Association Control for Wireless LANs: Pursuing Throughput Maximization and Energy Efficiency
Résumé
Because the access points (APs) and the stations (STAs) of a community access network are deployed at the users' desired places, the APs and STAs tend to concentrate in certain areas. A concentration of STAs often results in the AP(s) and STAs in that particular area suffering from severe congestion. A concentration of APs, on the other hand, may cause energy wastage. While a number of association control schemes are proposed to alleviate congestion in WLANs, the existing schemes do not necessarily maximize throughput and do not consider energy consumption. In this paper, we analytically formulate the network throughput as the multiplication of the success probability, frame transmission rate, and channel air-time ratio. The second and third components can easily be monitored and controlled based on measurements of local link and channel condition using the off-the-shelf WLAN devices. On the other hand, the first component, success probability is a function of the number of contending nodes that is extremely difficult to monitor in overlapping WLANs. Due to this reason, we extend our theoretical study and show that success probability can be indirectly maximized by controlling air-time ratio. Finally, we propose an association control scheme that aims at maximizing throughput and reducing energy consumption by taking account of the multiplication of frame transmission rate and air-time ratio. The proposed scheme is evaluated by computer simulations and testbed experiments conducted under real-world complex scenarios with UDP and TCP traffic. Both the simulations and actual implementations confirm the correctness of the theoretical work and the effectiveness of the proposed scheme.
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