A Deterministic Approach to Predicting Microwave Diffraction by Buildings

Designers of low-power radio systems for use in urban areas would benefit from accurate computer-based predictions of signal loss due to shadowing. This paper presents a propagation prediction method that exploits a building database and considers the three-dimensional profile of the radio path. Models and algorithms are provided that allow the application of Fresnel-Kirchhoff diffraction theory to arbitrarily oriented buildings of simple shapes. Building location information used by the diffraction models is in a form compatible with a geographic information systems (GIs) database. Diffraction screens a re constructed a t all building edges, for both horizontal and vertical orientations, in order to consider all possible diffractions and to compute field contributions often ignored. Multiple buildings and edges of the same building that introduce multiple successive diffractions a re considered with a rigorous, recursive application of the diffraction theory that requires sampling the field distribution in each aperture. Robust and computationally efficient numerical methods a re applied to solve the diffraction integrals. Tests of the software implementation of these methods through example runs and comparisons with 914-MHz continuous-wave measurements taken on the Virginia Tech campus show promise for predicting radio coverage in the shadows of