Throughput-Optimal Scheduling for Downlink Zero-Forcing SDMA Systems

The downlink zero-forcing beamforming strategy in the case of random packet arrivals is investigated. Under this setting, the relevant fairness criterion is the stabilization of all buffer queues which guarantees a bounded average delay for all users. It has been shown that maximizing a queue-length-weighted sum of the rates is an optimal in the sense that it can guarantee stability of the system. A good cross layer scheduling scheme should jointly consider the queue length and the channel variation of the channel from the physical layer. The average delay, average throughput, and average user queue length of the channel-aware-only scheduling, queue-aware-only scheduling and joint channel-aware and queue-aware scheduling are evaluated. Simulation results show that the joint channel-aware and queue-aware scheduling algorithm can take full advantage of the multiuser diversity gain and provide average delay (or throughput) and fairness improvement compared with channel-aware-only schemes and queue-aware-only schemes.