A linear decoder for vector quantization over a CDMA channel

The problem of joint source-channel and multiuser decoding for code division multiple access (CDMA) channels is considered. The block source-channel encoder is defined by a vector quantizer (VQ). The jointly optimum solution to such a problem has been considered before, but its high complexity makes it impractical for systems with medium to large number of users. Instead, the optimum linear decoder with a lower complexity that minimizes the mean squared error is introduced. The linear decoder is soft in the sense that it utilizes all the soft information available at the receiver. Analytical and simulation results show that at low channel signal to noise ratio, the proposed decoder's performance is almost the same as that of the jointly optimum decoder and significantly better than that of a tandem approach which uses separate multiuser detection and table-lookup decoding.