Soft-decision COVQ for turbo-coded AWGN and Rayleigh fading channels

A robust soft-decision channel-optimized vector quantization (COVQ) scheme for Turbo-coded additive white Gaussian noise (AWGN) and Rayleigh fading channels is proposed. The log likelihood ratio (LLR) generated by the Turbo decoder is exploited via the use of a q-bit scaler soft-decision demodulator, The concatenation of the Turbo encoder, modulator, AWGN channel or Rayleigh fading channel, Turbo decoder, and q-bit soft-decision demodulator is modeled as an expanded discrete memoryless channel (DMC), A COVQ scheme for this expanded discrete channel is designed. Numerical results indicate substantial performance improvements over traditional tandem coding systems, COVQ schemes designed for hard-decision demodulated Turbo-coded channels(q = 1), as well as performance gains over a recent soft decoding COVQ scheme by Ho.