Soft multiuser decoding for vector quantization over Rayleigh fading CDMA channels

Joint optimization of the source and multiuser decoder is considered for vector quantization over a frequency-selective Rayleigh fading synchronous CDMA channel. The optimal (minimum mean squared error) decoder and a suboptimal “user-separated” version are presented. The proposed decoders are soft in the sense that they utilize the soft information available from the channel at the receiver. Simulation results show a significant performance gain of the soft decoders with respect to the conventional scheme that uses maximum likelihood multiuser detection followed by table look-up decoding