Non-Terrestrial Networks in 6G

In recent years, a high connectivity demand started being experienced in wireless communication. Practically, everyone and everything needs to be connected because of the huge variety of applications existing today. This is a challenging situation for terrestrial telecommunications infrastructure that they cannot address on their own. Therefore, the 3rd Generation Partnership Project (3GPP) started in 2017 to study the integration of satellites as a part of the 5G ecosystem involving both cellular and satellite stakeholders. The substantial value added by satellites as part of the access technology mix for 5G is now becoming clear, especially for mission critical and other applications where ubiquitous coverage is crucial. For example, NTN can broaden service delivery to unserved or underserved areas, by complementing and extending terrestrial networks (Liolis, K., Geurtz, A., Sperber, R. et al. (2018). Use cases and scenarios of 5G integrated satellite-terrestrial networks for enhanced mobile broadband: the SaT5G approach. International Journal of Satellite Communications and Networking 37: 91–112; Hofmann, M. (2020). Satellite communication in the age of 5G. Journal of ICT Standardization 8(3). https://journals.riverpublishers.com/index.php/JICTS/article/view/4327/3093). In this chapter, we will elaborate on the current standardization of NTN in 5G and further detail the architecture and research challenges toward 6G-NTN.