Transmitter precoding for CDMA in fading multipath channels: strategy and analysis

The desire to reduce complexity at the mobile unit in cellular systems has led to the investigation of signal processing techniques that move computational complexity from the mobile unit to the base station. In this paper we investigate transmitter precoding for downlink time diversion duplex (TDD) code-division multiple-access (CDMA) communications. In particular, we develop a linear MMSE-based precoding strategy using blind channel estimation for fading multipath channels that allows for simple matched filtering at the mobile unit and is easy to make adaptive. We also present a performance analysis using tools developed for the analysis of conventional (receiver-based) linear blind multiuser detection in unknown channels. We compare the analytical and simulation results to traditional receiver-based blind multiuser detection. It is seen that transmitter precoding offers a reasonable alternative for TDD-mode CDMA when minimizing computational complexity at the mobile unit is a priority.