Adaptive signal detection over fast frequency-selective fading channels under class-A impulsive noise

The problem of adaptive detection of signals contaminated with Middleton's class-A impulsive noise and transmitted over a fast time-varying frequency-selective fading channel is addressed. Adaptive algorithms are derived to update the estimate of the channel parameters to the detector. A theoretical performance evaluation of the detector is provided. Computer simulations are performed to validate the theoretical developments.     

Multidimensional M-PSK trellis codes for fading channels

This paper investigates the code search problem for trellis-coded multidimensional phase modulation for Rayleigh fading channels. New set partitionings for multiple phase-shift keying (M-PSK) are proposed using the effective code length (ECL) and the minimum product distance (PD) as the code design criteria. By using these set-partitionings rules, new multidimensional codes which are optimum for Rayleigh fading channels are constructed. The proposed codes compare favorably with the existing multidimensional trellis codes on fading channels in terms of bit error performance. The bit error performance is evaluated by simulation     

On optimum combining of M-PSK signals with unequal-power interferers and noise

In this letter, we derive a closed-form symbol-error probability expression for adaptive antenna array with optimum (or, equivalently, linear minimum mean-square error) combining. We consider coherent detection of M-ary phase-shift keying signals in the presence of unequal-power interferers and thermal noise. The analysis is based on our new results on the eigenvalues distribution of central Wishart matrices with correlation.     

Performance of phase-invariant trellis coding for differentially-encoded coherent M-PSK signals on Rayleigh fading channels

Rate(n-1)/n phase-invariant trellis coding with unquantised maximum-likelihood Viterbi decoding for differentially-encoded coherent M-ary (M-2/sup n/) PSK signals on Rayleigh fading channels is considered. The simulated bit error probability performance of the trellis-coded modulation is presented for four- and eight-state linear and nonlinear codes for constraint lengths 3 and 4, respectively, with coding gains of at least 2.5 dB at a bit error rate of 10/sup -3/.<>     

On diversity reception over fading channels with impulsive noise

In this paper, we analyze the performance of different diversity combining techniques over fading channels with impulsive noise. We use Middleton's Class A model for the noise distribution and adopt two noise models, which assume dependent and independent noise components on each branch. We systematically analyze the performance of maximum ratio combing (MRC), equal gain combining (EGC), selection combining (SC), and post-detection combining (PDC) under these impulsive noise models, and derive insightful lower and upper bounds. We show that even under impulsive noise, the diversity order is retained for each combining scheme. However, we also show that under both models, there is a fundamental tradeoff between diversity gain and coding gain. Under the independent noise model, PDC is shown to combat impulsive noise more effectively than MRC, EGC, and SC. Our simulation results also corroborate our analysis.     

Linear diversity analyses for M-PSK in Rician fading channels

Symbol and bit error rates of M-ary differentially encoded/differentially decoded phase-shift keying (MDPSK) and coherent M-ary phase-shift keying (M-PSK) over slow, flat, Rician fading channels are derived when linear diversity combining is applied to combat degradation due to fading. These closed-form solutions are general enough to cover several cases of nondiversity, additive white Gaussian noise (the nonfading mode), Rayleigh fading, mixtures of Rayleigh and Rician fading (the mixed mode), and Rician fading. The results presented here can also be applied to predict the error-rate performance when recent transmit diversity techniques are employed. The solutions for the nonuniform fading profile are included as well. Error probabilities are graphically displayed for both modulation schemes.     

Outage probability of dual-branch coherent equal-gain combining in correlated Nakagami-m fading

The exact outage probability of mobile radio receivers using dual-branch coherent equal-gain combining is analytically derived for correlated Nakagami-m fading. Expressions in the form of infinite series are obtained for the two cases of identical parameters on both diversity branches, and identical m-parameters (multiples of a half-integer) but not-necessarily identical fading powers on each branch.     

Performance analysis of coherent equal gain combining overNakagami-m fading channels

We study the exact average output signal-to-noise ratio (SNR) and symbol error rate (SER) of M-ary phaseshift-keying (PSK) signals with coherent equal gain combining reception. The analysis assumes independent Nakagami-m (1960) fading paths, which are not necessarily identically distributed. On one hand, we use geometric summations to obtain closed-form expressions for the average output SNR over diversity paths with an exponentially decaying power delay profile. On the other hand, capitalizing on an alternative integral representation of the conditional SER along with Gauss-Hermite quadrature integration, we derive an average SER expression in the form of a single finite-range integral and an integrand composed of tabulated functions. We also present a simpler but approximate approach for the closed-form evaluation of the SER of these signals over independent identically distributed Nakagami-m fading paths     

脉冲噪声和衰落环境下比特交织差分编码调制的性能

根据脉冲噪声产生的机制和Viterbi译码器的要求,提出一种利用比特度量限幅改善比特交织差分编码调制系统性能的新方法,研究结果表明,这种方法可以有效抑制脉冲噪声对差分编码调制系统性能的影响.     

Diversity for binary noncoherent frequency shift keying in impulsive reverberation noise

The error rate in active sonar is given for binary non-coherent frequency shift keying (FSK) in slow and non-selective Rayleigh fading (multipath) and additive non-Gaussian reverberation noise. The improvement achieved by using time-diversity is derived from the expression for the probability of error. It is shown that for error probabilities of the order of 10?5 the improvement factor is 10 dB.     

Coding and signal space diversity for a class of fading and impulsive noise channels

The transmission over the Gaussian mixture noise channel with perfect channel state information at the receiver side is considered. Lower and upper bounds on the achievable pairwise error probability (PEP) are derived for finite and infinite codeword lengths. It is shown that diversity codes, i.e., unitary transforms, can be applied to achieve a diversity gain. A large class of diversity codes is determined for which-if the codeword length is increased-the PEP between any two codewords approaches either zero or the lower bound on the PEP.     

Characteristics and reduction of coherent fading noise in Rayleighbackscattering measurement for optical fibers and components

The characteristics of fading noise in Rayleigh backscattering measurements made with coherent lightwaves such as in coherent-OTDR (optical time-domain reflectometry) and coherent-OFDR (optical frequency-domain reflectometry) are studied. The effects of frequency shift averaging on fading noise reduction are clarified theoretically, and the relationships between measurement accuracy and other parameters, such as spatial resolution and frequency variation range are derived. The calculated results of loss measurement accuracy are in good agreement with experimental data. The formula can also be applied to low-coherence interferometric OTDR     

Diversity codes for differential phase modulation in a correlatedRayleigh fading channel

This paper proposes a simple diversity scheme that makes use of nonlinear block coding, symbol interleaving, and differential phase modulation. The resultant signaling mechanism merits intrinsic time diversity within each codeword, which is resistant to correlated fading. The maximum-likelihood noncoherent receiver which operates over correlated Rayleigh fading is developed. Exact and approximate upper bounds are derived to assess the codeword-error probability characteristics of the proposed system     

Classical coherent receivers for differentially encoded M-PSK are optimal

In this letter, we show that classical coherent receivers for differentially encoded M-PSK are optimal in the sense of the maximum a posteriori (MAP) sequence detection criterion.     

Adaptive path selective fuzzy decorrelating detector under impulsive noise for multipath fading CDMA systems

This letter proposes a novel adaptive path selective fuzzy decorrelating (APSFD) detector for direct-sequence code- division multiple-access (DS-CDMA), systems with time-varying multipath fading channels under impulsive noise. The proposed detector combines adaptive path selective decorrelating (APSD) detector with a fuzzy median filter which is based on fuzzy rank ordering of samples to eliminate the effect of impulsive noise. Simulation results clearly show that the proposed detector eliminates the effect of impulsive noise and improves the performance of APSD detector under high impulsive noise.     

Diversity combining for DS/SS systems with time-varying, correlated fading branches

Diversity combining of multiple time varying and correlated fading branches is investigated for direct-sequence spread-spectrum systems. The correlated branches are modeled and estimated jointly as a vector autoregressive (VAR) process. The joint estimation is shown to provide performance gain over separate estimation of the fading branches. The parameter matrices of the VAR model are estimated via the method of expectation maximization (EM) with two algorithms. The first algorithm, using results from Kalman smoothing, provides a closed-form solution to the maximization problem in the iterative EM procedure. However, the iterative EM-Kalman algorithm operates repeatedly on a batch of training data and results in large storage requirements and long processing delays. To overcome these disadvantages, a new algorithm with only forward-time recursions is proposed that approximates the iterative EM solution and efficiently adapts to slowly changing Doppler spreads. As a result, the new algorithm significantly reduces memory and training sequence requirements. Through computer simulations, a near ideal bit-error rate performance is found for both algorithms, and the efficacy of the new adaptive algorithm for channels with changing Doppler spreads is demonstrated.     

Error probability for coherent and differential PSK over arbitraryRician fading channels with multiple cochannel interferers

This paper discusses the performance of communication systems using binary coherent and differential phase-shift keyed (PSK) modulation, in correlated Rician fading channels with diversity reception. The presence of multiple Rician-faded cochannel users, which may have arbitrary and nonidentical parameters, is modeled exactly. Exact bit error probability (BEP) expressions are derived via the moment generating functions (MGFs) of the relevant decision statistics, which are obtained through coherent detection with maximum ratio combining for coherent PSK modulation, and differential detection with equal gain combining (EGC) for differential modulation. Evaluating the exact expressions requires a complexity that is exponential in the number of interferers. To avoid this potentially time-consuming operation, we derive two low-complexity approximate methods each for coherent and differential modulation formats, which are more accurate than the traditional Gaussian approximation approach. Two new and interesting results of this analysis are: (1) unlike in the case of Rayleigh fading channels, increasing correlation between diversity branches may lead to better performance in Rician fading channels and (2) the phase distribution of the line-of-sight or static fading components of the desired user has a significant influence on the BEP performance in correlated diversity channels     

RBF network assisted adaptive path selective decorrelating detector under impulsive noise for multipath fading CDMA systems

This paper proposes a novel radial basis function assisted adaptive path selective decorrelating detector for direct sequence code division multiple access systems with time-varying multipath fading channels under impulsive noise. The proposed detector combines adaptive path selective decorrelating detector (APSDD) with a radial basis function (RBF) network to eliminate the effect of impulsive noise. Simulation results clearly show that the proposed detector eliminates the effect of impulsive noise and improves the performance of APSDD under high impulsive noise.     

Comparison of coherent and differential detection of BPSK and QPSKin a quasistatic fading channel

The advantage of coherent detection over differential detection for quadrature phase-shift keying (QPSK) and binary phase-shift keying (BPSK) in a flat-fading channel is evaluated based on receiver-sensitivity analysis using three performance criteria. QPSK is concentrated upon to perform simulations for a frequency-selective fading channel. Spectral efficiency improvement due to better frequency reuse for the more sensitive coherent detection is evaluated with a combination of analysis and simulation. It is found that coherent detection with perfect carrier recovery is superior to differential detection by at least 2.4 dB, which converts to about a 30% improvement in spectral efficiency in a two-dimensional, frequency reuse system with a fourth-power propagation exponent. This advantage is preserved even if diversity selection is used to mitigate fading     

光纤激光相干合成与谱合成的比较

相干合成和谱合成是两种不同的光束合成方案,近年来均取得了显著进展.为了比较系统地研究这两种新兴的光束合成技术,从光纤激光器的基本要求、关键技术、可扩展性、光束质量、系统稳定性和光束控制等6个方面,对目前已经获得高功率且有望获得更高功率输出的两种典型方案进行了比较研究.结果表明,基于主振荡功率放大器结构的相干合成方案和谱合成方案均难以同时获得高功率、高光束质量的激光输出.对于不同的应用场合,需要在高功率和高光束质量中选择较好的平衡点.