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IEEE Communications Letters

Improper Gaussian Signaling for Secrecy Transmission in RIS-Aided Downlink NOMA

Honglei Jin, Zhe Li, Jide Yuan, Yili Xia

Published Nov 7, 2024• 1 citation
Publisher

Abstract

This letter investigates the physical layer security of a downlink non-orthogonal multiple access (NOMA) system aided by a reconfigurable intelligent surface (RIS), where artificial noise (AN) is introduced to confuse the eavesdropper. To enhance secrecy, we employ improper Gaussian signaling (IGS) to alleviate the influence of AN on legitimate users. This is formulated as a sum secrecy rate maximization problem, where the reflecting coefficients of RIS and transmit covariance matrices of legitimate users and eavesdroppers are jointly optimized. An alternating optimization framework aided by the minorization-maximization method is adopted to address this non-convex optimization problem. Numerical results show that IGS significantly outperforms proper Gaussian signaling in improving the secrecy performance of RIS-aided NOMA systems, and such a secrecy advantage is more pronounced in RIS-aided NOMA than in traditional NOMA.

DOI
10.1109/lcomm.2024.3493427

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arXiv:2007.15902•Electronics Letters•Oct 2, 2020•52 citations
This letter investigates the physical layer security of a downlink non-orthogonal multiple access (NOMA) system aided by a reconfigurable intelligent surface (RIS), where artificial noise (AN) is introduced to confuse the eavesdropper. To enhance secrecy, we employ improper Gaussian signaling (IGS) to alleviate the influence of AN on legitimate users. This is formulated as a sum secrecy rate maximization problem, where the reflecting coefficients of RIS and transmit covariance matrices of legitimate users and eavesdroppers are jointly optimized. An alternating optimization framework aided by the minorization-maximization method is adopted to address this non-convex optimization problem. Numerical results show that IGS significantly outperforms proper Gaussian signaling in improving the secrecy performance of RIS-aided NOMA systems, and such a secrecy advantage is more pronounced in RIS-aided NOMA than in traditional NOMA.
This paper investigates the uplink secrecy performance of a reconfigurable intelligent surface (RIS)-aided multiple-input multiple-output non-orthogonal multiple access (MIMO-NOMA) network. In the proposed system model, users communicate with the base station (BS) via a strategically partitioned RIS. However, a silent passive eavesdropper overhears the data through a direct link. As part of the proposed security design, we propose a user-centric artificial noise (AN) transmission strategy that degrades the decoding ability of the eavesdropper without sacrificing the power budget. The AN is nullified in the composite channel utilizing singular value decomposition. After analyzing the channel statistics, which consider all channels experiencing Nakagami-mmmfading, we derive theoretical closed-form expressions for the ergodic secrecy rate (ESR) for each user in the NOMA pair using Gauss-Chebyshev quadrature and Taylor-Maclaurin expansions. Monte Carlo simulations validate the correctness of our analysis. The numerical results confirm that our proposed scheme consistently achieves a positive ESR. We also explore the impact of channel fading and RIS-partitioning ratio on the uplink ESR and comment on optimal power allocation. Notably, the results also confirm that the proposed system outperforms the benchmark MIMOorthogonal multiple access-based scheme.
The reconfigurable intelligent surface (RIS) aided non-orthogonal multiple access (NOMA) network is applied to improve spectral efficiency and energy efficiency of wireless systems. Due to the incorporation of NOMA, RIS-aided NOMA system suffers from physical layer security (PLS) problem when an internal near user (NU) is the eavesdropper. In this case, it is difficult to always guarantee positive secrecy rate. Therefore, a scheme of artificial noise (AN) cooperative jamming and beamforming design is proposed against internal eavesdropper for RIS-aided NOMA in this paper. It is proved theoretically that the positive secrecy rate can be guaranteed if providing sufficient power. In addition, the power allocation of base station is further studied to minimize the total power consumption under the constraints of data rate and secrecy rate, and the closed-form solutions are achieved. Simulation results show that the performance of the proposed scheme is superior to the existing solutions.
Spectrum sharing and successive interference cancellation (SIC) techniques used in power-domain non-orthogonal multiple access (NOMA) systems impose secrecy challenges because untrusted users can decode the information of trusted ones. In this context, physical layer security (PLS) appears as an alternative to address the possible risks. In this paper, the secrecy performance of a power-domain NOMA network that employs improper Gaussian signals (IGS) is explored for the first time. The system model considers the downlink where a base station (BS) employs IGS to transmit information to a couple of users. It is assumed that the user closest to the BS is the trusted user and the user furthest away is the untrusted user. The network security is evaluated in terms of the secrecy outage probability (SOP) considering imperfect SIC at the receivers. Expressions to evaluate the achievable rate for each user are calculated and, with these results, an expression to evaluate the SOP is also obtained. Results show that IGS allow the security to be improved, i.e., the SOP can be reduced if the impropriety degree of the transmitted signals is properly selected based on the operation parameters.
Hardware impairments (HWI) and the channel state information (CSI) estimation errors inevitably degrade the security performance of the communication system. In this work, we explore a robust beamforming solution for a reconfigurable intelligence surface (RIS)-assisted multiple-input single-output (MISO) multi-user secure network under HWI and imperfect CSI. Artificial noise (AN) is designed to jam eavesdroppers while non-orthogonal multiple access (NOMA) is employed to suppress the interference between legitimate users. Aimed at maximizing secrecy sum rate, the active beamforming with AN at the BS and the passive beamforming at the RIS are jointly optimized. The nonconvex optimization problem is handled using the semi-definite relaxation (SDR), where the eavesdropper's channel uncertainty is tackled by the S-procedure. Then the multi-variable coupling problem is decomposed into two sub-problems and three blocks of variables are alternately optimized using the block coordinate descent (BCD) method. The results suggest that the developed scheme outperforms the benchmark ones in terms of security and resistance to HWI.
This paper studies a downlink single-input-single-output (SISO) non-orthogonal multiple access (NOMA) systems in which a transmitter and a pair of legitimate receivers communicate with each other by using improper Gaussian signalings. There is an eavesdropper who overhears the information transmitted to the pair of legitimate receivers. Proper Gaussian signalings have been known as optimal on channels without interference, due to which proper Gaussian signalings have been widely used in many areas. Recently, it has been shown that improper Gaussian signalings improve achievable rates of NOMA systems. In this paper, we extend the application of improper Gaussian signalings to the secure NOMA systems. More specifically, we derive closed-form expressions of secrecy outage probability for users and analyze the effects of impropriety on the secrecy outage probability. Based on the mathematical analysis, we propose an algorithm to find the optimal impropriety degree for the secure NOMA. To confirm the analytic results, we perform extensive numerical evaluations and show that the analytic and numerical results are well matched each other. In addition, the NOMA systems based on improper and proper Gaussian signalings are compared in terms of the secrecy outage probability. The comparison substantiates our claim that a better secrecy performance is achievable with the improper Gaussian signalings.
In this Letter, the physical layer security for a novel reconfigurable intelligent surface (RIS)‐assisted non‐orthogonal multiple access (NOMA) system in a multi‐user scenario is investigated, where the authors consider the worst case that the eavesdropper also utilises the advantage of the RISs. More specifically, they derive analytical results for the secrecy outage probability (SOP). From the numerical results, they observe that the use of RISs can improve the secrecy performance compared to traditional NOMA systems. However, for the worst case that the received signals at the eavesdropper come from the RISs and source, increasing the number of intelligent elements on the RIS has a negative impact on the secrecy performance. At high signal‐to‐noise ratios, the system's SOP tends to a constant. Finally, the secrecy performance can be improved through group selection.