Analysis of iterative multiuser receiver for DS-CDMA in Rayleigh fading environment

The performance of a parallel interference cancellation (PIC) multiuser receiver for the direct sequence-code division multiple access (DS-CDMA) system over the frequency-selective and slowly Rayleigh fading uplink channel is analyzed in this research. Our analysis framework assumes random signature sequences, asynchronous transmission, coherent detection, perfect estimation of channel parameters including time delays, carrier phases and fading coefficients. To yield a good demodulation performance in a multipath environment at the receiver, the maximal ratio combining (MRC) is concatenated with PIC. By using the recursive relation between the receiver outputs for consecutive iterations, we obtain the decision statistic for every user at each iteration. The decision statistic is used to derive the asymptotic limit on the bit error rate (BER) of the multiuser receiver as the number of iterations approaches infinity. The asymptotic limit demonstrates the maximal performance improvement that can be achieved by the multiuser receiver, which can be interpreted as the lower bound for BER performance of a PIC receiver in the Rayleigh fading channel.