Radio Wave Propagation in Confined Environments - Measurements and Models

Abstract: This thesis deals with radio wave propagation in environments where the propagation is severely influenced by surrounding objects, mainly walls and other building structures. As an introduction, a brief description is given on propagation terms like loss, delay and dispersion along with system functions relevant for the topic. The focus is then placed on propagation from an outdoor transmitter to an indoor receiver at frequency bands aimed at personal communications and wireless local area networks. Penetration loss is measured at 1.8 and 5.8 GHz for various small scale wall and window structures. Empirical models have been evaluated for the dependence on incidence angle in order to provide a simple yet accurate model for the loss. The wideband characteristics of the penetrating radio wave are determined from measurements at 5.8 GHz and from the results some system aspects are discussed. Penetration characteristics have been further evaluated by using different simulation methods in order to calculate propagation parameters. Both ray-tracing and full wave methods like the method of moments have been applied. Comparisons of the results have been made in order to determine under what conditions each model can be considered valid. For propagation further inside a complex office environment, an empirical model showing non linear relation with the number of penetrated wall sections in the direct path is proposed. The structure of this model can be directly related to the wideband results obtained for the environment. The spatial properties of the radio wave were investigated in order to determine distributions for the angle of arrival while relating this to the propagation environment. Improvements in carrier to noise as well as carrier to interference ratios using directive antennas were estimated based on the spatial dispersion. Two types of antennas were compared, one switchable array and one adaptive circular array. The performance of the switched array was further established by measurements. By applying the antenna diagrams on the measured angular spectra of the receiver, improvements of several dBs were obtainable. Finally, the issue of interference from indoor to outdoor systems was addressed. Measurements of penetration loss along with angle of arrival showed how an average transmission loss could be determined from the indoor sites and how the propagation characteristics were influenced when the interference was observed from an elevated outdoor position.