On the Impact of Diversity Combining Schemes to the Performance of RAKE Receivers over GWSSUS Fading Channels

Signal-to-interference ratio (SIR) experienced by users is the major quality and capacity indicator of CDMA systems. In this paper, we analyze the impact of diversity combining schemes - maximal-ratio combining (MRC) and equal-gain combining (EGC) - on the SIRs achievable with diversity-reception RAKE receivers over GWSSUS time-variant fading uplink DS-CDMA channels based on finite-dimensional generalized random spreading performance evaluation methodology. Through the results of random matrix theory on the non-asymptotic eigenvalue distributions of finite-size random matrices, SIR statistics with linear RAKE multiuser receivers with MRC and EGC are derived in terms of the key system parameters. It turns out that MRC that is much complex than EGC in terms of channel estimation and computational complexity slightly outperforms EGC at low diversity orders and low channel specularity; however the performance of EGC converges to that with MRC as the diversity order Drarr infin and the channel specularity tends to 1 as well as at low SNRs