Supervisors info:
Λάππας Βάιος, Καθηγητής, Τμήμα Αεροδιαστημικής Επιστήμης και Τεχνολογίας, ΕΚΠΑ
Summary:
Non-Terrestrial Networks (NTNs) are integral to the 5G ecosystem, extending its capabilities beyond terrestrial boundaries to deliver robust, cost-effective connectivity in remote and underserved areas. Operating predominantly in low Earth orbit (LEO), NTNs enhance throughput, capacity and latency performance in dynamic and challenging environments.
These networks leverage advanced proprietary technologies to provide reliable global communication and seamless connectivity for mobile users. However, NTNs face significant challenges, mainly due to the considerable distance between the User Equipment (UE) and the satellites. This issue is further exacerbated by signal attenuation from atmospheric phenomena, such as precipitation, gaseous absorption, clouds, fog and tropospheric scintillations, which degrade signal quality, especially at frequencies above 10 GHz. Furthermore, the Doppler effect, caused by the relative motion between the satellite and the terminal, results in frequency shifts, leading to additional degradation of signal quality.
The present thesis explores these challenges in depth, through a review of relevant literature and 3GPP and ITU specifications and proposes selection diversity as an effective mitigation strategy against the effects of atmospheric attenuation, frequent handovers and fading.
Selection diversity, the simplest form of diversity, dynamically selects the strongest signal from multiple satellites, ensuring optimal signal quality in high-mobility conditions and maintaining seamless connectivity in regions with limited terrestrial infrastructure. By prioritizing signals with the highest carrier-to-noise ratio (C/N), it enhances the effective signal-to-noise ratio (SNR), reduces bit error rates (BER) and supports reliable high-speed communication.
The proposal presented in this thesis was validated through simulations conducted using STK and MATLAB. Simulation results, after comparing two LEO constellations, demonstrated the critical benefits of diversity technique in improving signal reliability and connectivity under varying mobility conditions. Despite differences in design and operational characteristics, both constellations achieved robust performance, with diversity enabling higher SNR levels than would be possible without it. These findings underscore the pivotal role of diversity in enhancing the performance of satellite-based communication networks.
As 5G networks evolve, the adoption of selection diversity is proposed as a crucial strategy for ensuring reliable, uninterrupted connectivity across diverse environments.
Keywords:
5G, Non-Terrestrial Networks, Selection Diversity, Link Budget, Satellite Communications
