A High-Accuracy ADI Scheme for the Vector Parabolic Equation Applied to the Modeling of Wave Propagation in Tunnels

The vector parabolic equation has been widely used to model radio wave propagation in tunnels. For its numerical solution, the Crank-Nicolson as well as the Alternating Direction Implicit (ADI) methods have been employed, with the latter being significantly faster than the former. This letter focuses on a modified ADI method, namely a Mitchell-Fairweather scheme. Applied to the vector parabolic equation, this scheme significantly improves the accuracy of the original ADI formulation while retaining its computational efficiency. The relative advantages of the Mitchell-Fairweather scheme are demonstrated in a case study involving an actual tunnel geometry.