A Scheduling Scheme under a Ratio Constraint for the Multiuser MIMO Systems

A scheduling scheme for MIMO systems which has the capability of obtaining multiuser diversity gain and controlling the link connection ratio among users simultaneously is proposed. Based on the Gaussian assumption of MIMO channel capacity which is fed back to the base station from each mobile, a Gaussian cost function with an appropriate mean and variance is used as a scheduling criteria. The mean and variance of the cost function permits the resources for the proposed scheduler to be controlled. We first consider the optimal scheduler, which maximizes overall system capacity with the desired link connection ratio(a priori desired ratio), and a method is proposed to obtain weights for the optimal scheduler using some properties of the Gaussian statistics. Although the optimal scheduler has the major impact on system capacity, the complexity associated with weight calculation is high. Thus, two types of suboptimal schedulers, weights of which are not dependent on the channel statistics, denoted as the Control Variance(CV) scheduler and the Control Mean(CM) scheduler, are proposed. The overall system capacity of the proposed schedulers, which is significantly enhanced by multiuser diversity, was evaluated analytically and verified by computer simulation. The simulation results show that the overall system capacity of the CM and the CV scheduler is above 99% that of the optimal scheduler. In addition, another result show that the proposed schedulers manage resources accurately, for a relatively small number of antennas.