Urban Propagation Modeling for next-generation Non-Terrestrial Networks

The study of air-to-ground propagation is a highly researched topic since future generation wireless networks will involve a three-dimensional heterogeneous architecture in which terrestrial infrastructures communicate with non-terrestrial stations like satellites, these network are referred as Non-Terrestrial Networks. The Third Generation Partnership Project (3GPP) NTN channel model is the main channel modeling work for NTN, but the scientific community has found some counterintuitive behavior of propagation parameter tables such as the K-factor used to parameterize the model. A very plausible cause for the inconsistencies in the 3GPP NTN channel model is the fact that the ray-tracing simulators used to calculate the parameters neglect the diffuse scattering phenomenon which is proved to be determinant in air-to-ground propagation when satellite elevation is low. Therefore, using a more realistic and physically sound ray-tracing simulator also capable of modeling the scattering phenomenon, we aimed to verify if the K-factor trends were justified. First of all, we relied on a theoretical analysis supported by the ray-tracing simulator to study the effect of each propagation mechanisms in an ideal urban environment and considering the S-band. These preliminary studies allowed us to interpret the final results in more depth. Secondly, a statistical characterization of the fast fading was carried out by extracting the K-factor tables for different elevation and azimuth angle and receiver positions. The results are in complete agreement with the theoretical analysis we carried out and with what was expected. Comparing them with the 3GPP model tables shows that they are in strong disagreement therefore we can conclude that the tables of the K-factor values in the 3GPP model are incorrect as they present completely unrealistic and incomprehensible trends at least as regards the urban environment and the S band studied in this work.