Maximization of System Throughput Subject to Access Time Fairness Constraints in Multi-Rate 802.11 WLANs

In the field of wireless communications, it is difficult to achieve good performance and fairness simultaneously, especially in advanced wireless local area networks (LANs), such as 802.11a/b/g, with multi-rate modulation. Although the long-term equal access probability results in throughput fairness, there is considerable performance degradation and unfair channel access time. We address the problem from the perspective of channel access time fairness. The objective of this paper is to design a contention-based Media Access Control (MAC) protocol for data communications in WLAN that can achieve near-fairness access times and maximize the aggregate throughput simultaneously. Our approaches utilize Contention Windows (CW), packet size, and multiple back-to-back packets as decision variables. Of these the multiple back-to-back packets approach offers the best solution. To evaluate our approaches, we introduce the Fairness Index (FI), which evaluates the throughput and the time fairness. In addition, we utilize the Network Simulation 2 (NS2) as a simulation tool to evaluate the theoretical maximum throughput. The simulation results show that our approach not only achieves near-fairness access times, but also improves the total throughput.