# A Survey on Satellite Communication System Security
## 2 Existing Surveys and Motivation
### Existing Surveys  
As the importance of understanding SCSs grows, various kinds of research concentrating on specific aspects have been published. We categorize the existing works into three categories. First, some studies deal with satellite security issues in the physical layer (PHY). [PERSON] et al. [8] compile security techniques in the PHY based on Physical Layer Security (PLS). They present solutions to counterattacks like eavesdropping. However, a limitation of this research is that it only briefly addresses attacks and solutions specific to SCSs. [PERSON] et al. [9] address terrestrial- and space-integrated network architectures and present their PLS-based solutions. This study summarizes that properly designed interference or jamming can be used to enhance the secrecy performance of legitimate users in satellite-terrestrial integrated networks (STINs), and also focuses on the PLS that has been applied to strengthen secure transmission in a cognitive STIN (CSTN), where the secondary terrestrial system shares downlink spectral resources with the primary satellite system. This approach has shown that interference from terrestrial networks can improve the secrecy performance of satellite users. However, this study did not present solutions other than security in the PHY and did not provide detailed methods for attacks that can occur in SCSs. [PERSON] et al. [10] focus on the PHY security of UAVs in 6G systems based on reinforcement learning (RL); they also delve into RL-based frameworks for safeguarding security and privacy, demonstrating the application of RL algorithms in optimizing security policies for 6G. This research includes strategies for security resource allocation and tuning authentication parameters to counteract various threats such as jamming, eavesdropping, spoofing, inference attacks, and selfish attacks. Second, some studies explore alternative approaches to address security problems related to specific types of SCSs. [PERSON] et al. [11] also categorize threats such as false data injection and denial of service (DoS) and distributed denial of service (DDoS) attacks into five categories and propose methods to build a reliable and trustworthy network using blockchain technology. However, they did not provide solutions for security in the PHY, such as defenses against spoofing or jamming attacks. [PERSON] et al. [12] focus on methods for converging terrestrial and satellite networks based on software-defined networks (SDNs)/network function virtualization (NFV). Since satellite communications are conducted through wireless channels, which are open and thus vulnerable to issueslike eavesdropping, this paper presents methods to address this challenge. However, it does not mention other threats beyond eavesdropping, nor does it provide solutions for them. [PERSON] et al. (2018) focus on a new security framework in SCSs, QKD, which is significant for its potential to fundamentally prevent attacks like eavesdropping. It comprehensively covers research from the traditional optical fiber-based QKD to the recent advancements in wireless-based QKD. However, these studies may address some solutions for specific attacks and not provide enough solutions for other areas. Third, some papers present new space-ground integrated networks and address both the security threats and solutions associated with them. [PERSON] et al. (2018) address security issues across various layers including terrestrial, maritime, submarine, and space. They discuss potential threats and solutions in these layers, as well as natural disasters that can occur within this communication framework. [PERSON] et al. (2018) focus on the wireless communications used in Internet of Things (IoT), categorizing potential attacks in IoT wireless communications into physical, software, and network areas. They provide an analysis of deep learning (DL)-based methods for the IoT. However, the study scarcely covers attacks related to SCSs and their corresponding solutions. [PERSON] et al.