Analysis of 5G Channel Characteristics Based on Ray Tracing for the Straight Tunnel of High Speed Railway

The tunnel is one of the most important scenarios for high-speed railway (HSR). However, it exists many gaps about the coverage, the path loss and the number of signal paths in the HSR tunnel. In this paper, we first simulate the coverage of base station (BS) at the 2.6, 3.5 and 4.9 GHz by the ray tracing (RT) simulator, when the BS is arranged outside the tunnel. Simulation results show that the BS outside the tunnel can cover more than 200 meters of the tunnel. And decreasing the elevation angle between the BS and the tunnel can increase the covered tunnel distance of the BS. Moreover, we propose the three-slope path loss model to predict signal attenuation at different areas for the tunnel scenario. Finally, we analyze the number of signal paths and find that the multipath effect is more severe at the tunnel entrance, rather than inside the tunnel.