Joint Resource Allocation and Power Control in Rate-Splitting Multiple Access-Based Integrated Terrestrial and Non-Terrestrial Networks with HAP Assistance

This paper proposes a novel network architecture integrating a non-terrestrial network (NTN) with low-earth orbit (LEO) satellites and high-altitude platforms (HAPs) and terrestrial network (TN) with ground base stations under rate-splitting multiple access (RSMA) to enhance spectral efficiency (SE). A new resource allocation strategy is developed for efficient resource utilization across all layers. A joint resource block and power control framework (JRPS) is formulated to maximize sum-rate under quality-of-service (QoS) constraints. The non-convex JRPS problem is reformulated as a linear program and solved using an iterative successive convex approximation algorithm that ensures local optimality. Additionally, a heuristic resource allocation and power control method is also proposed to provide an effective initialization for JRPS and to serve as a performance baseline. Simulations confirm the superior performance of the proposed JRPS framework over existing benchmarks. Specifically, the proposed scheme achieves an average sum-rate improvement of up to 80% compared to conventional baselines without RSMA and up to 60% compared to RSMA combined with other allocation methods. Moreover, it ensures that approximately 90% of ground stations achieve an SE above 0.5 bps/Hz, significantly outperforming alternative strategies. Notably, integrating both LEO satellites and HAPs yields better performance than using either one alone.