A Survey on Space-Air-Ground-Sea Integrated Network Security in 6G

Space-air-ground-sea integrated network (SAGSIN), which integrates satellite communication networks, aerial networks, terrestrial networks, and marine communication networks, has been widely envisioned as a promising network architecture for 6G. In consideration of its cooperation characteristics of multi-layer networks, open communication environment, and time-varying topologies, SAGSIN faces many unprecedented security challenges, and there have been a number of researches related to SAGSIN security performed over the past few years. Based on such observation, we provide in this paper a detailed survey of recent progress and ongoing research works on SAGSIN security in the aspects of security threats, attack methodologies, and defense countermeasures. To the best of our knowledge, we are the first to present the state-of-the-art of security for SAGSIN, since existing surveys focused either on a certain segment or on several segments of the integrated network, and little can be found on the full coverage network. In addition to reviewing existing works on SAGSIN security, we also present some discussions on cross-layer attacks and security countermeasure in SAGSIN, and identify new challenges ahead and future research directions.

I. Introduction

Over the past few years, with the development of mobile communication technology, especially the commercialization of 5G in many countries around the world, traditional terrestrial networks have experienced an explosive growth in terms of throughput and user access amount. Nevertheless, with the advance of the Internet of Things (IoT), relying solely on the ground network can no longer meet the exploding requirements on high-speed and reliable network access at anytime and anywhere on the earth, in consideration of its limited coverage and network capacity. This has aroused widespread concern in the academia and industry on the air-ground coordination and the space-air-ground integrated network (SAGIN) [1], [2]. In particular, many telecommunications companies around the world have released their plans for SAGIN development in the coming years. For example, in 2020, China Unicom launched their SAGIN construction plan and began to promote the maturity of the SAGIN industry chain. In academia, Liu et al. [1] reviewed recent works on SAGIN ranging from network design and resource allocation to performance analysis and optimization, and presented some challenges and future research directions. Kato et al. [3] focused on the utilization of artificial intelligence (AI) in optimizing the performance of SAGIN including intelligent traffic control, intelligent Resource Allocation, Smart Anomaly Detection, etc. After that, Cheng et al. [4] developed a SAGIN simulation platform, which adopts centralized and decentralized controllers to optimize network functions, such as access control and resource scheduling.