Sensing-Assisted Robust Secure Communication for Satellite–HAPS–Ground ISAC Networks

Abstract

The integration of satellite, high-altitude platform station (HAPS), and ground networks is emerging as a promising paradigm for wide-area communication and environmental sensing in the forthcoming sixth-generation wireless networks. However, the information leakage risk posed by the broadcast and open nature of such networks remains largely unexplored. In this article, we propose a robust secure integrated sensing and communication (ISAC) scheme for satellite–HAPS–ground integrated networks. In the considered network, a low Earth orbit satellite acts as a data provider and connects to a HAPS via a capacity-limited free-space optical feeder link. The HAPS serves as an ISAC platform, providing radio-frequency links to multiple ground users while simultaneously sensing potential eavesdroppers/targets for secure beamforming. First, an omni-directional probing waveform with artificial noise (AN) is transmitted to detect and estimate the angular directions of the targets. Then, utilizing the sensing information, a joint transmit beamforming and AN covariance design is developed to maximize the worst-case sum secrecy rate under target angular uncertainty. The formulated nonconvex problem is tackled by an efficient iterative algorithm based on successive convex approximation. Simulation results demonstrate that the proposed design achieves superior communication security performance while maintaining robustness compared with existing benchmark schemes.