An Enhanced Beyond-Diagonal RIS-Assisted Secure ISAC Network

Abstract

Recently, the development of a new reconfigurable intelligent surface (RIS) variant, known as beyond-diagonal (BD)-RIS, paved the way for enhanced network communication and sensing performance. Unlike the conventional RIS, BD-RIS’s phase-shift matrix structure is not limited to a diagonal form, which offers additional degrees of freedom in manipulating the wireless channel. In this paper, a novel robust BD-RISaided scheme for the realization of a secure ISAC network is proposed and analyzed. The studied ISAC network consists of a dual-functional radar communication base station (BS) utilizing collocated transmit and receive multi-antenna arrays to serve various downlink users while aiming at detecting the presence of several targets by virtue of the received and processed sensing echo signals. The targets are assumed to act as potential eavesdroppers threatening the confidentiality of the communication. By formulating an optimization problem representing the communication, secrecy, and sensing metrics of the network, an optimized transmit beamforming matrix, artificial noise (AN) covariance matrix, and a non-diagonal phase shift matrix are obtained, which maximizes the system’s sensing performance, subject to secrecy and total power constraints.