Distributed Multiuser Scheduling for Improving Throughput of Wireless LAN

In wireless LANs, the performance of CSMA/CA might be degraded by several problems: (i) severe collisions in the uplink, (ii) head-of-line problem caused by fading in the downlink, and (iii) serious unfairness between uplink and downlink. In this paper, a distributed multiuser scheduling (DMUS) scheme is proposed to simultaneously address these problems. In DMUS, a node (i) computes its normalized SNR (signal to noise ratio) as the ratio of its instantaneous SNR to its average SNR, and (ii) contends via a contention window (CW) for the channel to initiate its uplink or downlink transmission when its normalized SNR is greater than a threshold. The contribution is threefold: (i) All three problems are solved in a unified framework by applying multiuser diversity in both uplink and downlink. Fresh SNR is exploited for distributed scheduling meanwhile airtime fairness is retained. (ii) SNR threshold and CW are jointly optimized to maximize throughput, taking into account time-variant link quality, collision probability and protocol overhead. (iii) Network performance is theoretically analyzed. Extensive simulations confirm that DMUS greatly improves total throughput under almost all scenarios compared with both the contention-based CSMA/CA scheme and the contention-free PCF scheme.