Non-terrestrial Network

This chapter provides an overview of non-terrestrial network (NTN), which is expected to become an important component of the sixth-generation (6G) mobile communication networks. We first introduce the heterogeneous NTN architecture that consists of satellites, high-altitude platform system (HAPS), and unmanned aerial system (UAS). Then, we discuss the recent advancement on NTN and introduce some use cases. By considering the important characteristics of NTN communications, we further present the mathematical analysis for NTN, such as antenna modelling, channel modelling, link budget analysis, and mobility modelling. Some important design issues in NTN are discussed, including multiple access, handover management, interference control, and mobility management. Finally, to support the ambitious goals of 6G, several future research directions of NTN are summarized, including flexible mobility management for heterogeneous networks, cross-layer resource management, seamless and continuous coverage in three-dimensional (3D) space, and NTN integrated sensing and localization.