A New Heuristic Geometrical Approach for Finding Non-Coplanar Multiple Edge Diffraction Ray Paths

Rooftop diffraction can contribute significantly to the propagation path loss in outdoor microcellular environments. For non-coplanar multiple edges, the finding of exact ray paths requires a complex algebraic analysis that is infeasible for rapid application in deterministic ray tracing models. A new heuristic geometrical approach is reported that finds the ray paths for arbitrary height rooftop diffraction and rooftop-to-building corner diffraction. This method can be applied to any 3-D image based ray tracing model. The accuracy of the new method is first quantified using two specific test cases. The method is then implemented in an existing microcellular ray model and path loss predictions are compared with measured data. The heuristic diffraction approach is shown to be simple to implement and lowers the prediction error when compared with the traditional Vertical Plane diffraction approximation