Radiowave propagation through periodic building structures.

Wireless communication systems can be optimised through more accurate radio modelling processes. Ray-tracing methods, based on geometrical optics (GO) and the uniform theory of diffraction (UTD), have emerged as the preferred technique to predict the electric field distribution and area coverage in both indoor and outdoor environments. There have been a number of investigations on improving the accuracy of ray-tracing methods in both indoor and outdoor environments, but few pay attention to the inner structure of the walls. In existing ray- tracing algorithms, wall structures are usually modelled as half-space materials or dielectric slab and layered models, with reflection and transmission characteristics calculated by Fresnel coefficients. These models are good approximations for homogeneous wall structures where a substantial specular component dominates. However, when the wall structure possesses periodic variations, standard GO ray-tracing is insufficient to accurately model radio propagation through building interfaces, for coverage and interference studies, as significant power can be carried away from the periodic wall in non-specular directions. Therefore, more accurate models are needed to take into account the effect of these periodic wall structures on radio wave propagation. The work presented in this thesis concentrates on the investigation of transmission and reflection characteristics of common periodic building structures. Propagation properties of building walls in terms of transmission and reflection characteristics are examined theoretically by the proposed 3D modal transmission-line (3D-MTL) and rigorous coupled-wave analysis (RCWA) methods. A novel deterministic hybrid model combining ray-tracing and RCWA is developed to predict radio propagation through building interfaces from outdoor to indoor environments. It was shown that the proposed hybrid method can produce more accurate results than the ray-tracing model. Key words: radio wave propagation, ray-tracing, periodic wall structure, modal transmission-line (MTL), rigorous coupled-wave analysis (RCWA) and hybrid model