Radio wave diffraction and scattering models for wireless channel simulation

The ability to accurately and efficiently predict the effects of the propagation environment on a radio signal is essential in the development and design of a low cost, low power communication system. Current approaches to the modeling of a communications channel tend to be overly simplistic, highly heuristic in nature, and in general do not account for the physical processes involved.; With this as a motivation, a physics-based approach is taken to accurately predict the effects of various electromagnetic scattering and diffraction mechanisms on the radio signal. A methodology is defined in which a series of canonical models are developed to account for the effects of various diffraction and scattering mechanisms on propagation. Within each model the appropriate technique is applied, whether it be analytic, numeric or a hybrid. Relevant approximations, based on the problem physics, retain a high degree of accuracy while minimizing the amount of computer resources necessary for simulation. Eventual integration of these models will provide for a highly accurate, efficient, and general method of simulating the propagation channel.; In this thesis two diffraction models encountered in a rural environment are developed, which are intended to serve as a basis for integration into a more complete propagation model. The first is an analytic model which predicts the scattering and diffraction from an impedance surface with a general one-dimensional impedance variation such as caused by a river or land/sea interface. The effects of the homogeneous surface are accounted for by application of an integral transform technique to the original Sommerfeld type expressions, resulting in an increase in computational efficiency of several orders of magnitude. Analysis of a land/sea transition show a significant effect on the total dipole fields, even distant from the transition. The second model is a high-frequency technique which predicts diffraction from convex surfaces, which can represent terrain obstacles such as hills or mountains. An algebraic formulation is developed, based on the asymptotic behavior of the Fock currents, to predict the surface currents on electrically large cylinders. The method is highly accurate and eliminates the need for numerical integration of the highly oscillatory Fock type integrals. The technique is extended to the case of a general convex surface in a standard fashion.