QoS provisioning in IEEE 802.11 wireless LANs

The service differentiation provided in the IEEE 802.11e can only offer soft guarantees to the real-time traffic. Admission control is to provide better Quality of Service guarantees. We present the performance study of distributed admission control for IEEE 802.11e EDCF mechanism. Our observations show that using a distributed or centralized approach may not be the best solution and proper partitioning of the bandwidth is crucial in achieving better channel utilization and goodput. It has been shown that EDCF performs better at low load and has better delay characteristics, where as HCF has better jitter characteristics and works better in medium to high load conditions. We propose class-based admissibility ratio based on WFQ and priorities of the traffic classes. We also introduce the mechanism of provisional TXOP allocation using which the unused time of higher priority flows can be allocated to lower priority flows. We feel that an integrated approach adapting to the changes in the network and load of each of the access categories could perform better.