Comparison of downlink transmit diversity schemes for RAKE and SINR maximizing receivers

In DS-CDMA communications, the conventional receiver is the RAKE receiver. In the downlink (base station to mobile) signalling with celldependent scrambling, orthogonal codes and a common channel for all the users, this receiver does not maximize the Signal-to-Interference-plus-Noise Ratio (SINR) at its output. Another receiver, with the same structure as the RAKE receiver, is suitable for downlink DS-CDMA communications; the one in which the channel matched filter gets replaced by a filter that is designed to maximize the SINR at the receiver output. In this paper, we analyze the use of three different Transmission Diversity (TD) techniques, namely Space-Time TD (STTD), Orthogonal TD (OTD) and Delay TD (DTD). All of them are compared for the two receiver structures: RAKE and max-SINR receivers. The max-SINR receiver structures proposed here for the three TD modes are new and are shown to usually significantly outperform the RAKE schemes. We also discuss the relative performance merits of the three TD schemes for one or the other receiver structure.