Site-specific modeling of indoor radio wave propagation

Abstract

Accurate characterization of the indoor radio propogation channel is an important requirement for the effective design, assessment, and installation of a radio network inside buildings. The thesis is concerned with the development of a cost-effective site-specific simulation tool of indoor radio propogation.

First a refined 3D ray tracing model is developed in this thesis, which is based on more accurate electromagnetic theories and incorporates polarization characteristics and antenna effects. Next, we propose the hybrid technique based on combining ray tracing method with FDTD method, which uses ray tracing to analyze wide areas and FDTD to treat areas close to complex discontinuities, where ray based solutions are not sufficiently accurate. Besides much improved accuracy, the hybrid method only applies FDTD to a small portion of the entire modeling environment, which ensures practicality in terms of computational resources. The proposed hybrid method enables the study of effects of generic indoor structural features, furniture, inhomogeneity inside walls, and any objects that may have significant effect on signal coverage and statistics inside buildings. Furthermore, the thesis provides solution to the problem of outdoor-indoor signal coupling in the presence of inhomogeneous walls by using the ray tracing - FDTD - ray tracing approach. The method makes it possible to study the effect of inhomogeneity inside walls more accurately without adding much to computational complexity, especially when the incident wave can be approximated to be plane waves and the wall structure is periodic. Examples are used to show that in the areas where the specular signal is blocked by metallic structures, the proposed method can accurately predicted signal coverage by taking into account the fields scattered by the inhomogeneity inside walls while the ray tracing method is not satisfactory. The ability of the developed method to analyze fading in signal strength, Doppler spread and time dispersion caused by multipath is also demonstrated in this thesis.