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IEEE Vehicular Technology Conference

Physical Layer Security in Power-Domain NOMA Using Improper Gaussian Signals

Mariani Sfredo, Evelio Martin Garcia Fernandez, Henry Carvajal Mora

Published Sep 1, 2021• 4 citations
Publisher

Abstract

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.

DOI
10.1109/vtc2021-fall52928.2021.9625188

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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.
Non-orthogonal multiple access (NOMA) has come to the fore as a spectrally efficient technique for fifth-generation networks and beyond. At the same time, NOMA faces severe security issues in the presence of untrusted users due to successive interference cancellation (SIC)-based decoding at receivers. In this paper, to make the system model more realistic, we consider the impact of imperfect SIC during the decoding process. Assuming the downlink mode, we focus on designing a secure NOMA communication protocol for the considered system model with two untrusted users. In this regard, we obtain the power allocation bounds to achieve a positive secrecy rate for both near and far users. Analytical expressions of secrecy outage probability (SOP) for both users are derived to analyze secrecy performance. Closed-form approximations of SOPs are also provided to gain analytical insights. Lastly, numerical results have been presented, which validate the exactness of the analysis and reveal the effect of various key parameters on achieved secrecy performance.
In this paper, we investigate the secrecy performance of an uplink-downlink power domain non-orthogonal multiple access (PD-NOMA) system with imperfect successive interference cancellation (SIC) in physical layer security (PLS). In the proposed system, two source users (SUs) communicate with two destination users (DUs) with the help of a cluster of multi-relay nodes using the decode-and-forward (DF) protocol in the presence of multi-eavesdroppers. These eavesdroppers try to overhear the wireless signal around the DUs. In our system, the selected DF-relay node also works as a jammer to improve security and protect confidential information from multi-eavesdroppers. In this role, the DF-relay node generates a jamming signal, creating artificial interference to reduce the quality of the eavesdropping channels. To evaluate the secrecy performance of the system, we derived the analytical expressions of the secrecy outage probability (SOP) for both DUs using three relay selection strategies over Rayleigh fading channels and used Monte Carlo simulations to confirm the accuracy of our calculations. Furthermore, we examined the effects of system parameters such as the number of eavesdroppers and DF relaying nodes, the power allocation, SIC performance, the position of eavesdropper on the SOP of the two DUs. We compared the performance of our proposed NOMA system with those of conventional orthogonal multiple access (OMA) schemes.
Non-orthogonal multiple access (NOMA) serves multiple users simultaneously via the same resource block by exploiting superposition coding at the transmitter and successive interference cancellation (SIC) at the receivers. Under practical considerations, perfect SIC may not be achieved. Thus, residual interference (RI) occurs inevitably due to imperfect SIC. In this work, we first propose a novel model for characterizing RI to provide a more realistic secrecy performance analysis of a downlink NOMA system under imperfect SIC at receivers. In the presence of untrusted users, NOMA has an inherent security flaw. Therefore, for this untrusted users' scenario, we derive new analytical expressions of secrecy outage probability (SOP) for each user in a two-user untrusted NOMA system by using the proposed RI model. To further shed light on the obtained results and obtain a deeper understanding, a high signal-to-noise ratio approximation of the SOPs are also obtained. Lastly, numerical investigations are provided to validate the accuracy of the desired analytical results and present valuable insights into the impact of various system parameters on the secrecy rate performance of the secure NOMA communication system.
Non-orthogonal multiple access (NOMA) can be combined with physical layer security technology to greatly improve spectral efficiency while tackling security issues for the Internet of Things (IoT) networks. This paper investigates the security performance in a fifth-generation (5G) downlink NOMA system with an untrusted user in the presence of imperfect successive interference cancellation (SIC). Analytical expressions of secrecy outage probability (SOP) and connection outage probability (COP) are derived as performance metrics to evaluate the secrecy of the proposed system. In order to further improve the secrecy performance, we propose an optimal power allocation scheme based on two users' different quality of service (QoS) requirements and obtain a closed-form solution of the optimal parameter. Through numerical simulations and exhaustive search algorithm, we validate the correctness of the derived analytical results. It is proved that the proposed power allocation scheme can achieve the optimal secrecy performance.
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 paper investigates the physical-layer security (PLS) aspects of the uplink cooperative non-orthogonal multiple access (NOMA) in the context of two user scenario. More specifically, this work employs the decode-and-forward (DF) relay for not only establishing a connection between the far user and base station (BS) but also enhancing the performance of far user whose channel is prone to the detrimental effects of fading and shadowing. The secrecy performance comparison between two users i.e., near user and far user is obtained under perfect and imperfect successive interference cancellation (SIC) assumptions and even the performance of FU is improved by using DF relay and instantaneous channel gain decoding order is considered at the BS under two cases. This paper analyses the performance of cooperative uplink NOMA network in the presence of an external eavesdropper in terms of secrecy ergodic capacity (SEC), secrecy ergodic sum capacity (SESC), and secrecy outage probability (SOP). This work derives the closed-form analytical expressions of SOP and SEC metrics for both strong and weak users with perfect and imperfect SIC cases in order to characterise the secrecy performance of the proposed secure cooperative NOMA network. Further, the outcomes of the simulations are shown as evidence for both the validation of the mathematical analysis and the performance of the proposed method.