Traditional covert communication often relies on the knowledge of the warden's channel state information, which is inherently challenging to obtain due to the non-cooperative nature and potential mobility of the warden. The integration of sensing and communication technology provides a promising solution by enabling the legitimate transmitter to sense and track the warden, thereby enhancing transmission covertness. In this paper, we develop a framework for sensing-then-beamforming in reconfigurable intelligent surface (RIS)-empowered integrated sensing and covert communication (ISACC) systems, where the transmitter (Alice) estimates and tracks the mobile aerial warden's channel using sensing echo signals while simultaneously sending covert information to multiple legitimate users (Bobs) with the assistance of RIS, under the surveillance of the warden (Willie). Considering channel estimation errors, we formulate a robust non-convex optimization problem that jointly designs the communication beamformers, the sensing signal covariance matrix at Alice, and the phase shifts at the RIS to maximize the covert sum rate of Bobs while satisfying the constraints related to covert communication, sensing, transmitter power, and the unit modulus of the RIS elements. To solve this complex problem, we develop an efficient algorithm using alternating optimization, successive convex approximation, S-procedure, sequential rank-one constraint relaxation, and semidefinite relaxation techniques. Numerical results confirm the convergence of the proposed algorithm and demonstrate its effectiveness in tracking the warden's channel while ensuring robust covert transmission. Furthermore, the results highlight the advantages of using RIS to enhance the covert transmission rate compared to baseline schemes, and also illustrate the intricate trade-off between communication and sensing in ISACC systems.

翻译：传统隐蔽通信通常依赖于对监视者信道状态信息的了解，但由于监视者的非合作特性和潜在移动性，获取该信息本质上具有挑战性。感知与通信技术的融合为合法发射机提供了感知与跟踪监视者的能力，从而提升传输隐蔽性，成为一种前景广阔的解决方案。本文针对可重构智能表面（RIS）赋能的集成感知与隐蔽通信（ISACC）系统，提出了一种感知后波束赋形框架。在该框架中，发射机（Alice）利用感知回波信号估计并跟踪移动空中监视者的信道，同时在监视者（Willie）的监控下，借助RIS的辅助向多个合法用户（Bobs）发送隐蔽信息。考虑到信道估计误差，我们构建了一个鲁棒的非凸优化问题，联合设计通信波束赋形器、Alice处的感知信号协方差矩阵以及RIS的相移，以最大化Bobs的隐蔽总速率，同时满足隐蔽通信、感知、发射机功率及RIS单元模值约束。为解决这一复杂问题，我们开发了一种高效算法，融合了交替优化、逐次凸逼近、S-过程、序列秩一约束松弛及半定松弛等技术。数值结果验证了所提算法的收敛性，并证明了其在跟踪监视者信道的同时确保鲁棒隐蔽传输的有效性。此外，结果突显了相较于基准方案，使用RIS在提升隐蔽传输速率方面的优势，同时揭示了ISACC系统中通信与感知之间复杂的权衡关系。