Evolution of Non-Terrestrial Networks From 5G to 6G: A Survey

TLDR

Non‑terrestrial networks (NTNs) traditionally had limited applications, but recent advances and cost reductions have broadened their use in 5G and beyond, especially when integrated with terrestrial networks. This article surveys the evolution of NTNs, emphasizing their relevance to 5G and their pivotal role in the 6G ecosystem. The survey examines NTNs integration into terrestrial networks, covering new services, architectures, enablers, higher‑layer aspects, challenges, and approaches for efficient ground‑air‑space networks, and reviews academic and industrial progress toward 6G.

Abstract

Non-terrestrial networks (NTNs) traditionally have certain limited applications. However, the recent technological advancements and manufacturing cost reduction opened up myriad applications of NTNs for 5G and beyond networks, especially when integrated into terrestrial networks (TNs). This article comprehensively surveys the evolution of NTNs highlighting their relevance to 5G networks and essentially, how it will play a pivotal role in the development of 6G ecosystem. We discuss important features of NTNs integration into TNs and the synergies by delving into the new range of services and use cases, various architectures, technological enablers, and higher layer aspects pertinent to NTNs integration. Moreover, we review the corresponding challenges arising from the technical peculiarities and the new approaches being adopted to develop efficient integrated ground-air-space (GAS) networks. Our survey further includes the major progress and outcomes from academic research as well as industrial efforts representing the main industrial trends, field trials, and prototyping towards the 6G networks.