The Research On Medium Access Control Mechanism Oriented Wireless Local Area Network

Wireless local area network as the extendibility of wired network has a lot of advantages such as supporting application flexibility, rapid installation, shortened construction period, breakthrough geographic limitations and so on. It has been widely used in every way of life. There is an essential technical issue which is how to distribute the usufruct of channel when competition happens. In wireless local area network the function of distributing the channel usufruct is accomplished by Medium Access Control layer. Studying MAC mechanism of wireless local area network, establishing proper MAC layer rule, optimizing the channel allocation mechanism and improving the network quality of service are the important tasks in the field of wireless local area network.In this thesis, medium access control mechanism oriented wireless local area network has been researched. Based on all varieties of standards we press emphasis on IEEE 802.11 wireless local area network MAC mechanism and the pivotal technologies. Aimed at two primary channel allocation mechanisms of MAC layer in IEEE 802.11 WLAN, Distributed Coordination Function (DCF) and Point Coordination Function (PCF), a performance analysis and comparisons have been done. Analog simulations have been carried out at application background of campus WLAN which show that these two different mechanisms are adaptable to different application environment. Compared with DCF, PCF is better for real-time traffic which has specified throughput, delay and jitter and has good QOS performance adaptable to campus application.At the base of analysis and research of MAC mechanism and its limits, in order to guarantee the WLAN quality of service and satisfy the specified throughput, delay and jitter, a certain differentiated services mechanism is needed which can provide different service quality for different traffic. In the thesis, a MAC layer QOS mechanism possessing priority function has been put forward at the base of distributed coordination function. The new mechanism introduces the differentiation of priority and sets different maximal transmission time according to different priority. In this mechanism, the high priority station or flow not only gains the long service time but also preferentially gets the usufruct of channel. A backoff threshold also has been introduced in the mechanism which reduces the channel conflict and idle latency...