Research,Optimization And Implementation Of IEEE 802.11 MAC Protocol

With the development of wireless communication technology,WLAN has been applied in different kinds of fields.WLAN is composed of PHY layer and MAC layer.The MAC layer is responsible for the management and control of wireless medium.The performance of the MAC Layer directly affects the entire WLAN.Therefore,the in-depth study of the MAC layer is the key to improving WLAN performance.In order to solve the problem of low throughput and serious packet loss in intensive networks and the difficulty of setting up the test platform in practical applications,the research which is based on the DCF of IEEE 802.11 n protocol MAC layer is discussed in this thesis.The point of research results and innovations are as follows:1.A low-cost,multi-purpose platform was designed to test MAC layer protocol.In order to meet the needs of MAC layer protocol research and test,and to overcome the problem of redesigning the hardware platform for different protocol standards,a low-cost,multi-purpose MAC layer protocol test platform is designed which uses a high-performance ARM processor and Open Wrt Operating system,and runs MAC layer protocol designed by C language.In order to test other specific standard protocols,the wireless network card can be replaced by the USB and MINI-PCIe interfaces reserved by the test platform.2.An improved MAC layer backoff algorithm based on retransmission times is proposed.In order to solve the problems such as low throughput and serious packet loss caused in intensive applications,a new MAC layer backoff algorithm which is based on retransmission times is proposed.The newly proposed algorithm adjusts the CW update rule according to the historical data transmission of the current station to achieve the purpose of improving the network performance,and performs simulation verification on the newly proposed algorithm through the NS-2 simulation tool.In intensive applications(100 active stations),compared with the standard algorithms specified in the protocol,in the basic access mode,the throughput is increased by 15.8%,the packet loss rate is reduced by 81.4%,and the delay is reduced by 6.6%,in the RTS/CTS access mode,the throughput increased by 8.7%,the delay decreased by 1.8%,and the packet loss rate was at the same level.Compared with other improved backoff algorithms,the proposed algorithm has better overall performance in basic access mode.3.Implementation and test of improved backoff algorithm.Aiming at the types of protocol used by different wireless network cards,the proposed improved algorithm is implemented based on Soft MAC architecture wireless network card and the mac80211 protocol framework,and is tested in a practical application scenario through a test platform.Due to the limitation of the testing environment,the number of Access Points in the channel is used to simulate the number of active stations.The test results show that the function of AP and STA implemented by the proposed algorithm are correct.In the dense network(such as channel 11),Compared with the algorithm used in the protocol standard,in the basic access mode,the proposed algorithm improves the throughput by 87.9%,the network delay is decreased by 68.2% and the packet loss rate is increased by 155.3%,in the RTS/CTS access mode,the proposed algorithm improves the throughput by 2.5%,the network delay is decreased by 27.4%,and the packet loss rate is decreased by 91%.