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arXiv:2308.08811 · European Signal Processing Conference (EUSIPCO)

Secrecy Outage Probability Analysis for Downlink NOMA with Imperfect SIC at Untrusted Users

Sapna Thapar, Insha Amin, Deepak Mishra, Ravikant Saini

Published Aug 23, 2021• 9 citations
arXivHTMLPDF

Abstract

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.

DOI
10.23919/eusipco54536.2021.9615975

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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.
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.
Spectrally-efficient secure non-orthogonal multiple access (NOMA) has recently attained a substantial research interest for fifth generation development. This work explores crucial security issue in NOMA which is stemmed from utilizing the decoding concept of successive interference cancellation. Considering untrusted users, we design a novel secure NOMA transmission protocol to maximize secrecy fairness among users. A new decoding order for two users' NOMA is proposed that provides positive secrecy rate to both users. Observing the objective of maximizing secrecy fairness between users under given power budget constraint, the problem is formulated as minimizing the maximum secrecy outage probability (SOP) between users. In particular, closed-form expressions of SOP for both users are derived to analyze secrecy performance. SOP minimization problems are solved using pseudoconvexity concept, and optimized power allocation (PA) for each user is obtained. Asymptotic expressions of SOPs, and optimal PAs minimizing these approximations are obtained to get deeper insights. Further, globally-optimized power control solution from secrecy fairness perspective is obtained at a low computational complexity and, asymptotic approximation is obtained to gain analytical insights. Numerical results validate the correctness of analysis, and present insights on optimal solutions. Finally, we present insights on global-optimal PA by which fairness is ensured and gains of about 55.12%, 69.30%, and 19.11%, respectively are achieved, compared to fixed PA and individual users' optimal PAs.
Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique to improve the spectral efficiency of the fifth-generation (5G) and beyond networks. However, the successive interference cancellation (SIC) based decoding used at the receivers makes NOMA prone to critical security risks. In this paper, we consider a regenerative relay-assisted dual-user downlink NOMA communication model. To ensure the robustness of the model, we also take into account the error propagation in SIC occurring in the decoding process. Our design goal being to provide security to both users, we propose an optimal power management strategy, so as to maximize the secrecy rate of the users under the impact of imperfect SIC. The optimal power allocation solution is obtained such that positive secrecy rate is achieved at both of the end receivers, while accounting for SIC errors. Analytical expressions of the secrecy rates are derived to analyze the secrecy performance. Simulation results are also presented, and provide key insights on the obtained secrecy rate and power allocation coefficients with residual interference. The achieved gains prove that the proposed model can substantially improve the secrecy performance.
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.
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.