Εφαρμογή τεχνικών πολλαπλών εισόδων - πολλαπλών εξόδων (ΜΙΜΟ) σε δορυφορικά συστήματα κινητών και σταθερών επικοινωνιών
The advantages introduced by using multiple-input multiple-output (Multiple Input Multiple Output, MIMO) techniques in modern terrestrial communications generate further interest in researching their applications in satellite communications. The aim of this thesis is the investigation and modeling of terrestrial and satellite MIMO channels, taking into account physical phenomena as the Line of Sight (LOS) component and the effect of spatial correlation. Initially, the main propagation phenomena and principles by using MIMO techniques are described. It is proven that MIMO systems are more reliable and efficient than conventional SISO systems due to the increase in capacity and diversity gain and the decrease in bit error rate (BER) that they provide. The main goal is to estimate the required satellite antenna separation in order to achieve an uncorrelated satellite MIMO channel matrix. This is important because using multiple antennas on single satellite does not give the opportunity to exploit the advantages and capabilities of MIMO technology. We analytically derive a design method that allows for the construction of orthogonal channel matrices in Line of Sight satellite MIMO channel via the explicit positioning of two satellite antennas in the geostationary orbit in order to increase the channel capacity and multiplexing gain. Simultaneously, a particular arrangement of an arbitrary number of ground station antennas placed on earth is assumed. The satellite LOS MIMO capacity calculation performed for both Broadcast and Fixed Satellite Services. Moreover, we investigate the extent to which the MIMO satellite channel capacity is affected by atmospheric signal attenuation and the percentage of time for which the link capacity degradation exceeds a particular value.