Performance analysis of DS-CDMA systems with polyphase signature sequences in multipath fading environment

Abstract

Direct sequence code division multiple access (DS-CDMA) communication systems using random polyphase sequences with coherent reception in multipath fading channels are considered. The analysis assumes BPSK modulation, asynchronous channel, and a rake receiver. By examining the multiple access interference and self-noise terms due to the multiple access and multipath waveforms, we show that the DS-CDMA system performance with random $m_p$-phase sequences, for $m_p ≥ 3$, differs from that with random binary sequences in multipath fading environment. In the analysis, we use both the Gaussian approximation and characteristic function methods to clearly show that the performance of the DS-CDMA systems varies depending on the number $m_p$ of phases. It is shown that the Gaussian approximation method is not effective in revealing the performance difference: using the characteristic function method, which is a more accurate one, we show that the performance of the DS-CDMA system differs for different values of $m_p$.