Turbo Coding for a Coherent DS-CDMA System Employing a MMSE Receiver on a Rayleigh Fading Channel

Previous research which analyzed the performance of a convolutionally coded CDMA system with a MMSE receiver for interference suppression showed that lower rate codes are not always the best choice on Rayleigh fading channels. In this paper, we analyze the performance of a turbo-coded CDMA system with the MMSE receiver. Theoretical bounds are derived based on the optimum tap weights of the MMSE receiver and the tangential bounds of turbo codes. Simulation results incorporating the effects of finite interleaving and RLS adaptation are also presented. The results show that with the MMSE receiver, the high rate turbo code is the best choice. They also show that, except for a bit error rate (BER) lower than 10−3, the capacity of the system is not increased by using turbo codes with small block sizes. ∗This work was supported by the National Science Foundation, TRW, CoRe project and Center for Wireless Communcations, UCSD.