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Satellite communication systems serve as an indispensable component of heterogeneous wireless networks in the next generation era for providing various critical civil and military applications. However, due to the broadcast nature and full accessibility of the wireless medium, such systems exist serious security threats. As an effort to address this issue, this paper, for the first time, investigates secure communication in a dual-hop communication system consisting of a satellite working as an amplified-and-forward relay. We first provide the theoretical modeling to analyze the fundamental system metrics in terms of secrecy outage probability and connection outage probability. By using the modeling, we then study the security-reliability tradeoffs and propose to transmit power schemes depending on the search algorithm. We further analyze asymptotic expressions of outage performance, which was further utilized to simplify the transmit power schemes. Simulation results show the validation of the proposed secure transmission model and design schemes of transmit power. Results also illustrate that transmit power schemes based on asymptotic analysis effectively achieve the optimal performance for the relay satellite communication system.

Satellite communication systems serve as an indispensable component of wireless heterogeneous networks in 5G era for providing various critical civil and military applications. However, due to the broadcast nature and full accessibility of wireless medium, serious security threats exist from such systems. As an effort to address this issue, this paper, for the first time, investigates the secure communication in a non-geostationary orbit (NGSO) satellite system from a physical layer security perspective. Specifically, we focus on the downlink of an NGSO satellite which provides services to a fixed earth station and is wiretapped by a fixed eavesdropper. We first apply three types of orbiting models to characterize the movement state of the satellite. Based on the orbiting models, we then provide theoretical analysis for the secure communication performance of such a system. The expressions of two fundamental performance metrics, secrecy capacity and secrecy outage probability, are derived in a closed form for any system time. Finally, we conduct extensive simulations to validate our theoretical performance analysis and illustrate the security performance in a practical NGSO satellite communication system.

With a wide application of wireless hand-held devices in human life, the relationship among human beings may affect some wireless communication systems. Inspired by it, this paper investigates the influence of social relationships on the secrecy performance of a two-hop wireless communication system with multiple jammers. We model the secrecy problem of the whole transmission as a cooperative jamming game consisting of two independent sub-games, and design a cooperative jamming strategy based on the concept of community detection to seek the minimum secrecy outage probability among all Nash equilibriums. In our proposed strategy, each jammer is divided into different groups due to its relationships with the source, the relay and the destination. Simulations demonstrate that the proposed strategy can successfully have a good secrecy performance for the two-hop system and a high average utility.

Satellite communication system is expected to play an important role in wireless networks because of its appealing contributions to ubiquitous coverage, content multicast and caching, reducing user expenditure, and so on. However, due to the inherent broadcasting nature and serious channel conditions, satellite communication system is highly vulnerable to eavesdropping attacks. As an initial step towards this end, this paper focuses on the physical layer security technique and explores the secrecy performance of a multibeam satellite system, where multiple legitimate users are served and each user is exposed to an eavesdropper located in the same beam. With perfect channel state information at the satellite and adopting the complete zero-forcing approach for signal processing, we first derive the optimal beamforming vectors to maximize the achievable secrecy rate. Based on this, we further calculate the secrecy outage probabilities of an individual user and the whole system, respectively. Finally, simulation and numerical results are provided to show the secrecy performance of the multibeam satellite system.