Modeling and Analysis of Non-Terrestrial Networks by Spherical Stochastic Geometry: A Survey

Non-terrestrial networks (NTNs) are anticipated to be indispensable in extending coverage and enabling global communication access in next-generation wireless networks. With the extensive deployment of non-terrestrial platforms, evaluating the performance of NTN-enabled communication systems becomes a challenging task. Spherical stochastic geometry (SG) is a recently proposed analytical framework that has garnered increasing attention. Due to its suitability for modeling large-scale dynamic topologies and its ability to provide an analytical framework for interference analysis and low-complexity performance evaluation, spherical SG has been widely applied in NTN performance analysis. This paper surveys the modeling and analysis of NTN networks based on spherical SG. We begin by introducing the spherical SG framework, detailing its history and development. Next, we categorize existing spherical SG models into three types based on orbital modeling methods and provide algorithm implementations for common models. Furthermore, we investigate the accuracy and necessity of spherical modeling through case studies. On the topology level, concepts such as association strategy, central angle, zenith angle, contact angle, and availability probability are introduced, with simple derivations provided. On the channel level, we detail the modeling of large-scale fading, small-scale fading, and beam gain for different channel links. Finally, we discuss several advanced topics that have not been fully explored but have strong motivation and research potential, and we predict future research directions.