A Novel Cross-Entropy Receiver for Random Time-Hopping Covert Satellite Systems

Satellite communications, characterized by their wide coverage, flexible deployment, and short construction cycles, play an indispensable role in modern communication systems. However, the inherent openness of satellite channels makes transmitted signals highly susceptible to detection and interception. To address these security challenges, this paper proposes an energy-dispersed random time-hopping (ED-RTH) covert communication scheme based on time-uncertain transmission, which effectively enhances system covertness. To overcome the multi-slot combining challenge in the highly dynamic and low-SNR environment of low Earth orbit (LEO) satellite communications, a cross-entropy-based joint reception (CE-JR) algorithm is developed, achieving minimal performance loss with significantly reduced computational complexity. Furthermore, the detection performance of an eavesdropping satellite against the proposed scheme is analyzed, and closed-form expressions for the miss detection probabilities under two typical detection methods are derived, providing valuable insights for the design and optimization of covert satellite communication systems. Finally, a simple implementation of the CE-JR algorithm was carried out on an FPGA development board, demonstrating the feasibility of the proposed algorithm.