Power control for space-time multiuser CDMA

The objective of this research is to improve the spectral efficiency of the uplink (mobile user to base station) of a CDMA system. Space-time multiuser receivers that jointly decode all the received signals have been shown to provide significant improvements in spectral efficiency relative to a single-user, matched-filter receiver. However, despite the great promises, these receivers have not been embraced by industry. This lack of commercial interest is primarily because issues regarding complexity, robustness to estimation errors, and power control have not been addressed adequately. This dissertation studies the viability of space-time multiuser receivers for a cellular system.; Due to their relatively low complexity in an asynchronous, multipath channel, receivers employing successive interference cancellation (SIC) show promise as a practical approach towards multiuser detection. This dissertation focuses on two such receivers, the space-time matched filter receiver with SIC (STMF-SIC) and the spatial MMSE receiver with SIC (MMSE-SIC). Optimal power allocation for the spatial MMSE-SIC and the STMF-SIC receivers are derived. Power control is also used to compensate for cancellation errors. Fixed-step, binary feedback, iterative power control is shown to converge to close to the optimal solution. Tracking properties in fast-fading channels are investigated through simulations and are shown to be similar for both the matched-filter receiver and the SIC receivers. Simulations are also used to study the performance of SIC receivers in a multicellular system. With equal rate allocation, and under some reasonable assumptions of cancellation error, system capacity with SIC is almost 50% greater than the capacity with a space-time matched-filter receiver. With unequal rate allocation, the capacity improvements with SIC are even more significant.; Thus, using analysis, simulations and reasonable approximations, this dissertation demonstrates that the STMF-SIC and the spatial MMSE-SIC receivers can be practically deployed in a commercial cellular system and promise much higher spectral efficiencies compared to a matched-filter receiver.