Blind optimal MMSE receiver for asynchronous CDMA in the presence of multipath

We consider multiple users in a DS-CDMA system operating in a multipath environment. The received cyclostationary spread signal sampled at the chip rate is converted to a stationary vector signal, leading to a linear multichannel model. Prior knowledge of the transmission pulse (spreading sequence) is exploited to obtain the desired user channel estimate blindly. It is shown that the multiple user problem can be decoupled and a single user scenario can be obtained to apply the blind estimation and interference cancelation algorithms banking on limited a priori knowledge. The FIR channel estimation problem is investigated and the optimal MMSE receiver for multipath channels is presented along with a computationally more efficient interference canceling RAKE receiver (ICRR). Both the MMSE receiver and the ICRR are parameterized in terms of the desired user´s channel and quantities that can be estimated from second-order statistics.