A THEORY FOR PROPAGATION PATH-LOSS CHARACTERISTICS IN A CITY-STREET GRID

This paper presents a new propagation model for micro-cellular communications in an urban scene in which the buildings and streets form a rectangular grid, 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, It is based on the uniform theory of diffraction (UTD) and takes into account multiple reflections between wall-to-wall, wall-to-ground and ground-to-wall, as well as the diffraction from corners of buildings and also subsequent reflections from such diffracted signals, These multiple reflections and diffraction result in an extremely complex problem of tracking the wave or ray propagation, We use the concept of multiple images and the generalized Fermat's principle to facilitate the location of each point of reflection in a wall or ground or a point of diffraction at an edge, and to determine which of the multiple scattered rays will reach the receiver at a line-of-sight (LOS) or out-of-sight (OOS) position, The signal path loss along the LOS street, OOS side streets, as well as a street which runs parallel to the LOS street, are calculated and the general features and trends of the propagation characteristics are highlighted, Calculations are also done to study the profile of the signal distribution across a street width at various points in a OOS street.