Multi-Code MC-CDMA Using Joint CDTD and Inter-Code Interference Cancellation

In multicarrier code division multiple access (MC-CDMA), a good bit error rate (BER) performance can be achieved by using frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion. However, the presence of residual inter-code interference (ICI) after MMSE-FDE and despreading degrades the BER performance of the multi-code MC-CDMA. The use of ICI cancellation can improve the BER performance of the multi-code MC-CDMA. To further improve the BER performance, transmit diversity technique is effective. In this paper, cyclic delay transmit diversity (CDTD) is considered. CDTD can achieve the frequency diversity gain, whereas the well-known space-time transmit diversity (STTD) can achieve the antenna diversity gain owing to the space-time coding and provide a better BER performance than CDTD. It is shown in this paper that the performance degradation of CDTD is mainly due to the residual ICI after MMSE-FDE. In order to achieve a good BER performance, the multi-code MC-CDMA using joint CDTD and ICI cancellation is proposed, and its BER performance is evaluated by computer simulation.