Performance analysis of MC-CDMA in Rayleigh fading channels with correlated envelopes and phases

The performance analysis of a multicarrier code division multiple access (MC-CDMA) system in Rayleigh fading channels with correlated envelopes and phases is presented, and the effect of phase correlation on the bit error rate (BER) performance is demonstrated. An equivalence relation between independent phases and random spreading sequences for asynchronous MC-CDMA is established, which can explain why the problem of code-independent variance of multiple access interference (MAI) has appeared in the past. Furthermore, it is found that the interference from other subcarriers is always less than half the interference from the same subcarriers for asynchronous MC-CDMA with random spreading sequences. It is also found that Gold, orthogonal Gold, Walsh and random sequences yield similar BER performance in an asynchronous MC-CDMA system with a relatively large number of users. For an uplink MC-CDMA, time synchronisation does not improve BER performance significantly. Finally, asynchronous MC-CDMA systems benefit from the increase of delay spread of the channel, while the opposite conclusion holds for the downlink of MC-CDMA.