Multicode DS-CDMA with joint transmit/receive frequency-domain equalization

Bit error rate (BER) performance of multicode direct-sequence code division multiple access (DS-CDMA) in a frequency-selective channel severely degrades due to strong inter-chip interference (ICI). Frequency-domain equalization (FDE) based on the minimum mean square error (MMSE) criterion can take advantage of the channel frequency-selectivity and significantly improve the BER performance. However, the performance improvement is limited by the residual ICI which is present after MMSE-FDE. In this paper, we apply a joint transmit/receive MMSE-FDE (called double MMSE-FDE in this paper) for multicode DS-CDMA signal transmissions to further improve the BER performance. We derive the conditional BER for the given channel realization and evaluate the achievable average BER performance by Monte-Carlo numerical computation method. The BER performance is confirmed by the computer simulation.