Μοντελοποίηση ραδιοδιαύλου πολλαπλών-εισόδων πολλαπλών-εξόδων για ασύρματα ευρυζωνικά συστήματα στρατοσφαιρικών επικοινωνιών

Abstract

High altitude platforms (HAPs) are one of the most promising alternative infrastructures for realizing next generation high data‐rate wireless communications networks. Considering the continuous demand for enhanced spectral efficiency, increased channel capacity, and improved link reliability, multiple‐input multiple‐output (MIMO) technology is the leading candidate for future communications systems. The development of MIMO‐based communications networks depends on a proper characterization and modeling of the propagation channel. To enable the successful design and performance evaluation of broadband wireless HAP‐MIMO systems, this doctoral thesis focuses on modeling of HAP‐MIMO channels. Novel three‐dimensional (3‐D) geometry‐based reference models for Ricean fading channels are proposed that encompass narrowband and wideband HAPMIMO channel scenarios with line‐of‐sight (LoS) and non‐line‐of‐sight (NLoS) connections at L and S frequency bands licensed for mobile communications through HAPs. From these models, the statistical properties and the capacity performance are analytically and thoroughly studied in terms of various parameters, such as the elevation angle of the platform, the antenna array configuration, the Doppler and delay spread, and the 3‐D non‐isotropic distribution of the local scatterers. Using the theoretical expressions one can easily evaluate numerically the HAP antenna inter‐element spacing required to achieve uncorrelated responses in the HAP‐MIMO channel matrix. Moreover, novel 3‐D deterministic and statistical simulation models for HAPMIMO channels based on the reference narrowband and wideband models are developed by using the sum‐of‐sinusoids (SoS) method, which has been widely accepted by academia and industry. The efficiency, the accuracy, and the complexity of these models are thoroughly investigated with respect to the statistical properties. The results indicate that the proposed simulation models yield high performance and satisfactorily approximate the statistical properties of the reference models. Finally, a novel geometrical design approach to construct high‐capacity HAPMIMO communications systems in LoS propagation environments is proposed, considering the Ka and V frequency bands licensed for fixed broadband communications through HAPs. In these mm‐wave frequencies, the rain has a significant effect on the quality of the link. The potential channel capacity gain of the optimized LoS‐HAP‐MIMO architecture is investigated, under clear sky and rain conditions. The proposed models for HAP‐MIMO channels would provide other researchers a convenient framework and guidelines for the characterization, analysis, test, and design of future mobile and fixed HAP‐MIMO communications systems.