Gideon Kaplan

On information rates for mismatched decoders

Reliable transmission over a discrete-time memoryless channel with a decoding metric that is not necessarily matched to the channel (mismatched decoding) is considered. It is assumed that the encoder knows both the true channel and the decoding metric. The lower bound on the highest achievable rate found by Csiszar and Korner (1981) and by Hui (1983) for DMCs, hereafter denoted C/sub LM/, is shown to bear some interesting information-theoretic meanings. The bound C/sub LM/ turns out to be the highest achievable rate in the random coding sense, namely, the random coding capacity for mismatched decoding. It is also demonstrated that the /spl epsiv/-capacity associated with mismatched decoding cannot exceed C/sub LM/. New bounds and some properties of C/sub LM/ are established and used to find relations to the generalized mutual information and to the generalized cutoff rate. The expression for C/sub LM/ is extended to a certain class of memoryless channels with continuous input and output alphabets, and is used to calculate C/sub LM/ explicitly for several examples of theoretical and practical interest. Finally, it is demonstrated that in contrast to the classical matched decoding case, here, under the mismatched decoding regime, the highest achievable rate depends on whether the performance criterion is the bit error rate or the message error probability and whether the coding strategy is deterministic or randomized. >

Phase noise effects on M-ary PSK trellis codes

The performance of M-ary phase-shift keying (PSK) coded systems in the presence of added white Gaussian noise (AWGN), with a noisy carrier reference in the receiver, is examined. The results are obtained by combining the Chernoff bound technique with the generating function approach. The bit error probability analysis is carried out for 8- and 16-PSK with code rates of 2/3 and 3/4, respectively. The numerical results obtained demonstrate the error performance degradation due to a Tikhonov phase noise process with parameter alpha . >

On the design and selection of convolutional codes for an uninterleaved, bursty Rician channel

This article focuses on code design and code selection rules under power and decoding delay constraints for an antipodal (BPSK) modulated and convolutionally encoded communication system. The system operates over a slowly fading AWGN channel, described by the block-fading model. We emphasize perfect coherent detection with maximum likelihood decoding assuming ideal channel information (the instantaneous fading values). The dominant design criterion in this scenario is the code diversity level in terms of blocks while the standard Hamming distance plays a secondary role. A code design procedure, based on maximum distance separable (MDS) cyclic block codes is presented along with a code-search algorithm. The performance results of selected codes are assessed via simulation and compared to those achieved by Reed-Solomon codes with erasure and error decoding.

Optimum soft decision demodulation for ISI channels

Two different methods of soft-decision demodulation for channels with finite intersymbol interference (ISI) in the presence of additive white Gaussian noise (AWGN) are analyzed. In both schemes, the cutoff rate R/sub 0/ of the discrete channel created by the demodulator output quantization is chosen as the design criterion. Expressions for the optimal thresholds of the quantizer associated with the demodulation of binary signals are derived. Results for the channel with memory equal to one symbol duration are presented. As a special case, the (1-D) channel with soft decision demodulation is analyzed. Closed-form solutions show that a 4-b quantizer improves performance substantially in this case. >

On information rates in fading channels with partial side information

A coded antipodal communication system operating over a Rayieigh fading channel is considered. A partial Side Information (SI) scheme is addressed, where the receiver has an access to the sum of received faded energies over several consecutive symbols. The generalized cut-off rate is examined both for the independent and for the correlated fading models, and conclusions regarding the usefulness of this particular SI scheme are drawn.

Error Performance Over the Uninterleaved Correlated Rician Channel

In [l], an upper bound on the error probability of block- or convolutionally- coded BPSK over this channel (with similar assumptions on the receiver) was presented. The fading process in [l] is assumed to be piecewise constant (p.c), that is, considered to be constant over a symbol’s duration. We analyze the correlated fading channel both with and without the above mentioned p.c approximation. Coded BPSK performance, as well as the exponential behavior of the error piobability are discussed. For the continuous channel it is assumed that the receiver has an accurate knowledge of the sample path of the realized fading process. We focus on obtaining the limit of ultimate performance and on verifying under what conditions the above mentioned p.c approximation is adequate. Comparisons to the blockfading model are also discussed.

On the Design and Selection of Convolutional Codes for a Bursty Rician Channel

This work addresses code design and code selection rules under power and decoding delay constraints for antipodal (BPSK) modulated and convolutkmally encoded communication system. The system operates over a slowly-fading AWGN channel, described here by the ‘block fading’ model. We specialize to coherent detection and maximum likelihood decoding with ideal channel information (the instantaneous fading values). The dominant design criterion in this scenario is the code diversity level in terms of blocks while the standard Hamming distance plays a secondary role. A code design procedure is presented along with a code-search algorithm. Performance results of a selected code are assessed via simulation and compared to those achieved by a Reed-Solomon code with erasure and error decoding.

Bounds on the Cut‐Off Rate of the Peak Shift Magnetic Recording Channel

We address the peak shift channel, introduced recently by Shamai and Zehavi to provide a simple statistical model for peak shift generated errors in magnetic recording employing peak detectors. This impairment has been identified as a major cause of performance degradation in such devices. We examine the cut-off rate, which is considered as a practical measure to reliable communication rates. Lower bounds on the cut-off rate as well as the zero-error and noiseless (ideal channel) cut-off rates are derived and presented for some interesting parameters. It is shown that the cut-off rate behaves similarly to capacity. We also show that interleaving degrades the performance considerably. The extended model of a peak shift channel concatenated in tandem with a binary symmetric channel, which accounts for both dominant impairments - randomly as well as peak shift generated errors, is also treated and a lower bound on the corresponding cut-off rate is presented.