Precoding with Partial Channel Information for CDMA with Ultra-Low Complexity Receivers

We consider transmitter precoding for interference suppression and diversity exploitation for multi-antenna CDMA. The receivers are constrained to matched filter detection without channel state information (CSI) or receiver-based multiuser detection. We first develop precoders for scenarios where perfect downlink channel information is available at the transmitter. We show that full transmit antenna diversity is achievable, even for nonorthogonal codes, though we suffer an SNR loss that is a simple function of the spreading code crosscorrelations. We also develop precoders for cases in which the transmitter has partial channel information, modelled as knowledge of conditional channel correlation matrices, and we apply them to Jake’s fading model. We show, in summary, that transmitter precoding offers a reasonable alternative to receiver-based multiuser signal processing when minimizing computational complexity at the mobile unit is a priority.