Dimitrios P. Bouras

Optimal decoding of coded PSK and QAM signals in correlated fast fading channels and AWGN: a combined envelope, multiple differential and coherent detection approach

The maximum likelihood sequence estimator for the reception of coded digital phase modulated signals with single or multiamplitude constellations, transmitted over a multiplicative, frequency-nonselective (i.e., flat) correlated fast fading Rayleigh or Rician channel and corrupted by additive white Gaussian noise (AWGN), is derived. Due to this correlation, the errors caused by fading tend to occur in bursts. In the analysis, no assumption simplifying the problem is made. For fast fading the authors consider the most general case where both phase and amplitude distortion resulting from the fading process could change significantly and thus cannot be assumed to be constant over a number of transmitted symbols. It is shown that the estimators hardware structure consists of a combination of envelope, multiple differential and coherent detectors. With multiple differential detectors they define a receiver structure consisting of a combination of more than one distinct differential detectors each of them employing a progressively increasing (by the symbol duration) time-delay element. The outputs of these detectors are jointly processed by means of an algorithm which is presented in a recursive form. The derivation of this new receiver is general enough to accommodate trellis coded phase shift keying (PSK) and quadrature amplitude modulated (QAM) systems. Differentially encoded signals, such as the /spl pi//4-shift differential quadrature phase shift keying (DQPSK) scheme can also be incorporated. In order to reduce the overall receiver implementation complexity, several reduced complexity, near-optimal versions of the algorithm are presented. These reduced complexity receivers are based on the use of only a few multiple differential detectors. Performance evaluation results for reduced complexity trellis coded /spl pi//4-shift DQPSK, /spl pi//4-shift 8-DQAM (differential quadrature amplitude modulation) and 8-DPSK (differential phase shift keying) systems have demonstrated that the proposed receivers significantly reduce the error floors caused by fading. >

Optimal detection of coded differentially encoded QAM and PSK signals with diversity reception in correlated fast Rician fading channels

The optimal sequence estimator for digital signals received over Lambda different channels is derived. Each of these channels corrupts the transmitted signal by a mixture of additive white Gaussian noise (AWGN) and frequency-nonselective, correlated, fast Rician fading. By analysis it is shown that for the lth (1 >

Neural-net-based receiver structures for single- and multiamplitude bandlimited signals in CCI and ACI channels

This paper presents analysis and performance-evaluation results for several neural-network-based nondecision-feedback receiver structures, which improve the performance of bandlimited single- and multiamplitude signals transmitted over additive interference channels, such as cochannel interference (CCI) and adjacent channel interference (ACI). In particular, we propose, analyze, and evaluate a training algorithm for Nyquist-filtered single- and multiamplitude signals, based upon a novel nonuniform signal-sampling technique. We also introduce a novel nonlinear activation function for multiamplitude signals and evaluate its performance via computer simulation and in conjunction with various bandlimited signaling formats, detection techniques, and neural-network structures. Bit-error rate (BER) performance-evaluation results of the proposed neural-network receivers for coherent and noncoherent detection of Nyquist- and Butterworth-filtered single- and multiamplitude signals have shown performance improvements in the presence of CCI and ACI.

HDTV picture quality performance in the presence of random errors, analysis and measures for improvement

Abstract We study the performance of the picture quality of HDTV in the presence of random errors and find the different kinds of picture impairments that may arise. The problems associated with picture coding, including variable length and Huffman coding, are investigated in great detail. The use of DC differential coding and the loss of block synchronization cause errors to perpetuate to other regions of the picture, and hence are identified as the major causes of poor performance. Motivated by these observations, two novel techniques which significantly improve the picture quality are proposed, analyzed and evaluated. The first technique is based upon encoding the actual values of the DC coefficients instead of the commonly used differential DC coding. This is done by means of a new set of Huffman codewords. It is shown that, contrary to present belief, by coding the actual DC values it is possible to maintain the high compression obtained by the commonly employed differential DC coding and at the same time significantly improve the noise resistance of the coding scheme. The second proposed technique introduces a simple but effective synchronization scheme which restricts the effects of residual errors to within 32 × 16 pixel superblocks thus improving the quality of the received picture. This synchronization area is much smaller than the 5632, 4024 and 3072 pixel areas proposed by the four HDTV proposals. Incorporation of the two techniques yields a scheme which has excellent noise performance characteristics and increases the overall noise resistance of the HDTV system. This scheme is applied to both reference frames and inter-frames and improves the SNR at which the HDTV picture suddenly deteriorates by 2.5–3 dB. After that the deterioration is more graceful, as the error propagation is limited to the superblock boundaries.

Maximum likelihood decoding of coded digital signal in frequency selective fast fading channels

The maximum likelihood sequence estimation (MLSE) receiver is derived for coded digital signals transmitted over frequency-selective fast Rician fading channels. The derivation is general enough to accommodate single as well as multilevel signals. For the channel model the authors have adopted the TIA (Telecommunications Industry Association) standard 2-ray model with both direct and reflected signal components subject to fast Rician fading. In addition, they have proposed suboptimal, reduced-complexity versions of the MLSE receiver, the performance of which was evaluated by means of computer simulation.<<ETX>>

Noncoherent trellis coded pi /4-shift DQAM with diversity reception for future digital mobile/cellular communication systems

The authors derive the optimal sequential noncoherent diversity receiver for trellis coded pi /4-shift differentially encoded quadrature amplitude modulated ( pi /4shift DQAM) signals received over l (1<or=l<or= Lambda ) independent channels. Each of these channels corrupts the transmitted signal by a mixture of additive white Gaussian noise (AWGN) and flat fading. To reduce the overall implementation complexity, the authors have proposed and evaluated suboptimal (e.g., having a small number of differential detectors and equal combining diversity structures) versions of the receivers. Some bit error rate (BER) performance evaluation results are presented for a pi /4-shift 8-DQAM scheme, clearly indicating significant performance improvements, including substantial error floor reductions, as compared to a conventional differentially detected Pi /4-shift differentially encoded quadrature phase shift keying ( pi /4-shift DQPSK) scheme.<<ETX>>

Comment on "Maximum likelihood decoding of uncoded and coded PSK signal sequences transmitted over Rayleigh flat-fading channels"

This comment points out some papers published before the paper of Vitetta and Taylor (see ibid., vol.43, no.11, p.2750-58, 1995). These early papers have dealt with the general problem of maximum-likelihood sequence estimation of coded/uncoded phase-shift keying (PSK) and quadrature amplitude modulation (QAM) signals in correlated Rician and Rayleigh-fading channels. These publications did not assume use of interleaving or use of optimal codes, designed for interleaved systems. The statistical properties of the multiplicative fading process have been included in the design of the receivers which were proposed, analyzed, and evaluated. The research contributions documented in these papers have also shown for the first time in the open literature the link between conventional detection techniques and the maximum-likelihood detection of signals in this type of fading channels.

Non-coherent diversity receivers for mobile and personal satellite communications

Improved non-coherent receivers for mobile and personal satellite communications are presented and evaluated. The channel is assumed as being corrupted by shadowing and multipath fading. The results demonstrate that the receivers are capable of reducing the error floors considerably and provide improvements higher than 12 dB. The technology is promising and a good candidate for use in the development of future wireless multimedia personal communication terminals.