Combined MMSE interference suppression and turbo coding for a coherent DS-CDMA system

The performance of a turbo-coded code division multiaccess system with a mi nimum mean-square error (MMSE) receiver for interference suppression is ana lyzed on a Rayleigh fading channel. In order to accurately estimate the per formance of the turbo coding, two improvements are proposed on the conventi onal union bounds: the information of the minimum distance of a particular turbo interleaver is used to modify the average weight spectra, and the tan gential bound is extended to the Rayleigh fading channel. Theoretical resul ts are derived based on the optimum tap weights of the MMSE receiver and ma ximum-likelihood decoding. Simulation results incorporating iterative decod ing, RLS adaptation, and the effects of finite interleaving are also presen ted. The results show that in the majority of the scenarios that we are con cerned with, the MMSE receiver with a rate-1/2 turbo code will outperform a rate-1/4 turbo code. They also show that, for a bit error rate lower than 10(-3), the capacity of the system is increased by using turbo codes over c onvolutional codes, even with small block sizes.