Blind channel and linear MMSE receiver determination in DS-CDMA systems

We consider p users in a S-CDMA system operating asynchronously in a multipath environment. Oversampling w.r.t. the chip rate is applied to the cyclostationary received signal and multi-antenna reception is considered, leading to a linear multi-channel model. Channels for different users are considered to be FIR and of possibly different lengths. We consider an individualized linear MMSE receiver for a given user, exploiting its spreading sequence and timing information. The blind determination of the receiver boils down to the blind channel identification. We explore blind channel identifiability requirements. Sufficiency of these requirements is established and it is shown that if zero-forcing conditions can be satisfied, then the CDMA channel (and hence the receiver) is identifiable with probability 1. It is also shown that linear MMSE receivers obtained by different criteria(including a new one) have the same identifiability requirements asymptotically in SNR.