SINR maximizing equalizer receiver for DS-CDMA

The conventional receiver for DS-CDMA communications is the RAKE receiver which is a (linear) matched filter (MF), matched to the operations of spreading, pulse shape filtering and channel filtering. Such a MF maximizes the Signal-to-Interference-plus-Noise Ratio (SINR) at its output if the interference plus noise is white noise. This may be approximately the case if user-dependent scrambling (aperiodic spreading) is used. However, if no scrambling (hence the spreading is periodic) or only cell-dependent scrambling is used, then the interference exhibits cyclostationarity with symbol period and hence is far from white noise. In that case, the SINR at the output of a RAKE receiver can be far from optimal in the sense that other linear receivers may perform much better. In this paper we propose a restricted class of linear receivers that have the same structure as a RAKE receiver, but the channel MF and the pulse shape MF get replaced by equalizer filters that are designed to maximize the SINR at the output of the receiver. The complexity of the equalizer filters is variable and can possibly be taken to be as low as in the RAKE receiver, while its adaptation(s) guarantees improved performance with respect to the RAKE receiver. The adaptation of the SINR maximizing equalizer receiver can be done in a semi-blind fashion at symbol rate, while requiring the same information (channel estimate) as the RAKE receiver.