A Novel Framework for Near-Field Covert Communications with RIS and RSMA

TL;DR

This paper introduces a new near-field covert communication framework using RIS and RSMA, optimizing beamforming and employing low-complexity techniques to enhance covert rates against adversaries.

Contribution

It proposes a novel near-field RIS-RSMA framework with optimized beamforming and low-complexity methods, advancing covert communication capabilities.

Findings

The proposed algorithm significantly improves covert communication rate.

RIS in the near field enhances signal quality for legitimate users.

Low-complexity techniques effectively reduce adversary's received power.

Abstract

This paper explores the near field (NF) covert communication with the aid of rate-splitting multiple access (RSMA) and reconfigurable intelligent surfaces (RIS). In particular, the RIS operates in the NF of both the legitimate user and the passive adversary, enhancing the legitimate users received signal while suppressing the adversarys detection capability. Whereas, the base station (BS) applies RSMA to increase the covert communication rate composed of a private and a shared rate component. To characterize system covertness, we derive closed form expressions for the detection error probability (DEP), outage probability (OP), and optimal detection threshold for the adversary. We formulate a non-convex joint beamforming optimization problem at the BS and RIS under unit-modulus constraints to maximize the covert rate. To tackle this, we propose an alternating optimization (AO) algorithm, where the BS beamformer is designed using a two-stage iterative method based on successive convex approximation (SCA). Additionally, two low-complexity techniques are introduced to further reduce the adversarys received power. Simulation results demonstrate that the proposed algorithm effectively improves the covert communication rate, highlighting the potential of near field RSMA-RIS integration in covert communication.