Soft-quantized demodulation for BPSK over discrete-time memoryless fading channel

The demapping method that simply multiplies the received symbols with channel state information (CSI) coefficients is proved optimal in this paper for any BPSK modulated discrete-time memoryless fading channel (DMFC) from the viewpoint of channel capacity, when CSI is available at the receiver. A generic method to calculate the channel capacity of BPSK modulated DMFC subjected to uniform soft quantization is proposed, which offers a powerful criterion for optimal quantizer design. Numeric results of the Rayleigh fading case are presented, showing that 6-bit uniform quantization offers effective demodulation compared with unquantized demodulation, losing less than 0.1 dB for both with and without CSI cases.