Joint Overt–Covert Dual-Robust Beamforming for Satellite Communications

This paper investigates a dual-robust beamforming design for covert satellite communication, where covert transmission is embedded within an overt channel. While prior studies on covert communication over overt channels typically address robustness for covert user under wiretap channel (WC) uncertainty, achieving simultaneous robustness for both overt and covert users remains challenging in satellite-to-ground links with uncertain channel state information (CSI). We propose a dual-robust beamforming framework that jointly designs overt and covert beamformers to maximize the minimum covert rate, subject to the overt user’s rate outage constraints (ROCs) and covertness constraints. The resulting optimization problem is intrinsically nonconvex due to CSI and WC uncertainties, variable coupling, and the absence of closed-form expressions for the ROCs. To solve the problem, we reformulate the problem into a sequence of convex subproblems by utilizing semidefinite relaxation, the S-procedure, large deviation inequality, and fractional programming. We then develop a dual-robust beamforming algorithm (DRBA) that yields near-optimal beamforming vectors. Numerical results demonstrate that the proposed approach achieves superior covert communication performance while ensuring robust service for both overt and covert users, outperforming benchmark schemes.