Minimum mean-square error design of decorrelator detectors for QS-CDMA

We consider a quasi-synchronous CDMA cellular system (QS-CDMA), in which all users attempt to transmit in synchrony using local GPS-derived clocks. A linear decorrelator detector for QS-CDMA is presented, which is designed according to a minimum mean-square error (MMSE) criterion. By using a time-averaged version of the interfering signal covariance matrix, it is shown that multiuser interference can be rejected without the need to estimate signal time-of-arrival. Furthermore, unlike previous MMSE receiver designs, estimation of the received signal covariance matrix is not required. Bit-error rate results are presented which demonstrate the superiority of the MMSE receiver compared with the conventional matched-filter detector under strong near-far conditions.