Distributed Access Time Control for Per-Station Fairness in Infrastructure WLANs

Abstract

SUMMARY Fairness among uplink and downlink TCP flows can notbe supported in infrastructure IEEE 802.11 Wireless LANs using the dis-tributed coordination function (DCF). In order to resolve this problem, wepropose the Distributed Access Time Control (DATC) scheme, in whicheach station controls the rates of its TCP flows based on channel accesstime. The DATC scheme can provide per-station fairness even when thenumber and direction of flows in each station are different. This schemecan be simply implemented in mobile stations without having to modifythe access points. The properties of the proposed scheme are investigatedand its effectiveness is verified through simulations. key words: wireless LAN, TCP, fairness 1. Introduction As the Internet has become an essential part of the daily lifeof an ordinary man, it must be accessible at any time andat any place. To satisfy such public demand, wireless localarea networks (WLANs) based on IEEE 802.11 standard [1]are widely deployed in public areas such as airports, cafes,hotels, etc. Consequently, due to the large number of peopleaccessing the Internet via WLANs [2], it should be ensuredthat such services be provided to users fairly.In the 802.11 standard, fairness is assured at the MediaAccess Control (MAC) layer by the Distributed Coordina-tion Function (DCF), which aims to give equal access op-portunity to all wireless devices. Meanwhile, the other MAClayer protocol, i.e., the Point Coordinate Function (PCF),gives more control to an Access Point (AP), but there areonly a few WLAN devices that support PCF. The issue offairness in WLANs has been studied extensively, but most ofwhich have focused on the enhancement of DCF for fairnessat the MAC layer [3]–[5]. Although these MAC layer fair-ness mechanisms canprovide fair access opportunity to eachstation, these solutions require changes at the MAC layerand are targeted for ad-hoc networks. Therefore, these so-lutions are impractical to be used in infrastructure WLANs.In infrastructure networks, it is necessary to provide fairnessamong stations that have numerous flows moving in differ-ent directions.Bottigliengo et al.[6] showed that the unfairness be-