Mitigating starvation in CSMA-based wireless ad hoc networks using carrier sense threshold

DCF (Distributed Coordination Function), the most used one of MAC schemes in IEEE 802.11, is based on CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance). Though it is true that CSMA/CA is very effective and efficient, it can cause serious unfairness or flow starvation in multihop wireless networks. This is a general MAC coordination problem due to the random access protocol using carrier sensing. In this paper, we focus on suggesting algorithms to solve FIM (Flow-in-the-Middle) problem among starvation problems. FIM occurs when a transmitter of the middle flow senses transmitters of outer flows which are independent of each other. To mitigate starvation caused by FIM-like topology, we propose a simple and efficient algorithm which adjusts carrier sense threshold heuristically. Moreover, we suggest an algorithm to make a node be aware of itself in FIM situation. We test our algorithms with NS simulation and show that the middle flow overcomes starvation and achieves some fairness among nodes in the network.