An RLS-based algorithm for estimation and demodulation of QS-CDMA signals

In order to construct the optimal decorrelator for a quasi-synchronous (QS) CDMA receiver, it is necessary to estimate the user delays. However since the system is quasi-synchronous, it is shown that delay estimation is equivalent to estimating a parameter vector which is related linearly to the received signal. A recursive least-squares (RLS) algorithm is developed that approximately computes the joint maximum-likelihood (ML) estimates of the delays and user amplitudes. It is shown that the optimal decorrelator and demodulated symbols are also generated by the RLS algorithm. Simulation and analytical results are presented for the bit-error rate (BER) performance of the adaptive receiver and the averaged squared error (ASE) of the estimated delay vectors is compared with the Cramer-Rao bound.