Optimal downlink power-control design methodology for a mobile radio DS-CDMA system

A design methodology for a downlink power-control technique that maximizes the user-capacity of a DS-CDMA cellular system is proposed. First, the downlink beam-forming weights for the base-station antenna-array are designed based on the maximum SIR criterion. Then by optimizing the downlink power-control algorithm subject to a fixed total transmit power constraint, we further increase the SINR at the mobile terminal, thus increasing the capacity of the system. Due to the quasi-convex property of the SINR expression, we formulate the power optimization process as a feasibility problem with linear constraints, which can be solved efficiently by linear programming methods. With the same methodology, we can also minimize the required transmit power while satisfying the SINR threshold constraints. Computer simulations are given to evaluate the optimized downlink capacity, received SINR, and the required transmit power of a DS-CDMA system using antenna-arrays at the base-station.