This paper deals with a receiver scheme where adaptive equalization and channel decoding are jointly optimized in an iterative process. This receiver scheme is well suited for transmissions over a frequency-selective channel with large delay spread and for high spectral efficiency modulations. A low-complexity soft-input soft-output M-ary channel decoder is proposed. Turbo equalization allows intersymbol interference to be reduced drastically. For most time-invariant discrete channels, the turbo-equalizer performance is close to the coded Gaussian channel performance, even for low signal-to-noise ratios. Finally, results over a time-varying frequency-selective channel proves the excellent behavior of the turbo equalizer.

In this paper, a receiver is proposed to combat intersymbol interference (ISI) generated over a frequency selective channel. The receiver is based on a symbol detector and a channel decoder separated by a deinterleaver. Through an iterative detecting-decoding process, using turbo-codes principle, the so-called turbo-detector manages to overcome frequency selectivity, especially over a Gaussian channel. Simulation results show the turbo-detector efficiency over both Gaussian and GSM channels.

This paper presents a new family of convolutional codes, nicknamed turbo-codes, built from a particular concatenation of two recursive systematic codes, linked together by nonuniform interleaving. Decoding calls on iterative processing in which each component decoder takes advantage of the work of the other at the previous step, with the aid of the original concept of extrinsic information. For sufficiently large interleaving sizes, the correcting performance of turbo-codes, investigated by simulation, appears to be close to the theoretical limit predicted by Shannon.

The performance of noncoherent reception with orthogonal frequency division multiplexing (OFDM) and binary frequency-shift-keying (BFSK) modulation over multipath fading channels with noise is investigated. This analysis demonstrates that it is possible to transmit information in selective channels with no symbol interference. Expressions of the bit error probability (BEP) are derived in the context of frequency selective Rayleigh and frequency selective Rician fading channels with and without convolutional coding.>

The performance of noncoherent reception in fast frequency hopped spread-spectrum (FFH-SS) communication systems operating through noisy, fading multipath channels is investigated. Systems operating with binary frequency-shift keying (BFSK) modulation and noncoherent demodulation are examined under the assumption of very slow fading. These analyses demonstrate the frequency hopping benefits in selective channels. Expressions are derived for the bit error rate in the context of selective Rayleigh and selective Rician fading channels, as a function of channel and system parameters.>

The authors present the performance analysis of an FFH-SSMA system with a binary frequency-shift keying modulation scheme and noncoherent demodulation, operating in a combined environment of Rayleigh selective fading, other users interference, and additive white Gaussian noise. Improvement due to the use of equal gain diversity (EGD) is studied in terms of bit-error rate (BER). Expressions of the BER are evaluated when a maximum-likelihood decision criterion is used to show the advantages of the use of frequency hopping selective Rayleigh fading channels. Results show the equivalence between frequency hopping and direct-sequence (DS) modulation in combating multipath fading. The performance, in terms of irreducible error probability, of the system under study and that of the DS-CPSK when using EGD are not significantly different.>

The noncoherent reception performance of a slow frequency-hopped binary frequency-shift-keying (SFH-BFSK) modulation scheme in an underwater acoustic channel is investigated. Expressions of the bit error rate (BER) are obtained in the context of Rayleigh selective and Rician selective fading channels as a function of channel and system parameters. Improvements due to the use of error correcting codes (convolutional coding with Viterbi decoding algorithm) are investigated. Because of the difficulty in exact evaluation of the BER, upper bounds are generally used. In this case, the Monte Carlo simulation approach was used to obtain numerical results for high BERs. The Union-Bhattacharyya upper bound is used for low BERs.>