Abstract-Under a multirate network scenario, the IEEE 802.11 DCF MAC fails to provide airtime fairness for all competing stations since the protocol is designed for ensuring max-min throughput fairness. As such, 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 the rate anomaly problem of IEEE DCF multirate networks could be mitigated. We call our proposal Time Fair CSMA (TFCSMA) which utilizes an interesting baseline property for estimating a target throughput for each competing station so that its minimum contention window could be adjusted 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 toward providing high throughput and time fair channel allocation.
In addition, I would like to thank all my lab mates, in particular, Anindo, Anurag, Lakshmi, and Torsha at the Center for Distributed and Mobile Computing (CDMC) for their constant support and helpful suggestions during the course of my thesis work. My friends have made my life wonderful and memorable in Cincinnati. Special thanks to Akshay, Altaf, Andreas, Ashish, Hemant, Lynda, Mamoon, Mary, Matt and Naveen. I will cherish their friendship and all the good times we have shared. I would also like to express special appreciation to the Singhals for their constant support, love and encouragement.
Performance evaluation of IEEE 802.11 DCF has been widely studied under the assumption of a single transmission rate by all competing nodes. In practice, however, stations typically use different transmission rates. This is done to match to the changing channel conditions. Stations with poor channel conditions typically employ lower transmit rates in comparison to stations with better channel conditions. Under such scenarios, the throughput of each station becomes independent of its own transmit rate; rather it gets bounded by the slowest transmitting peer. This has been popularly classified as the performance anomaly problem. This paper provides a simple yet accurate analytical framework to study the link delay characteristics of such multi-rate networks.
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