Study On QoS Of IEEE 802.11e

WLAN (Wireless Local Area Network) becomes more and more popular recently. In contrast to LAN, WLAN has a series of advantages such as mobility, flexibility and expansibility. As a result, WLAN develops rapidly and widely, and people begin to expect QoS support for multimedia applications. To achieve the goal, IEEE Std. 802.11eTM, is published on Nov. 2005, and provide guidance to implement QoS Guarantees.The main QoS facility of IEEE 802.11e is Hybrid Coordination Function (HCF) mechanism. The HCF uses both a contention-based channel access method, called the Enhanced Distributed Channel Access (EDCA) mechanism for Prioritized QoS Services, and a controlled channel access method, referred to as the HCF Channel Access (HCCA) mechanism for Parameterized Qos Services. HCCA is a central controlled method, hard to realize and does not fit market request. EDCA is more popular, but it just provide Prioritized QoS, and cannot provide QoS guarantees based on traffic streams. Several admission control schemas are proposed to provide further QoS control, but the existing schemas still have many problems, such as have no link with upper layer, cannot adjust dynamically to make full use of bindwith, the bindwidth is dithering and so on. The article provides a overall QoS mechanism based on IEEE 802.11e EDCA. It covers following parts: Traffic shapper, which will decrease dithering;Admission control, which will avoid channel become too busy, and provide guarantee for admitted traffic streams; EDCA parameters adjust method, which will adjust EDCA parameters dynamically to decrease collisions. The mechanism is considerate, easy to realize, and it can be implemented in distuibuted...