Non-orthogonal multiple access (NOMA)-inspired integrated sensing and communication (ISAC) facilitates spectrum sharing for radar sensing and NOMA communications, whereas facing privacy and security challenges due to open wireless propagation. In this paper, active reconfigurable intelligent surface (RIS) is employed to aid covert communications in NOMA-inspired ISAC wireless system with the aim of maximizing the covert rate. Specifically, a dual-function base-station (BS) transmits the superposition signal to sense multiple targets, while achieving covert and reliable communications for a pair of NOMA covert and public users, respectively, in the presence of a warden. Two superposition transmission schemes, namely, the transmissions with dedicated sensing signal (w-DSS) and without dedicated sensing signal (w/o-DSS), are respectively considered in the formulations of the joint transmission and reflection beamforming optimization problems. Numerical results demonstrate that active-RIS-aided NOMA-ISAC system outperforms the passive-RIS-aided and without-RIS counterparts in terms of covert rate and trade-off between covert communication and sensing performance metrics. Finally, the w/o-DSS scheme, which omits the dedicated sensing signal, achieves a higher covert rate than the w-DSS scheme by allocating more transmit power for the covert transmissions, while preserving a comparable multi-target sensing performance.

翻译：非正交多址接入启发的集成感知与通信技术促进了雷达感知与NOMA通信的频谱共享，但由于无线传播的开放性，面临着隐私与安全挑战。本文采用主动可重构智能表面辅助NOMA启发的ISAC无线系统中的隐蔽通信，旨在最大化隐蔽速率。具体而言，在存在监视者的情况下，双功能基站发射叠加信号以感知多个目标，同时分别为一对NOMA隐蔽用户和公共用户实现隐蔽可靠的通信。在联合传输与反射波束成形优化问题的构建中，分别考虑了两种叠加传输方案：即采用专用感知信号的传输方案与不采用专用感知信号的传输方案。数值结果表明，在隐蔽速率以及隐蔽通信与感知性能指标之间的权衡方面，主动RIS辅助的NOMA-ISAC系统优于被动RIS辅助和无RIS的系统。最后，省略专用感知信号的w/o-DSS方案通过为隐蔽传输分配更多发射功率，在保持可比的多目标感知性能的同时，实现了比w-DSS方案更高的隐蔽速率。