CS-CDMA/CP with M-ZCZ Codes Over a Multipath Fading Channel with Excess Spreads

Convolutional spreading CDMA with cyclic prefix (CS-CDMA/CP) enables multiuser interference-free (MUI-free) transmission over multipath channels with the use of zero correlation zone (ZCZ) codes. In our previous work, we proposed application of a class of binary ZCZ codes generated from an M- sequence, the M-ZCZ code, which has larger user capacity than known binary ZCZ codes and high robustness against transmitter nonlinearity. CS-CDMA/CP guarantees MUI-free transmission only when the data length D, multipath channel length L, and the ZCZ length Z satisfy Z ges D + L - 1, and, for a long spread multipath channel of length L_e > L, CS-CDMA/CP suffers from MUI. In this paper we discuss the effect of MUI over the CS-CDMA/CP system employing an M-ZCZ code and propose MUI cancellation schemes for channels with excess spreads, D + L_e - 1 > Z. Some simulation results show that the proposed schemes show good BER performance and, more importantly, allows increased user population, compared to the fully MUI- free case with a graceful performance degradation.