Abstract
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.
Highlights
Scalability has been a key design requirement for both the wired Internet and wireless networks
The parameters are chosen according to the specification of 802.11a standard [4] and the leading proposal of 802.11n [2].) distributed coordination function (DCF) medium access control (MAC) delivers as low as 30 Mb/s throughput at the MAC layer with the bit-rate of 216 Mbps, utilizing merely 14% of channel capacity
The network throughput obtained with DCF reduces by approximately 50% as the user population reaches 300
Summary
Scalability has been a key design requirement for both the wired Internet and wireless networks. The next-generation wireless data networks (e.g., IEEE 802.11n [1]) promise to deliver much higher data rates in the order of 100 seconds of Mbps [2], through advanced antennas, enhanced modulation, and transmission techniques This requires MAC-layer solutions to develop in pace with high-capacity physical layers. High-speed wireless networks are being deployed in much more diversified environments, which typically include conference, enterprise, hospital, and campus settings In some of these scenarios, each access point (AP) has to support a much larger user population and be able to accommodate considerable variations in the number of active stations. Simulation results demonstrate that TMAC achieves a scalable network throughput and high efficiency of channel utilization, under different population sizes and diverse transmission rates.
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