Downlink DS-CDMA Transmission with Joint MMSE Equalization and ICI Cancellation

The bit error rate (BER) performance of downlink DS-CDMA in a frequency-selective fading channel can be significantly improved by the use of frequency-domain equalization (FDE) based on minimum mean square error (MMSE) criterion. However, the presence of residual inter-chip-inference (ICI) after FDE produces the orthogonality distortion among the spreading codes and the BER performance degrades as the number of multiplex order increases. In this paper, we propose a joint MMSE-FDE and ICI cancellation to improve the BER performance of the DS-CDMA downlink. In the proposed scheme, the residual ICI replica in the frequency-domain is generated and subtracted from each frequency component of the received signal after MMSE-FDE. The MMSE weight at each iteration is derived taking into account the residual ICI. The effect of the proposed ICI cancellation scheme is confirmed by computer simulation