Performance evaluation of the quasi-FIFO back-off scheme for wireless access networks

The binary exponential back-off (BEB) scheme is widely adopted in both wire and wireless networks for collision resolution. Since the back-off windows among competing users are not synchronized, the BEB algorithm results in a "capture effect" and, in the limit as the number of users approaches infinity, the BEB is unstable for every arrival rate greater than 0. Taking the advantage that a common back-off window size can be broadcast by the base-station or access point in wireless networks, the capture effect can be substantially alleviated. We first show that maximum throughput can be achieved when the back-off window size is equal to the number of competing users and there are on the average 2.3922 users involved in each collision. Then, a novel quasi-FIFO back-off scheme is proposed, not only to improve the fairness in bandwidth usage, but also to maximize the throughput. In quasi-FIFO, packets generated in the current cycle are guaranteed to be serviced in the next cycle and the FIFO principle can be semi-accomplished.