Propagation in tunnel in case of WLAN applied to Communications — Based Train Control system

The requirements of radio CBTC (Communications — Based Train Control) system are considered and the characteristics of the propagation of WLAN (Wireless Local Area Network) in tunnels are analyzed. The concept of near field zone and far field zone is used to predict the propagation in typical metro tunnels at frequency of 2.4GHz and 5.8GHz. The ray tracing method is also used to judge the path loss. The radio coverage link budget is suggested to ensure the field strength strong enough to support available and reliable communication for CBTC.