Research On Fast Handover Technology Of Wireless MESH Network For Rail Transit

The Vehicle ground communication system plays an important role on the train scheduling and control and information collection of the status for the running train and passenger information service In the rail transit system.At present,the 2G and 3G cellular network technology are widely used in rail transit train ground communication system,but due to the characteristics of low transmission rate,small bandwidth,especially signal difference in the subway,its development is restricted seriously in rail transportation.In order to improve the data transmission rate,the development of wireless local area network(WLAN)makes it become a kind of new vehicle ground communication technology,but due to the wireless LAN technology using single hop wired architecture makes the system a high deployment cost,network does not extend easily,and they cannot support mobile nodes,wireless mesh networks appear to make up for the shortage of wireless local area network in urban rail transit applications.The wireless MESH network uses wireless multi hop network structure,network can quickly expand,while eliminating the need for wiring cost savings,which makes it have a wide application prospect in the communication network in railway traffic.However,the fast movement of the train makes the train need to switch frequently when crossing different access points,and the high switching delay of the traditional mobile switching technology has seriously affected people's communication experience.Therefore,how to reduce the switching delay of the network in the rail transit has become one of the hot spots in the research.In order to reduce the handover delay and improve the system energy of the wireless MESH network,the main work of this paper is as follows:(1)In view of the wireless MESH network technology and its advantages in the rail traffic communication network,the current mainstream mobile switching technology is summarized.(2)For railway wireless mesh network handoff latency problem,through the analysis of IEEE 802.11 access mode,according to thecharacteristics of the rail transit node distribution proposed a channel switching strategy based on selective scanning,by minimizing the channel scanning method to reduce the detection delay,this paper analysis the selective channel scan and full scan channel switching delay detection in theory,and through the OPNET of scene change is simulated and analyzed.The simulation results show that selective channel scan can effectively reduce handoff delay,improve the switching efficiency.(3)For the balance of the system throughput and handoff delay seeking,this paper uses adaptive method of adjusting the minimum contention window,and on this basis puts forward a number of competing nodes estimation method,through the simulation experiment,the results show that,in this paper,the number of competing nodes estimation method to estimate the number of competing nodes effectively,and when the number of competing nodes more,adaptive adjustment method of the minimum contention window although have more high handover latency than selective channel scanning,but improve on the performance of the system has certain significance.