Channel Characteristics Analysis of Ultra-high Mobility MIMO Wireless System in Tunnel Scenario

The maximum speed of a train in a tunnel is closely related to the size of the tunnel. Facing the demand of increasing train speed, it is particularly important to choose a reasonable tunnel radius, because the size of tunnel has a great influence on the channel characteristics of wireless communication. This paper studies the effect of various arch tunnel radius on the performance of multiple-input multiple-output (MIMO) wireless system in 3.5GHz and 28GHz tunnel scenarios. The channel of train communication under ultra-high speed is simulated based on ray-tracing (RT) approach. By analyzing the Root Mean Square delay spread (RMS DS) and Doppler spread of signals under different arch radius in straight tunnel, it is found that the delay spread and Doppler spread increase with the tunnel radius increment. In addition, we analyze the eigenvalue distribution of the channel in the ultra-high speed mobile scenario. The results show that with the increase of tunnel radius, the eigenvalue distribution of channel matrix becomes more uneven and the tunnel state becomes worse. These findings will have prolific values for the applications of MIMO channel based mobile communications in underground tunnels, and railways.