Implications of complex wall structures on indoor wireless systems engineering

Abstract

Engineering high performance indoor wireless communication systems requires good system deployment strategies. In order to deploy systems effectively, propagation models that can reliably and yet efficiently characterise wireless propagation behaviour are required. Propagation models which are based on high-frequency asymptotic techniques (and which are usually referred to as `ray models') are commonly used. A fundamental limitation of ray models is that walls need to be modelled as homogeneous or multi-layered slabs. In reality, walls are complex inhomogeneous structures, which may affect wireless propagation. In addition, system planners often make simplified assumptions regarding the antenna radiation characteristics when using ray models, usually assuming radiation patterns in free-space can be used reliably for performance prediction. In reality, access point antennas are usually mounted on complex inhomogeneous wall structures, which may affect their radiation characteristics. This thesis investigates the effects that complex wall structures have on (i) electromagnetic wave propagation, (ii) antenna radiation characteristics, and (iii) their overall influence on indoor wireless systems' performance estimation using ray models. In these investigations, interior cavity walls (consisting of two drywall layers attached to a timber/steel frame) are considered due to their prevalence in modern construction, and the lack of data available for these walls in the literature. To investigate the transmission properties of complex wall structures, the transmission coefficients have been quantified as nominal values using a full-wave method, allowing comparisons to be made with analytically known solutions for simpler homogeneous walls. Furthermore, characterising the transmission coefficients as nominal values allows them to be straightforwardly integrated into ray models, which are computationally more efficient than their full-wave counterparts. The effects of antenna radiation performance in the presence of complex wall structures are investigated in this thesis via numerical analysis using a full-wave solver. The radiation patterns of a patch antenna mounted on complex interior cavity walls (at various locations) were compared to its radiation pattern in free-space conditions. The transmission coefficients and radiation patterns were then integrated into a ray model to investigate their overall influence on indoor wireless systems engineering. The results presented in this thesis have shown that the transmission properties of complex interior cavity walls may be represented by the transmission coefficients of homogeneous/multilayered slabs in ray models to estimate average power levels. In addition, the results in this thesis suggest that antenna radiation characteristics can be significantly altered (compared to free-space) when mounted on corners, and subsequently, utilising the antenna radiation patterns measured in free-space leads to erroneous predictions.