Research on Radio Wave Coverage of Railway Wireless Communication System in Rectangular Curved Tunnels

The reliable wireless communication is the guarantee for safe operation of high speed train, especially in the complicated confined spaces like curved tunnels in mountain areas, and the prediction of radio wave propagation in these kinds of spaces is the foundation of designing reliable wireless communications. Unlike straight tunnels, the propagation characteristic in curved tunnel is more complicated and there exist energy coupling and conversion between different modes. Therefore, it's important to study the propagation characteristics of radio wave in curved tunnel from both perspectives of propagating characteristic and mode coupling and conversion. A hybrid method based on alternating direction implicit parabolic equation (ADI-PE) and modal analysis is proposed in this paper to investigate the propagation characteristics and mode coupling, and the mode coefficients at a series of sampling cross-sections along the tunnel is extracted by point matching method. By analyzing the variations of receiving power and mode coefficients, the propagation property and energy coupling and conversion law between different modes in curved tunnels with different curvature radius are found. The results are helpful in better understanding of the propagating characteristics of radio wave in curved tunnels.