Double Refraction Modeling for Accurate Visibility Trees in the Method of Images

Method of images (MI) is one of the oldest methods for radio wave propagation prediction based on the ray-tracing principle. Although the MI was originally restricted to the radio environments with prevailing reflection phenomena, it is also used in indoor scenarios in which through-wall transmission make a significant contribution to the received signal power. Exact handling of propagation paths, either in the form of polyhedra bounding regions or in the form of some other equivalent geometrical description, is usually complemented with the use of visibility trees to contain excessive growth of source images. However, strict visibility trees and double refractions on parallel planes involved in through-wall transmissions are not well-suited to each other. Here we study visibility inaccuracy, which is usually ignored. We propose a source image translation heuristic based on the wall depth, material and field of view. We show that the proposed double refraction modeling improves accuracy of strict visibility trees, which gives a better fit of predicted signal to the theoretically correct solution. Key–Words: Ray tracing, Radio propagation prediction, Method of images, Double refraction