Waveform Design for MIMO Covert Sensing and Communications

In this paper, we consider a multiple-input multiple-output (MIMO) integrated sensing and communications (ISAC) system, aiming at simultaneously communicating with multiple users and sensing targets that serve as adversarial observers, under multiple signal-dependent interference sources. A novel concept of covert sensing, preventing adversarial observers from detecting our sensing action or sensing intentions, is proposed, and a new metric named covert sensing distance (CSD) is established to evaluate the corresponding performance. Specifically, we develop a two-stage scheme. The first stage is to minimize the multi-user interference (MUI) while designing an omnidirectional transmit beampattern by constraining the CSD, to guarantee both reliable communications and covert sensing. Leveraging receiver design flexibility, the second stage formulates a trade-off optimization problem by maximizing the sensing signal-to-interference-plus-noise ratio (SINR) and imposing a similarity constraint to obtain a directional receive beampattern to improve the sensing performance. To solve the formulated nonconvex problem, we propose an efficient alternating optimization algorithm aided by the gradient-projection framework. Finally, the effectiveness of the proposed scheme is validated by simulation results.