Throughput and Fairness of Collision Avoidance Protocols in Ad Hoc Networks

We present an analytical model for the saturation throughput of sender-initiated collision avoidance protocols in multi-hop ad hoc networks with nodes randomly placed according to a two-dimensional Poisson distribution. We show that these protocols can accommodate much fewer competing nodes within a region in a network infested with hidden terminals than in those cases without hidden terminals or with just a few. These results are validated through computer simulations. We then introduce a framework to address the fairness problem inherent in ad hoc networks using IEEE 802.11 and propose a topology-aware fair access (TAFA) scheme to realize the framework. Simulation results show that TAFA can solve the fairness problem in UDP-based applications with negligible degradation in throughput, and the notorious problem of the starvation of flows in TCP-based applications while incurring only some throughput degradation. This work was supported in part by the Defense Advanced Research Projects Agency (DARPA) under Grant No. DAAD19-01-C-0026, the US Air Force/OSR under Grant No. F49620-00-1-0330 and the Jack Baskin Chair of Computer Engineering at UCSC.