NOMA solutions and scheduling for multiuser transmissions to multiple satellites.

Sixth-generation (6G) networks are expected to integrate non-terrestrial infrastructures, with Low Earth Orbit (LEO) satellites playing a central role in extending connectivity to a global scale. LEO constellations provide lower latency, higher data rates, and cost-efficient deployment compared to traditional satellite systems; however, their dense deployment creates the fundamental challenge of coordination among satellites. At the same time, uplink Non-Orthogonal Multiple Access (NOMA), a promising multiple access technique for 6G, introduces substantial inter-user interference due to simultaneous transmissions over shared resources. This thesis investigates advanced decoding methods that exploit satellite coordination to address the interference management problem inherent in uplink NOMA. A system model is developed to characterize user distribution and satellite coverage, and cooperative decoding algorithms with limited inter-satellite information exchange are proposed. The strategies are evaluated through extensive simulations under realistic assumptions of user density, coverage, and channel conditions. Results demonstrate that cooperative decoding significantly enhances system performance compared to non-cooperative approaches, particularly in dense user scenarios. By addressing the dual challenges of coordination and interference management, this work contributes to the development of scalable and efficient access schemes for future 6G non-terrestrial networks.