Research On Channel Access Control Algorithm Based On Time Fairness In Multirate WLAN

With the continuous development of wireless technology and the popularity of wireless terminals,Wireless Local Area Networks(WLAN)have begun to be widely used in people's lives,learning and working.More and more users choose WLAN to access the Internet because of its outstanding features in mobility and convenience.However,the ever-increasing number of users and the ever-increasing user experience demands are placing increasing demands on the performance of WLAN.IEEE 802.11 protocol becomes the main protocol for WLAN because of its simplicity of deployment and maintenance.However,in the actual work,the 802.11 protocol has problems such as high collision rate and performance abnormally,resulting in low network utilization and wasting valuable channel resources.In the view of the above problems,this thesis combines the current standard Distributed Coordination Function(DCF)and Enhanced Distributed Channel Access(EDCA)mechanism to study an effective Media Access Control(MAC)layer integrated solution to prevent low bitrate stations from over occupying channels and high bitrate stations cannot get their corresponding high throughput,which reduces the performance of the entire network;at the same time,this thesis also studies the efficient transmission in the high-density stations deployment environment.The specific work is as follows:This thesis first proposes a time-based fairness differentiated reserved channel access control mechanism,which adjusts the way of competing channels according to the transmit status of success or failure and after a station accesses the channel,it determines the number of packets that can be transmitted at once according to the transmit status and features such as bitrate.The proposed mechanism can reduce the collision rate effectively and achieve the time fairness among these stations.The results through quantitative analysis of mathematical model and experimental simulation show that the proposed mechanism has a large performance improvement in both throughput and time fairness compared with other mechanisms.In addition,an extensible analysis model is proposed for the application of the mechanism in some non-ideal channel environments.Secondly,aiming at the problem that the performance of the above mechanisms is not ideal in a high-density stations environment,a time-based channel access control mechanism suitable for high-density stations environment is proposed.This mechanism divides these stations into several groups according to the bitrate,reducing the collision rate through reducing the number of competing stations at the same time.So the mechanism above can improve the overall performance of the network and also expand its application in a high-density deployment environment.Finally,the experimental schemes in various application environments are designed for the proposed two mechanisms.It is proved that the proposed mechanisms can combine the standard DCF and EDCA mechanisms effectively and improve performance greatly in terms of time fairness,collision rate and throughput.