Low-complexity performance optimization for MIMO CDMA systems

A low-complexity approach is proposed for optimizing the performance of a multiple input multiple-output (MIMO) direct sequence code division multiple-access (DS-CDMA) system in the uplink for frequency selective fading channels. Each user transmits a weighted form of its symbols through its multiple antennas, and a receive antenna array at the base station is equipped with minimum mean square error (MMSE) receivers. We arrive at our system by attempting to find a suboptimal solution based on maximizing the multiuser signal-to-noise interference plus noise ratio (SINR) and minimizing the MMSE of the received signal simultaneously. This provides a noniterative solution for joint transmit beamformer weights of each user and coefficients of the corresponding receiver. In addition, a power control algorithm for suppressing interference is also derived. Numerical results reveal that significant system performance and capacity improvement over conventional approaches are possible.