Chernoff bound coded DS-CDMA system using MMSE receiver in Rayleigh fading channel

Abstract

This paper analyzes the performance of convolutionally coded direct sequence code division multiple access (DS-CDMA) system based adaptive minimum mean square error (MMSE) receiver using chernoff bound in both AWGN and flat fading channel. Upper bound pairwise error probability is derived for the adaptive receiver. The performance of the system is investigated for LMS adaptive algorithm and optimum implementation of the tap weights for the MMSE receiver and results are compared in terms of both BER and system capacity for different code rates in Rayleigh fading channel. A system with matched filter (MF) receiver is used for the purpose of comparison. Higher code rate have been found to perform better than lower code rate when MMSE receiver is used in fading channel. Results show that the use of Gaussian approximation in coded CDMA system supported by Gaussian nature of the error signal from the MMSE receiver tends to under bound the chernoff upper bound performance. It is shown that for band limited channel, the use of coding provide coding gain at small number of users, while for higher system capacity uncoded system becomes advantage for both MMSE and MF receivers.