Bridging Earth and Space: A Survey on HAPS for Non-Terrestrial Networks
G. Svistunov, A. Akhtarshenas, D. López-Pérez, M. Giordani, G. Geraci, H. Yanikomeroglu
TL;DR
This survey addresses how HAPS can bridge terrestrial and non-terrestrial networks within 6G by analyzing architectures (transparent vs regenerative), platforms (aerostatic, aerodynamic, hybrid), and gateways, and by detailing frequency bands from sub-7 GHz to FSO. It keys in on TN-NTN integration through SAGIN, multi-link connectivity, and ML-driven management, while highlighting trials, channel models, resource allocation, and mobility solutions. The work identifies open challenges in channel modeling, spectrum sharing, interoperability, energy efficiency, and regulatory frameworks, and argues for HAPS as intelligent, on-demand nodes rather than passive relays. The findings underscore HAPS’ potential to deliver wide-area coverage, reduced latency, and energy-efficient backhaul, enabling resilient, scalable connectivity and enabling services such as MEC, URLLC, IoT, and immersive AR/VR for global digital inclusion.
Abstract
HAPS are emerging as key enablers in the evolution of 6G wireless networks, bridging terrestrial and non-terrestrial infrastructures. Operating in the stratosphere, HAPS can provide wide-area coverage, low-latency, energy-efficient broadband communications with flexible deployment options for diverse applications. This survey delivers a comprehensive overview of HAPS use cases, technologies, and integration strategies within the 6G ecosystem. The roles of HAPS in extending connectivity to underserved regions, supporting dynamic backhauling, enabling massive IoT, and delivering reliable low-latency communications for autonomous and immersive services are discussed. The paper reviews state-of-the-art architectures for terrestrial and non-terrestrial network integration, highlights recent field trials. Furthermore, key enabling technologies such as channel modeling, AI-driven resource allocation, interference control, mobility management, and energy-efficient communications are examined. The paper also outlines open research challenges. By addressing existing gaps in the literature, this survey positions HAPS as a foundational component of globally integrated, resilient, and sustainable 6G networks.