Spectrum Sharing for Satellite-Terrestrial Integrated Networks: A Spherical Poisson Hole Process-Based Approach

The rapid evolution of next-generation wireless networks poses new challenges for delivering ultra-high data rates and seamless connectivity across diverse environments. In remote areas, where licensed spectrum bands in terrestrial networks (TNs) are often underutilized, it is possible to allow non-terrestrial networks (NTN) to opportunistically access these spare spectrum resources. However, such spectrum sharing must maintain TN performance while enhancing the overall performance of the satellite-terrestrial integrated network (STIN), including network capacity and area spectral efficiency. In this paper, we propose a spectrum-sharing mechanism that enables an NTN to share TN bandwidth, using a three-dimensional (3D) conical protection-zone-based approach to mitigate co-channel interference from NTN to TN users. Leveraging tools from stochastic geometry, we introduce a novel spherical Poisson hole process (SPHP) to model the spatial distribution of satellites and derive tractable expressions for user coverage probabilities and the weighted-sum area data rate (WS-ADR) of the spectrum-sharing-enabled STIN (SS-STIN). Analytical results are validated through extensive Monte Carlo simulations based on Starlink constellations. Moreover, we investigate the impact of key design parameters on coverage probabilities of typical users and the WS-ADR. Simulation results indicate that optimizing the protection angle and bandwidth allocation factor enables the proposed SS-STIN to achieve up to 30 times higher WS-ADR than STINs without spectrum sharing, and more than threefold WS-ADR compared to SS-STINs without protection zones, while ensuring that the area data rate threshold for each user type is met.