IEEE 802.11 over multi-hop wireless networks: problems and new perspectives

The distributed coordination function (DCF) mode of the IEEE 802.11 MAC standard, though proposed for medium access in wireless local area networks, is seen as the de-facto medium access standard in multi-hop wireless networks. In this paper we contend that the unique characteristics that differentiate multi-hop wireless ad-hoc networks from local area wireless networks render the IEEE 802.11 MAC protocol inefficient in ad-hoc networks. Specifically, we focus on the band of contention and the fairness model employed by the IEEE 802.11 MAC protocol in our study. We substantiate our arguments through simulations of idealized (centralized) protocols, and consider the key changes required to adapt the IEEE 802.11 MAC protocol for multi-hop wireless networks. We then propose a simple medium access scheme within the IEEE 802.11 MAC framework, called flow based medium access (FBMA) that achieves significantly better fairness properties while adhering to the purely distributed operations of the basic IEEE 802.11 MAC scheme. We demonstrate the performance of the proposed MAC protocol through simulations.