Demanding for real-time multimedia applications in wireless access is increasing, and this has driven recent research in QoS. The upcoming IEEE 802.11e standard will give a firm impulse towards QoS provisioning in 802.11 wireless LANs. In parallel, during the last years, other enhanced MAC schemes have also been proposed to improve QoS metrics. Some of these approaches modify the 802.11e Backoff procedure, either by changing the way the Contention Window is determined or by changing the way the backoff timer is decreased. Supported by these previous works, we describe three new approaches. One of them is designated by Differentiated Exponential Collision Recover – DECR, which uses exponential decrease functions in the backoff timer, with different exponential decrease rate for each Access Category. Using simulation results, we conclude that DECR, when compared with other approaches, improves channel utilization without significantly increasing the collision rate.

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Medium Access Control (MAC),Backoff,Service differentiation,Wireless LAN,IEEE 802.11e,Quality of Service (QoS)