A microcellular communications propagation model based on the uniform theory of diffraction and multiple image theory

This paper presents a comprehensive uniform theory of diffraction (UTD) propagation model for a city street grid, using the multiple image concept and the generalized Fermat's principle to describe the multiple reflections and diffractions. The model is a quasi three-dimensional one in the sense that the building walls are assumed to be much higher than the transmitter height so that the diffractions from the rooftops can be neglected, The model includes all possible specular wall and ground reflections and corner diffractions in the main street, side streets, and parallel streets of a microcell, This enables the signal propagation through all the possible paths to be tracked to-the receiver at various line-of-sight (LOS) or out-of-sight (OOS) positions, Previous papers on such propagation models have included only a limited number of specular reflections and diffractions or they are restricted to a rectilinear grid where all the buildings walls on each side of the streets are coplanar, Our model includes contributions to the received signal from all possible propagation paths, including ground and wall reflections from diffracted and specularly reflected signals both in the LOS and OOS regions, Within the scope of the UTD model, the accuracy of our model is limited mainly by the assumptions of characterizing the building walls as ''smoothed-out'' flat surfaces with average relative permittivity epsilon(r) and conductivity sigma. Our theoretical results of the signal path loss along the streets are compared with measurements which have been reported for city streets in Tokyo and New York City for various values of the propagation parameters, The good agreement with these measurements indicates that our UTD model works well for such microcellular communication applications.