Soft-Decision COVQ for M-ary PAM Modulated AWGN and Rayleigh Fading Channels

Developments in vector quantization based joint source-channel coding have produced codes which efficiently and reliably transmit data signals over noisy channels. Further advancements through soft-decision decoding have shown improvements in signal-to-distortion ratio (SDR) over hard-decoding. We present a q-bit soft decision demodulator for the vector quantization of Gaussian and Gauss-Markov sources over M -Pulse Amplitude Modulated (M -PAM) additive white Gaussian noise (AWGN) channels and Rayleigh fading channels. Observations are made on the transition probability matrix of the equivalent channel corresponding to the concatenation of the modulator, physical channel and soft-decision demodulator. Gains of almost 0.5 and 0.45 dB in SDR are noted for the AWGN channel and the Rayleigh fading channel, respectively. We observe that most of the gain is achieved by increasing the demodulator resolution from q = 1 to q = 2, and that the gain is negligible for q > 2. Our system has a higher storage requirement at the decoder to store codewords. The system’s decoding complexity is dependent on q but is still lower than other soft decoding schemes.