Radio propagation in frequency selective buildings.

Predicting and improving Radio propagation conditions has been a major topic of research since wireless communications started to emerge. The aim is to increase signal coverage and reliability, meet the increased traffic demands and provide high quality signal to the higher levels of the OSI model. Moreover, the coexistence of various wireless networks in a wireless communication environment, operating on various frequency bands increases the need for a frequency selective solution for improving radio propagation conditions of the various networks. For this reason, this work proposes a novel way to improve and controllably manipulate radio propagation by transforming the building interfaces into frequency selective. Naturally, buildings can present some natural frequency selectivity. The web and void design of the individual blocks and their arrangement within a building wall/interface, creates a periodic structure, which exhibits frequency dependent transmission and reflection characteristics. This behaviour as well as the scattering behaviour of conventional periodic building structures have been studied through the RCWA method. However, since the internal structure and the parameters of the building interfaces are usually unknown, it is not currently very practical to utilise this natural frequency selectivity. This may change if an easy way is found to "x-ray" the wall. Therefore, the novel way proposed, is to artificially transform the building interfaces into frequency selective ones, tuneable at a desired frequency through the deployment of Frequency Selective Surfaces (FSS). FSS are planar periodic structures consisting of identical thin conducting elements, usually printed on dielectric substrates. They behave as spatial electromagnetic filters selectively reflecting or attenuating a desired frequency band. Investigation was focused on studying through CFDTD simulations and anechoic chamber measurements the behaviour of FSS when these are attached on conventional building materials. It was found that beyond a certain distance (one tenth of the wavelength) away from the wall, the frequency response of the FSS remains unchanged. The potential benefits in signal coverage, interference reduction and capacity increase through a MIMO system have been studied through a custom written Hybrid Ray Tracing model, which incorporates the behaviour of frequency selective surfaces. It is to the author best knowledge that such a hybrid Ray Tracing model has never been proposed in open literature