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In this paper, we propose a semi-random backoff (SRB) mechanism to combat network collisions for 802.11 DCF/EDCA in wireless LANs. SRB is fundamentally different from traditional random backoff methods because it provides a form of resource reservation at no extra cost. The key idea of SRB is to set the backoff counter to a deterministic value upon a successful transmission. This allows a station to reuse a time slot in consecutive backoff cycles without colliding with other stations, thus achieving resource reservations. In cases of failed transmissions due to network collisions or channel errors, SRB automatically reverts to the standard random backoff method. SRB can be readily applied to both 802.11 DCF and 802.11e EDCA networks with minimum modification to the existing DCF/EDCA implementations. Theoretical analysis and simulations are conducted to evaluate this new method and our results validate its good performance in small to middle-sized 802.11 wireless LANs.
Date of Conference: 13-16 Oct. 2009