UWB Wireless Communication Based Train Control in Tunnel
an evaluation of UWB radio technology and Time-Reversal (TR) technique in tunnel environments for train-to-wayside communication. UWB technology has the potential to offer simultaneous ground-totrain communication, train location and obstacle detection in front of the trains. Time-Reversal channel pre-filtering facilitates signal detection and helps reduce interference. Thus, UWB-TR combination provides a challenging, economically sensible, as well as technically effective alternative solution to existing signaling technologies used in urban transport systems. This paper deals with deterministic channel modeling and its characterization in tunnel environment. It reports simulation performance evaluation of UWB-TR combinations in the developed channel model.
For high-performance, economical and reliable transportation networks, optimization of railway infrastructure and train communication equipment are required. In order to provide wireless services and safety feeling anywhere at any time to passengers, advanced control and command systems integrate intelligent embedded radio frequency (RF) solutions in the railroad and aboard the trains. Through the computer-aided dispatching platforms, centralized traffic control centers (CTC) collect information about status, speed and location from the existing signal infrastructure. This information is used to send specific command instructions (voice and data) to each train and to display traffic information to passengers. This train-towayside data exchange is known by the acronym CBTC for Communication-Based Train Control.
Current requirements for CBTC, especially for driverless subway systems, necessitate real-time high datarate communication, typically several Mbps. To achieve this high transmission rate, current commercial solutions use radio modems working at high carrier frequencies, between 2 and 6 GHz . For some industrial suppliers , the radio modems are very close to the existing Wireless Local Area Network (WLAN) standards i.e. research 802.11 a, b/g, but could migrate, when available, to the research 802.11p standard (WAVE 1). Some other Wireless Access in the Vehicular Environment industrial suppliers develop proprietary schemes CBTC radio systems . The whole transport network (infrastructure and trains) is built over a variety of environments (open-space, subway tunnels, viaducts, etc.). As a result, the characteristics of the train-to-wayside propagation channel will change while the train is moving. This impacts the communication system level of performance. Thus, the considered communication system has to match these environment changes. However, the tunnel is the most common environment for subway guided transport. Indeed, managing and optimizing the use of rail transport necessitates the exploitation of underground environments in order to decongest urban sites. In such environments, narrow bandwidth communication suffers from frequency and spatial selectivities. Due to signal attenuation along the tunnel according to the distance and the frequency used and due to heavy multi-path effect, RF transmission is subject to several problems. Previous studies have shown that free propagation in subway tunnels is effective at frequencies starting at 900 MHz and up to several GHz. As a result, and regarding frequency bands allowed for UWB communication, UWB has, inter alia, the advantage of considerably improving the conditions for an effective radio transmission in tunnels.