Intelligent Reflecting Surface-Aided Full-Duplex Covert Communications: Information Freshness Optimization

Abstract

Although reconfigurable intelligent surfaces (RISs) can improve the performance of wireless networks by smartly reconfiguring the radio environment, existing passive RISs face two key challenges, i.e., double-fading attenuation and dependence on grid/battery. To address these challenges, this paper proposes a new RIS architecture, called multi-functional RIS (MF-RIS). Different from conventional reflecting-only RIS, the proposed MF-RIS is capable of supporting multiple functions with one surface, including signal reflection, amplification, and energy harvesting. As such, our MF-RIS is able to overcome the double-fading attenuation by harvesting energy from incident signals. Through theoretical analysis, we derive the achievable capacity of an MF-RIS-aided communication network. Compared to the capacity achieved by the existing self-sustainable RIS, we derive the number of reflective elements required for MF-RIS to outperform self-sustainable RIS. To realize a self-sustainable communication system, we investigate the use of MF-RIS in improving the sum-rate of multi-user wireless networks. Specifically, we solve a non-convex optimization problem by jointly designing the transmit beamforming and MF-RIS coefficients. As an extension, we investigate a resource allocation problem in a practical scenario with imperfect channel state information. By approximating the semi-infinite constraints with the Sprocedure and the general sign-definiteness, we propose a robust beamforming scheme to combat the inevitable channel estimation errors. Finally, numerical results show that: 1) compared to the self-sustainable RIS, MF-RIS can strike a better balance between energy self-sustainability and throughput improvement; and 2) unlike reflecting-only RIS which can be deployed near the transmitter or receiver, MF-RIS should be deployed closer to the transmitter for higher spectrum efficiency.

A Comprehensive Survey on Full-Duplex Communication: Current Solutions, Future Trends, and Open Issues

“…Zheng et al [461] investigate the average age of information for a two-hop network in which an FD relay wirelessly powered by an AP receives environmental monitoring information from a sensor and forwards it to the AP. In [462], the information freshness maximization problem in RISaided FD covert communications under the non-retransmission protocol and the automatic repeat-request protocol has been studied. Jeganathan et al [463] investigate the performance of an FD-UAV-assisted WPT system in terms of the average age of information at the data sink.…”

Disguised Full-Duplex Covert Communications

“…Utilizing an active IRS, which is naturally FD, for covert communications between a pair of users was discussed in [ 25 ]. The age of information was minimized in [ 26 ] when a receiver covertly transmits confidential messages to the transmitter, shielded under public transmissions from the transmitter to the receiver with the aid of an IRS.…”

PHY Security Enhancement Exploiting STAR-RIS for Dual-Functional Radar-Communication

“…One of the promising approaches for realizing DFRC is to adopt communication waveforms to perform radar sensing, where the object information can be extracted from the received echo signals [2], [3]. Besides, the recently proposed STAR-RIS has enabled the signal transmission and reflection simultaneously, which achieves a larger coverage area than the reconfigurable intelligent surfaces (RIS) technique [4]- [7]. Recently, some works such as [8], have studied the STAR-RISaided DFRC.…”