Active-RIS-Aided Covert Communications in NOMA-Inspired ISAC Wireless Systems

TL;DR

This paper proposes an active RIS-assisted NOMA-inspired ISAC system to enhance covert communication rates and sensing performance, outperforming passive RIS and non-RIS systems, with a focus on optimizing transmission schemes.

Contribution

It introduces active RIS to improve covert rate in NOMA-inspired ISAC systems and compares two transmission schemes, providing new insights into joint beamforming optimization.

Findings

Active RIS outperforms passive RIS in covert rate.

The w/o-DSS scheme achieves higher covert rate than w-DSS.

Active RIS enhances the trade-off between sensing and communication.

Abstract

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.