Based On The Ieee 802.11 Edca Plus Service Quality Assurance Mechanism

Since it presented as the result of combination between computer network technology and mobile communication technology in 1990's, WLAN(Wireless Local Area Network) has satisfy people's press for QoS(Quality of Service). Along with the rapid development of multimedia application, such as, voice, audio, video, different requirement of QoS for different users is needed. IEEE 802.11, which is the main standard for WLAN products, can not provide QoS support by its MAC(Media Access Control) coordination function–DCF(Distributed Coordination Function) and PCF (Point Coordination Function). To solve it, IEEE 802.11 WG. published IEEE 802.11e standard in November 2005, which is contained in IEEE 802.11-2007 std that is published in June 2007.IEEE 802.11e brought forward the HCF(Hybrid Coordination Function). HCF contains EDCA(Enhanced Distributed Channel Access) and HCCA(HCF Control Channel Access). EDCA is the enhanced edition of DCF, providing prioritized QoS. HCCA is similar to PCF, providing parameterized QoS. Lots of researches has indicated the lacking of good QoS ensurance by HCF.After analyzing information about the status of QoS support in WLAN and the MAC protocol of IEEE 802.11 std, this thesis aims at upgrading the QoS support in IEEE 802.11 MAC layer and pay great attention to EDCA based on competitive mechanism. This thesis try to scheme out the complete scheme for QoS guarantee based on EDCA. The reason of choosing EDCA but not HCCA as the research object is its wider application bound and simplicity of realization.Different EDCA Parameter Sets are set for different application classes in MAC layer of EDCA, to realize differentiation service. In practice, fixed EDCA parameters can not lead to an ideal state easily. Dynamic tuning of EDCA parameters following the load status of WLAN can only fit the network, and provide good QoS support. Admission control is necessary as well, because it can protect flows that has existed in network from influence brought by new flows. As a result, a scheme contains both dynamic tuning and admission control is good approach to solve the problem of QoS lacking in WLAN.This thesis gives a complete QoS guarantee scheme that is faced to application and adaptive. It contains dynamic tuning and admission control. Dynamic tuning is executed in two periods: differentiation_adaptation and based_adaptation. The former is for decreasing end-to-end delay, while the later is for upgrading total throughput under low delay. Admission control is only executed on real-time application to reduce the likely influence by coming real-time application. This sheme involves QoS parameters entirely, including throughput, end-to-end delay, packer loss rate. The policies of parameter tuning and admission control are simple and effective. In the last part of this thesis, simulation by OPNET modeler is carried out and the result of it is analyzed.