Predicting the radio channel beyond second-generation wireless systems

Ray-optical methods incorporating Geometric Optics (GO) and the Uniform Theory of Diffraction (UTD) are appropriate for the representation of radiowave propagation in cities for frequencies in the UHF band and above, where the wavelength is small compared to building dimensions. Various ray codes have been written to implement the ray representation. Because the rays undergo multiple interactions with the buildings over long distances, the codes make various assumptions to reduce running time. This paper reviews the types of assumptions that have been made, the ways in which the ray procedures have been implemented, and the accuracy that can be expected from the predictions. The paper gives examples of how the computed ray quantities have been used to simulate the characteristics of the radio channel (besides received power) that impact the designs of different radio systems.