Research On The Communication-Based Train Control System Using IEEE 802.11 Protocol

High-Speed Railway and the subway is very important for economic development, which takes a key role in country and urban construction, so every country in the world make great effort in developing high-Speed Railway and subway. The existing Track-circuit Based Train Control (TBTC) has been unable to meet the needs of modern railway development. With the development of wireless communication technology, the Communication- Based Train Control (CBTC) system has been invented and greatly improved the operational efficiency of railway. At the same time, IEEE 802.11 WLAN has been developing rapidly in recent years because its easy establishment, easy expansion, free-band features. Applying IEEE 802.11 protocol in metropolitan subway is a current research spot in the field of CBTC.In this paper, we first introduce IEEE 802.11 protocol and CBTC system respectively, and analyze the feasibility of the system. Then we analyze the characteristics of wireless channel in rail transportation environment, and give the emulation model in the environment. Then we analyze IEEE 802.11 roaming mechanisms and give a fast roaming mechanism in rail transportation environment, and emulate the mechanism using previous model. The emulation results shows that: the fast roaming mechanisms can greatly reduce the time spend in the handoff process, which can meet the requeirements of the signaling for train control and audio、video signals, reducing packet error rate, provid possibility of 802.11 protocol in the application of CBTC system.Although we can use fast handoff mechanism to meet the requirements of minimum delay, but the network throughput still suffers frequently jitter because of frequent handoff. In the high reliability requirement scenes, adding redundancy is an effective method. Based on the subway environment and 802.11 features, add additional receiver and transmitter on the train and along the track side, using multi-antenna technology, which can greatly increase system stability. The emulation result shows that the multi-antenna technology can increase the communication stability and improve system performance without affecting the network bandwidth and latency.Finally, we summarize all the work in this paper, and give out further studies associated with this paper.