Optimum linear decoding of vector quantisation transmitted over a CDMA channel

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