Performance Improvement of 802.11 MAC by Enhancements in DCF

Date Added: Jan 2012
Format: PDF

In the 802.11 protocol, the fundamental mechanism to access the medium is called Distributed Coordination Function (DCF). This is a random access scheme, based on the Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) protocol. Retransmission of collided packets is managed according to Binary Exponential Back-off (BEB) rules. BEB increases the waiting time of each node exponentially by 2 with every unsuccessful transmission. Also, after each successful transmission, the back-off stage will resume to the initial stage 0, and the contention window will be set to minimum regardless of network conditions such as number of competing nodes. This method, referred to as 'Heavy decrease' tends to work well when the number of competing nodes is less.