Joint power control, multiuser detection and beamforming for CDMA systems

CDMA systems are limited by the interference that users create for each other. Several methods of controlling and/or suppressing the interference through power control, multiuser detection (temporal filtering) and beamforming (spatial filtering) are studied to increase the capacity of CDMA systems. We investigate the capacity increase that is possible by combining power control with intelligent temporal and spatial receiver filter design. The SIR maximizing joint temporal-spatial receiver filters in unconstrained and constrained filter spaces are derived. Two-step iterative power control algorithms that converge to the optimum powers and the joint temporal and spatial receiver filters in the corresponding filter domains are given. A power control algorithm with less complex filter update procedure is given. It is observed that significant savings in total transmit power expended by all users in the system are possible if filtering in both domains are utilized compared with conventional power control and joint optimal power control and filtering in one domain.