Oversampling diversity versus dual antenna diversity for chip-level equalization on CDMA downlink

We examine through numerical simulations the performance of three equalizers for CDMA downlink in which the channel is frequency-selective: the traditional RAKE receiver, and chip-spaced MMSE (minimum mean square error) and ZF (zero-forcing) equalizers. These simulation results provide an upper-bound on average BER performance for users near a single transmitting base-station, in which the channel is assumed static and known. We present results for two channel models: a random 4-path multipath channel with delay spread of 10 micro seconds, and an empirically derived random multipath channel generated by the commercial software package SMRCIM. We compare the cases of diversity obtained by two spatially separated antennas to two "virtual channels" obtained through oversampling a single antenna's received signal. This simulation study has yielded the expected result that spatial diversity is preferable to diversity obtained via oversampling. Furthermore, the MMSE always out-performs both RAKE and ZF equalizers.