Successive interference cancellation in asynchronous CC-CDMA systems under Rician fading channels

Abstract

The unprecedented frequency diversity gain offered by complementary coded code-division multiple access (CC-CDMA) makes it more attractive than conventional CDMA systems in frequency selective fading channels. CC-CDMA loses its interference-resilient capability due to non-ideal correlation characteristics of complementary codes (CC) under uplink asynchronous communications. The existence of multiple access interference (MAI) in asynchronous systems results in drastic reduction in error rate performance in CC-CDMA systems. In this paper, the analysis of successive interference cancellation (SIC) is proposed for CC-CDMA systems as an alternative to existing non-interference cancellation schemes in uplink communication. The average bit error probability expressions for single branch and M-branch CC-CDMA systems operating under Rician fading channels are derived using alternate integral expression of Q-function. The accuracy of obtained closed form error probability expressions are confirmed through the proposed joint SIC with maximal ratio combining and minimum mean square error combining techniques in uplink CC-CDMA systems. The significance of soft-decision compared to hard decision SIC for CC-CDMA systems is also analyzed for both equal power and extreme near-far conditions. Furthermore, the simulation results exposed that significant performance improvement is obtained under near-far situations in uplink asynchronous CC-CDMA systems overcoming the effects of MAI and achieving improved system capacity.