Hybrid Relay-Reflecting Intelligent Surface-Aided Covert Communications

Abstract

In this paper, we propose to use a hybrid relayreflecting intelligent surface (HR-RIS) to enhance the performance of a covert communication system. Specifically, the HR-RIS consists of passive reflecting elements and active relay elements to manipulate the wireless signals from a transmitter to a desired receiver while ensuring the covertness of the transmission via avoiding such signals being detected by a warden. To fully explore the benefits offered by the HR-RIS, we first formulate the joint design of the transmit power and relay/reflection coefficients of the HR-RIS as an optimization problem to maximize the covert rate subject to a covertness constraint. To tackle the solution to this optimization problem, we then derive a closedform expression for an upper bound on covert rate, based on which we develop an alternate algorithm to solve the formulated optimization problem. Our examination shows that the HR-RIS outperforms the traditional RIS in term of achieving a higher covert rate. Interestingly, we also observe the major part of the performance gain brought by the HR-RIS can be obtained by a small number of active relay elements (e.g., 5) and further increasing this number does not improve the covert communication performance.

Joint Beamforming and Phase Shift Design for Hybrid IRS and UAV-Aided Directional Modulation Networks

“…In [37], to explore the potential of hybrid relay-IRS in helping singleuser mobile edge computing systems in computational offloading, an efficient scheme was proposed to design received beamforming, IRS reflection coefficients, and computational parameters, and the latency was dramatically reduced with the help of the IRS. In [38], a hybrid IRS-assisted covert transmission network was proposed to boost the performance of traditional covert communication networks, and an alternate algorithm with closed-form expression was derived to obtain the transmission power and IRS PSM. Unlike previous works that only considered single or multiple users and a single objective, a hybrid IRSaided integrated sensing and communication network with multiple users and objectives was investigated in [39], aimed at maximizing the worst-case target illumination power; an approach was proposed to design precoding and IRS coefficients.…”