Specular coherent and noncoherent optimal detection for unresolvedmultipath Ricean fading channels

This paper considers specular coherent and noncoherent optimal detection for unresolved multipath Ricean fading channels with known delays. The focus is on receiver structures and performance. Specular coherent detection employs the carrier phase of the Ricean specular component, while noncoherent detection does not. Therefore, a specular coherent detector must be augmented with a carrier phase estimator for the specular component. The structures considered are generalization of the well-known RAKE receiver to the unresolved multipath case. It is shown that both optimal structures perform a decorrelation operation before combining, which is essential to eliminating error floors under multipath unresolvability conditions. Furthermore, the noncoherent optimal receiver includes an inherent estimator for the specular component phasor. It is shown that the specular coherent and noncoherent structures converge at high SNR. This result is confirmed through analytical and numerical performance evaluation. Little performance gains can be obtained by the use of specular coherent detection for orthogonal frequency-shift keying and to a lesser extent for differential phase-shift keying over mixed mode Ricean/Rayleigh fading channels, making noncoherent demodulation attractive in these cases     

Decision-feedback differential detection based on linear predictionfor MDPSK signals transmitted over Ricean fading channels

In this paper, linear prediction-based decision-feedback differential detection (DF-DD) for M-ary differential phase-shift keying (MDPSK) signals transmitted over Ricean fading channels is proposed. This scheme can improve conventional DD significantly for a multitude of frequency-nonselective channels, as shown analytically and by computer simulations. Prediction-based DF-DD is particularly well suited for application in mobile communications since the predictor coefficients may be updated regularly using the recursive least squares (RLS) algorithm. Here, adaptation can start blind, i.e., no training sequence and no a prior knowledge about the channel statistics are required. A further important characteristic of the proposed detection scheme is that no degradation occurs under frequency offset. The bit error rate (BER) performance of QDPSK with genie-aided prediction-based DF-DD is analyzed, and it is shown under which conditions the irreducible error floor of conventional DD can be removed entirely. In addition, the influence of Doppler shift is discussed. Last, the proposed scheme is compared with a second DF-DD scheme, which is based on multiple-symbol detection     

Decision-feedback differential detection based on linear predictionfor 16DAPSK signals transmitted over flat Ricean fading channels

In this article, prediction-based decision-feedback differential detection (DF-DD) for 16-level differentially encoded amplitude/phase-shift keying is proposed. Unlike previously reported DF-DD schemes, this scheme provides a performance gain over conventional differential detection under general Ricean fading conditions. A further important advantage of the novel scheme is that it is able to compensate a small carrier frequency offset. The linear predictor coefficients may be updated using the recursive least-squares algorithm, which can start blind, i.e., without a priori knowledge about the channel statistics and without a training sequence. This makes the scheme attractive for application in mobile communications since the statistics of a nonstationary mobile channel can be tracked     

莱斯多径衰落信道下OFDM系统的容量方差分析

方差是系统容量的一个重要参数,可以用来估计通信系统的中断容量。该文研究了正交频分复用（OFDM）系统在莱斯衰落信道下的容量方差。首先该文建立了多径莱斯信道的模型并且定义了多径莱斯信道的莱斯因子,基于此信道模型推出了一个OFDM系统容量方差新的数学表达式,此表达式以OFDM系统的子载波数、信噪比、信道的多径时延等为参数。基于此表达式,计算机仿真和数值计算研究了信噪比、多径数目、莱斯因子对OFDM系统容量方差的影响。结果表明:计算机仿真和数值计算基本吻合,验证了所推导数学表达式的正确性;系统容量方差与信噪比成正比,与莱斯因子和信道的多径数目成反比。另外,该文以积分的形式给出了任意两个相关莱斯随机变量的联合概率密度函数。      

Performance analysis of SSC diversity receiver over correlated Ricean fading channels in presence of co-channel interference

A novel infinite-series-based approach for the performance analysis of a dual-branch switched-and-stay combining (SSC) diversity receiver operating over Ricean correlated fading channels in the presence of correlated Nakagami-m distributed co-channel interference (CCI) is presented. The performance analysis is based on outage probability (P_out) and average bit error probability (ABEP) criteria.     

Optimal noncoherent detection of FSK signals transmitted overlinearly time-selective Rayleigh fading channels

Linearly time-varying fading models are used to investigate noncoherent detection of frequency shift keying (FSK) signals transmitted over frequency-flat fading channels. The structure of the optimal noncoherent FSK detector is derived and a novel analytical technique is proposed to compute the error performance of noncoherent FSK detectors in fast fading. Error performance results obtained by computer simulation are in excellent agreement with the analytical predictions     

A noncoherent receiver for interleaved trellis-coded CPFSK signalstransmitted over frequency-flat fading channels

We propose a novel two-stage noncoherent receiver for interleaved trellis-coded CPFSK signals transmitted over time-selective channels. The first stage of the receiver computes reliability information about the transmitted symbols and delivers it to the second stage which operates as a trellis decoder. Simulation results show that the proposed detection strategy outperforms previous noncoherent receivers with a moderate increase in complexity     

Estimation of phase differential of signals transmitted over fading channels

The authors show that it is possible to use the Hilbert transform to estimate the absolute value of the phase differential of signals transmitted over fading channels from the envelope of the signal. This is demonstrated on a mobile radio channel and on an indoor radio channel.<>     

Layered space-time codes over Ricean fading channels by reducing the correlation of spatial shaping pulses

In this paper, an asynchronous layered space-time architecture is proposed to realize the spatial multiplexing over the Ricean multiple-input multiple-output (MIMO) channels. Based on reducing the correlation of spatial shaping pulses between the multiplexed streams, this approach can be used to solve the problem of detection in the ill-conditioned channel matrix. It is shown that at the receiver, the reduction of the correlation enables the requirement on the number of the receive antennas to be removed by the zero forcing (ZF) detector compared with the conventional synchronous layered space-time architecture. First, this paper presents how to exploit the correlation of spatial shaping pulses between the multiplexed streams. Then deriving the exact closed-form expression of error rate for the proposed scheme, this paper finds that the maximum possible diversity gain can be achieved based on the independent layered architecture by the ZF detector at the cost of limited multiplexing gain.     

A Reed-Solomon coded DS-CDMA system using noncoherent M-aryorthogonal modulation over multipath fading channels

The performance of Reed-Solomon (RS) coded direct-sequence code division multiple-access (DS-CDMA) systems using noncoherent M-ary orthogonal modulation is investigated over multipath Rayleigh fading channels. Diversity reception techniques with equal gain combining (EGC) or selection combining (SC) are invoked and the related performance is evaluated for both uncoded and coded DS-CDMA systems. “Errors-and-erasures” decoding is considered, where the erasures are based on Viterbi's (1982) so-called ratio threshold test (RTT). The probability density functions (PDF) of the ratio associated with the RTT conditioned on both the correct detection and erroneous detection of the M-ary signals are derived. These PDFs are then used for computing the codeword decoding error probability of the RS coded DS-CDMA system using “errors-and-erasures” decoding. Furthermore, the performance of the “errors-and-erasures” decoding technique employing the RTT is compared to that of “error-correction-only” decoding refraining from using side-information over multipath Rayleigh fading channels. As expected, the numerical results show that when using “errors-and-erasures” decoding, RS codes of a given code rate can achieve a higher coding gain than without erasure information     

Convolutional coding for BPSK with pilot tone over Rayleigh fading channels

To improve the performance of digital communication systems over fading channels, several pilot signal techniques have been proposed in the literature. The authors investigate the use of binary convolutional coding for such systems and derives an upper bound on the bit error probability (BEP), the optimum power split ratio between data and pilot signals, and the channel cutoff rate.<>     

A BEM-based detector for CPM signals transmitted over frequency-flat fading channels

In this paper, the expectation-maximization (EM) algorithm for maximum a posteriori (MAP) estimation of a random vector is applied to the problem of symbol detection for continuous phase modulation signals transmitted over time-selective Rayleigh-fading channels. This results in a soft-in-soft-out detection algorithm suitable for iterative detection/decoding schemes. Simulation results show that the error performance provided by the proposed solution is very close to that of a MAP detector endowed with an ideal knowledge of the channel state both in uncoded and coded transmissions.     

Maximum-likelihood frequency recovery for OFDM signals transmitted over multipath fading channels

In this paper, a novel feedback frequency synchronizer for orthogonal frequency-division multiplexing signals transmitted over multipath fading channels is described. Its derivation is based on maximum-likelihood estimation techniques and assumes an approximate statistical knowledge of the communication channel. The performance of the proposed algorithm is assessed by computer simulation, and is compared with that provided by other synchronization algorithms and with Cramer-Rao bounds.     

Performance of an in-band adjacent-channel DAB system forfrequency-selective Rayleigh and Ricean slow fading channels underanalog FM interference

In support of the 1995-1997 DAB (digital audio broadcasting) testing conducted by the NRSC (National Radio Systems Committee), an IBAC (in-band adjacent-channel) scheme was developed by AT&T. Although not for use in the United States, bit error rate (BER) system performance under both fading environments and the existing analog FM broadcasting is important to quantify. This is because there may still exist other countries and environments where an IBAC approach to DAB is feasible and economical. Given this situation, an IBAC simulation model has been developed to allow for a performance analysis study within the mobile reception environment, which is dominated by Rayleigh and Ricean fading statistics. This paper presents the simulation results for coherent quadrature phase-shift-keying (QPSK) with nonlinear equalization for both frequency-selective Rayleigh and Ricean slow fading channel environments, along with co-channel, 1st-adjacent and 2nd-adjacent analog FM interference. The results indicate that for a country where spectrum availability dictates an IBAC solution, this approach may perform well under various fading and interference environments     

Exact BER analysis of M‐ary orthogonal signaling with MRC over Ricean fading channels

A new approach for analyzing the performance of coherent M‐ary orthogonal signaling with maximal ratio combining over Ricean fading channels is presented here. A new series representation for the bit‐error rate is derived, making it possible to compute error rates with guaranteed accuracy. Copyright © 2007 John Wiley & Sons, Ltd.     

Average bit-error probability performance for optimum diversity combining of noncoherent FSK over Rayleigh fading channels

We derive the performance of the optimum noncoherent frequency-shift keying diversity combining receiver and compare it with that which implements the more traditional noncoherent postdetection equal gain combining scheme to reveal the degree of suboptimality of the latter.     

A blind particle filtering detector of signals transmitted over flat fading channels

A new particle filtering detector (PFD) is proposed for blind signal detection over flat Rayleigh fading channels whose model coefficients are unknown. The detector employs a hybrid importance function and a mixture Kalman filter. It also incorporates an auxiliary particle filtering strategy with a smoothing kernel in the resampling step. Further, by considering practical information of communication systems and the physical interpretation of the adopted second-order autoregressive (AR) channel model, a fully blind particle filtering implementation is developed. The structure of the proposed PFD can be easily adapted to other system requirements. Simulations are provided that demonstrate the performance of the new PFD.     

Fusion of decisions transmitted over Rayleigh fading channels in wireless sensor networks

In this paper, we revisit the problem of fusing decisions transmitted over fading channels in a wireless sensor network. Previous development relies on instantaneous channel state information (CSI). However, acquiring channel information may be too costly for resource constrained sensor networks. In this paper, we propose a new likelihood ratio (LR)-based fusion rule which requires only the knowledge of channel statistics instead of instantaneous CSI. Based on the assumption that all the sensors have the same detection performance and the same channel signal-to-noise ratio (SNR), we show that when the channel SNR is low, this fusion rule reduces to a statistic in the form of an equal gain combiner (EGC), which explains why EGC is a very good choice with low or medium SNR; at high-channel SNR, it is equivalent to the Chair-Varshney fusion rule. Performance evaluation shows that the new fusion rule exhibits only slight performance degradation compared with the optimal LR-based fusion rule using instantaneous CSI.     

Maximum likelihood estimation of the K factor in Ricean fading channels

Estimation of the K factor in a Ricean fading channel is studied. Unlike most previous estimators which employ exclusively samples of the fading envelope, new maximum likelihood estimators that use samples of both the fading envelope and the fading phase, or samples of the fading phase only, are derived and examined. Simulation results show that these estimators have good performances when operating in a Ricean fading channel, and in some cases outperform envelope-sample-based estimators.     

Error performance of noncoherent MFSK with L-diversity oncorrelated fading channels

Noncoherent diversity reception of M-ary frequency-shift keying (MFSK) signals becomes increasingly important due to its widespread use in wireless communications. Its error performance analysis, however, is not available in the literature except for the simple case using binary modulation. We address the problem directly based on the decision variables, ending up with closed-form solutions to both conditional and average error probabilities for a general noncoherent MFSK diversity system operating on Rayleigh, Rician, and Nakagami fading channels. The solutions involve some higher order derivatives, and efficient recursive algorithms have been derived for their calculation. The solutions are very general permitting arbitrary diversity order, symbol size, channel parameters, and antenna-array covariance matrix. Numerical examples are also presented for illustration