Coding for a coherent DS-CDMA system employing an MMSE receiver in a Rayleigh fading channel

This paper analyzes the performance of a convolutionally coded code-division multiple-access system, which employs a linear, minimum mean-square error (MMSE) receiver for interference suppression. A flat, Rayleigh fading channel is considered, where convolutional encoding and interleaving are employed in order to combat the effects of the fading. Theoretical results are derived for the average bit-error probability of the MMSE receiver, where the optimum tap weights for the adaptive filter are determined by the solution of the Wiener-Hopf equations. Simulation results showing the average bit-error rate of the MMSE receiver are also presented, which incorporate the effects of recursive least squares adaptation, channel estimation using pilot symbol-assisted modulation, and finite interleaving. Results show that the MMSE receiver with coding can provide a substantial gain over the matched-filter receiver in a rapidly varying, Rayleigh fading channel. The results also reiterate the fact that lower rate codes are not necessarily the best choice when used with the MMSE receiver.