Channel Modeling and Performance Analysis of RIS-Assisted MIMO Communications in High-Speed Rail Tunnels

As a typical application scenario of the fifth-generation(5G) mobile communication system, the high-speed mobile scenario attracts much attention and the tunnel is a typical application scenario for high-speed rail communication. As one of the key beyond 5G(B5G) technologies with the greatest development, Reconfigurable Intelligence Surface(RIS) has the advantages of low complexity, low cost, and easy deployment, providing new opportunities for the development of communications in 5G smart high-speed rail tunnel scenarios. The traditional high-speed rail communication in the tunnel is covered by leaky coaxial cables. The spectrum efficiency of the communication system covered by leaky coaxial cables is limited by deployment and is difficult to significantly improve. Based on the fixed scatterer distribution characteristics in the tunnel and considering the angular relationship between the transmitter, the reflecting surface, and the receiver, the deployment position and quantity of RIS are designed. The paper considers deploying RIS at the top inside the tunnel, thereby establishing a single-bounced channel model for RIS-assisted wireless communication. The model considers the direct path from the transmitter to the receiver and the assisted path provided by the RIS, supporting the deployment of multiple RIS relays. Under this model, the paper carries out a simulation evaluation for RIS-assisted MIMO communication. The simulation results show that the introduction of RIS can effectively expand coverage and demonstrate that the large size and appropriate location of the RIS can significantly improve the channel capacity.