Backoff Schemes for Mobile Adhoc Networks – A Survey

A Mobile Adhoc Network (MANET) consists of wireless nodes that can be formed anywhere and any time without any fixed infrastructure in which every node can act as a host or router. Nodes that want to access the channel may compete in a distributed way via Carrier Sensing Multiple Access with Collision Avoidance (CSMA/CA) scheme in MAC (Medium Access Control) layer. Due to the distributed nature of the nodes and heavy traffic, packet collisions cannot be fully eliminated. MAC layer adopts Binary Exponential Backoff (BEB) for collision avoidance. In BEB, the contention window of a node is reset to an initial value after each successful transmission. In case of collision, window size is doubled. This sudden change in window size may degrade the performance of the network. Several existing backoff algorithms are discussed in this article and a comparative analysis of these existing algorithms is presented.