Simulation Researches On New MAC Layer Access Mechanism In WLAN

In recent years,with the rapid development of wireless communication technology,the Wireless Local Area Network(WLAN),which has the advantages of high data throughput,high flexibility,low cost,easy expansion and etc,has been widely used in our work and daily life.At the same time,compared with the traditional wired network,WLAN has a big gap in performance and service quality,due to which,WLAN becomes a hot research topic.As an important part of Wireless LAN,the Media Access Control(MAC)layer protocol plays an vital role in affecting the performance of WLAN.In order to make WLAN satisfy the requirements of modern communication network better,the research and optimization of MAC mechanisms in WLAN is of great importance and practical value.Thus,this thesis focuses on the investigation of DCF mechanisms in WLAN.Based on the brief analysis of the research background,significance,status and related basic concepts,the thesis introduces the contents and principles of MAC layer protocol in detail.Because Distributed Coordination Function(DCF)access mechanism is the basic access control method of MAC protocol,the thesis studies the DCF mechanism deeply,with the focus on the research of the improved DCF.Firstly,through the study of working principles of DCF access mechanisms,the performance of DCF mechanisms is simulated,including the system throughput,collision probability and so on.Simulation results demonstrate that the minimum contention window,transmission rate,the number of stations,the length of data frame would affect the system performance to some extent.Secondly,an improved backoff mechanism of DCF is studied and simulated in the thesis.The performances of the improved mechanism is compared with that of the traditional one,which shows that the improved scheme behaves better.Finally,two improved schemes of CSMA/CA(Carrier Sense Multiple Access with Collision Avoidance)access mechanism,CCA(Clear Channel Assessment)Threshold Setting based Throughput Optimization and Dynamic Adjustment of CCA based RSSI(Received Signal Strength Indication),are proposed.The thesis verifies that these two improved schemes exhibit better system performance compared with the traditional mechanism through simulating.