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International Conference on Information and Communication Technology Convergence (ICTC)

Improper Gaussian Signalings for Secure Non-Orthogonal Multiple Access

Hyeonsik Yeom, Jeongseok Ha

Published Oct 19, 2022• 0 citations
Publisher

Abstract

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.

DOI
10.1109/ictc55196.2022.9952828

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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.
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.
In this paper, we analyze the outage probability and secrecy capacity of a non-orthogonal multiple access (NOMA) system in the presence of an eavesdropper. In order to enhance spectral efficiency, a base station communicates with two users simultaneously in the same frequency band by superpimposing the transmit signals to the users in the power domain. Specifically, the user with the worse channel conditions is allocated higher power such that it is able to directly decode its signal from the received superimposed signal. At the user with the better channel conditions, the interference due to NOMA is processed by successive interference cancelation. Given these system settings and accounting for decoding thresholds, we analyze the outage probability of the NOMA system over Rayleigh fading channels. Furthermore, based on the locations of the users and eavesdropper, the secrecy capacity is analyzed to assess the level of security provided to the legitimate users in the presence of an eavesdropper. Here, the decoding thresholds of legitimate users and eavesdropper are also included in the analysis of the secrecy capacity. Through numerical results, the effects of network parameters on system performance are assessed as well as the the superiority of NOMA in terms of secrecy capacity over traditional orthogonal multiple access.
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.
In this paper, we study uplink-downlink non-orthogonal multiple access (NOMA) systems by considering the secure performance at the physical layer. In the considered system model, the base station acts a relay to allow two users at the left side communicate with two users at the right side. By considering imperfect channel state information (CSI), the secure performance need be studied since an eavesdropper wants to overhear signals processed at the downlink. To provide secure performance metric, we derive exact expressions of secrecy outage probability (SOP) and and evaluating the impacts of main parameters on SOP metric. The important finding is that we can achieve the higher secrecy performance at high signal to noise ratio (SNR). Moreover, the numerical results demonstrate that the SOP tends to a constant at high SNR. Finally, our results show that the power allocation factors, target rates are main factors affecting to the secrecy performance of considered uplink-downlink NOMA systems.
This paper investigates secure transmission for non-orthogonal multiple access (NOMA) systems where the imperfect successive interference cancellation (SIC) is considered at both legitimate users and eavesdropper (Eve). A power allocation scheme is designed for the legitimate users to mitigate the effect of the SIC error caused by imperfect SIC. For characterizing the secrecy performance of the NOMA system, the closed-form expressions for connection outage probability (COP), secrecy outage probability (SOP), and effective secrecy throughput (EST) are derived over Nakagami-m fading channels in both NOMA and benchmark orthogonal multiple access (OMA) systems. We also provide security and reliability trade-off results (SRT) for the users in the NOMA and OMA systems. Simulation results verify our analysis and show that the strong users achieve better secrecy performance but worse reliability performance and NOMA outperforms OMA in terms of SRT.
In this letter, we investigate the information security problem for non-orthogonal multiple access (NOMA) networks against an external eavesdropper. Considering the overhead of the channel state information (CSI) feedback, we utilize the quantized CSI during the secure NOMA transmission, and derive the secrecy rate for each receiver by adopting the successive interference cancellation. In order to optimally allocate the transmit power, an optimization problem is formulated such that the minimum secrecy rate of the receivers is maximized. For the proposed scheme, we also analyze the secrecy outage and transmission outage probabilities, and their closed-form expressions are derived. In addition, the security-reliability tradeoff is analyzed. Numerical results are demonstrated to verify the analytical results.