Fast Radio-Wave Propagation Modeling in Tunnels With a Hybrid Vector Parabolic Equation/Waveguide Mode Theory Method

Radio-wave propagation modeling in tunnels plays an important role in designing reliable train communication systems. In recent years, various channel modeling techniques have been presented, each with its own advantages and limitations. This paper presents an accurate and efficient propagation modeling technique, combining the vector parabolic equation (VPE) and waveguide mode theory. The VPE method is applied to analyze the propagation for a short distance from the transmitter. Subsequently, with the fields generated using VPE, a rectangular waveguide model of the tunnel is extracted, leading to rapid, analytical computation of fields over arbitrarily long distances. This hybrid model takes into account realistic tunnel geometries and antenna radiation patterns while ensuring significant computational savings. The accuracy and efficiency of the proposed hybrid model are demonstrated by comparing it with measurements and simulation models in practical cases of road and subway tunnels.