Towards Scalable MAC Design for High-Speed Wireless LANs

The growing popularity of wireless LANs has spurred rapid evolution in physical-layer technologies and wide deployment in diverse environments. The ability of protocols in wireless data networks to cater to a large number of users, equipped with high-speed wireless devices, becomes ever critical. In this paper, we propose a token-coordinated random access MAC (TMAC) framework that scales to various population sizes and a wide range of high physical-layer rates. TMAC takes a two-tier design approach, employing centralized, coarse-grained channel regulation, and distributed, fine-grained random access. The higher tier organizes stations into multiple token groups and permits only the stations in one group to contend for the channel at a time. This token mechanism effectively controls the maximum intensity of channel contention and gracefully scales to diverse population sizes. At the lower tier, we propose an adaptive channel sharing model working with the distributed random access, which largely reduces protocol overhead and exploits rate diversity among stations. Results from analysis and extensive simulations demonstrate that TMAC achieves a scalable network throughput as user size increases from 15 to over 300. At the same time, TMAC improves the overall throughput of wireless LANs by approximately 100% at link capacity of 216 Mb/s, as compared with the widely adopted DCF scheme.