An Asymmetric Access Point for Solving the Unfairness Problem in WLANs

Abstract

In atypical deployment of IEEE 802.11 wireless LANs in the infrastructure mode, an access point acts as abridge between the wireless and the wired parts of the network. Under the current IEEE 802.11 Distributed Coordination Function (DCF) access method, which provides equal channel access probability to all devices in a cell, the access point cannot relay all the frames that it receives on the downlink. This causes significant unfairness between upload and download connections, long delays, and frame losses. This unfairness problem comes from the not-so-complex interaction of transport-layer protocols with the MAC-layer access method. The main problem is that the access point requires more transmission attempt probability than wireless stations for correct operation at the transport layer. In this paper, we propose to solve the unfairness problem in a simple elegant way at the MAC layer. We define the operation of an Asymmetric Access Point that benefits from a sufficient transmission capacity with respect to wireless stations so that the overall performance improves. The proposed method of operation is intrinsically adaptive so that when the access point does not need the increased capacity, it is used by wireless stations. We validate the proposed access method by simulation to compare it with other solutions based on IEEE 802.11e. Unlike many papers in this domain, which only validate MAC-layer modifications through simulation or analytical modeling, we provide measurement data gathered on an experimental prototype that uses wireless cards implementing the proposed method.