A Practical WLAN Based 3D Approach On Propagation Prediction Of Radio Wave In Subway Tunnels

Our work is about the WLAN 802.11 based communication technology in subway tunnels. It is necessary since subway wireless communication is one of the most important contributions to the traffic construction plan in cities.This paper is based on the key part of WLAN based train-to-wayside communication project in Siemens, which is to find a practical approach to predict the propagation of wireless radio electromagnetic wave. To accurately evaluate the receive power of each position along the tunnels, we first set up the propagation environment, including making a three dimensional model and setting the correct parameters for the antennas on wireless access points and receive points. Then, image based ray tracing and ray launching algorithm are adopted separately to predict the propagation of radio wave and calculate the receive power of each position along the tunnel. Thanks to the characteristic of the tunnels, some mechanisms are put forward to significantly improve the computational efficiency of the ray-optic approaches. Finally, by the large amount of simulations in various conditions, we find the main factors that affect the strength of radio wave.The amazing agreement between simulation and measurement result indicates that both our optimized prediction approach and the fitting formula can provide a good approximation of radio wave propagation inside tunnels where reflection is dominant.