Achieving MAC fairness in wireless ad-hoc networks using adaptive transmission control

Abstract

Achieving MAC layer fairness in wireless ad-hoc networks is a very challenging issue. We first show that IEEE 802.11 exhibits substantial short-term unfairness due to the randomness in the binary exponential back-off (BEB), the freezing mechanism of the back-off timer, and the concealed information problem (introduced in this paper). To achieve short-term fairness, we propose a novel fairness scheme, called adaptive transmission control (ATC). The basic idea of ATC is to make the senders to contend for the shared medium in a cooperative and adaptive manner by exploiting the overheard information. The ATC includes three mechanisms: CW-tuning, early-reset, and receiver-coordination, which are able to tackle the underlying problems that cause short-term unfairness in IEEE 802.11. Specifically, the CW-tuning mechanism reflects the past usage of the medium among the nodes, and thus greatly reduces the randomness in BEB, while the early-reset mechanism largely prevents the short-term unfairness caused by the freezing mechanism. At last, the receiver-coordination mechanism copes effectively with the concealed information problem by using information available at the receiver side. Extensive simulation results show that the proposed ATC substantially improves the short-term fairness without unduly degrading the throughput.