Secure Spatial Signal Design for ISAC in a Cell-Free MIMO Network
For ISAC network designers, this work provides a waveform design that enhances security against eavesdroppers while maintaining sensing and communication functionality, though the results are simulation-based and incremental.
This paper addresses secure spatial signal design for integrated sensing and communication (ISAC) in a cell-free MIMO network, where a target eavesdropper (Eve) is also sensed. The proposed method uses artificial noise to degrade Eve's channel, and simulations reveal trade-offs between sensing and communication performance, with the optimal artificial noise covariance being rank-1 and directed toward Eve.
In this paper, we study a cell-free multiple-input multiple-output network equipped with integrated sensing and communication (ISAC) access points (APs). The distributed APs are used to jointly serve the communication needs of user equipments (UEs) while sensing a target, assumed to be an eavesdropper (Eve). To increase the system's robustness towards said Eve, we develop an ISAC waveform model that includes artificial noise (AN) aimed at degrading the Eve channel quality. The central processing unit receives the observations from each AP and calculates the optimal precoding and AN covariance matrices by solving a semi-definite relaxation of a constrained Cramer-Rao bound (CRB) minimization problem. Simulation results highlight an underlying trade-off between sensing and communication performances: in particular, the UEs signal-to-noise and interference ratio and the maximum Eve's signal to noise ratio are directly proportional to the CRB. Furthermore, the optimal AN covariance matrix is rank-1 and has a peak in the eve's direction, leading to a surprising inverse-proportionality between the UEs-Eve distance and optimal-CRB magnitude.