A Tutorial on Non-Terrestrial Networks: Towards Global and Ubiquitous 6G Connectivity
Muhammad Ali Jamshed, Aryan Kaushik, Sanaullah Manzoor, Muhammad Zeeshan Shakir, Jaehyup Seong, Mesut Toka, Wonjae Shin, Malte Schellmann
TL;DR
This tutorial surveys Non-Terrestrial Networks (NTN) as a cornerstone of future 6G, outlining its role in extending coverage and enabling resilient, sustainable communications. It captures the evolution of NTN standardization in 3GPP from Release 14 to Release 19, detailing payload concepts, Stage 1 requirements, and key use cases across GEO/LEO/MEO, HAPS, and UAV platforms. The paper highlights AI- and NGMA-driven approaches for network optimization, trajectory planning, and green operation, and surveys enabling technologies such as RIS, OTFS, and AI lifecycles, alongside real-world fronthaul/backhaul challenges. It also discusses integration with terrestrial networks, interference management, security, and future directions, emphasizing practical constraints like latency, channel estimation, cost, and mobility. Overall, NTN offers a path to truly global, ubiquitous connectivity, with socio-economic benefits and broad implications for 6G infrastructure, IoT, and emergency response, provided coordinated policy, standardization, and technology development keep pace with deployment needs.
Abstract
The International Mobile Telecommunications (IMT)-2030 framework recently adopted by the International Telecommunication Union Radiocommunication Sector (ITU-R) envisions 6G networks to deliver intelligent, seamless connectivity that supports reliable, sustainable, and resilient communications. Recent developments in the 3rd Generation Partnership Project (3GPP) Releases 17-19, particularly within the Radio Access Network (RAN)4 working group addressing satellite and cellular spectrum sharing and RAN2 enhancing New Radio (NR)/IoT for NTN, highlight the critical role NTN is set to play in the evolution of 6G standards. The integration of advanced signal processing, edge and cloud computing, and Deep Reinforcement Learning (DRL) for Low Earth Orbit (LEO) satellites and aerial platforms, such as Uncrewed Aerial Vehicles (UAV) and high-, medium-, and low-altitude platform stations, has revolutionized the convergence of space, aerial, and Terrestrial Networks (TN). Artificial Intelligence (AI)-powered deployments for NTN and NTN-IoT, combined with Next Generation Multiple Access (NGMA) technologies, have dramatically reshaped global connectivity. This tutorial paper provides a comprehensive exploration of emerging NTN-based 6G wireless networks, covering vision, alignment with 5G-Advanced and 6G standards, key principles, trends, challenges, real-world applications, and novel problem solving frameworks. It examines essential enabling technologies like AI for NTN (LEO satellites and aerial platforms), DRL, edge computing for NTN, AI for NTN trajectory optimization, Reconfigurable Intelligent Surfaces (RIS)-enhanced NTN, and robust Multiple-Input-Multiple-Output (MIMO) beamforming. Furthermore, it addresses interference management through NGMA, including Rate-Splitting Multiple Access (RSMA) for NTN, and the use of aerial platforms for access, relay, and fronthaul/backhaul connectivity.