTIC Science & Technology

    2014-04-01

    Estimation . . . . . . . 47 Q. Experimental Testbed Setup . . . . . . . . . . . . . . . . . . . . . 50 R. USRP2 Receiver: Low-cost, Commercial SDRs ...we design and implement a wireless software defined radio ( SDR ) testbed for cognitive channelization in multipath fading environments. Pri- mary and...while at the same time maintains interference to primary users below a prespec- ified threshold. We deployed four commercial, low-cost SDR

  11. Effects of the Wireless Channel, Signal Compression and Network Architecture on Speech Quality in Voip Networks

    DTIC Science & Technology

    2007-06-01

    coding and compression on the received speech quality. Both simulation and experimentation are conducted using Matlab code and Speex software and...using Matlab code and Speex software and across commercial VoIP networks. Simulation shows that fading channel parameters can heavily affect the...73 MATLAB CODE

  12. Explore the Effects of Microstructural Defects on Voltage Fade of Li- and Mn-Rich Cathodes

    SciTech Connect

    Hu, E.; Lyu, Y.; Xin, H.; Xin, H. L.; Liu, J.; Han, L.; Bak, S. -M.; Bai, J.; Yu, X.; Li, H.; Yang, X. Q.

    2016-09-26

    Li- and Mn-rich (LMR) cathode materials have been considered as promising candidates for energy storage applications due to high energy density. However, these materials suffer from a serious problem of voltage fade. Oxygen loss and the layer to spinel phase transition are two major contributors of such voltage fade. In this paper, using a combination of x-ray diffraction (XRD), pair distribution function (PDF), x-ray absorption (XAS) techniques and aberration-corrected scanning transmission electron microscopy (STEM), we studied the effects of micro structural defects, especially the grain boundaries on the oxygen loss and layered-to-spinel phase transition through prelithiation of a model compound Li2Ru0.5Mn0.5O3. It is found that the nano-sized micro structural defects, especially the large amount of grain boundaries created by the prelithiation can greatly accelerate the oxygen loss and voltage fade. Defects (such as nano-sized grain boundaries) and oxygen release form a positive feedback loop, promote each other during cycling, and accelerate the two major voltage fade contributors: the transition metal reduction and layered-to-spinel phase transition. These results clearly demonstrate the important relationships among the oxygen loss, microstructural defects and voltage fade. The importance of maintaining good crystallinity and protecting the surface of LMR material are also suggested.

  13. Explore the Effects of Microstructural Defects on Voltage Fade of Li- and Mn-Rich Cathodes

    DOE PAGES

    Hu, E.; Lyu, Y.; Xin, H.; ...

    2016-09-26

    Li- and Mn-rich (LMR) cathode materials have been considered as promising candidates for energy storage applications due to high energy density. However, these materials suffer from a serious problem of voltage fade. Oxygen loss and the layer to spinel phase transition are two major contributors of such voltage fade. In this paper, using a combination of x-ray diffraction (XRD), pair distribution function (PDF), x-ray absorption (XAS) techniques and aberration-corrected scanning transmission electron microscopy (STEM), we studied the effects of micro structural defects, especially the grain boundaries on the oxygen loss and layered-to-spinel phase transition through prelithiation of a model compoundmore » Li2Ru0.5Mn0.5O3. It is found that the nano-sized micro structural defects, especially the large amount of grain boundaries created by the prelithiation can greatly accelerate the oxygen loss and voltage fade. Defects (such as nano-sized grain boundaries) and oxygen release form a positive feedback loop, promote each other during cycling, and accelerate the two major voltage fade contributors: the transition metal reduction and layered-to-spinel phase transition. These results clearly demonstrate the important relationships among the oxygen loss, microstructural defects and voltage fade. The importance of maintaining good crystallinity and protecting the surface of LMR material are also suggested.« less

  14. Relationship between DAPI-fluorescence fading and nuclear DNA content: An alternative method to DNA quantification?

    PubMed

    Gallardo-Escárate, Cristian; Alvarez-Borrego, Josué; Von Brand, Elisabeth; Dupré, Enrique; Del Río-Portilla, Miguel Angel

    2007-01-01

    In observations by confocal or conventional fluorescence microscopy, important factors should be considered in order to obtain accurate images. One of them, such as the fluorescence bleaching from highest intensity to lowest signal of fluorescence is a common problem with several DNA fluorochromes and especially for DAPI stain. The fluorescence of DAPI fades rapidly when it is exposed to UV light, under optimal conditions of observation. Although the fading process can be retarded using a mounting medium with antifading reagents, the photochemical process underlying the fluorescence decay has not yet been fully explained. In addition, no relationship between fluorescence fading and nuclear DNA content has been tested. In order to test this relationship, we measured by means of image analysis the DAPI-fluorescence intensity in several cellular types (spermatozoa, erythrocytes and haemocytes) during their fluorescence bleaching. An algorithm specifically built in MATLAB software was used for this approach. The correlation coefficient between nuclear DNA content and DAPI-fluorescence fading was found equal to 99%. This study demonstrates the feasibility to measure nuclear DNA content by fluorescence fading quantification, as an alternative method concurrently with image analysis procedures.

  15. Explore the Effects of Microstructural Defects on Voltage Fade of Li- and Mn-Rich Cathodes

    SciTech Connect

    Hu, E.; Lyu, Y.; Xin, H.; Xin, H. L.; Liu, J.; Han, L.; Bak, S. -M.; Bai, J.; Yu, X.; Li, H.; Yang, X. Q.

    2016-09-26

    Li- and Mn-rich (LMR) cathode materials have been considered as promising candidates for energy storage applications due to high energy density. However, these materials suffer from a serious problem of voltage fade. Oxygen loss and the layer to spinel phase transition are two major contributors of such voltage fade. In this paper, using a combination of x-ray diffraction (XRD), pair distribution function (PDF), x-ray absorption (XAS) techniques and aberration-corrected scanning transmission electron microscopy (STEM), we studied the effects of micro structural defects, especially the grain boundaries on the oxygen loss and layered-to-spinel phase transition through prelithiation of a model compound Li2Ru0.5Mn0.5O3. It is found that the nano-sized micro structural defects, especially the large amount of grain boundaries created by the prelithiation can greatly accelerate the oxygen loss and voltage fade. Defects (such as nano-sized grain boundaries) and oxygen release form a positive feedback loop, promote each other during cycling, and accelerate the two major voltage fade contributors: the transition metal reduction and layered-to-spinel phase transition. These results clearly demonstrate the important relationships among the oxygen loss, microstructural defects and voltage fade. The importance of maintaining good crystallinity and protecting the surface of LMR material are also suggested.

  16. Evaluation of FEC for the atmospheric optical IM/DD channel

    NASA Astrophysics Data System (ADS)

    Henniger, Hennes; David, Florian; Giggenbach, Dirk; Rapp, Christoph

    2003-07-01

    Channel measurements were performed by the German Aerospace Center in various near ground optical channels including a 1.5 km horizontal path as well as a 61km path. These measurements clearly showed that the atmosphere causes very slow fading (compared to the high data rates usually used in optical communication systems), which significantly degrades the transmission quality. As transmitter power and receiver sensitivity are limited by the transmission technology, fading depicts a severe problem, that can be reduced by the use of forward error correction schemes (FEC) in order to improve system performance. Therefore FEC was subject of investigations by means of simulations. To figure out which FEC methods are useful for applications in the atmospheric optical channels simulations of standard block codes and interleavers have been done. They were based on data sets taken in the various channel measurements. The simulations point out that only very long interleaving can increase performance significantly.

  17. Intergranular Cracking as a Major Cause of Long-Term Capacity Fading of Layered Cathodes

    DOE PAGES

    Liu, Hao; Wolf, Mark; Karki, Khim; ...

    2017-05-26

    Capacity fading has limited commercial layered Li-ion battery electrodes to <70% of their theoretical capacity. Higher capacities can be achieved initially by charging to higher voltages, however, these gains are quickly eroded by a faster fade in capacity. In-creasing lifetimes and reversible capacity is contingent on identifying the origin of this capacity fade to inform electrode design and synthesis. We must understand how the battery reactions change following capacity loss after long-term cycling. Using operando X-ray diffraction, we followed the reaction of a LiNi0.8Co0.15Al0.05O2 (NCA) electrode after months of charge-discharge cycles. Furthermore, the heterogeneous reaction kinetics observed during extended cyclesmore » quantitatively explain the capacity loss, which is ultimately attributed to inter-granular fracturing that degrades the connectivity of sub-surface grains within the polycrystalline NCA aggregate.« less

  18. Investigation of signal fading in lithium formate EPR dosimeters using a new sensitive method

    NASA Astrophysics Data System (ADS)

    Adolfsson, Emelie; Karlsson, Mattias; Alm Carlsson, Gudrun; Carlsson Tedgren, Åsa; Lund, Eva; Olsson, Sara; Gustafsson, Håkan

    2012-04-01

    The aim of this study was to investigate signal fading in lithium formate electron paramagnetic resonance (EPR) dosimeters used for clinical applications in radiotherapy. A new experimental method for determination of signal fading, designed to resolve small changes in signal from slowly decaying unstable radicals, was used. Possible signal fading in lithium formate due to different storage temperatures was also tested. Air humidity was kept at a constant level of 33% throughout the experiments. The conclusion drawn from the investigations was that the EPR signal from lithium formate is stable during at least 1 month after irradiation and is not sensitive to variations in storage temperature <40 °C when kept at a relative air humidity of 33%. This makes lithium formate a suitable dosimeter for transfer dosimetry in clinical audits.

  19. Systems implications of L-band fade data statistics for LEO mobile systems

    NASA Technical Reports Server (NTRS)

    Devieux, Carrie L.

    1993-01-01

    This paper examines and analyzes research data on the role of foliage attenuation in signal fading between a satellite transmitter and a terrestrial vehicle-mounted receiver. The frequency band of measurement, called L-Band, includes the region 1610.0 to 1626.5 MHz. Data from tests involving various combinations of foliage and vehicle movement conditions clearly show evidence of fast fading (in excess of 0.5 dB per millisecond) and fade depths as great or greater than 16 dB. As a result, the design of a communications link power control that provides the level of accuracy necessary for power sensitive systems could be significantly impacted. Specific examples of this include the communications links that employ Code Division Multiple Access (CDMA) as a modulation technique.

  20. Influence of time interval and filter bandwidth on measured rain fade slope

    NASA Astrophysics Data System (ADS)

    van de Kamp, M. M. J. L.; CléRivet, P.

    2004-04-01

    The rate of change of rain attenuation, or `fade slope,' observed on a microwave link, is dependant on system parameters of the receiver. This paper assesses its dependence on two data processing parameters: the time interval over which the fade slope is defined, and the low-pass filter bandwidth used to remove tropospheric scintillation. A theoretical expression of this dependence is derived. The expression is compared with measured results, which show a good agreement. The results show that the time interval has a strong influence when it is larger than the inverse of the filter bandwidth, and the filter bandwidth has a strong influence when its inverse is larger than the time interval. In general, the fade slope always depends strongly on at least one of the two parameters.

  1. Joint Parameter Estimation for the Two-Wave with Diffuse Power Fading Model.

    PubMed

    Lopez-Fernandez, Jesus; Moreno-Pozas, Laureano; Lopez-Martinez, Francisco Javier; Martos-Naya, Eduardo

    2016-06-30

    Wireless sensor networks deployed within metallic cavities are known to suffer from a very severe fading, even in strong line-of-sight propagation conditions. This behavior is well-captured by the Two-Wave with Diffuse Power (TWDP) fading distribution, which shows great fit to field measurements in such scenarios. In this paper, we address the joint estimation of the parameters K and Δ that characterize the TWDP fading model, based on the observation of the received signal envelope. We use a moment-based approach to derive closed-form expressions for the estimators of K and Δ, as well as closed-form expressions for their asymptotic variance. Results show that the estimation error is close to the Cramer-Rao lower bound for a wide range of values of the parameters K and Δ. The performance degradation due to a finite number of observations is also analyzed.

  2. A pancultural perspective on the fading affect bias in autobiographical memory.

    PubMed

    Ritchie, Timothy D; Batteson, Tamzin J; Bohn, Annette; Crawford, Matthew T; Ferguson, Georgie V; Schrauf, Robert W; Vogl, Rodney J; Walker, W Richard

    2015-01-01

    The fading affect bias (FAB) refers to the negative affect associated with autobiographical events fading faster than the positive affect associated with such events, a reliable and valid valence effect established by researchers in the USA. The present study examined the idea that the FAB is a ubiquitous emotion regulating phenomenon in autobiographical memory that is present in people from a variety of cultures. We tested for evidence of the FAB by sampling more than 2400 autobiographical event descriptions from 562 participants in 10 cultures around the world. Using variations on a common method, each sample evidenced a FAB: positive affect faded slower than negative affect did. Results suggest that in tandem with local norms and customs, the FAB may foster recovery from negative life events and promote the retention of the positive emotions, within and outside of the USA. We discuss these findings in the context of Keltner and Haidt's levels of analysis theory of emotion and culture.

  3. Stimulus Fading and Response Elaboration in Differential Reinforcement for Alternative Behavior

    PubMed Central

    Schlichenmeyer, Kevin J.; Dube, William V.; Vargas-Irwin, Mariela

    2015-01-01

    A hallmark of applied behavior analysis is the development of function-based interventions for problem behavior. A widely recommended function-based intervention is differential reinforcement of alternative behavior (DRA), in which reinforcement is contingent upon socially acceptable alternatives to problem behavior (e.g., teaching communication skills). Typically, DRA is introduced under rich schedules of reinforcement. Although effective for initiating behavior change, rich schedules are often impractical in the natural setting. In this study, we evaluated the extent to which a stimulus fading program could be employed to elaborate alternative behavior (mands) in two individuals diagnosed with an Autism Spectrum Disorder. For both participants, problem behavior was reduced substantially upon implementation of the DRA procedure. Further, problem behavior rates remained low and mand rates decreased to more practical levels as the DRA behavioral requirements increased during the fading program. The fading approach demonstrated in this paper may be a useful component of intervention packages for clinicians. PMID:25844032

  4. Joint Parameter Estimation for the Two-Wave with Diffuse Power Fading Model

    PubMed Central

    Lopez-Fernandez, Jesus; Moreno-Pozas, Laureano; Lopez-Martinez, Francisco Javier; Martos-Naya, Eduardo

    2016-01-01

    Wireless sensor networks deployed within metallic cavities are known to suffer from a very severe fading, even in strong line-of-sight propagation conditions. This behavior is well-captured by the Two-Wave with Diffuse Power (TWDP) fading distribution, which shows great fit to field measurements in such scenarios. In this paper, we address the joint estimation of the parameters K and Δ that characterize the TWDP fading model, based on the observation of the received signal envelope. We use a moment-based approach to derive closed-form expressions for the estimators of K and Δ, as well as closed-form expressions for their asymptotic variance. Results show that the estimation error is close to the Cramer-Rao lower bound for a wide range of values of the parameters K and Δ. The performance degradation due to a finite number of observations is also analyzed. PMID:27376293

  5. Study of ageing and fading in CR-39 detectors for different storage conditions.

    PubMed

    Franci, Daniele; Aureli, Tommaso; Cardellini, Francesco

    2015-12-01

    The aim of this study was to investigate the effect of ageing and fading on PADC detector response, as a function of the storage time and temperature. Several groups of CR-39 detectors provided by Radosys, Ltd. were exposed at the reference radon chamber of the Istituto Nazionale di Metrologia delle Radiazioni Ionizzanti, at the ENEA centre in Casaccia. The results indicate that low-temperature storage inhibits the effect of both ageing and fading. Finally, the overall reduction in CR-39 sensitivity due to the combined ageing/fading effect was estimated. In particular, the sensitivity of the detectors continuously exposed in air at room temperature over 6 and 3 months was reduced, respectively, by 7.5 and 4 %. © The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.

  6. Bayesian and Frequentist Estimation of the Average Capacity of Log Normal Wireless Optical Channels

    NASA Astrophysics Data System (ADS)

    Katsis, A.; Nistazakis, H. E.; Tombras, G. S.

    2008-11-01

    We investigate the average (ergodic) capacity of practical free-space optical communication channels using the frequentist and the Bayesian approach. We concentrate on the cases of weak and moderate atmospheric turbulence leading to channels modeled by Log-Normal distributed intensity fading and derive closed-form expressions and estimation procedures for their achievable capacity and the important parameters of interest. Each methodology is reviewed in terms of their analytic convenience and their accuracy is also discussed.

  7. Exponential fading to white of black holes in quantum gravity

    NASA Astrophysics Data System (ADS)

    Barceló, Carlos; Carballo-Rubio, Raúl; Garay, Luis J.

    2017-05-01

    Quantization of the gravitational field may allow the existence of a decay channel of black holes into white holes with an explicit time-reversal symmetry. The definition of a meaningful decay probability for this channel is studied in spherically symmetric situations. As a first nontrivial calculation, we present the functional integration over a set of geometries using a single-variable function to interpolate between black-hole and white-hole geometries in a bounded region of spacetime. This computation gives a finite result which depends only on the Schwarzschild mass and a parameter measuring the width of the interpolating region. The associated probability distribution displays an exponential decay law on the latter parameter, with a mean lifetime inversely proportional to the Schwarzschild mass. In physical terms this would imply that matter collapsing to a black hole from a finite radius bounces back elastically and instantaneously, with negligible time delay as measured by external observers. These results invite to reconsider the ultimate nature of astrophysical black holes, providing a possible mechanism for the formation of black stars instead of proper general relativistic black holes. The existence of both this decay channel and black stars can be tested in future observations of gravitational waves.

  8. Lava Channels

    NASA Image and Video Library

    2013-12-03

    The channels and linear depression in this image captured by NASA 2001 Mars Odyssey spacecraft are located on the western margin of the Elysium Volcanic complex. The channels were created by lava flow.

  9. Tracking Performance of the RLS Algorithm Applied to an Antenna Array in a Realistic Fading Environment

    DTIC Science & Technology

    2002-05-01

    n [n + m ). (14) The complex Gaussian process un [k] is defined relative to t»o[n], and E(a[n]isn t[k]) = Q VA; E(Vn[k]) = 0 E(vn[i]"n*[k...its effect on the estimation of the time variant autocorrelation matrix and cross-correlation vector. Specifically, the case of a flat Rayleigh ...Specifically, the case of a flat Rayleigh fading desired signal applied to an array in the presence of static interferers is considered with an AR2 fading

  10. Adaptive control of satellite EIRP to reduce outage caused by fading

    NASA Astrophysics Data System (ADS)

    Bakken, P. M.; Maseng, T.

    1983-05-01

    The effectiveness of dynamic satellite EIRP allocation in reducing the effects of up and downlink fading is assessed. Analytical methods using numerical convolution performed by fast Fourier transforms are used to evaluate the performance of allocation techniques in terms of the probability distribution of the satellite link quality obtained from the link fading statistics at the terminal sites. The results are presented in the form of outage statistics for particular systems and allocation methods. They represent the entire range of performance which can be envisaged, ranging from CTP to ASEIRP.

  11. Atmospheric-Fade-Tolerant Tracking and Pointing in Wireless Optical Communication

    NASA Technical Reports Server (NTRS)

    Ortiz, Gerardo; Lee, Shinhak

    2003-01-01

    An acquisition, tracking, and pointing (ATP) system, under development at the time of reporting the information for this article, is intended to enable a terminal in a free-space optical communication system to continue to aim its transmitting laser beam toward a receiver at a remote terminal when the laser beacon signal from the remote terminal temporarily fades or drops out of sight altogether. Such fades and dropouts can be caused by adverse atmospheric conditions (e.g., rain or clouds). They can also occur when intervening objects block the line of sight between terminals as a result of motions of those objects or of either or both terminals

  12. Pilot-Assisted Channel Estimation for Orthogonal Multi-Carrier DS-CDMA with Frequency-Domain Equalization

    NASA Astrophysics Data System (ADS)

    Shima, Tomoyuki; Tomeba, Hiromichi; Adachi, Fumiyuki

    Orthogonal multi-carrier direct sequence code division multiple access (orthogonal MC DS-CDMA) is a combination of time-domain spreading and orthogonal frequency division multiplexing (OFDM). In orthogonal MC DS-CDMA, the frequency diversity gain can be obtained by applying frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion to a block of OFDM symbols and can improve the bit error rate (BER) performance in a severe frequency-selective fading channel. FDE requires an accurate estimate of the channel gain. The channel gain can be estimated by removing the pilot modulation in the frequency domain. In this paper, we propose a pilot-assisted channel estimation suitable for orthogonal MC DS-CDMA with FDE and evaluate, by computer simulation, the BER performance in a frequency-selective Rayleigh fading channel.

  13. "Paintings Fade Like Flowers": Pigment Analysis and Digital Reconstruction of a Faded Pink Lake Pigment in Vincent van Gogh's Undergrowth with Two Figures.

    PubMed

    Fieberg, Jeffrey E; Knutås, Per; Hostettler, Kurt; Smith, Gregory D

    2017-01-01

    Color fading in Vincent van Gogh's Undergrowth with Two Figures was studied chemically to facilitate the creation of a digital reconstruction of fugitive colors . The painting contains a field of white, green, orange, and yellow flowers under a canopy of poplar trees with two central figures-a man and a woman, arms entwined. From Van Gogh's letters, however, it is known that he painted the picture with some pink flowers, which appear to have altered, presumably to white. Raman spectroscopy was applied to microsamples of paint to identify the faded pigment as geranium lake, which in this painting consists of the dye, eosin (2',4',5',7'-tetrabromofluorescein). For the first time, lead(II) sulfate has been specifically identified as the likely inorganic substrate for a geranium lake used by Van Gogh in the last months of his life. Microfocus X-ray fluorescence (MXRF) spectroscopy was subsequently used in situ to analyze the white flowers to identify bromine as a proxy for eosin, thus indicating an original pink coloration. Of the 387 white flowers analyzed, 37.7% contained measurable bromine and were, therefore, originally pink. Several cross-sections from these formerly pink areas were assessed using a combination of visual inspection and microcolorimetry to create a colored mask in Adobe Photoshop to digitally reconstruct a suggestion of the original appearance of the painting with regard to the faded flowers. Additionally, microfadeometry was undertaken for the first time on a painting cross-section sample to understand the actual fading kinetics of the underlying bright pink geranium lake used by Van Gogh. A combination of Raman microspectroscopy, MXRF, and scanning electron microscopy energy dispersive spectroscopy (SEM-EDS) were utilized in situ and on paint microsamples to identify the complete palette used to create Undergrowth with Two Figures.

  14. Backwards Faded Scaffolding Impact on Pre-Service Teachers’ Cognition

    NASA Astrophysics Data System (ADS)

    Slater, T. F.; Slater, S. J.

    2009-12-01

    In response to national reform movements calling for future teachers to be prepared to design and deliver science instruction using the principles of inquiry in the context of Earth system science, we created and evaluated an innovative curriculum for specially designed courses for pre-service elementary education and secondary undergraduates based upon an inquiry-oriented teaching approach framed by the notions of backwards faded-scaffolding as an overarching theme for inquiry-oriented instruction. Students completed both structured- and open-inquiry projects using online scientific data bases, particularly those available from NASA, and presented the results of their investigations several times throughout the semester as a mini-science conference. Using a single-group, multiple-measures, quasi-experimental design, students demonstrated enhanced content knowledge of astronomy and inquiry as well as attitudes and self-efficacy toward teaching as measured by the Test of Astronomy STandards (TOAST), the Science Teaching Efficacy Belief Instrument - Version B, and the Attitudes Toward Science Inventory. We adopted a model of inquiry where: (i) students are engaged in questions; (ii) students are designing plans to pursue data; and (iii) students are generating and defending conclusions based on evidence they have collected. We developed an approach that is directly in contrast with the open inquiry “science fair” model to specifically use carefully scaffolded, shorter term inquiries, placing the most challenging aspects of “question generation” at the end of the lessons. In this model, during students' first experience with inquiry they are guided through the entire process, from research question to the appropriate content and format for a scientific conclusion. In their second experience, students generate their conclusions independently, with the previous experience set out as a guide for content and format. They are required to make sense of data that has

  15. An exploration of the relationship among valence, fading affect, rehearsal frequency, and memory vividness for past personal events.

    PubMed

    Lindeman, Meghan I H; Zengel, Bettina; Skowronski, John J

    2017-07-01

    The affect associated with negative (or unpleasant) memories typically tends to fade faster than the affect associated with positive (or pleasant) memories, a phenomenon called the fading affect bias (FAB). We conducted a study to explore the mechanisms related to the FAB. A retrospective recall procedure was used to obtain three self-report measures (memory vividness, rehearsal frequency, affective fading) for both positive events and negative events. Affect for positive events faded less than affect for negative events, and positive events were recalled more vividly than negative events. The perceived vividness of an event (memory vividness) and the extent to which an event has been rehearsed (rehearsal frequency) were explored as possible mediators of the relation between event valence and affect fading. Additional models conceived of affect fading and rehearsal frequency as contributors to a memory's vividness. Results suggested that memory vividness was a plausible mediator of the relation between an event's valence and affect fading. Rehearsal frequency was also a plausible mediator of this relation, but only via its effects on memory vividness. Additional modelling results suggested that affect fading and rehearsal frequency were both plausible mediators of the relation between an event's valence and the event's rated memory vividness.

  16. Using Audio Script Fading and Multiple-Exemplar Training to Increase Vocal Interactions in Children with Autism

    ERIC Educational Resources Information Center

    Garcia-Albea, Elena; Reeve, Sharon A.; Brothers, Kevin J.; Reeve, Kenneth F.

    2014-01-01

    Script-fading procedures have been shown to be effective for teaching children with autism to initiate and participate in social interactions without vocal prompts from adults. In previous script and script-fading research, however, there has been no demonstration of a generalized repertoire of vocal interactions under the control of naturally…

  17. An Investigation of the Impact of Instructional Fading Using Completion Problems on Student Performance in Principles of Accounting Instruction

    ERIC Educational Resources Information Center

    Kingry, Mary Ann

    2012-01-01

    The effects of instructional fading using completion problems on student performance were investigated in this study. Instructional fading is the gradual withdrawal of the amount of assistance provided to the student and was accomplished in this study using completion problems. They were used to gradually transition the student from completely…

  18. TRP Channels

    PubMed Central

    Venkatachalam, Kartik; Montell, Craig

    2011-01-01

    The TRP (Transient Receptor Potential) superfamily of cation channels is remarkable in that it displays greater diversity in activation mechanisms and selectivities than any other group of ion channels. The domain organizations of some TRP proteins are also unusual, as they consist of linked channel and enzyme domains. A unifying theme in this group is that TRP proteins play critical roles in sensory physiology, which include contributions to vision, taste, olfaction, hearing, touch, and thermo- and osmosensation. In addition, TRP channels enable individual cells to sense changes in their local environment. Many TRP channels are activated by a variety of different stimuli and function as signal integrators. The TRP superfamily is divided into seven subfamilies: the five group 1 TRPs (TRPC, TRPV, TRPM, TRPN, and TRPA) and two group 2 subfamilies (TRPP and TRPML). TRP channels are important for human health as mutations in at least four TRP channels underlie disease. PMID:17579562

  19. Adaptive detection technique for optical wireless communication over strong turbulence channels

    NASA Astrophysics Data System (ADS)

    Wang, Jin; Huang, Dexiu; Xiuhua, Yuan

    2007-11-01

    Optical wireless communication (OWC) systems use the atmosphere as a propagation medium, so the atmospheric turbulence effects lead to fading related with signal intensity. The received signal of OWC over strong turbulence channels is assumed to be a mixture of K-distributed fading and Gaussian distributed thermal noise. Second-order spectral analysis is unable to separately estimate the mixed signal. In order to mitigate the fading induced by turbulence, the decision threshold-updating algorithm based on second and higher order cumulants is proposed and is able to operate in an unknown turbulence environment. The performance of the adaptive processing scheme has been evaluated by means of Monte Carlo simulations. Simulation results show the improvement of the bit error rate (BER) performance.

  20. Using Reinforcer Pairing and Fading to Increase the Milk Consumption of a Preschool Child

    ERIC Educational Resources Information Center

    Tiger, Jeffrey H.; Hanley, Gregory P.

    2006-01-01

    The present study replicates and extends previous research on the treatment of food selectivity by implementing pairing and fading procedures to increase a child's milk consumption during regularly scheduled preschool meals. The treatment involved mixing a small amount of chocolate syrup into a glass of milk and gradually eliminating the…

  1. A short-time fading study of Al2O3:C

    NASA Astrophysics Data System (ADS)

    Nascimento, L. F.; Vanhavere, F.; Silva, E. H.; Deene, Y. De

    2015-01-01

    This paper studies the short-time fading from Al2O3:C by measuring optically stimulated luminescence (OSL) signals (Total OSL: TOSL, and Peak OSL: POSL) from droplets and Luxel™ pellets. The influence of various bleaching regimes (blue, green and white) and light power is compared. The fading effect is the decay of the OSL signal in the dark at room temperature. Al2O3:C detectors were submitted to various bleaching regimes, irradiated with a reference dose and read out after different time spans. Investigations were carried out using 2 mm size droplet detectors, made of thin Al2O3:C powder mixed with a photocured polymer. Tests were compared to Luxel™-type detectors (Landauer Inc.). Short-time post-irradiation fading is present in OSL results (TOSL and POSL) droplets for time spans up to 200 s. The effect of short-time fading can be lowered/removed when treating the detectors with high-power and/or long time bleaching regimes; this result was observed in both TOSL and POSL from droplets and Luxel™.

  2. Effects of Script Fading on the Abilities of Children with Autism to Reciprocate Information

    ERIC Educational Resources Information Center

    Tedoff, Marc Alan

    2009-01-01

    Teaching communication skills to children with autism is a primary concern because speech and/or language delay characterize autism. One method of teaching verbal communication skills to children with autism is script fading. This study examined the effects of teaching children with autism to exchange information to peers about objects and…

  3. Physical Theory of Voltage Fade in Lithium- and Manganese-Rich Transition Metal Oxides

    SciTech Connect

    Rinaldo, Steven G.; Gallagher, Kevin G.; Long, Brandon R.; Croy, Jason R.; Bettge, Martin; Abraham, Daniel P.; Bareno, Javier; Dees, Dennis W.

    2015-03-04

    Lithium- and manganese-rich (LMR) transition metal oxide cathodes are of interest for lithium-ion battery applications due to their increased energy density and decreased cost. However, the advantages in energy density and cost are offset, in part, due to the phenomena of voltage fade. Specifically, the voltage profiles (voltage as a function of capacity) of LMR cathodes transform from a high energy configuration to a lower energy configuration as they are repeatedly charged (Li removed) and discharged (Li inserted). Here, we propose a physical model of voltage fade that accounts for the emergence of a low voltage Li phase due to the introduction of transition metal ion defects within a parent Li phase. The phenomenological model was re-cast in a general form and experimental LMR charge profiles were de-convoluted to extract the evolutionary behavior of various components of LMR capacitance profiles. Evolution of the voltage fade component was found to follow a universal growth curve with a maximal voltage fade capacity of ≈ 20% of the initial total capacity.

  4. Capacity fade modelling of lithium-ion battery under cyclic loading conditions

    NASA Astrophysics Data System (ADS)

    Ashwin, T. R.; Chung, Yongmann M.; Wang, Jihong

    2016-10-01

    A pseudo two-dimensional (P2D) electro-chemical lithium-ion battery model is presented in this paper to study the capacity fade under cyclic charge-discharge conditions. The Newman model [1,2] has been modified to include a continuous solvent reduction reaction responsible for the capacity fade and power fade. The temperature variation inside the cell is accurately predicted using a distributed thermal model coupled with the internal chemical heat generation. The model is further improved by linking the porosity variation with the electrolyte partial molar concentration, thereby proving a stronger coupling between the battery performance and the chemical properties of electrolyte. The solid electrolyte interface (SEI) layer growth is estimated for different cut-off voltages and charging current rates. The results show that the convective heat transfer coefficient as well as the porosity variation influences the SEI layer growth and the battery life significantly. The choice of an electrolyte decides the conductivity and partial molar concentration, which is found to have a strong influence on the capacity fade of the battery. The present battery model integrates all essential electro-chemical processes inside a lithium-ion battery under a strong implicit algorithm, proving a useful tool for computationally fast battery monitoring system.

  5. Differences in the dynamic properties of rain fade between temperate and tropical regions

    NASA Astrophysics Data System (ADS)

    Chodkaveekityada, Peeramed; Fukuchi, Hajime

    2017-03-01

    Understanding the dynamic properties of rain attenuation is important for designing effective attenuation mitigation methods, especially for Ka-band frequencies, which are particularly sensitive to degradation by rain attenuation. In this paper, the fade duration and fade slope are estimated using satellite data from Thailand and Japan, to investigate the characteristics of rain attenuation in tropical and temperate regions, respectively. For the tropical region, data from the Thaicom 2 and 3 satellites are used, and data from a Japanese communication satellite (CS) are used for the temperate area. Due to the different operating frequencies of the Thaicom 2 and 3 and the CS satellites, the scaling formula from the International Telecommunications Union (ITU) R P.618-12 is used to standardize the data. The Thaicom satellite frequencies of 12.57 (Thaicom 2) and 12.59 (Thaicom 3) GHz in the Ku-band are scaled up to 19.45 GHz, the operating frequency of the CS satellite. Finally, differences of the fade duration and fade slope property in tropical and temperate areas are found and it is confirmed that the rain attenuation effect in tropical areas is more serious than in temperate areas.

  6. Script Fading to Promote Unscripted Bids for Joint Attention in Children with Autism

    ERIC Educational Resources Information Center

    Pollard, Joy S.; Betz, Alison M.; Higbee, Thomas S.

    2012-01-01

    We used a script-fading procedure to teach 3 children with autism to initiate bids for joint attention. We examined the effects of (a) scripts, (b) varied adult scripted responses, and (c) multiple-exemplar script training on promoting unscripted language during bids for joint attention. All 3 participants learned to initiate bids for joint…

  7. HF radio signal fading and atmospheric radio noise measurements at low latitudes

    NASA Astrophysics Data System (ADS)

    Rao, S. Vijaya Bhaskara; Rao, T. Rama; Reddy, V. Gunasekhara; Lakshmi, D. R.; Veenadhari, B.; Dabas, R. S.; Ahmed, Iqbal; Gupta, M. M.; Reddy, B. M.

    2002-10-01

    Two HF broadcast transmissions, one originating from Sri Lanka (7.1°N, 79.9°E) at 11.800 MHz around the geomagnetic equator and the other from BBC, Masirah (20.6°N, 58.9°E), at 15.310 MHz several degrees north of the geomagnetic equator were monitored at Tirupati (13.5°N, 79.5°E) in southern India to compare the fading characteristics of the links. It is found that the link over the geomagnetic equator exhibits much higher fade rates as compared to the other link. The fade ranges also are, in general, higher for Sri Lanka. Fade allowances derived from these data do indicate that margins higher than those recommended by the International Telecommunication Union Radiocommunication Sector (ITU-R) need to be provided at these latitudes. The diurnal variation in the atmospheric radio noise (ARN), which sets a lower limit to the satisfactory reception of signal, over the Indian subcontinent is in total disagreement with the variations obtained at higher latitudes. This rather puzzling phenomenon has been interpreted as being due to path attenuation differentials between the LOS mode and the ionospheric mode from the lightning source because of significantly greater cloud height in the Indian region.

  8. The Use of Differential Reinforcement and Fading Time Away Caregiver Child with Separation Anxiety Disorder

    ERIC Educational Resources Information Center

    Flood, William A.; Wilder, David A.

    2004-01-01

    The use of differential reinforcement of other behavior (DRO) and fading of time away from year old boy with Separation Anxiety is illustrated. During baseline, the participant exhibited emotional behavior (i.e., crying, whining, asking to contact parents) as soon as his caregiver left the therapy room. During intervention, the participant was…

  9. Capacity fade study of lithium-ion batteries cycled at high discharge rates

    NASA Astrophysics Data System (ADS)

    Ning, Gang; Haran, Bala; Popov, Branko N.

    Capacity fade of Sony US 18650 Li-ion batteries cycled using different discharge rates was studied at ambient temperature. The capacity losses were estimated after 300 cycles at 2 C and 3 C discharge rates and were found to be 13.2 and 16.9% of the initial capacity, respectively. At 1 C discharge rate the capacity lost was only 9.5%. The cell cycled at high discharge rate (3 C) showed the largest internal resistance increase of 27.7% relative to the resistance of the fresh cells. The rate capability losses were proportional with the increase of discharge rates. Half-cell study and material and charge balances were used to quantify the capacity fade due to the losses of primary active material (Li +), the secondary active material (LiCoO 2/C)) and rate capability losses. It was found that carbon with 10.6% capacity loss after 300 cycles dominates the capacity fade of the whole cell at high discharge rates (3 C). A mechanism is proposed which explains the capacity fade at high discharge rates.

  10. Investigating Human Impact in the Environment with Faded Scaffolded Inquiry Supported by Technologies

    ERIC Educational Resources Information Center

    Campbell, Todd; Longhurst, Max; Duffy, Aaron M.; Wolf, Paul G.; Nagy, Robin

    2012-01-01

    Teaching science as inquiry is advocated in all national science education documents and by leading science and science teaching organizations. In addition to teaching science as inquiry, we recognize that learning experiences need to connect to students' lives. This article details how we use a sequence of faded scaffolded inquiry supported by…

  11. From Logos to Orthographic Symbols: A Multilevel Fading Computer Program for Teaching Nonverbal Children with Autism

    ERIC Educational Resources Information Center

    Hetzroni, Orit E.; Shalem, Uri

    2005-01-01

    This study investigated the use of a computer-based intervention for teaching orthographic symbols to children with autism. Through a structured seven-step fading procedure, children were taught to identify words from commercially available logos depicting food items. A multiple-probe design across participants was used to examine the effects of…

  12. Capacity Fade Analysis of Sulfur Cathodes in Lithium–Sulfur Batteries

    PubMed Central

    Yan, Jianhua; Liu, Xingbo

    2016-01-01

    Rechargeable lithium–sulfur (Li–S) batteries are receiving ever‐increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S‐cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li2S2 and Li2S, and poly‐shuttle effects. To determine these degradation factors, a comprehensive study of sulfur cathodes with different amounts of electrolytes is presented here. A survey of the fundamentals of Li–S chemistry with respect to capacity fade is first conducted; then, the parameters obtained through electrochemical performance and characterization are used to determine the key causes of capacity fade in Li–S batteries. It is confirmed that the formation and accumulation of nonconductive Li2S2/Li2S films on sulfur cathode surfaces are the major parameters contributing to the rapid capacity fade of Li–S batteries. PMID:27981001

  13. Fading test using the SAAD-POSL method for retrospective accidental dosimetry of building materials

    NASA Astrophysics Data System (ADS)

    Kim, M. J.; Lee, Y. J.; Lee, J. I.; Kim, J. L.; Hong, D. G.

    2015-11-01

    Fading test using the single aliquot additive dose method with pulsed optically stimulated luminescence (SAAD-POSL method) was applied to core-disc samples extracted from heated red brick, tile, roof-tile, and toilet porcelain after X-ray and beta irradiation. From thermoluminescence measurements of each material, the optimal preheat condition of the SAAD-POSL method was first determined as 170 °C for 10 s. Fading characteristics of core-disc samples of heated red brick obtained using the SAAD-POSL method were similar to those of quartz grains (90-250 μm) obtained using the SAR-OSL method, regardless of the differences in the sample and radiation type. Fading evaluations of the core-disc samples of these building materials two weeks after irradiation showed that the equivalent dose (ED) decreased between 5% and 42%. The results indicate that the fading characteristics will be able to contribute to a more accurate estimation of the ED value using the SAAD-POSL method.

  14. Investigating Human Impact in the Environment with Faded Scaffolded Inquiry Supported by Technologies

    ERIC Educational Resources Information Center

    Campbell, Todd; Longhurst, Max; Duffy, Aaron M.; Wolf, Paul G.; Nagy, Robin

    2012-01-01

    Teaching science as inquiry is advocated in all national science education documents and by leading science and science teaching organizations. In addition to teaching science as inquiry, we recognize that learning experiences need to connect to students' lives. This article details how we use a sequence of faded scaffolded inquiry supported by…

  15. Chebyshev-based technique for automated restoration of digital copies of faded photographic prints

    NASA Astrophysics Data System (ADS)

    Uchaev, Dmitry V.; Uchaev, Denis V.; Malinnikov, Vasiliy A.

    2017-01-01

    We present a technique for automated restoration of digital images obtained from faded photographic prints. The proposed defading technique uses our early proposed image contrast enhancement algorithm based on a contrast measure of images in the Chebyshev moment transform domain. Obtained experimental results demonstrate some advantages of the technique as compared to other widely used image enhancement methods.

  16. Storage fading of a commercial 18650 cell comprised with NMC/LMO cathode and graphite anode

    NASA Astrophysics Data System (ADS)

    Wu, She-huang; Lee, Po-Han

    2017-05-01

    In this study, the storage capacity fade of a commercial 18650 lithium ion cell comprised with a composite cathode of LiNi0.5Mn0.3Co0.2O2 (NMC) and Li1.1Mn1.9O4 (LMO) and graphite anode at various depths-of-discharge (DoDs) and temperatures have been investigated. The results manifest that the capacity fading is strongly affected by the storage temperature and becomes prominent as temperatures higher than 45 °C. Results of the incremental capacity analysis of the charging/discharging curves cycled at C/25 rate under 25 °C after cells been stored at various DoDs at 60 °C for various durations are used to reveal the factors of storage capacity fade of this commercial cell in company with the results of post-mortem studies on the electrodes harvested from the 12 month storage-aged cells with SEM, EDX, XPS, XRD, and electrode capacity retention study with those of a fresh commercial cell for comparison. The contributions of these factors are also estimated quantitatively. The losses of active electrode materials are the main reasons of the storage capacity fade of the commercial cell comprised with composite NMC/LMO cathode and graphite anode, while the loss of lithium inventory is less influential. The degradation of the electrodes and the loss the lithium inventory are strongly DoD dependent.

  17. Coverage area and fading time of surfactant-amended herbicidal droplets on cucurbitaceous leaves

    USDA-ARS?s Scientific Manuscript database

    Proper use of appropriate surfactants to control droplet behaviors on leaf surfaces is critical to improve herbicide application efficacy for controlling paddy melons. An esterified seed oil surfactant and a petroleum oil surfactant were investigated to modify spread areas and fading times of water ...

  18. Script Fading to Promote Unscripted Bids for Joint Attention in Children with Autism

    ERIC Educational Resources Information Center

    Pollard, Joy S.; Betz, Alison M.; Higbee, Thomas S.

    2012-01-01

    We used a script-fading procedure to teach 3 children with autism to initiate bids for joint attention. We examined the effects of (a) scripts, (b) varied adult scripted responses, and (c) multiple-exemplar script training on promoting unscripted language during bids for joint attention. All 3 participants learned to initiate bids for joint…

  19. Physical Theory of Voltage Fade in Lithium- and Manganese-Rich Transition Metal Oxides

    DOE PAGES

    Rinaldo, Steven G.; Gallagher, Kevin G.; Long, Brandon R.; ...

    2015-03-04

    Lithium- and manganese-rich (LMR) transition metal oxide cathodes are of interest for lithium-ion battery applications due to their increased energy density and decreased cost. However, the advantages in energy density and cost are offset, in part, due to the phenomena of voltage fade. Specifically, the voltage profiles (voltage as a function of capacity) of LMR cathodes transform from a high energy configuration to a lower energy configuration as they are repeatedly charged (Li removed) and discharged (Li inserted). Here, we propose a physical model of voltage fade that accounts for the emergence of a low voltage Li phase due tomore » the introduction of transition metal ion defects within a parent Li phase. The phenomenological model was re-cast in a general form and experimental LMR charge profiles were de-convoluted to extract the evolutionary behavior of various components of LMR capacitance profiles. Evolution of the voltage fade component was found to follow a universal growth curve with a maximal voltage fade capacity of ≈ 20% of the initial total capacity.« less

  20. Capacity Fade Analysis of Sulfur Cathodes in Lithium-Sulfur Batteries.

    PubMed

    Yan, Jianhua; Liu, Xingbo; Li, Bingyun

    2016-12-01

    Rechargeable lithium-sulfur (Li-S) batteries are receiving ever-increasing attention due to their high theoretical energy density and inexpensive raw sulfur materials. However, their rapid capacity fade has been one of the key barriers for their further improvement. It is well accepted that the major degradation mechanisms of S-cathodes include low electrical conductivity of S and sulfides, precipitation of nonconductive Li2S2 and Li2S, and poly-shuttle effects. To determine these degradation factors, a comprehensive study of sulfur cathodes with different amounts of electrolytes is presented here. A survey of the fundamentals of Li-S chemistry with respect to capacity fade is first conducted; then, the parameters obtained through electrochemical performance and characterization are used to determine the key causes of capacity fade in Li-S batteries. It is confirmed that the formation and accumulation of nonconductive Li2S2/Li2S films on sulfur cathode surfaces are the major parameters contributing to the rapid capacity fade of Li-S batteries.

  1. Mitigating Voltage Fade in Cathode Materials by Improving the Atomic Level Uniformity of Elemental Distribution

    SciTech Connect

    Zheng, Jianming; Gu, Meng; Genc, Arda; Xiao, Jie; Xu, Pinghong; Chen, Xilin; Zhu, Zihua; Zhao, Wenbo; Pullan, Lee; Wang, Chong M.; Zhang, Jiguang

    2014-04-07

    Li-rich and Mn-rich (LMR) layered structured materials are very promising cathodes for high-energy lithium-ion batteries. However, their fundamental structure and voltage fading mechanisms are far from being well understood. Here we report the first evidence on the reduced voltage and energy fade of LMR cathode by improving the atomic level spatial distribution of the chemical species. LMR cathode (Li[Li0.2Ni0.2M0.6]O2) prepared by co-precipitation and sol-gel methods are dominated by R-3m phase and show significant Ni-segregation at the surface of the particles. They exhibit large voltage-fade and fast capacity degradation. In contrast, LMR cathode prepared by hydrothermal assisted method is dominated by C2/m phase and minimal Ni-segregation. It also demonstrates much smaller voltage-fade and excellent capacity retention. The fundamental correlation between the atomic level spatial distribution of the chemical species and the functional stability of the materials found in this work also guide the design of other functional materials with enhanced stabilities.

  2. Channel capacity of next generation large scale MIMO systems

    NASA Astrophysics Data System (ADS)

    Alshammari, A.; Albdran, S.; Matin, M.

    2016-09-01

    Information rate that can be transferred over a given bandwidth is limited by the information theory. Capacity depends on many factors such as the signal to noise ratio (SNR), channel state information (CSI) and the spatial correlation in the propagation environment. It is very important to increase spectral efficiency in order to meet the growing demand for wireless services. Thus, Multiple input multiple output (MIMO) technology has been developed and applied in most of the wireless standards and it has been very successful in increasing capacity and reliability. As the demand is still increasing, attention now is shifting towards large scale multiple input multiple output (MIMO) which has a potential of bringing orders of magnitude of improvement in spectral and energy efficiency. It has been shown that users channels decorrelate after increasing the number of antennas. As a result, inter-user interference can be avoided since energy can be focused on precise directions. This paper investigates the limits of channel capacity for large scale MIMO. We study the relation between spectral efficiency and the number of antenna N. We use time division duplex (TDD) system in order to obtain CSI using training sequence in the uplink. The same CSI is used for the downlink because the channel is reciprocal. Spectral efficiency is measured for channel model that account for small scale fading while ignoring the effect of large scale fading. It is shown the spectral efficiency can be improved significantly when compared to single antenna systems in ideal circumstances.

  3. The Effects of Spatial Diversity and Imperfect Channel Estimation on Wideband MC-DS-CDMA and MC-CDMA

    DTIC Science & Technology

    2009-10-01

    input multiple-output (MIMO) system which employs Alamouti spacetime block coding at each sub-carrier frequency to achieve spatial diversity. We...number of pilot symbols per channel estimate. 13 N/A MC-DS-CDMA, MC-CDMA, Alamouti spacetime block coding, frequency-selective Rayleigh fading

  4. 2-Step Maximum Likelihood Channel Estimation for Multicode DS-CDMA with Frequency-Domain Equalization

    NASA Astrophysics Data System (ADS)

    Kojima, Yohei; Takeda, Kazuaki; Adachi, Fumiyuki

    Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can provide better downlink bit error rate (BER) performance of direct sequence code division multiple access (DS-CDMA) than the conventional rake combining in a frequency-selective fading channel. FDE requires accurate channel estimation. In this paper, we propose a new 2-step maximum likelihood channel estimation (MLCE) for DS-CDMA with FDE in a very slow frequency-selective fading environment. The 1st step uses the conventional pilot-assisted MMSE-CE and the 2nd step carries out the MLCE using decision feedback from the 1st step. The BER performance improvement achieved by 2-step MLCE over pilot assisted MMSE-CE is confirmed by computer simulation.

  5. DAPI-fluorescent fading: a problem in microscopy or a way to measure nuclear DNA content?

    NASA Astrophysics Data System (ADS)

    Gallardo-Escárate, Cristian; Álvarez-Borrego, Josué; Kober, V.; del Río-Portilla, Miguel Á.

    2006-01-01

    In observation by confocal or conventional fluorescence microscopy, the retardation of the lost in fluorescence, from highest signal of fluorescence to lowest intensity are important factors in order to obtain accurate images. This problem is very common in fluorochromes for nuclear DNA and especially for DAPI stain. The fluorescence of DAPI is rapidly lost when it is exposure to excitation by ultra violet (UV) light, and especially under optimal condition of observation. Although the fading process could be retardate by using of mounting medium with antifading solutions, the photochemical process underlying the fluorescence decay has not yet been fully explained. In addiction, neither relationship has been tested between the fluorescence fading and nuclear DNA content. However, the capacity of the DNA to absorb UV light is knows. In order to test this relationship we measured by means of image analysis the fluorescence intensity in several nuclei types during a fading period. The analysis was performed by an algorithm specifically built in MATLAB software. The relationship between nuclear DNA content and DAPI-fluorescence fading was found equal to 99%. This study demonstrates the feasibility for estimates genome size by quantification of fluorescence fading. In this context, the present method allows to measure nuclear DNA content in several medical applications (cancer, HIV, organ transplants, etc). Nowadays, for measuring DNA content, flow cytometry is widely used; however, with the flow cytometry method it is not possible to select a specific group of cells, such as from a specific region of a tumor. Moreover, the using of image analysis allows automatizing diagnostics procedures.

  6. Unexpected Voltage Fade in LMR-NMC Oxides Cycled below the “Activation” Plateau

    SciTech Connect

    Li, Yan; Bareno, Javier; Bettge, Martin; Abraham, Daniel P

    2015-01-01

    A common feature of lithium-excess layered oxides, nominally of composition xLi2MnO3•(1-x)LiMO2 (M = transition metal) is a high-voltage plateau (~4.5 V vs. Li/Li+) in their capacity-voltage profile during the first delithiation cycle. This plateau is believed to result from activation of the Li2MnO3 component, which makes additional lithium available for electrochemical cycling. However, oxides cycled beyond this activation plateau are known to display voltage fade which is a continuous reduction in their equilibrium potential. In this article we show that these oxides display gradual voltage fade even on electrochemical cycling in voltage ranges well below the activation plateau. The average fade is ~0.08 mV-cycle-1 for Li1.2Ni0.15Mn0.55Co0.1O2 vs. Li cells after 20 cycles in the 2–4.1 V range at 55°C; a ~54 mV voltage hysteresis, expressed as the difference in average cell voltage between charge and discharge cycles, is also observed. The voltage fade results from a gradual accumulation of local spinel environments in the crystal structure. Some of these spinel sites result from lithium deficiencies during oxide synthesis and are likely to be at the particle surfaces; other sites result from the migration of transition metal atoms in the partially-delithiated LiMO2 component into the lithium planes during electrochemical cycling. The observed rate of voltage fade depends on a combination of factors that includes the phase equilibrium between the layered and spinel components and the kinetics of transition metal migration.

  7. Intensification and fading of auroral arcs in the dusk-midnight sector of the polar cap

    SciTech Connect

    Wu, Q.; Rosenberg, T.J. ); Berkey, F.T. ); Eather, R.H. )

    1991-05-01

    Observations of the aurora from South Pole station (magnetic latitude = {minus}74.2{degree}) have been used to study the intensification and fading of polar arcs observed near the dusk meridian. Most of the cases examined have the following features in common: (1) a preexisting auroral form intensifies for about 10 min; (2) this activation is followed by a pronounced decrease of luminosity; (3) the auroral fade terminates after 30-60 min with the onset of intense aurora which sweeps rapidly overhead. The availability of all-sky camera, auroral electrojet (AE) index and interplanetary magnetic field (IMF) data for some of the cases enables the following additional characterizations of these events. The preexisting form is a Sun- or oval-aligned arc (or part of a multiple arc system) which disappears following the activation; equatorward drift of the arc (or system) accompanies the luminosity change. There is some evidence to suggest that the arc is poleward of the auroral oval. The brief intensification and/or the onset of fading occurs during the growth phase or near the start of the expansive phase of a substorm; termination of the fade is near the maximum in AE and is probably indicative of the beginning of the recovery phase of the substorm. For all three cases for which IMF data were available the onset of fading occurred 20-30 min after B{sub z} turned southward. Sun-aligned arcs are a common feature of the polar cap during northward B{sub z} but disappear during the increasingly disturbed conditions that accompany southward B{sub z}. The present results suggest that brief intensifications of southern hemisphere polar cap arcs near dusk may be linked in part to the sunward orientation of the IMF which favors enhanced electron fluxes in the southern lobe of the magnetotail.

  8. A brief review of ionospheric scintillation fading effects as observed in NASA satellite tracking and data acquisition networks.

    NASA Technical Reports Server (NTRS)

    Golden, T. S.

    1972-01-01

    Discussion of some results of the effects of ionospheric irregularities on NASA satellite tracking and data acquisition operations. Ionospheric scintillation fading produced by irregularities has been observed at 136 MHz (vhf), 400 MHz (uhf), 1550 MHz (L-band) and 1700 to 2200 MHz (S-band). Details of these observations are presented. Vhf scintillation effects are evident in both auroral and equatorial regions. Fading effects decrease with increasing radio frequency in the auroral region. The same frequency dependence for fading is not observed in the equatorial region. Although there is a seasonal and diurnal character to scintillation in the equatorial region, fading effects are usually more severe than in the auroral region for a given radio frequency. Space diversity measurements indicate that reasonable solutions for vhf telemetry problems are available for either region. Space diversity should provide a solution for microwave frequencies as well. Ionospheric fading amplitude for 1700 MHz is relatively small in the auroral region. In the equatorial region amplitude fading levels for 1550-MHz signals from ATS-5 are often much larger than expected. Observations of the Apollo Lunar Surface Experiment Package (ALSEP) operating at 2300 MHz observed near the geomagnetic equator show fading peaks in excess of 15 dB.

  9. TRP Channels

    NASA Astrophysics Data System (ADS)

    Voets, Thomas; Owsianik, Grzegorz; Nilius, Bernd

    The TRP superfamily represents a highly diverse group of cation-permeable ion channels related to the product of the Drosophila trp (transient receptor potential) gene. The cloning and characterization of members of this cation channel family has experienced a remarkable growth during the last decade, uncovering a wealth of information concerning the role of TRP channels in a variety of cell types, tissues, and species. Initially, TRP channels were mainly considered as phospholipase C (PLC)-dependent and/or store-operated Ca2+-permeable cation channels. More recent research has highlighted the sensitivity of TRP channels to a broad array of chemical and physical stimuli, allowing them to function as dedicated biological sensors involved in processes ranging from vision to taste, tactile sensation, and hearing. Moreover, the tailored selectivity of certain TRP channels enables them to play key roles in the cellular uptake and/or transepithelial transport of Ca2+, Mg2+, and trace metal ions. In this chapter we give a brief overview of the TRP channel superfamily followed by a survey of current knowledge concerning their structure and activation mechanisms.

  10. Coded Modulations for Mobile Satellite Communication Channels

    NASA Astrophysics Data System (ADS)

    Rhee, Dojun

    1995-01-01

    The mobile satellite (MSAT) channel is subject to multipath fading, shadowing, Doppler frequency shift, and adjacent channel interference (ACI). Therefore, transmitted signals face severe amplitude and phase distortions. This dissertation investigates various high performance and low decoding complexity coded modulation schemes for reliable voice and data transmissions over the shadowed mobile satellite channel and the Rayleigh fading channel. The dissertation consists of four parts. The first part presents a systematic technique for constructing MPSK trellis coded modulation (TCM) codes for voice transmission over the MSAT channel. The multilevel coding method is used for constructing TCM codes using convolutional codes with good free branch distances as the component codes or using both convolutional and block codes as the component codes. Simulation results show that these codes achieve good coding gains over the uncoded reference system and outperform existing TCM codes with the same decoding complexity. In the second part, using the multilevel coding method, multilevel block coded modulation (BCM) codes are constructed for voice transmission over the MSAT channel. Even though BCM is generally less power efficient than TCM for AWGN channels, BCM has a great potential to compete with TCM in the MSAT channel because of its shorter decoding depth and hence more effective interleaving. Binary Reed -Muller (RM) codes of length up to 32 are used as component codes. Simulation results show that these codes achieve good coding gains over the uncoded reference system and outperform TCM codes with the same decoding complexity. In the third part, a simple and systematic technique for constructing multilevel concatenated BCM schemes for data transmission over the shadowed MSAT channel and the Rayleigh fading channel is presented. These schemes are designed to achieve high-performance or large coding gain with reduced decoding complexity. Construction is based on a

  11. Rippley Channel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    18 September 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a narrow channel on the upper east flank of the martian volcano, Hadriaca Patera. Because it is located on a volcano, most likely this channel was formed by lava, perhaps as a lava tube at which the thin roof later collapsed. Large ripples of windblown sediment now occur on the channel floor; their crests are generally perpendicular to the channel walls, suggesting that winds blow up and down through this channel.

    Location near: 30.5oS, 266.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Autumn

  12. Rippley Channel

    NASA Technical Reports Server (NTRS)

    2006-01-01

    18 September 2006 This Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) image shows a narrow channel on the upper east flank of the martian volcano, Hadriaca Patera. Because it is located on a volcano, most likely this channel was formed by lava, perhaps as a lava tube at which the thin roof later collapsed. Large ripples of windblown sediment now occur on the channel floor; their crests are generally perpendicular to the channel walls, suggesting that winds blow up and down through this channel.

    Location near: 30.5oS, 266.2oW Image width: 3 km (1.9 mi) Illumination from: upper left Season: Southern Autumn

  13. Protection of oxidative hair color fading from shampoo washing by hydrophobically modified cationic polymers.

    PubMed

    Zhou, Y; Foltis, L; Moore, D J; Rigoletto, R

    2009-01-01

    The fading of oxidative color in hair as a result of daily shampoo washing activities has become a common problem and a source of frequent complaints by consumers. The fading occurs primarily through hair dye solubility in water. One aspect of the current study investigates the physical and chemical factors that influence hair color fading during the washing process. This is accomplished by testing hair dye dissolution in water from dyed hair samples with variation of surfactant type, pH, and hair type. Furthermore, a new approach to preventing color fading is developed aiming to provide an effective barrier function for hair dye from dissolving into water. The preliminary investigation of a series of polymers with various functional groups indicates that polymers with hydrophobically modified and cationic functionalities are most effective in preventing hair dye dissolution in water. It is also evident that a synergistic effect of the polymer's hydrophobic moieties and cationic charges are important on hair color protection during shampoo washing processes. A primary example of a polymer within this category is a cationic terpolymer of vinylpyrrolidone, dimethylaminopropyl methacrylamide, and methacryloylaminopropyl lauryldimonium chloride (INCI: Polyquaternium-55). The color protection benefit of this polymer is evaluated using newly developed methodologies for evaluating hair color changes, such as hair color fading tests through multiple shampoo washes with mannequin heads and hair tresses, both derived from human hair, colorimetry, and quantitative digital image analysis. In addition, new infrared spectroscopic imaging techniques are used to detect the hair dye deposition behavior inside hair fibers both with and without the color protection treatment. Both visual and instrumental measurement results indicate that Polyquaternium-55 provides a high level of color protection when formulated in a hair color protection regimen with up to 50% color protection. This

  14. Channel measurement decoding for troposcatter communications

    NASA Astrophysics Data System (ADS)

    Chase, D.

    1981-02-01

    The object of this program is to theoretically investigate and experimentally verify the performance improvement possible by the use of channel-measurement (soft-decision) information when decoding an interleaved (24,12) Golay code. The experimental results obtained during this effort indicate that under certain conditions, such as pulse jamming, significant gains can be achieved by the use of channel measurement decoding. For typical multipath profiles, coding gains in the 5 to 10 dB range have been achieved by fairly simple binary decoding techniques. Unfortunately, the predicted theoretical gains due to the use of channel measurement decoding have not been achieved by the experimental results. While channel measurement decoding did offer a 3-dB gain over binary decoding for flat fading, this gain is well below the theoretical prediction of 7.2 dB. The discrepancy between the theoretical and experimental results is still an open question which may be resolved by future work in this area. Nevertheless, in the presence of pulse jamming, channel measurement decoding doubled the effective pulse duration that can be handled by the Golay code. This result is in agreement with theory and a strong indication of the importance of optimum decoding techniques in an ECCM environment.

  15. Reduced Complexity in Antenna Selection for Polarized MIMO System with SVD for the Practical MIMO Communication Channel Environment

    NASA Astrophysics Data System (ADS)

    Sann Maw, Maung; Sasase, Iwao

    In the conventional multi-input multi-output (MIMO) communication systems, most of the antenna selection methods considered are suitable only for spatially separated uni-polarized system under Rayleigh fading channel in non-line of sight (NLOS) condition. There have a few antenna selection schemes for the cross-polarized system in LOS condition and Ricean fading channel, and no antenna selection scheme for the MIMO channel with both LOS and NLOS. In the practical MIMO channel case, influence of LOS and NLOS conditions in the channel can vary from time to time according to the channel parameters and user movement in the system. Based on these influences and channel condition, uni-polarized system may outperform a cross-polarized. Thus, we should consider this kind of practical MIMO channel environment when developing the antenna selection scheme. Moreover, no research work has been done on reducing the complexity of antenna selection for this kind of practical MIMO channel environment. In this paper, reduced complexity in antenna selection is proposed to give the higher throughput in the practical MIMO channel environment. In the proposed scheme, suitable polarized antennas are selected based on the calculation of singular value decomposition (SVD) of channel matrix and then adaptive bit loading is applied. Simulation results show that throughput of the system can be improved under the constraint of target BER and total transmit power of the MIMO system.

  16. Experimental and theoretical studies of perceptible color fading of decorative paints consisting of mixed pigments

    NASA Astrophysics Data System (ADS)

    Auger, Jean-Claude; McLoughlin, Daragh

    2017-01-01

    We study the color fading of paints films composed of mixtures of white rutile titanium dioxide and yellow arylide pigments dispersed in two polymer binders at different volume concentrations. The samples were exposed to ultraviolet radiations in an accelerated weathering tester during three weeks. The measured patterns in color variations appeared to be independent of the chemistry of the binders. We then developed a theoretical framework, based on the Radiative transfer Equation of light and the One Particle T-Matrix formalism to simulate the color fading process. The loss of color is correlated to the progressive decrease of the original colored pigment volume-filling fraction as the destructive UV radiations penetrate deeper into the films. The calculated patterns of color variations of paints film composed by mixtures of white pigments with yellow Cadmium Sulfate (CdS) and red Cerium Sulfide (Ce2S3) pigments showed the same trend as that seen experimentally.

  17. Disclosing Whole Reaction Pathways of Photochromic 3H-Naphthopyrans with Fast Color Fading.

    PubMed

    Brazevic, Sabina; Sliwa, Michel; Kobayashi, Yoichi; Abe, Jiro; Burdzinski, Gotard

    2017-03-02

    Instantaneous coloration with large absorbance and quick color fading in the dark are desired properties for thermally reversible photochromic compounds. In the case of naphthopyran derivatives, which have been employed to commercial ophthalmic lenses, the quick color fading has been recently achieved by suppression of the generation of the transoid-trans (TT) form by steric hindrance of bulky substituents. However, there are still open questions whether the steric hindrance decreases the photochromic reaction efficiency, which is a crucial problem for industrial applications. Herein, we apply a wide range of electronic and vibrational time-resolved spectroscopies and reveal that the photochromic reaction yields of the naphthopyrans with bulky substituents are almost comparable (∼0.7) to that of nonsubstituted naphthopyran. The suppression of the formation of the TT form and the effect of solvent polarity on the photodynamics are systematically investigated. These findings are important for fundamental photochemistry and developing naphthopyran-based optimal photofunctional materials.

  18. Fade-resistant photochromic reactions in a self-healable polymer.

    PubMed

    Saito, Mitsunori; Nishimura, Tatsuya; Hamazaki, Takamasa

    2015-10-05

    Molecular diffusion in a polymer matrix was studied to prevent degradation of photochromic reactions during repeated coloration-decoloration processes. Photochromic diarylethene was dispersed in polydimethylsiloxane (cured polymer), since it promoted exchange of damaged and fresh molecules owing to high diffusivity. The diffusion coefficient was evaluated by measuring a distribution of dye molecules that were colored within a narrow laser beam path. Temporal change of the distribution fitted well to theoretical curves that were drawn according to the 2-D solutions of Fick's equation. The experimental results indicated a fifteen-fold enhancement of the diffusion coefficient (0.0015 mm(2)/s) when the polymer was swollen with toluene. Fading of this photochromic polymer was examined by repeating alternative irradiation of violet and green laser beams. Although a non-swollen polymer faded seriously within 1,000 photochromic cycles, a swollen polymer exhibited an excellent photochromic function even after 30,000 cycles.

  19. The role of mechanically induced separator creep in lithium-ion battery capacity fade

    NASA Astrophysics Data System (ADS)

    Peabody, Christina; Arnold, Craig B.

    2011-10-01

    Lithium-ion batteries are well-known to be plagued by a gradual loss of capacity and power which occur regardless of use and can be limiting factors in the development of emerging energy technologies. Here we show that separator deformation in response to mechanical stimuli that arise under normal operation and storage conditions, such as external stresses on the battery stack or electrode expansion associated with lithium insertion/deinsertion, leads to increased internal resistance and significant capacity fade. We find this mechanically induced capacity fade to be a result of viscoelastic creep in the electrochemically inactive separator which reduces ion transport via a pore closure mechanism. By applying compressive stress on the battery structure we are able to accelerate aging studies and identify this unexpected, but important and fundamental link between mechanical properties and electrochemical performance. Furthermore, by making simple modifications to the electrode structure or separator properties, these effects can be mitigated, providing a pathway for improved battery performance.

  20. The Effects of Reinforcer Pairing and Fading on Preschoolers' Snack Selections

    PubMed Central

    Solberg, Katherine M; Hanley, Gregory P; Layer, Stacy A; Ingvarsson, Einar T

    2007-01-01

    The effects of reinforcement pairing and fading on preschoolers' snack selections were evaluated in a multiple baseline design. Baseline preferences for snack options were assessed via repeated paired-item preference assessments. Edible, social, and activity-based reinforcers were then exclusively paired with a less preferred snack option. Once the snack paired with reinforcement was selected most frequently, the three types of reinforcement were systematically faded. Frequent selections of the previously less preferred snack option were produced with paired reinforcement, but were disrupted for all children as the paired reinforcement was reduced to low levels. These data showed that paired reinforcement was initially effective in increasing preference for the originally less preferred snack options, but more permanent changes in the value of the snack options were not achieved. Conditions for producing persistent changes in children's snack choices are discussed. PMID:18189095

  1. Systems, methods and computer-readable media for modeling cell performance fade of rechargeable electrochemical devices

    DOEpatents

    Gering, Kevin L

    2013-08-27

    A system includes an electrochemical cell, monitoring hardware, and a computing system. The monitoring hardware periodically samples performance characteristics of the electrochemical cell. The computing system determines cell information from the performance characteristics of the electrochemical cell. The computing system also develops a mechanistic level model of the electrochemical cell to determine performance fade characteristics of the electrochemical cell and analyzing the mechanistic level model to estimate performance fade characteristics over aging of a similar electrochemical cell. The mechanistic level model uses first constant-current pulses applied to the electrochemical cell at a first aging period and at three or more current values bracketing a first exchange current density. The mechanistic level model also is based on second constant-current pulses applied to the electrochemical cell at a second aging period and at three or more current values bracketing the second exchange current density.

  2. A comparison between characteristics of various laser-based denim fading processes

    NASA Astrophysics Data System (ADS)

    Ortiz-Morales, Martín.; Poterasu, Marian; Acosta-Ortiz, Sofia E.; Compean, Isaac; Hernandez-Alvarado, Ma. Rosa

    2003-01-01

    Our experiments show that the laser fading process has similar, even better results, in some cases, than the conventional technologies of indigo-dyed denim. Using the beams from Nd:YAG laser (1064 nm and its second harmonic 532 nm), CTH:YAG laser (2.09 μm), CO 2 laser (10.6 μm) and various laser beam parameters we found the optimum fluence and power density in order to obtain a similar fading appearance like the one obtained by conventional processes. The purpose of this work was to determine the effectiveness of laser-based technologies and to measure the wear characteristics of the processed textile like colorfastness, strength resistance, tearing strength, and dimensional changes.

  3. Amplitude fading of simultaneous transionospheric L-band and VHF signals received at the geomagnetic equator

    NASA Technical Reports Server (NTRS)

    Sessions, W. B.

    1972-01-01

    At Ancon, Peru, simultaneous observations of 1550-MHz and 136-MHz signals from the ATS 5 and Intelsat-1 spacecraft showed ionospheric fading as great as 27 db at 136 MHz and 6 db at 1550 MHZ. The observations were made on 48 days during the 1970 autumnal and 1971 vernal equinox periods. Comparison of the two frequencies, in respect to rates and depths of fades, is made. Statistical distributions of the received signal levels during ionospheric scintillation occurrences are presented which may be of use to communications system engineers with operational requirements in the equatorial regions. The distributions show that during expected periods of scintillation, the L band signal typically falls 1.1 db below the median for 1.0 percent of the time, and the VHF signal falls 11.5 db below the median for 1.0 percent of the time.

  4. Experimental Validation of Stochastic Wireless Urban Channel Model: Estimation and Prediction

    SciTech Connect

    Kuruganti, Phani Teja; Ma, Xiao; Djouadi, Seddik M

    2012-01-01

    Stochastic differential equations (SDE) can be used to describe the time-varying nature of wireless channels. This paper validates a long-term fading channel model for estimation and prediction from solely using measured received signal strength measurements. Such channel models can be used for optimizing wireless networks deployed for industrial automation, public access, and communication. This paper uses two different sets of received signal measurement data to estimate an predict the signal strength based on past measurements. The realworld performance of the estimation and prediction algorithm is demonstrated.

  5. Power Scaling of Uplink Massive MIMO Systems With Arbitrary-Rank Channel Means

    NASA Astrophysics Data System (ADS)

    Zhang, Qi; Jin, Shi; Wong, Kai-Kit; Zhu, Hongbo; Matthaiou, Michail

    2014-10-01

    This paper investigates the uplink achievable rates of massive multiple-input multiple-output (MIMO) antenna systems in Ricean fading channels, using maximal-ratio combining (MRC) and zero-forcing (ZF) receivers, assuming perfect and imperfect channel state information (CSI). In contrast to previous relevant works, the fast fading MIMO channel matrix is assumed to have an arbitrary-rank deterministic component as well as a Rayleigh-distributed random component. We derive tractable expressions for the achievable uplink rate in the large-antenna limit, along with approximating results that hold for any finite number of antennas. Based on these analytical results, we obtain the scaling law that the users' transmit power should satisfy, while maintaining a desirable quality of service. In particular, it is found that regardless of the Ricean $K$-factor, in the case of perfect CSI, the approximations converge to the same constant value as the exact results, as the number of base station antennas, $M$, grows large, while the transmit power of each user can be scaled down proportionally to $1/M$. If CSI is estimated with uncertainty, the same result holds true but only when the Ricean $K$-factor is non-zero. Otherwise, if the channel experiences Rayleigh fading, we can only cut the transmit power of each user proportionally to $1/\\sqrt M$. In addition, we show that with an increasing Ricean $K$-factor, the uplink rates will converge to fixed values for both MRC and ZF receivers.

  6. Study on capacity fading of 18650 type LiCoO2-based lithium ion batteries during storage

    NASA Astrophysics Data System (ADS)

    Zheng, Liu-Qun; Li, Shu-Jun; Zhang, Deng-Feng; Lin, Hai-Jun; Miao, Yan-Yue; Chen, Shou-Wei; Liu, Hai-Bin

    2015-05-01

    The capacity fading of LiCoO2-based lithium ion batteries during storage was studied. The discharging capacity fading is attributed to the decreasing in the charging capacity at the constant current stage. After 300 cycles, the ratio of the charging capacity of batteries at the constant current stage to the total charging capacity decreases from 87.2 to 71.2%. The bounce-back voltage is closely related to the internal resistance when the battery is discharged to the cut-off voltage of 3.0 V. Batteries were disassembled in the fully discharged state, and then a assembled again in order to deeply understand the causes of the capacity fading of the cathode and anode. The results shows that the SEI film thickness increasing, breaking or repairing process at the anode could be responsible for the high bounce-back voltage, the increase of the internal resistance and the capacity fading during storage.

  7. Advanced Communications Technology Satellite (ACTS) Fade Compensation Protocol Impact on Very Small-Aperture Terminal Bit Error Rate Performance

    NASA Technical Reports Server (NTRS)

    Cox, Christina B.; Coney, Thom A.

    1999-01-01

    The Advanced Communications Technology Satellite (ACTS) communications system operates at Ka band. ACTS uses an adaptive rain fade compensation protocol to reduce the impact of signal attenuation resulting from propagation effects. The purpose of this paper is to present the results of an analysis characterizing the improvement in VSAT performance provided by this protocol. The metric for performance is VSAT bit error rate (BER) availability. The acceptable availability defined by communication system design specifications is 99.5% for a BER of 5E-7 or better. VSAT BER availabilities with and without rain fade compensation are presented. A comparison shows the improvement in BER availability realized with rain fade compensation. Results are presented for an eight-month period and for 24 months spread over a three-year period. The two time periods represent two different configurations of the fade compensation protocol. Index Terms-Adaptive coding, attenuation, propagation, rain, satellite communication, satellites.

  8. Using audio script fading and multiple-exemplar training to increase vocal interactions in children with autism.

    PubMed

    Garcia-Albea, Elena; Reeve, Sharon A; Brothers, Kevin J; Reeve, Kenneth F

    2014-01-01

    Script-fading procedures have been shown to be effective for teaching children with autism to initiate and participate in social interactions without vocal prompts from adults. In previous script and script-fading research, however, there has been no demonstration of a generalized repertoire of vocal interactions under the control of naturally occurring relevant stimuli. In this study, 4 boys with autism were taught to initiate a conversation in the presence of toys through the use of a script and script-fading procedure. Training with multiple categories and exemplars of toys was used to increase the likelihood of generalization of vocal interactions across novel toys. A multiple-probe design across participants was used to assess the effects of these procedures. The intervention successfully brought interactions by children with autism under the control of relevant stimuli in the environment. Future research pertaining to the specific implementation of these procedures (e.g., fading, script placement, participant characteristics) is discussed.

  9. Advanced Communications Technology Satellite (ACTS) Fade Compensation Protocol Impact on Very Small-Aperture Terminal Bit Error Rate Performance

    NASA Technical Reports Server (NTRS)

    Cox, Christina B.; Coney, Thom A.

    1999-01-01

    The Advanced Communications Technology Satellite (ACTS) communications system operates at Ka band. ACTS uses an adaptive rain fade compensation protocol to reduce the impact of signal attenuation resulting from propagation effects. The purpose of this paper is to present the results of an analysis characterizing the improvement in VSAT performance provided by this protocol. The metric for performance is VSAT bit error rate (BER) availability. The acceptable availability defined by communication system design specifications is 99.5% for a BER of 5E-7 or better. VSAT BER availabilities with and without rain fade compensation are presented. A comparison shows the improvement in BER availability realized with rain fade compensation. Results are presented for an eight-month period and for 24 months spread over a three-year period. The two time periods represent two different configurations of the fade compensation protocol. Index Terms-Adaptive coding, attenuation, propagation, rain, satellite communication, satellites.

  10. A reverberation chamber for rodents' exposure to wideband radiofrequency electromagnetic fields with different small-scale fading distributions.

    PubMed

    Li, Congsheng; Yang, Lei; Lu, Bingsong; Xie, Yi; Wu, Tongning

    2016-01-01

    A reverberation chamber (RC) is realized for the rodents' in vivo exposure to electromagnetic fields (EMFs) with various small-scale fading characteristics. Its performance is evaluated to ensure the exposure experiments from 0.85 to 2.60 GHz. By different configurations, line-of-sight and non-line-of-sight exposures can be established. The measured electric field in the RC is analyzed to determine its statistical distribution. We accordingly reconstruct the EMF environment by numerical methods. Simulations are carried to compare the dosimetric variability due to different small-scale fading characteristics. It demonstrates that the surveyed fading distribution will not change the specific absorption rate in the rats. The possibility to reproduce the realistic multi-reflective EMF environment by adjusting the structures of the RC is discussed. It is the first reported in vivo exposure system aiming to provide the EMF exposure with different small-scale fading distributions.

  11. All known hot RCB stars are fading fast over the last century

    NASA Astrophysics Data System (ADS)

    Schaefer, Bradley E.

    2016-08-01

    The R Coronae Borealis (RCB) stars are cool supergiants that display irregular and deep dips in their light curves, caused by dust formation. There are four known hot RCB stars (DY Cen, MV Sgr, V348 Sgr, and HV 2671), with surface temperatures of 15 000-25 000 K, and prior work has suggested that three of these have secular fading in brightness. I have tested this result by measuring century-long light curves in the Johnson B band with modern comparison star magnitudes, and I have extended this by measuring many magnitudes over a wide time range as well as for the fourth hot RCB star. In all four cases, the B band magnitude of the maximum light is now fast fading. The fading rates (in units of magnitudes per century) are 2.5 for DY Cen after 1960, 1.3 for MV Sgr, 1.3 for V348 Sgr, and 0.7 for HV 2671. This secular fading is caused by the expected evolution of the star across the top of the Hertzsprung-Russell (HR) diagram at constant luminosity, as the temperature rises and the bolometric correction changes. For DY Cen, the brightness at maximum light is rising from 1906 to 1932, and this is caused by the temperature increase from near 5800 to 7500 K. Before 1934, DY Cen had frequent dust dips, while after 1934 there are zero dust dips, so there is some apparent connection between the rising temperature and the formation of the dust. Thus, we have watched DY Cen evolve from an ordinary RCB star up to a hot RCB star and now appearing as an extreme helium star, all in under one century.

  12. Design of a 40/50 GHz satellite ground station for fade mitigation experiments

    NASA Astrophysics Data System (ADS)

    Koudelka, O.; Schmidt, M.; Ebert, J.

    2013-05-01

    Due to the increasing demand in satellite capacity, driven by applications such as high-definition television (HDTV), 3D-TV and interactive broadband services, higher frequency bands will have to be exploited. The capacity on Ku-band is already becoming scarce and Ka-band systems are more commonly used. It can be expected that 40 and 50 GHz (Q and V band) will have to be used in the future. At these frequencies the wave propagation effects have a significant impact on the performance. The traditional approach of implementing large fade margins in the system design is not suitable as it leads to expensive ground terminals. Fade mitigation by adaptive coding and modulation (ACM) is a cost-efficient method. To investigate the Q/V-band for future commercial exploitation, ESA's ALPHASAT satellite will provide experimental payloads for communications and wave propagation experiments. In Graz a Q/V-band ground station is currently under development. It will be equipped with a 3 m tracking antenna, a 50 W Klystron amplifier and a 290 K LNA. Fade mitigation experiments will be conducted, initially using DVB-S2 modems which allow to vary the modulation scheme, the Forward Error Correction code and the symbol rate under control of the ACM computer. In addition, uplink power control can be combined with the ACM methods. A specially developed signal analyser provides precise measurement of the signal/noise ratio. In addition, propagation data will be available from a beacon receiver, also developed by Joanneum Research. Important goals of the experiment are to investigate the reliability of links under realistic operating conditions using ACM and to develop efficient ACM and signal/noise ratio measurement algorithms which can be later implemented in optimised modems for Q/V-band. The paper describes the ground station design and addresses the planned fade mitigation experiments.

  13. Apparatus and Method for Elimination of Polarization-Induced Fading in Fiber-optic Sensor System

    NASA Technical Reports Server (NTRS)

    Chan, Hon Man (Inventor); Parker, Jr., Allen R. (Inventor)

    2015-01-01

    The invention is an apparatus and method of eliminating polarization-induced fading in interferometric fiber-optic sensor system having a wavelength-swept laser optical signal. The interferometric return signal from the sensor arms are combined and provided to a multi-optical path detector assembly and ultimately to a data acquisition and processing unit by way of a switch that is time synchronized with the laser scan sweep cycle.

  14. Fade Analysis of ORCA Data Beam at NTTR and Pax River

    DTIC Science & Technology

    2010-08-01

    FINAL REPORT: FADE ANALYSIS OF ORCA DATA BEAM AT NTTR AND PAX RIVER UCF DARPA Project ID: 16296051 HR0011-08-C-0111 R. Crabbs, D. Wayne, T ...1 , 1 , 1 1 ~ 30 40 50 60 Range (km) T ’ I — T 1 , — . | 0 PAX River...losses. Thus, the mean PIF is calculated from the relation PIF = rop,PIB/Aiiy ’ 4A SR t - (2) where SRf is the Strehl ratio associated with the

  15. Capacity Fade Analysis and Model Based Optimization of Lithium-ion Batteries

    NASA Astrophysics Data System (ADS)

    Ramadesigan, Venkatasailanathan

    Electrochemical power sources have had significant improvements in design, economy, and operating range and are expected to play a vital role in the future in a wide range of applications. The lithium-ion battery is an ideal candidate for a wide variety of applications due to its high energy/power density and operating voltage. Some limitations of existing lithium-ion battery technology include underutilization, stress-induced material damage, capacity fade, and the potential for thermal runaway. This dissertation contributes to the efforts in the modeling, simulation and optimization of lithium-ion batteries and their use in the design of better batteries for the future. While physics-based models have been widely developed and studied for these systems, the rigorous models have not been employed for parameter estimation or dynamic optimization of operating conditions. The first chapter discusses a systems engineering based approach to illustrate different critical issues possible ways to overcome them using modeling, simulation and optimization of lithium-ion batteries. The chapters 2-5, explain some of these ways to facilitate (i) capacity fade analysis of Li-ion batteries using different approaches for modeling capacity fade in lithium-ion batteries, (ii) model based optimal design in Li-ion batteries and (iii) optimum operating conditions (current profile) for lithium-ion batteries based on dynamic optimization techniques. The major outcomes of this thesis will be, (i) comparison of different types of modeling efforts that will help predict and understand capacity fade in lithium-ion batteries that will help design better batteries for the future, (ii) a methodology for the optimal design of next-generation porous electrodes for lithium-ion batteries, with spatially graded porosity distributions with improved energy efficiency and battery lifetime and (iii) optimized operating conditions of batteries for high energy and utilization efficiency, safer operation

  16. Transcriptome Analysis Reveals Candidate Genes Related to Color Fading of ‘Red Bartlett’ (Pyrus communis L.)

    PubMed Central

    Wang, Zhigang; Du, Hong; Zhai, Rui; Song, Linyan; Ma, Fengwang; Xu, Lingfei

    2017-01-01

    The red color of fruit is an attractive plant trait for consumers. Plants with color-faded fruit have a lower commercial value, such as ‘Red Bartlett’ pears (Pyrus communis L.) that have dark-red fruit in the early stages of fruit development that subsequently fade to red-green at maturity. To identify the reason for color fading, we first analyzed the anthocyanin content of peel from ‘Red Bartlett,’ which displays the color fading phenomenon, and ‘Starkrimson,’ which has no color fading. Results showed that the anthocyanin content of ‘Red Bartlett’ peel decreased significantly late in fruit development, while in ‘Starkrimson’ there was no significant decrease. Next, RNA-Sequencing was used to identify 947 differentially expressed genes (DEGs) between ‘Red Bartlett’ and ‘Starkrimson.’ Among them, 471 genes were upregulated and 476 genes were downregulated in ‘Red Bartlett’ at the late development stage relative to ‘Starkrimson.’ During ‘Red Bartlett’ color fading, the structural gene LDOX and six GST family genes were downregulated, while FLS, LAC, POD, and five light-responding genes were significantly upregulated. Additionally, 45 genes encoding transcription factors MYB, bHLH, WRKY, NAC, ERF, and zinc finger were identified among 947 DEGs. Changes in the expression of these genes may be responsible for the decrease in anthocyanin accumulation in ‘Red Bartlett’ fruit. Taken together, this study demonstrated that color fading of ‘Red Bartlett’ was closely linked to reduced anthocyanin biosynthesis, increased anthocyanin degradation and suppression of anthocyanin transport. It also provided novel evidence for the involvement of light signals in the color fading of red-skinned pears. PMID:28408914

  17. Fade Dynamics and Its Evolution: The Other Part of the Acts Rain Prediction Model

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1997-01-01

    The inception of the Advanced Communication Technology Satellite (ACTS) Project has required as similarly advanced statistical mathematical modeling formalism to describe the behavior of the 30/20 GHz links emanating to and from the earth terminals through the deleterious effects of the earth's atmosphere. The resulting ACTS Rain Attenuation Prediction Model has been thoroughly described in [Manning, 1990]. In the present paper, the basic rudiments of this model will be reviewed; Section 1 covers the static or time-independent portion of the model and Section 2 covers the dynamic of time-dependent portion. The results of Section 2 are then applied to a new approximate solution of the famous problem of the time duration tau of a fade of random process below some threshold. This is known as the fade duration. The new approximate solution was published in Russian [Denisenko] and, unfortunately, was never published into English. Hence, this work is restated following [Denisenko] in Section 3 which is immediately applied to the random rain fade process. The results for all five ACTS propagation sites as well as Tampa, FL are then given.

  18. Fade Dynamics and its Evolution: The Other Part of the ACTS Rain Prediction Model

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1997-01-01

    The inception of the Advanced Communication Technology Satellite (ACTS) Project has required a similarly advanced statistical mathematical modeling formalism to describe the behavior of the 30/20 GHz links emanating to and from the earth terminals through the deleterious effects of the earth's atmosphere. The resulting ACTS Rain Attenuation Prediction Model has been thoroughly described in (Manning). In the present paper, the basic rudiments of this model will be reviewed; Section 1 covers the static or time-independent portion of the model and Section 2 covers the dynamic or time-dependent portion. The results of Section 2 are then applied to a new approximate solution of the famous problem of the time duration tau of a fade of a random process below some threshold. This is known as the fade duration. The new approximate solution was published in Russian (Denisenko) and, unfortunately, was never published into English. Hence, this work is restated following (Denisenko) in Section 3 which is immediately applied to the random rain fade process. The results for all five ACTS propagation sites as well as Tampa, FL are then given.

  19. Capacity fade in thin-film lithium-V{sub 2}O{sub 5} cells

    SciTech Connect

    Kwak, B.S.; Bates, J.B.; Hart, F.X.

    1996-01-01

    Capacity fade with cycling of thin-film rechargeable Li/Lipon/V{sub 2}O{sub 5} cells, formed as electrochromic mirrors with ITO current collectors, has been studied by optical and impedance spectroscopy and extended cycling experiments. An irreversible decrease in the reflectivity observed in cells cycled between 3.6 to 1.5 V was attributed to a roughening of the Li surface at the Li-Lipon interface. Although the consequent loss of contact area might be the source of increasing cell resistance responsible for the capacity fade, this possibility was ruled out because of the large variability observed in the cycling performance of cells with different cathodes and the constancy of the reflectivity when the cutoff voltage was increased to 2.5 V. It was concluded from the analysis of impedance data that a decrease in Li{sup +} ion diffusivity in the cathode and the cathode-electrolyte interface with cycling is the major cause of capacity fade.

  20. Capacity fade of Sony 18650 cells cycled at elevated temperatures. Part I. Cycling performance

    NASA Astrophysics Data System (ADS)

    Ramadass, P.; Haran, Bala; White, Ralph; Popov, Branko N.

    The capacity fade of Sony 18650 Li-ion cells increases with increase in temperature. After 800 cycles, the cells cycled at RT and 45 °C showed a capacity fade of 30 and 36%, respectively. The cell cycled at 55 °C showed a capacity loss of about 70% after 490 cycles. The rate capability of the cells continues to decrease with cycling. Impedance measurements showed an overall increase in the cell resistance with cycling and temperature. Impedance studies of the electrode materials showed an increased positive electrode resistance when compared to that of the negative electrode for cells cycled at RT and 45 °C. However, cells cycled at 50 and 55 °C exhibit higher negative electrode resistance. The increased capacity fade for the cells cycled at high temperatures can be explained by taking into account the repeated film formation over the surface of anode, which results in increased rate of lithium loss and also in a drastic increase in the negative electrode resistance with cycling.

  1. Faded-example as a Tool to Acquire and Automate Mathematics Knowledge

    NASA Astrophysics Data System (ADS)

    Retnowati, E.

    2017-04-01

    Students themselves accomplish Knowledge acquisition and automation. The teacher plays a role as the facilitator by creating mathematics tasks that assist students in building knowledge efficiently and effectively. Cognitive load caused by learning material presented by teachers should be considered as a critical factor. While the intrinsic cognitive load is related to the degree of complexity of the material learning ones can handle, the extraneous cognitive load is directly caused by how the material is presented. Strategies to present a learning material in computational learning domains like mathematics are a namely worked example (fully-guided task) or problem-solving (discovery task with no guidance). According to the empirical evidence, learning based on problem-solving may cause high-extraneous cognitive load for students who have limited prior knowledge, conversely learn based on worked example may cause high-extraneous cognitive load for students who have mastered the knowledge base. An alternative is a faded example consisting of the partly-completed task. Learning from faded-example can facilitate students who already acquire some knowledge about the to-be-learned material but still need more practice to automate the knowledge further. This instructional strategy provides a smooth transition from a fully-guided into an independent problem solver. Designs of faded examples for learning trigonometry are discussed.

  2. Adaptive Estimation of Multiple Fading Factors for GPS/INS Integrated Navigation Systems

    PubMed Central

    Jiang, Chen; Zhang, Shu-Bi; Zhang, Qiu-Zhao

    2017-01-01

    The Kalman filter has been widely applied in the field of dynamic navigation and positioning. However, its performance will be degraded in the presence of significant model errors and uncertain interferences. In the literature, the fading filter was proposed to control the influences of the model errors, and the H-infinity filter can be adopted to address the uncertainties by minimizing the estimation error in the worst case. In this paper, a new multiple fading factor, suitable for the Global Positioning System (GPS) and the Inertial Navigation System (INS) integrated navigation system, is proposed based on the optimization of the filter, and a comprehensive filtering algorithm is constructed by integrating the advantages of the H-infinity filter and the proposed multiple fading filter. Measurement data of the GPS/INS integrated navigation system are collected under actual conditions. Stability and robustness of the proposed filtering algorithm are tested with various experiments and contrastive analysis are performed with the measurement data. Results demonstrate that both the filter divergence and the influences of outliers are restrained effectively with the proposed filtering algorithm, and precision of the filtering results are improved simultaneously. PMID:28587157

  3. Adaptive Estimation of Multiple Fading Factors for GPS/INS Integrated Navigation Systems.

    PubMed

    Jiang, Chen; Zhang, Shu-Bi; Zhang, Qiu-Zhao

    2017-06-01

    The Kalman filter has been widely applied in the field of dynamic navigation and positioning. However, its performance will be degraded in the presence of significant model errors and uncertain interferences. In the literature, the fading filter was proposed to control the influences of the model errors, and the H-infinity filter can be adopted to address the uncertainties by minimizing the estimation error in the worst case. In this paper, a new multiple fading factor, suitable for the Global Positioning System (GPS) and the Inertial Navigation System (INS) integrated navigation system, is proposed based on the optimization of the filter, and a comprehensive filtering algorithm is constructed by integrating the advantages of the H-infinity filter and the proposed multiple fading filter. Measurement data of the GPS/INS integrated navigation system are collected under actual conditions. Stability and robustness of the proposed filtering algorithm are tested with various experiments and contrastive analysis are performed with the measurement data. Results demonstrate that both the filter divergence and the influences of outliers are restrained effectively with the proposed filtering algorithm, and precision of the filtering results are improved simultaneously.

  4. Role of Manganese Deposition on Graphite in the Capacity Fading of Lithium Ion Batteries

    SciTech Connect

    Vissers, Daniel R.; Chen, Zonghai; Shao, Yuyan; Engelhard, Mark H.; Das, Ujjal; Redfern, Paul C.; Curtiss, Larry A.; Pan, Baofei; Liu, Jun; Amine, Khalil

    2016-05-06

    Lithium-ion batteries utilizing manganese based cathodes have received considerable interest in recent years for their lower cost and favorable environmental friendliness relative to their cobalt counterparts. However, Li-ion batteries using manganese based cathodes and graphite anodes suffer from severe capacity fading at higher operating temperature. In this article, we report on an astute investigation into how the dissolution of manganese impacts the capacity fading within the Li-ion batteries. Our investigation reveals that the manganese dissolves from the cathode, transports to the graphite electrode, and deposits onto the outer surface of the inner most solid electrolyte interphase (SEI) layer which is known to be a mixture of inorganic salts (e.g. Li2CO3, LiF, and Li2O). In this location, the manganese facilitates the reduction of the electrolyte and the subsequent formation of lithium containing products on the graphite which removes lithium ions from the normal operation of the cell and thereby induces the severe capacity fade.

  5. Mechanosensitive Channels

    NASA Astrophysics Data System (ADS)

    Martinac, Boris

    Living cells are exposed to a variety of mechanical stimuli acting throughout the biosphere. The range of the stimuli extends from thermal molecular agitation to potentially destructive cell swelling caused by osmotic pressure gradients. Cellular membranes present a major target for these stimuli. To detect mechanical forces acting upon them cell membranes are equipped with mechanosensitive (MS) ion channels. Functioning as molecular mechanoelectrical transducers of mechanical forces into electrical and/or chemical intracellular signals these channels play a critical role in the physiology of mechanotransduction. Studies of prokaryotic MS channels and recent work on MS channels of eukaryotes have significantly increased our understanding of their gating mechanism, physiological functions, and evolutionary origins as well as their role in the pathology of disease.

  6. Channel catfish

    USDA-ARS?s Scientific Manuscript database

    This book chapter provides a comprehensive overview of channel catfish aquaculture. Sections include fish biology; commercial culture; culture facilities; production practices; water quality management; nutrition, feeding and feed formulation; infectious diseases; harvesting and processing; and the...

  7. An algorithm for pre- and post-irradiation fade in the Thermo 8802 LiF:Mg,Ti thermoluminescent dosimeter.

    PubMed

    Hill, Carolyn D

    2005-05-01

    The diminished response of thermoluminescent phosphors over time is a well-documented challenge to thermoluminescent dosimetry. Wide ranges in fading rates for various phosphor types have been reported, making it necessary for many external dosimetry programs to perform individual studies on thermoluminescent fade. Sandia National Laboratories currently uses the Thermo 8802 LiF:Mg,Ti thermoluminescent dosimeter (TLD) in its personnel external dosimetry program. Doses received in the field are calculated by applying a fade algorithm published by the manufacturer to TLD readings. Since the algorithm was established by characterizing the diminished response of a TLD similar to the 8802, Sandia chose to model its fade study after the analysis done by Thermo. As a result, the parameters of each experiment were comparable, and data from the two studies were compared to determine whether or not the current algorithm should be modified specifically for use at Sandia. Cards were irradiated using an internal Sr/Y source, and pre- and post-irradiation fading rates were monitored over a period of 18 wk. While significant fading was demonstrated, results closely matched those found in the original Thermo study.

  8. Compilation and Analysis of 20 and 30 GHz Rain Fade Events at the ACTS NASA Ground Station: Statistics and Model Assessment

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1996-01-01

    The purpose of the propagation studies within the ACTS Project Office is to acquire 20 and 30 GHz rain fade statistics using the ACTS beacon links received at the NGS (NASA Ground Station) in Cleveland. Other than the raw, statistically unprocessed rain fade events that occur in real time, relevant rain fade statistics derived from such events are the cumulative rain fade statistics as well as fade duration statistics (beyond given fade thresholds) over monthly and yearly time intervals. Concurrent with the data logging exercise, monthly maximum rainfall levels recorded at the US Weather Service at Hopkins Airport are appended to the database to facilitate comparison of observed fade statistics with those predicted by the ACTS Rain Attenuation Model. Also, the raw fade data will be in a format, complete with documentation, for use by other investigators who require realistic fade event evolution in time for simulation purposes or further analysis for comparisons with other rain fade prediction models, etc. The raw time series data from the 20 and 30 GHz beacon signals is purged of non relevant data intervals where no rain fading has occurred. All other data intervals which contain rain fade events are archived with the accompanying time stamps. The definition of just what constitutes a rain fade event will be discussed later. The archived data serves two purposes. First, all rain fade event data is recombined into a contiguous data series every month and every year; this will represent an uninterrupted record of the actual (i.e., not statistically processed) temporal evolution of rain fade at 20 and 30 GHz at the location of the NGS. The second purpose of the data in such a format is to enable a statistical analysis of prevailing propagation parameters such as cumulative distributions of attenuation on a monthly and yearly basis as well as fade duration probabilities below given fade thresholds, also on a monthly and yearly basis. In addition, various subsidiary

  9. Compilation and Analysis of 20 and 30 GHz Rain Fade Events at the ACTS NASA Ground Station: Statistics and Model Assessment

    NASA Technical Reports Server (NTRS)

    Manning, Robert M.

    1996-01-01

    The purpose of the propagation studies within the ACTS Project Office is to acquire 20 and 30 GHz rain fade statistics using the ACTS beacon links received at the NGS (NASA Ground Station) in Cleveland. Other than the raw, statistically unprocessed rain fade events that occur in real time, relevant rain fade statistics derived from such events are the cumulative rain fade statistics as well as fade duration statistics (beyond given fade thresholds) over monthly and yearly time intervals. Concurrent with the data logging exercise, monthly maximum rainfall levels recorded at the US Weather Service at Hopkins Airport are appended to the database to facilitate comparison of observed fade statistics with those predicted by the ACTS Rain Attenuation Model. Also, the raw fade data will be in a format, complete with documentation, for use by other investigators who require realistic fade event evolution in time for simulation purposes or further analysis for comparisons with other rain fade prediction models, etc. The raw time series data from the 20 and 30 GHz beacon signals is purged of non relevant data intervals where no rain fading has occurred. All other data intervals which contain rain fade events are archived with the accompanying time stamps. The definition of just what constitutes a rain fade event will be discussed later. The archived data serves two purposes. First, all rain fade event data is recombined into a contiguous data series every month and every year; this will represent an uninterrupted record of the actual (i.e., not statistically processed) temporal evolution of rain fade at 20 and 30 GHz at the location of the NGS. The second purpose of the data in such a format is to enable a statistical analysis of prevailing propagation parameters such as cumulative distributions of attenuation on a monthly and yearly basis as well as fade duration probabilities below given fade thresholds, also on a monthly and yearly basis. In addition, various subsidiary

  10. Unexpected Voltage Fade in LMR-NMC Oxides Cycled below the “Activation” Plateau

    SciTech Connect

    Abraham, Daniel P; Li, Yan; Bareno, Javier; Bettge, Martin

    2015-01-01

    A common feature of lithium-excess layered oxides, nominally of composition xLi(2)MnO(3)center dot(1-x)LiMO2 (M = transition metal) is a high-voltage plateau (similar to 4.5 V vs. Li/Li+) in their capacity-voltage profile during the first delithiation cycle. This plateau is believed to result from activation of the Li2MnO3 component, which makes additional lithium available for electrochemical cycling. However, oxides cycled beyond this activation plateau are known to display voltage fade which is a continuous reduction in their equilibrium potential. In this article we show that these oxides display gradual voltage fade even on electrochemical cycling in voltage ranges well below the activation plateau. The average fade is similar to 0.08 mV-cycle(-1) for Li(1.2)Ni(0.1)5Mn(0.5)5Co(0.1)O(2) vs. Li cells after 20 cycles in the 2-4.1 V range at 55 degrees C; a similar to 54 mV voltage hysteresis, expressed as the difference in average cell voltage between charge and discharge cycles, is also observed. The voltage fade results from a gradual accumulation of local spinel environments in the crystal structure. Some of these spinel sites result from lithium deficiencies during oxide synthesis and are likely to be at the particle surfaces; other sites result from the migration of transition metal atoms in the partially-delithiated LiMO2 component into the lithium planes during electrochemical cycling. The observed rate of voltage fade depends on a combination of factors that includes the phase equilibrium between the layered and spinel components and the kinetics of transition metal migration. (C) The Author(s) 2014. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. All rights reserved.

  11. Underwater acoustic channel estimation using multiple sources and receivers in shallow waters at very-high frequencies

    NASA Astrophysics Data System (ADS)

    Kaddouri, Samar

    The underwater channel poses numerous challenges for acoustic communication. Acoustic waves suffer long propagation delay, multipath, fading, and potentially high spatial and temporal variability. In addition, there is no typical underwater acoustic channel; every body of water exhibits quantifiably different properties. Underwater acoustic modems are traditionally operated at low frequencies. However, the use of broadband, high frequency communication is a good alternative because of the lower background noise compared to low-frequencies, considerably larger bandwidth and better source transducer efficiency. One of the biggest problems in the underwater acoustic communications at high frequencies is time-selective fading, resulting in the Doppler spread. While many Doppler detection, estimation and compensation techniques can be found in literature, the applications are limited to systems operating at low frequencies contained within frequencies ranging from a few hundred Hertz to around 30 kHz. This dissertation proposes two robust channel estimation techniques for simultaneous transmissions using multiple sources and multiple receivers (MIMO) that closely follows the rapidly time-varying nature of the underwater channel. The first method is a trended least square (LS) estimation that combines the traditional LS method with an empirical modal decomposition (EMD) based trend extraction algorithm. This method allows separating the slow fading modes in the MIMO channels from the fast-fading ones and thus achieves a close tracking of the channel impulse response time fluctuations. This dissertation also outlines a time-varying underwater channel estimation method based on the channel sparsity characteristic. The sparsity of the underwater communication channel is exploited by using the MIMO P-iterative greedy orthogonal matching pursuit (MIMO-OMP) algorithm for the channel estimation. Both techniques are demonstrated in a fully controlled environment, using simulated

  12. Beamforming Transmission in IEEE 802.11ac under Time-Varying Channels

    PubMed Central

    2014-01-01

    The IEEE 802.11ac wireless local area network (WLAN) standard has adopted beamforming (BF) schemes to improve spectral efficiency and throughput with multiple antennas. To design the transmit beam, a channel sounding process to feedback channel state information (CSI) is required. Due to sounding overhead, throughput increases with the amount of transmit data under static channels. Under practical channel conditions with mobility, however, the mismatch between the transmit beam and the channel at transmission time causes performance loss when transmission duration after channel sounding is too long. When the fading rate, payload size, and operating signal-to-noise ratio are given, the optimal transmission duration (i.e., packet length) can be determined to maximize throughput. The relationship between packet length and throughput is also investigated for single-user and multiuser BF modes. PMID:25152927

  13. Beamforming transmission in IEEE 802.11ac under time-varying channels.

    PubMed

    Yu, Heejung; Kim, Taejoon

    2014-01-01

    The IEEE 802.11ac wireless local area network (WLAN) standard has adopted beamforming (BF) schemes to improve spectral efficiency and throughput with multiple antennas. To design the transmit beam, a channel sounding process to feedback channel state information (CSI) is required. Due to sounding overhead, throughput increases with the amount of transmit data under static channels. Under practical channel conditions with mobility, however, the mismatch between the transmit beam and the channel at transmission time causes performance loss when transmission duration after channel sounding is too long. When the fading rate, payload size, and operating signal-to-noise ratio are given, the optimal transmission duration (i.e., packet length) can be determined to maximize throughput. The relationship between packet length and throughput is also investigated for single-user and multiuser BF modes.

  14. Iterative Superimposed Pilot-Assisted Channel Estimation Using Sliding Wiener Filtering for Single-Carrier Block Transmission

    NASA Astrophysics Data System (ADS)

    Uchiumi, Tetsuya; Obara, Tatsunori; Takeda, Kazuki; Adachi, Fumiyuki

    In the conventional iterative superimposed pilot-assisted channel estimation (SI-PACE), simple averaging of the instantaneous channel estimates obtained by using the pilot over several single-carrier (SC) blocks (called the frame in this paper) is taken in order to reduce the interference from data symbols. Therefore, the conventional SI-PACE has low tracking ability against fading time variations. To solve the tracking problem, Wiener filtering (WF)-based averaging can be used instead of simple averaging. However, WF incurs high computational complexity. Furthermore, the estimation error of the fading autocorrelation function significantly degrades the channel estimation accuracy. In order to improve the channel estimation accuracy while keeping the computational complexity low, a new iterative SI-PACE using sliding WF (called iterative SWFSI-PACE) is proposed. The channel estimation is done by sliding a WF having a shorter filter size than the measurement interval. The bit error rate (BER) and throughput performances of SC-FDE using iterative SWFSI-PACE are investigated by computer simulation to show that the proposed scheme achieves good BER and throughput performances while keeping the computational complexity low irrespective of the fading rate (or maximum Doppler frequency).

  15. Frequency-Domain QR-Decomposed and Equalized MLD for Single-Carrier MIMO Systems over Multipath Fading Channels

    NASA Astrophysics Data System (ADS)

    Miyatani, Tetsuhiko

    This letter describes a new QR-decomposition maximum likelihood detector that is combined with frequency-domain equalization for single-carrier transmission based multiple-input multiple-output systems. By utilizing the equalized substreams to adjust the frequency selectivity in corresponding substreams in subsequent stages, the packet error rate performances of the proposed detector is superior to that of the minimum mean squared error receiver by a factor of the receive antenna diversity gain.

  16. Outage performance of multihop free-space optical communication system over exponentiated Weibull fading channels with nonzero boresight pointing errors

    NASA Astrophysics Data System (ADS)

    Liu, Xiao-xia; Wang, Ping; Cao, Tian

    2016-09-01

    The outage performance of the multihop free-space optical (FSO) communication system with decode-and-forward (DF) protocol is studied by considering the joint effects of nonzero boresight pointing errors and atmospheric turbulence modeled by exponentiated Weibull (EW) distribution. The closed-form analytical expression of outage probability is derived, and the results are validated through Monte Carlo simulation. Furthermore, the detailed analysis is provided to evaluate the impacts of turbulence strength, receiver aperture size, boresight displacement, beamwidth and number of relays on the outage performance for the studied system.

  17. Reliable Adaptive Modulation and Interference Mitigation for Mobile Radio Slow Frequency Hopping Channels

    DTIC Science & Technology

    2008-08-29

    transmitted frequencies r. The degrading effect of PBI is compensated for by the benefit of frequency diversity on the performance of LRP for these...diversity and AM was investigated for channels with PBI . Numerical and simulation results demonstrate that significant performance gains can be...Modulation and adaptive Frequency Diversity to mitigate the effects of fading and partial-band interference. Significant performance gains are

  18. Performance of Improved Channel Allocation for Multicarrier CDMA with Adaptive Frequency Hopping and Multiuser Detection

    DTIC Science & Technology

    2008-08-29

    SECURITY CLASSIFICATION OF: Subchannel allocation for the reverse link of multicarrier code-division multiplex-access (MC-CDMA) system with adaptive...Triangle Park, NC 27709-2211 15. SUBJECT TERMS subchannel allocation, fading channels, CDMA Tao Jia, Alexandra Duel-Hallen North Carolina State University... Subchannel allocation for the reverse link of multicarrier code-division multiplex-access (MC-CDMA) system with adaptive frequency hopping (AFH) is

  19. Channel Deviation-Based Power Control in Body Area Networks.

    PubMed

    Dinh Van, Son; Cotton, Simon L; Smith, David B

    2017-08-18

    Internet enabled body area networks (BANs) will form a core part of future remote health monitoring and Ambient Assisted Living (AAL) technology. In BAN applications, due to the dynamic nature of human activity, the off-body BAN channel can be prone to deep fading caused by body shadowing and multipath fading. Using this knowledge, we present some novel practical adaptive power control protocols based on the channel deviation to simultaneously prolong the lifetime of wearable devices and reduce outage probability. The proposed schemes are both flexible and relatively simple to implement on hardware platforms with constrained resources making them inherently suitable for BAN applications. We present the key algorithm parameters used to dynamically respond to the channel variation. This allows the algorithms to achieve a better energy efficiency and signal reliability in everyday usage scenarios such as those in which a normal person undertakes many different activities (e.g. sitting, walking, standing, etc). We also profile their performance against traditional, optimal and other existing schemes for which it is demonstrated that not only does the outage probability reduce significantly, but the proposed algorithms also save up to 35% average transmit power compared to the competing schemes.

  20. English Channel

    NASA Technical Reports Server (NTRS)

    1984-01-01

    The cloud covered earthscape of Northern Europe demonstrates the difficulty of photographing this elusive subject from space. The English Channel (51.0N, 1.5E) separating the British Islands from Europe is in the center of the scene. The white cliffs of Dover on the SE coast of the UK, the Thames River estuary and a partial view of the city of London can be seen on the north side of the Channel while the Normandy coast of France is to the south.