On downlink throughput maximization in DS-CDMA systems

In this paper, some important characteristics for the aggregate system capacity maximization in downlink of DS-CDMA systems are studied. We derive a close form solution for the optimal power allocation in the case that the users are orthogonal to each other. Theoretically, this orthogonality condition between M active users can be achieved by using null steering adaptive antenna array with at least M antenna elements. In addition, we study the loss of orthogonality and suggest a set of rules for finding the optimal active users. Based on the set of rules we propose two heuristic guided suboptimal scheduling algorithms, which can achieve close to optimal performance in non-orthogonal situation, moreover they can achieve the optimum performance in perfect orthogonal situation.