Parabolic equation and ray tracing formulations for the development of radiowave propagation models in non-homogeneous media

Abstract

The development of propagation models for accurate radiowave coverage prediction is a challenge for researchers and radio engineers. The greatest difficulty in the construction of these models is the appropriated characterization of the factors that affect the radiowave propagation, such as the non-homogeneous conditions of realistic environments (atmospheric variations, electromagnetic characterization of surfaces, irregular terrain profiles, etc.), since they produce several scattering phenomena. This thesis focuses on the exploration of the Ray Tracing (RT) technique and the Split-Step Fourier Transform Parabolic Equation (SSPE) numerical algorithm. The choice of these methods can be explained by the fact that both are fast and robust electromagnetic propagation modeling algorithms, widely used, and promising to include within their solutions the influence of the different non-homogeneous environments conditions. This research presents a radiopropagation algorithm based on RT technique that combines a modified multipath model for constant refractivity gradient profiles and the Uniform Theory of Diffraction (UTD). A novel formulation is proposed for calculation and ground-reflection analysis of ray paths depending on atmospheric refractivity. In paralell, the Discrete Mixed Fourier Transform (DMFT) method is included into the SSPE algorithm, becoming a DMFT-SSPE approach to solve radio propagation problems over surfaces with impedance boundary conditions. This work proposes comparative studies with the purpose of validating the proposed formulation for modified RT, and evaluating the DMFT-SSPE implementation. Initially, the algorithms introduced herein were evaluated in canonical cases and a mixed scenario, under conditions of constant refractivity gradient, lossy terrain profiles and using the frequency bands projected for 5G applications. Taking into account the results obtained, it is possible to affirm that both methods have a similar behavior for all the cases tested. A remarkable case study was the application of the two algorithms in Colombian environments, which present challenging conditions for propagation modelling. The propagation models obtained were applied to predict coverage and temporarily characterize the radio channel in suburban scenarios of the Andean region and the Pacific forest, at 5G frequency bands. The results of this case study showed the similarity of the pathloss curves obtained with both approaches. Therefore, the two radiopropagation models presented in this thesis, are project as useful coverage prediction tools in remote areas of the Colombian geography. Throughout this work, the DMFT-SSPE method and a modified RT proposal with atmospheric refractivity effect, are presented as alternatives that guarantee reasonable results, demonstrating precision and remarkable computational efficiency to analyze radiowave propagation.