Research On Media Access Control Protocol In Wireless Local Area Networks Using Multi-beam Directional Antennas

The application of multi-beam directional antennas in WLAN has many advantages,which can greatly reduce signal interference,enlarge transmission range and improve data rate.But the introduction of multi-beam directional antennas also brings challenges to the design of MAC protocol,such as "deaf node" and "directional hidden terminal" problem.Therefore,in the wireless local area networks,two asynchronous neighbor discovery algorithms based on multi-beam directional antennas are proposed,and a centralized directional MAC protocol is proposed based on neighbor discovery algorithm.At first we study the neighbor discovery algorithm for Wireless Local Area Networks based on multi-beam directional antennas,and propose two asynchronous neighbor discover algorithms which are based three-way handshaking mechanism: asynchronous hierarchical scanning(AHS)and asynchronous directional scanning(ADS)algorithm.Two or more than two nodes send messages to the access point(AP)simultaneously can cause collision,AHS and ADS can reduce collision.The algorithm is simulated,and also application scenarios and the factors that affect the performance of these algorithm are analyzed.The experimental results show that the AHS algorithm is suitable for the dense neighbor nodes around AP,and the ADS algorithm is suitable for most of the neighbor nodes far from the scene of AP.Finally,on the basis of neighbor discovery,the centralized directional MAC protocol for wireless LAN with multi-beam directional antennas is studied.Centralized directional MAC protocol is divided into downlink communication stage and uplink communication stage.In the downlink phase,AP transmits data to nodes in a directed way,tolds nodes when to start and end the uplink phase.In the uplink phase,the node uses the CSMA/CA competition mechanism and the RTS/CTS mechanism to access to the channel,and directionally transmits the data frame to the access point(AP),and the AP directional replies ACK to the node.The performance of centralized directional MAC protocol and traditional MAC protocol is compared theoretically,and simulation experiments show that the centralized directional MAC protocol has better performance.