Radio Channel Modeling And Capacity Analysis In Tunnels

The demand on reliable communications at anytime and anywhere is ever-increasing in the information age. Wireless communication is an important approach to reaching this goal. Nowadays, subway or railway tunnels have become a very common communication scenario which cannot be ignored. However, the radio environment in tunnels is significantly different from that for land mobile communications. It is critically important to investigate the radio channel characteristics in tunnels.Firstly, this paper introduces the main transmission modes of radio waves and the key methods of wireless channel modeling in tunnels. Several commonly used ray-tracing algorithms are highlighted.Secondly, an enhanced ray-tracing algorithm based on shooting and bouncing ray-tracing (SBR) is proposed in this paper, which can efficiently simulate the radio channel characteristics in tunnels with reduced computational complexity. In addition, a new method is employed to depict the geometry of the curved section, making it easier for ray-tracing in curved tunnels. The effectiveness of the proposed algorithm is verified through various test cases in a rectangle tunnel by comparing the simulated results against the theoretical results based on the method of images, and the efficiency is validated by comparing the number of calculating the intersection points of SBR and the enhanced algorithm.Thirdly, in this paper, simulations based on the enhanced algorithm are conducted for a section of Beijing Subway Line14, resulting in the simulated path loss, K factor, power delay profile in the straight tunnel and the curved tunnel. Then, the radio channel characteristics in tunnels are analyzed by comparing the simulated results and the measured results. In addition, this paper simulates the accumulated interference in tunnels for the first time (to our best knowledge).Finally, MIMO channel capacity is simulated with the enhanced ray-tracing algorithm. The simulated channel capacities for different antenna setting is obtained, and the key-hole effect is observed.