QoS-Constrained Information-Theoretic Sum Capacity of Reverse Link CDMA Systems

The information-theoretic sum capacity of reverse link CDMA systems is investigated in this paper. As the reverse link CDMA systems are interference-limited, for given channel and noise conditions, the information-theoretic system capacity can be achieved by optimaly allocating the transmit powers of the mobile stations. The maximum capacity is often achieved by unfair resource allocation. To avoid such a case, QoS constraints are imposed to individual mobile stations. The exhaustive search of the optimal power allocation solution that maximizes the aggregate capacity, requires O(N^M) computations, where M is the number of the mobile station in the system and N is the granularity of the transmit power of a mobile station. The paper shows that for a single cell, the optimal power allocation solution can be found by polynomial times of computations, without sacrificing the optimality. Numerical results are presented to show the multi-user diversity gain and the impact of QoS constraints.