Research Of Channel Access Algorithm Based On Contention/reservation In High Density WLAN

In recent years,with the continuous development of wireless communication services,the use of Wireless Local Area Network(WLAN)has become more and more popular.In high-density WLAN,with the increase of the number of stations,the use of Distributed Coordination Function(DCF)mechanism based on free contention makes the collision more serious and the network performance declines sharply.In addition,the adaptive rate adjustment mechanism between the station(STA)and the access point(AP)makes the stations have different rates.In a multi-rate network environment,the low-rate stations have the same chance of accessing channel as the high-rate stations,and they achieve the same throughput,resulting in performance abnomaly.This thesis mainly solves the problem of high collision rate and performance abnomaly in high-density WLAN.Firstly,to reduce collision and realize collision free data transmission,this thesis proposes a distributed decoupled media access control(MAC)algorithm based on the idea of contention/reservation,namely the DMAC(Decoupled MAC)algorithm.In this thesis,time slot is divided into contention period and data transmission period.During the contention period,the station attempts to transmit a short control frame to contend the channel and its ID will be piped into a queue if the transmission is successful.The stations transmit data packets in turn according to the order of successful contention the channel in the following data transmission period.Each successfully transmitted data packet is confirmed by the Acknowledgement Frame(ACK),and each ACK frame carries the station ID of the next transmission data packet.In this way,all stations can transmit data in an orderly manner during the data transmission period to avoid confilcts.Then,to solve the problem of performance abnomaly,baesd on the DMAC algorithm,this thesis proposes two channel access algorithms based on time fairness for different application scenarios.The first is to give the high-rate stations more opportunities to contend in the contention period to achieve time fairness.The second is give the number of times that the stations contending the channel are proportionate to their rate in the data transmission period,so that the high-rate stations can obtain the same channel occupancy time as the low-rate stations,and finally achieve channel time fairness.Finally,the above algorithms are simulated by MATLAB simulation software.The simulation results show that the proposed algorithm can effectively improve the overall network throughput and channel utilization.At the same time,the algorithm can also obtain better channel time fairness.