A generic doubly-selective 3d vegetation model using point scatterers

Resumo

Mobile and fixed radio communication systems, and thus services, have experienced an explosive growth in the last two decades. Such phenomenon was due to the significant increase of radio users, particularly in mobile communications, which in turn, forced the development of a plethora of services, not only in voice communications, but also in broadband applications and multimedia services. The design and implementation of such systems rely on the availability of appropriate radio channel models for propagation and coverage deployment scenarios. With the increasing system complexity required for new services, predicting tools are thus required to provide relatively good estimates of the radio signal behavior in such complex media. In the particular case of terrestrial mobile networks and/or wireless sensor networks in rural areas, the presence of trees and vegetation areas will substantially contribute to a degradation of the radio communication systems performance, causing signal attenuation (absorption), scattering and (de)polarization. Therefore, understanding the millimeter wave (mmWave) propagation phenomena in the presence of vegetation will be critical for next generation radio system design and deployment. The work reported in this thesis describes detailed studies aimed at the characterization of propagation mechanisms arising in the presence single trees of various types and at various signal frequencies. The thesis provides also a novel 3D ray-tracing based method to characterize and model the electromagnetic behavior of trees and vegetation volumes. This model uses various point scatterers with specific radiation characteristics, distributed within a computational volume, to describe the effect of the trees present in the radio propagation path. The performance of the proposed model was assessed against results from an extensive range of experimental data obtained in different environments, which included typical re-radiation (isolated trees), path-loss (line-of-trees) and directional spectra (tree formation) scenarios. This measurement campaign also included both indoor and outdoor measurement scenarios, which confirmed the good overall model performance in predicting the absorption and scattering effects caused by the presence of vegetation in the radio path at micro- and millimeter wave frequency bands. Additionally, the proposed propagation model was successively assessed against other modeling approaches present in the literature, namely the radiative energy transfer (RET) which is the basis of the current ITU-R recommendation for propagation in the presence of vegetation, and the discrete RET (dRET) for tree formation scenarios. The relationship between the model complexity and its accuracy on the propagation phenomena predictions achieved by the proposed propagation model, and the absence of readily plug-in ray-tracing based models for propagation through and/or around vegetation, makes this new modeling approach interesting for radio planning purposes.