Fixed Broadband Wireless Access in Vegetated Rural Residential Areas

This thesis discusses the propagation effects of fixed broadband wireless access systems in rural residential areas. The investigation is driven by a collaboration between industry and research institutes known as "WiMAX in Niedersachsen", which aims to provide broadband wireless access via radiowaves to remote households in the rural villages in Germany.This thesis outlines an approach to model the digital map of a rural area by combining topography terrain data with clutter information derived by laser scanning. The inferred digital elevation model serves as a basis to include the environmental modelling for the propagation studies in rural residential areas. The primary propagation study stems from the analysis of crossseasons measurement data collected in the rural areas at 800 and 3500 MHz. In particular, the effects of antenna height, carrier frequency and seasons on large and small scale fading effects as well as outdoor-to-indoor penetration loss are quantified.The vegetation loss at 800 MHz and 3500 MHz are studied in this thesis. In particular, the discrete scattering theory from Foldy-Lax-Twersky is used to model the vegetation loss at 3500 MHz and this approach is known as Torrico-Lang model. At 800 MHz, the vegetation loss is modeled using diffraction theory with tree canopies serving as rounded partial radiowaves absorbers. This thesis proposes a simplified analytical propagation prediction model that is catered for a typical vegetated rural residential area by theoretically combining the distinctive propagation behaviours of radiowaves at 800 and 3500 MHz in the presence of vegetation.The analytical propagation prediction model is a realization of an idea proposed in literature as Torrico-Bertoni-Lang model. The inferred multi-screen diffraction model is an important extension to the Walfisch-Bertoni model and the Maciel-Bertoni-Xia model. The multi-screen diffraction model proposed in this thesis is the first in literature to explain the behaviour of the multi-screen diffraction theoretically in a vegetated residential scenario. By combining the proposed multi-screen diffraction component with the rooftop-to-street-diffraction component and the incoherent tree scattering component from Foldy-Lax-Twersky scattering theory, a simplified propagation prediction model for vegetated rural residential areas is proposed.Furthermore, the propagation prediction in vegetated rural residential areas using 3D raytracing based prediction tool is discussed. For this, tree groups in the rural environment are modelled as groups of cylindrical prisms with different radii and number of facets. Using the incoherent scattering theory from Foldy-Lax-Twersky, the incoherent tree scattering in a rural residential area can be quantified using the ray tracing prediction tool.Lastly, this thesis demonstrates how the proposed propagation prediction model can be used to optimize the seasonal coverage for a fixed broadband wireless access system deployed in a rural residential area by adopting relay concepts. Algorithms and methods for automatic relay positioning as well as optimized power allocation for each relay station are discussed. The optimization of the season-dependent coverage aims to overcome the challenge posed by the presence of foliage for an improved radio network planning of broadband wireless access systems.