A hybrid geometrical optics, integral equation propagation model for fast accurate UHF propagation computation in urban microcells

We are interested in applying rigorous methods to the computation of UHF propagation in an urban environment. In this regard, the combined field integral equation (CFIE) formulation of the scattering problem is a trust-worthy starting point. The computational complexity of the direct solution of the CFIE is prohibitive for practical applications. However an accurate integral equation solution can still be obtained by incorporating some a priori knowledge based on geometrical optics. This paper is a report on some first results which we find very encouraging. We are satisfied that we will be able to develop more general approaches and these will be reported in due course. Buildings are treated as polygons with polygon edges (sides) representing building walls. The hybrid method achieves its computational speed-up by identifying significant edge-to-edge interactions, using a standard visibility algorithm. The results obtained using the method are compared with full method of moments solution of the CFIE. One of the advantages of the integral equation formulation is that it can handle surface irregularities. We apply our method to a rough surface problem and illustrate how it can give quite different values when compared with a smooth surface solution obtained using pure ray tracing or CFIE solution strategies