Performance Analysis And Improvement Of Wireless Access Based On IEEE 802.11E

Wireless Local Area Network (WLAN), as a kind of broadband wireless network, is playing a more and more important role in many occasions. There are many standards about the WLAN and the IEEE 802.11 standard serial is the most popular one. The Quality of Service (QoS) assurance in WLAN has been on the schedule when the real-time service such as media and voice becoming the main contributor of the services in WLAN. The IEEE 802.11e was released at the end of 2005 year to support QoS in WLAN. IEEE 802.11e has been defined as mandatory part in the newest edition of IEEE 802.11 standard serial in June 2007 because it can supply better QoS in WLAN. There are two kinds of MAC mechanisms in IEEE 802.11e, one is called Enhanced Distributed Channel Access (EDCA) while the other one is Hybrid Coordination Function Controlled Channel Access (HCCA). EDCA is a distributed network while HCCA is a centralized network. EDCA can be compatible with the DCF (the IEEE 802.11 legacy MAC protocol) and is widely used to support QoS in WLAN. EDCA adds some new QoS parameters compared with DCF, which are also called EDCA parameters. The IEEE 802.11e standard only defines a suite of default values but no principle or guideline for adjusting the EDCA parameters. How to set up the EDCA parameters is the key point of QoS assurance, which is a matter of great significance and deserves our attention.In this paper, we set up a two dimensional Markov chain model to analyze the performance of EDCA networks in saturation conditions. We obtain the expression of saturation throughput then analyze the relative unfair phenomenon in the allocation of channel resource in EDCA infrastructure networks. EDCA is the enhanced mechanism based on DCF, some performance evaluations are demonstrated in comparison with DCF by using Network Simulator Version 2 (NS-2) in this paper. After that, the guideline of adjusting EDCA parameters is also researched by means of NS-2. Finally, we provide an improved access scheme called Fair-EDCA (F-EDCA) to resolve the unfair phenomenon in the allocation of channel resource, by adjusting EDCA parameters according to the real-time services of every priority queue. We prove the validity of the F-EDCA scheme by NS-2.