Performance comparison of the multi-code fixed spreading length (MFSL) scheme and the variable spreading length (VSL) scheme for multi-rate MC-CDMA

摘要

In this paper, we compare the performance of two important multi-rate transmission schemes: the variable spreading length (VSL) scheme and the multicode fixed spreading length (MFSL) scheme for MC-CDMA systems. Minimum mean square error combining (MMSEC) is applied for both schemes to cancel the multiuser interference (MUI). It is found that by selecting orthogonal Walsh Hadamard sequences as spreading codes and properly assigning codes for each user, the intercarrier interference (ICI) caused by the nonorthogonality of subcarriers in the VSL scheme can be eliminated and the self-interference (SI) caused by employing multiple codes for each user in the MFSL scheme can also be reduced. The bit error rate (BER) performance of each scheme is obtained by analysis and simulation in a correlated Rayleigh fading channel.