Time-varying MMSE interference suppression in asynchronous DS/CDMA systems over multipath fading channels

The authors present a new MMSE-based multiuser detector for asynchronous DS/CDMA communications over frequency-selective fading channels. The proposed detector is able to simultaneously suppress both the multiaccess interference and a narrowband interference with known second-order statistics. It is shown that narrowband interference suppression requires in general a time-varying processing of the observables. As to the performance assessment, we give formulas for the system bit error rate for Rayleigh fading and we show that the detector is near-far resistant. Results demonstrate that the proposed system is effective in combating the overall interference. Moreover, enlarging the processing window and oversampling the signal space yield a remarkable improvement in the system performance, especially for large number of users