Airtime Fairness for IEEE 802.11 Multirate Networks

Under a multi rate network scenario, the IEEE 802.11 DCF MAC fails to provide air-time fairness for all competing stations since the protocol is designed for ensuring max-min throughput fairness and the maximum achievable throughput by any station gets bounded by the slowest transmitting peer. In this paper, we present an analytical model to study the delay and throughput characteristics of such networks so that rate anomaly problem of IEEE DCF multi-rate networks could be mitigated. We call our proposal as Time Fair CSMA (TFCSMA) which utilizes an interesting baseline property of estimating a target throughput for each competing station so that its minimum contention window could be mitigated in a distributed manner. As opposed to the previous work in this area, TFCSMA is ideally suited for practical scenarios where stations frequently adapt their data rates to changing channel conditions. In addition, TFCSMA also accounts for packet errors due to the time varying properties of the wireless channel. We thoroughly compare the performance of our proposed protocol with IEEE 802.11 and other existing protocols, under different network scenarios and traffic conditions. Our comprehensive simulations validate the efficacy of our method towards providing high throughput and time fair channel allocation.