Optimal Multi-user Space Time Scheduling for Wireless Communications

The multi-user MIMO space time scheduling problem is the prime focus of the paper. Optimizing the link level performance of the MIMO system does not always imply achieving scheduling level optimization. Therefore, the design optimization across the link layer and the scheduling layer is very important to fully exploit the temporal and spatial dimensions of the communication channel. In this paper, we shall address the design of the optimal space time scheduler for the multi-user MIMO system based on an information theoretical approach. We shall assume partial feedback channel, namely a scaler rate-feedback channel is available to the transmitter respectively but the full channel matrix is unknown to the transmitter. With the partial feedback, we found that the optimal resource allocation strategy is water-filling in both the temporal domain and spatial domain. The optimal scheduler should allocate all the power to at most nR users at any particular instant. The optimal scheduler performance depends on the total number of user (K), the number of receive antenna at the base station (nR), and the number of transmit antenna at the mobile (nT ). The scheduling gain increases with nR due to the distributed MIMO configuration formed between mobile users and base station. With single power feedback channel, the scheduling gain reduces as nT increases, illustrating that transmit diversity hurts the scheduling performance in the case of scalar feedback. Finally, scheduling performance improves as K increases due to the multi-user selection diversity.