Soft-decision demodulation design for COVQ over white, colored, and ISI Gaussian channels

In this work, the design of a -bit (scalar and vector) soft-decision demodulator for Gaussian channels with binary phase-shift keying modulation is investigated. The demodulator is used in conjunction with a soft-decision channel-optimized vector quantization (COVQ) system. The COVQ is constructed for an expanded ( 1) discrete channel consisting of the concatenation of the modulator, the Gaussian channel, and the demodulator. It is found that as the demodulator resolution increases, the capacity of the expanded channel increases, resulting in an improvement of the COVQ performance. Consequently, the soft-decision demodulator is designed to maximize the capacity of the expanded channel. Three Gaussian channel models are considered as follows: 1) additive white Gaussian noise channels; 2) additive colored Gaussian noise channels; and 3) Gaussian channels with intersymbol interference. Comparisons are made with a) hard-decision COVQ systems, b) COVQ systems which utilize interleaving, and c) an unquantized ( = ) soft-decision decoder proposed by Skoglund and Hedelin. It is shown that substantial improvements can be achieved over COVQ systems which utilize hard-decision demodulation and/or channel interleaving. The performance of the proposed COVQ system is comparable with the system by Skoglund and Hedelin—though its computational complexity is substantially less.