Demodulation and code acquisition using decorrelator detectors for QS-CDMA

A linear detector for a quasisynchronous code-division multiple-access (QS-CDMA) cellular system 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. An asymptotic form of the MMSE detector, corresponding to a decorrelator implemented using a projection operator, is also obtained. Bit-error rate (BER) results are presented which demonstrate the superiority of the MMSE receiver over the conventional matched-filter detector under strong near-far conditions. An analysis of the expected acquisition time T~/sub ACQ/ is given for the decorrelator detector using a serial search scheme. The results obtained show that T~/sub ACQ/ is far less for a code acquisition method using the decorrelator as opposed to a conventional matched filter.