Physical layer security in satellite communication: State-of-the-art and open problems

Satellite communications have emerged as a promising extension of terrestrial networks in future 6G network research due to their extensive coverage in remote areas and their ability to support the increasing traffic rate and heterogeneous networks. Like other wireless communication technologies, satellite signals are transmitted in a shared medium, making them vulnerable to attacks such as eavesdropping, jamming, and spoofing. A good candidate to overcome these issues is physical layer security (PLS), which utilizes physical layer characteristics to provide security, mainly due to its suitability for resource-limited devices such as satellites and IoT devices. This paper provides a comprehensive and up-to-date review of PLS solutions to secure satellite communication. Main satellite applications are classified into five domains: satellite-terrestrial, satellite-based IoT, satellite navigation systems, FSO-based, and inter-satellite. In each domain, how PLS can improve the overall security of the system, preserve desirable security properties, and resist widespread attacks are discussed and investigated. Finally, some gaps in the related literature are highlight and open research problems, including uplink secrecy techniques, smart threat models, authentication and integrity techniques, PLS for inter-satellite links, and machine learning-based PLS, are discussed.