Wireless Communication Subsystem Design In CBTC System

Communications-Based Train Control System (CBTC), which transmits real-time control commands and train localization information between train and wayside by wireless, is the developing direction of urban mass transit train control system. It has shorter operation interval. The train-wayside wireless communication is the key part of the CBTC, and it is also one of the hot. But currently there are a few researches for the urban railway wireless communication. This paper will design wireless communication subsystem based on the feature train-wayside wireless communication channel. A solution of wireless communication subsystem will be propose in the paper, and the solution will be simulated and actual tested.Firstly, this paper will introduce the research situation of domestic and foreign urban orbit transit, the function of CBTC and the architecture of each subsystem. Secondly, it will introduce the function and composition of CBTC data communication system. The train-wayside communication performance requirement will be listed, and transmission rate, packet loss, handoff time on high speed moving are the key function requirements of wireless communication in CBTC system. In order to sure the train control information can be reliable two-way transmitted in any time and any location, the reasonable AP spacing interval is the design key point. After the summarize of wireless communication subsystem design, it will analysis the radio channel characteristics of tunnel, the Fresnel zone and the Wireless loss model in tunnel. The tunnel will be considered as a oversize imperfect waveguide, the Near field communication will be determined by Fresnel Zone theory. The Transmission boundary of 2.4G radio will be reckoned by Fresnel Zone theory, and Radio propagation path loss and Wireless coverage can be calculated by Wireless loss model of tunnel.The selection of Wireless protocol and Handoff mechanism and the encryption techniques should also be considered. In the paper, it analysis's the wireless protocol, handoff mechanism and procedure in wireless communication. The encryption techniques of wireless communication are introduced. According to design results, the solution of wireless communication subsystem is proposed. And simulation tests and actual network performance tests was taken for the subsystem bandwidth, transmission delay and packer loss rate. Finally, this paper summarizes research results, and makes a outlook for the next research focal point for future.