Χαρακτηριστικά και επίδοση διαύλων ΜΙΜΟ για δορυφορικά συστήματα επικοινωνιών

This dissertation aims at the characterization and modeling of mobile & fixed satellite communication systems, with high elevation angles, in urban propagation environments, in indoor and outdoor locations. Having in our possession data of a dual polarized MIMO channel, that were obtained from a measurement campaign aiming at terrestrial and mobile satellite links in an urban environment using an Airship, we are given the opportunity to follow various processing methods that lead to innovative theoretical and practical results. These form the basis for further development and design of the new generation of satellite and stratospheric networks.Initially, the separation of the received signal into large and small scale fading is carried out, and then the characterization of each of them seperately is examined. The 1st & 2nd order statistics are calculated and the measurement data are compared with known statistical distributions, while the best fit is being confirmed by the Kullback-Leibler divergence criterion. Furthermore, a brief study is conducted regarding the level crossing rate and the average fade duration but also the diversity performance according to the available measurement data of a classical 2x2 MIMO system. The characterization is applied to multiple scenarios, either with a fixed transmitter or receiver, different elevation angles, areas with or without line of sight, and for different polarizations. Emphasis is given to the channel modeling based on the general model of multiple scattering. Specifically, for the first time, this model is extended to incorporate 3rd order scattering and the theoretical expressions for the probability density & the cumulative distribution functions are derived. At the same time comparison of the theoretical expressions and the empirical data confirm excellent applicability of this model.Additionally, we consider fundamental metrics such as the Demmel condition number, the ellipticity, and the cross-polar discrimination & isolation that reveal the efficiency of the channel. Of course, calculations regarding the channel capacity are made per scenario, for different elevation angles, and different propagation environments. Thereinafter, emphasis is given on the channel correlation properties by calculating and comparing them with known stochastic models, such as the Kronecker and Weichselberger models, providing useful information about the channel's multiplexing potential. It is noteworthy that for the first time, the stationarity of the channel is characterized and the non-stationary regions are estimated through the correlation matrix distance, which proves the direct relation of these regions with the propagation scenarios that we encounter.Finally, a study is performed for the building entry loss utilizing the indoor scenarios from the Airship measurements. Αn analytic but nonetheless simple procedure for calculating signal penetration losses into a building is presented, according to Ikegami's empirical propagation loss model. Capacity results are included from the measured data based on the different floor levels, the distance from the window, but also from areas with obstructed or no line of sight. The results reveal that there is a strong dependence on the propagation geometry and the orientation of the receiver in relation to the moving transmitter.