Experimental evaluation of postdetection diversity reception ofnarrow-band digital FM signals in Rayleigh fading

Postdetection diversity is attractive for narrowband digital FM signal reception because the cophasing function, which may be difficult to realize in a fast Rayleigh fading environment, is not required. The combining scheme evaluated here is to weight each frequency demodulator (FD) output in proportion to the νth power of the received signal envelope of that branch. Maximum diversity improvement can be obtained with ν=2 (this combiner is referred to as a postdetection maximal ratio chamber (MRC)). Experimental results are presented on postdetection diversity reception in the Gaussian minimum shift keying (GMSK) signal transmission system. Diversity combining and FD-decision algorithms (decision feedback equalizer (DFE) and maximum-likelihood sequence estimator (MLSE)) are performed by software on a computer using the data of the sampled FD output and received signal envelope obtained from a laboratory transmission system. It is shown that the MRC can attain about a 1-dB larger diversity gain than the selection combiner (SC) when two-branch diversity is used. The degradations of two-branch diversity improvement caused by the differences between demodulator sensitivities and between received signal envelope detector gains are evaluated     

Experiments on postdetection diversity for narrowband digital FMmobile radio

Postdetection diversity, in which the demodulator outputs are weighted in proportion to the vth power of each demodulator input signal envelope when they are added, is described for GMSK signal reception using a frequency demodulator and a one-bit decision feedback equaliser. Experiments on a 16 kbit/s GMSK with a premodulation filter bandwidth-bit duration product of B_bT=0.25, show that using v=2 provides a diversity gain about 1-1.5 dB larger than selection combining, at an average bit error rate of 10^-2 in a Rayleigh fading environment     

Effects of postdetection selection diversity reception in QDPSK land mobile radio

Postdetection selection diversity reception for Nyquist pulse shaped quadrature differential PSK (QDPSK) signal transmissions is addressed. Average bit error rate (BER) performance with differential and coherent demodulation is analysed for multiple-branch diversity reception under slow multipath Rayleigh fading. Diversity effects in real fading environments are verified by 8 and 16 kbit/s transmissions at 1.45 GHz carrier frequency.<>     

Revised analyses of postdetection switch-and-stay diversity in rician fading

The performances of dual-branch postdetection switch-and-stay combining (SSC) for noncoherent orthogonal binary frequency-shift keying and noncoherent orthogonal M-ary frequency-shift keying operating over slow, flat Rician fading channels are a topic of current interest. It is shown that recently published analyses obtain incorrect final results because some incorrect probability distribution parameters are used in the analyses. The previous results are corrected, and it is seen that the final results change significantly. The revised results are used to obtain optimum switching thresholds that minimize the average bit-error rate (BER) performance of these systems. Monte Carlo simulations are presented to verify the results, and it is shown that for a given BER, the signal-to-noise ratio difference of postdetection SSC and predetection SSC is much less than previously reported.     

Unified analysis of postdetection diversity for binary digital FMmobile radio

An analysis is presented of postdetection diversity using both selection combining and general combining for the reception of a binary digital FM signal in a Rayleigh fading environment. Noncoherent (differential and frequency) demodulation is assumed. In the general combiner, the output of each branch demodulator is weighted by the νth power of the demodulator input signal envelope (weighting factor). The optimum weighting factor is found to be ν=2. It is shown that postdetection general combiners using weighting factors of ν=1 and 2 correspond to predetection equal-gain and maximal-ratio combiners, respectively. A closed-form solution and a fairly simple expression are derived for the average bit error rate. Numerical calculations show that the postdetection two-branch diversity gain is only about 0.9 dB inferior to the predetection system when minimum shift keying (MSK) is used     

ARO scheme with combined channel coding and modulation using noncoherent detection

A new method for the combination of channel coding and modulation with noncoherent detection in automatic-repeat-request protocols is described. This scheme can be used in automatic-repeat-request protocols in which each codeword is transmitted m >or= 2 times consecutively. Theoretical analysis shows that this scheme offers a net increase in the performance with respect to other similar protocols.<>     

Arithmetic coding algorithm with embedded channel coding

A joint lossless source and channel coding approach that incorporates error detection and correction capabilities in arithmetic coding is exploited. The encoded binary data representation allows the source decoder to recover the source symbols, even with channel errors. The self-synchronisation property of arithmetic coding, the knowledge of the source statistics, and some added redundancy are used for error detection and correction     

Performances of 16QAM with fading compensation and postdetection diversity reception in satellite mobile channels

This paper studies the effects of N-branch postdetection selection diversity reception, where N = 1, 2, 3 or 4, incorporated with fading compensation on a digital satellite mobile system. The digital satellite mobile system transmits a pilot-symbol-aided 16-ary quadrature-amplitude modulated (PSA-16QAM) signal over the Rician channels. A selection method that makes use of the pilot symbols to select one of the N branches in the diversity reception system for signal detection, and a novel PSA technique that makes use of both the pilot symbols and data symbols for fading compensation, are proposed. Computer simulation tests are used to assess the effects of the proposed techniques on bit-error rate performances (BER) of the PSA-16QAM system in the presence of additive white Gaussian noise (AWGN) or co-channel interference (CCI) in the Rician faded channels. When frequency diversity is used, PSA-16QAM with 2-branch and 4-branch diversity reception occupies about the same bandwidths as quaternary phase-shift-keying (QPSK) without using diversity and with 2-branch diversity, respectively, yet achieving the same capacity. Thus, simulation tests on the BER performances of a QPSK system without diversity and with 2-branch diversity are also carried out and the results are used to determine the preferred system arrangements. © 1997 John Wiley & Sons, Ltd.     

Performance of MFSK signals with postdetection square-law diversity combining in arbitrarily correlated Nakagami-m fading channels

This letter presents an analysis of the error probability for noncoherent orthogonal multiple frequency-shift keying (MFSK) signals with postdetection square-law combining (SLC) when the signals transmitted over additive white Gaussian noise (AWGN) and slow frequency-nonselective arbitrarily correlated Nakagami-m fading channels. New exact expressions in a onefold integral for the probability of error of MFSK signals with postdetection square-law diversity combining operating in AWGN channel as well as in arbitrarily correlated Nakagami-m fading channels are derived. The effects of arbitrarily values of fading severity parameter m and the arbitrarily correlation between the L diversity channels are considered. The derived expressions can be easily computed, and hence, can be usefully exploited in the performance evaluation of digital mobile radio systems.     

Multilevel diversity coding with distortion

In a Diversity Coding System, an information source is encoded by a number of encoders. There are a number of decoders, each of which can access a certain subset of the encoders. We study a diversity coding problem in which there are two levels of decoders. The reconstructions of the source by decoders within the same level are identical, and are subject to the same distortion criterion. Our results imply a principle of superposition when the source consists of two independent data streams. Practical codes achieving zero error can easily be constructed for this special case. A class of open problems on this topic is also suggested     

On symmetrical multilevel diversity coding

Symmetrical multilevel diversity coding with independent data streams has been studied by Roche et al. (1992), and the admissible coding rate region was determined for the case of three levels. In particular, it was shown that coding by superposition is optimal, which means that optimality can be achieved by very simple coding. However, it is very difficult to generalize their proof to an arbitrary number of levels. In this paper, we use a new approach to study this problem, and we show that coding by superposition is optimal for symmetrical multilevel diversity coding in general. We also discuss how our result can be applied when the source consists of correlated data streams. The techniques we use are new in multiuser information theory, and our work sheds some light on the standing problem of characterizing those multilevel diversity coding systems for which coding by superposition is optimal     

Performance comparison of a linearly combined ordered-statistic detectors under postdetection integration and nonhomogeneous situations

Several Constant False Alarm Rate （CFAR） architectures, where radar systems often employ them to automatically adapt the detection threshold to the local background noise or clutter power in an attempt to maintain an approximately constant rate of false alarm, have been recently proposed to estimate the unknown noise power level. Since the Ordered-Statistics （OS） based algorithm has some advantages over the Cell-Averaging （CA） technique, we are concerned here with this type of CFAR detectors. The Linearly Combined Ordered-Statistic （LCOS） processor, which sets threshold by processing a weighted ordered range samples within finite moving window, may actually perform somewhat better than the conventional OS detector. Our objective in this paper is to analyze the LCOS processor along with the conventional OS scheme for the case where the radar receiver incorporates a postdetection integrator amongst its contents and where the operating environments contain a number of secondary interfering targets along with the primary target of concern and the two target types fluctuate in accordance with the Swerling Ⅱ fluctuation model and to compare their performances under various operating conditions.     

像面编码计算成像实验研究及重构图像的质量评价

针对国产化大面阵红外器件技术缺乏,用红外焦平面探测器获取图像时难以消除自身的非均匀性以及信噪比低,航空航天成像应用中的图像采集、传输、存储成本越来越高等问题.论文引入了像面编码计算成像,首先分析了这种成像系统的原理模型,然后将压缩感知理论应用于计算成像中,搭建成像原理样机,进行非压缩和压缩的计算成像实验.最后在重构的图像质量评价中引入了信号子空间分析方法,进行重构图像的信噪比估计,实验结果表明,这种信噪比估计方法更加准确有效,并且可以以此作为实验结论给出实际压缩成像时需要的合理采样次数.     

无线信道中的联合信源信道编码

该文提出了一种噪声信道下传输渐进图像的联合信源信道编码方法。该方法根据信道条件的好坏动态的调整信源编码速率和信道编码速率，因此极大地提高了系统的性能和编码效率。同时该方法还具有结构简单，易于实现等优点。试验证明本方法与以前文献中提出的EEP方法以及UEP方法相比，在信噪比低时即信道条件恶劣的情况下，能够明显提高恢复图像的质量。     

Performance of 16 kbit/s GMSK transmission with postdetection selection diversity in land mobile radio

Through laboratory simulation tests and field experiments in the Tokyo metropolitan area, 16 kbit/s Gaussian filtered minimum shift keying (GMSK) transmission performance has been experimentally clarified in the 920 MHz land mobile radio environment. The experimental results agree closely with theory, and they show that fast multipath fading severely degrades average bit error rate (BER) performance in GMSK transmission. However, a space diversity reception technique using a postdetection selection combining scheme is able to efficiently mitigate the fast multipath fading.     

Optimal quantizer design for noisy channels: An approach to combined source - channel coding

We present an analysis of the zero-memory quantization of memoryless sources when the quantizer output is to be encoded and transmitted across a noisy channel. Necessary conditions for the joint optimization of the quantizer and the encoder/decoder pair are presented, and an iterative algorithm for obtaining a locally optimum system is developed. The performance of this locally optimal system, obtained for the class of generalized Gaussian distributions and the binary symmetric channel, is compared against the optimum performance theoretically attainable (using rate-distortion theoretic arguments), as well as against the performance of Lloyd-Max quantizers encoded using the natural binary code and the folded binary code. It is shown that this optimal design could result in substantial performance improvements. The performance improvements are more noticeable at high bit rates and for broad-tailed densities.     

Adaptive error coding using channel prediction

In this paper, we construct a finite-state Markov chain model for a Rayleigh fading channel by partitioning the range of the received signal envelope into K intervals. Using a simulation of the classic two-ray Rayleigh fading model, a Markov transition probability matrix is obtained. Using this matrix to predict the channel state, we introduce an adaptive forward error correction (FEC) coding scheme. Simulation results are presented to show that the adaptive FEC coding scheme significantly improves the performance of a wireless communication system.     

Optimum symbol-by-symbol mean-square error channel coding

An(n,k)linear block code is used to conveykinformation digits, each having a numerical value attached, in such a way as to minimize the mean-square error of the individual information digits regardless of the other(k-1)positions. This criterion is used because it provides a graceful degradation in the coding performance when the channel temporarily becomes less reliable. Unambiguous encoding is employed, and the channel is assumed to obey a realistic additive property. An optimum pair of symbol encoding and decoding functions are derived, and it is shown that the optimum symbol encoding can be performed in a linear fashion. The related decoding role is the conditional mean estimator. Fourier transforms are central to the optimal design of both rules. The optimum symbol rules tire identical with the properly isolated parts of the optimum mean-square error rules when the code is used to carry the k Information digits considered as a single complete numerical entity, The same channel coding design is therefore optimum for a wide variety of Information configurations. Techniques for implementing the optimum symbol decoders are examined with special emphasis on memoryless channels where the storage requirements for the necessary weighting coefficients are drastically reduced.