| With the rapid development of multimedia service in wireless local area network system, the requirement of Quality of Service (QoS)supporting is becoming a problem needed to be solved quickly. IEEE802.11 can be considered as a wireless version of Ethernet by virtue of supporting a best-effort service, but not guaranteeing any service level to users/applications. The IEEE802.11 Working Group is currently defining a new supplement to the existing legacy IEEE802.11 Medium Access Control (MAC) sub-layer in order to support Quality of Service (QoS). The IEEE802.11e is an extension of the IEEE802.11 to provide Quality of Service (QoS) for applications requiring real-time services.Firstly, this paper introduces the IEEE 802.11 Medium Access Control sub-layer and the IEEE802.11e protocol. Secondly, we introduce the conception of transmission zone based on the Markov chain, which takes into account almost all the important MAC parameters, and use it to analysis the EDCF mechanism, give the throughput expressions of every portfolio.Since the parameter configuration of EDCF in IEEE 802.11 is performed in static mode, the change in the amount of service load is not considered in the setup processes of each station. A D-EDCF mechanism is proposed to modulate the minimum Contention Window based on how busy the channel is. At last, the simulation results prove that this mechanism utilizes the channel more efficiently and improves the QoS of Data Service when net is light. |
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