Non-orthogonal multiple access (NOMA) has been widely considered as a promising technology to enable high-efficient wireless transmissions in future 5G communication systems. In this chapter, we investigate single-input single-output (SISO) NOMA systems from the perspective of physical layer security. There into, two different SISO NOMA systems are studied in sequence so as to explore security issues in NOMA. First, we attempt the physical layer security technique in a SISO NOMA system which consists of a transmitter, multiple legitimate users and an eavesdropper who aims to wiretap the messages intended for all legitimate users. The objective is to maximise sum of secrecy rates subject to an individual quality of service constraint for each legitimate user, respectively. The investigations in this system will provide a preliminary analysis of the secure performance of SISO NOMA systems. Second, on the basis of the SISO NOMA system previously studied, a multi-antenna jammer is additionally equipped to enhance secure transmissions of the system. The joint optimisation of power allocation and beamforming design is considered. The efforts in this second system aim to propose an effective solution for realising secure transmissions for each legitimate user.
Non-orthogonal multiple access (NOMA) has been widely considered as a promising technology to enable high-efficient wireless transmissions in future 5G communication systems. In this chapter, we investigate single-input single-output (SISO) NOMA systems from the perspective of physical layer security. There into, two different SISO NOMA systems are studied in sequence so as to explore security issues in NOMA. First, we attempt the physical layer security technique in a SISO NOMA system which consists of a transmitter, multiple legitimate users and an eavesdropper who aims to wiretap the messages intended for all legitimate users. The objective is to maximise sum of secrecy rates subject to an individual quality of service constraint for each legitimate user, respectively. The investigations in this system will provide a preliminary analysis of the secure performance of SISO NOMA systems. Second, on the basis of the SISO NOMA system previously studied, a multi-antenna jammer is additionally equipped to enhance secure transmissions of the system. The joint optimisation of power allocation and beamforming design is considered. The efforts in this second system aim to propose an effective solution for realising secure transmissions for each legitimate user.
Non-orthogonal multiple access (NOMA) has been recognized as a promising technique for providing high data rates in 5G systems. This letter is to study physical layer security in a single-input single-output (SISO) NOMA system consisting of a transmitter, multiple legitimate users and an eavesdropper. The aim of this letter is to maximize the secrecy sum rate (SSR) of the NOMA system subject to the users' quality of service (QoS) requirements. We firstly identify the feasible region of the transmit power for satisfying all users' QoS requirements. Then we derive the closed-form expression of an optimal power allocation policy that maximizes the SSR. Numerical results are provided to show a significant SSR improvement by NOMA compared with conventional orthogonal multiple access (OMA).
Multiple Input Single Output (MISO) Non-orthogonal multiple access (NOMA), combining the benefits of spatial multiplexing with higher spectral efficiency, has recently attained a substantial research interest in 5G and upcoming mobile communication networks. This paper proposes an optimal power control algorithm for downlink secure MISO-NOMA communication involving untrusted users. Sum secure rate maximization of both single antenna users has been considered, while satisfying their quality of service requirements, numerical method is used for optimal power sharing between users, and optimal beamforming vectors have been derived. Simulations validate the analysis, demonstrate the efficacy of the proposed design, and offer design insights into secure MISO-NOMA communications.
In this paper, we study the physical layer security of a downlink multi-input single-output non-orthogonal multiple access (NOMA) system, in which transmit antenna selection (TAS) scheme, users’ quality of service (QoS) requirements, Nakagami-m fading channel, and user selection solution are considered for secure NOMA transmission. Specifically, we investigate the scenario that a base station (BS) (source) communicates with two legitimate user (LU) clusters with different priority depending on their QoS requirements in the presence of multiple passive eavesdroppers over Nakagami-m fading. To enhance the secrecy performance, we examine a TAS scheme and a user selection method. In this context, prior to transmission, a transmit antenna and a user in high-priority LU cluster are jointly selected to maximize the channel quality of the link from the BS to the selected user. Furthermore, together with the selected high-priority user, a user in low-priority LU cluster, which has the best channel condition, is chosen for performing two-user NOMA. In order to evaluate the secrecy performance, tight and asymptotic closed-form expressions of secrecy outage probability for selected LUs and overall system are derived. Our theoretical results confirmed by Monte–Carlo simulation show that in QoS-based NOMA system, high-priority users cause the higher effects on the overall secrecy performance in comparison with low-priority users. Finally, these results also indicate that our proposed communication protocol achieves the secrecy performance greater than conventional protocol.
NOMA (Non-Orthogonal Multiple Access) has been recognized as new multiple access technology for wireless communication networks of the fifth generation and beyond, owing to its ability to improve spectral efficiency, support massive connectivity, and provide user fairness. However, it has been observed that the superposition-based transmission principle of NOMA is highly susceptible to eavesdropping attacks, especially in an open wireless network where all wireless communications are inherently broadcast in nature. Hence, ensuring secure wireless communications for NOMA systems has now become an important area of research. This research aims to improve the secrecy level of wireless communications for NOMA systems by employing Physical Layer Security (PLS) techniques. Specifically, two prominent PLS techniques, Artificial Noise (AN) and Cooperative Jamming (CJ), have been employed to provide security against passive eavesdropping attacks. The cooperative NOMA system architecture is considered, and the secrecy enhancement is analyzed for two possible scenarios when the eavesdropper is close to the relay node and when the eavesdropper is close to the base station. The secrecy performance of the proposed system is analyzed through various parameters, namely, Secrecy Outage Probability (SOP), Secrecy Capacity (SC), Secrecy Rate (SR), and Secrecy Energy Efficiency (SEE) in terms of the Signal to Noise Ratio (SNR). The numerical results for the secrecy metrics are obtained through MATLAB-based simulations, whereas the system-level model is developed using the Simulink platform to verify the suggested system's functionality in the presence of AN and CJ for the legitimate NOMA users and the eavesdropper. The results show that the secrecy performance is significantly enhanced with the introduction of AN and CJ, and the system shows robust performance in terms of energy efficiency. This paper provides significant insights into the design of the NOMA system from the secrecy perspective and validates the potential of PLS techniques for the design of the future wireless system.
In this paper, the application of Non-Orthogonal Multiple Access (NOMA) is investigated in a multiple-input single-output network consisting of multiple legitimate users and a potential eavesdropper. To support secure transmissions from legitimate users, two NOMA Secrecy Sum Rate Transmit BeamForming (NOMA-SSR-TBF) schemes are proposed to maximise the SSR of a Base Station (BS) with sufficient and insufficient transmit power. For BS with sufficient transmit power, an artificial jamming beamforming design scheme is proposed to disrupt the potential eavesdropping without impacting the legitimate transmissions. In addition, for BS with insufficient transmit power, a modified successive interference cancellation decoding sequence is used to reduce the impact of artificial jamming on legitimate transmissions. More specifically, iterative algorithm for the successive convex approximation are provided to jointly optimise the vectors of transmit beamforming and artificial jamming. Experimental results demonstrate that the proposed NOMA-SSR-TBF schemes outperforms the existing works, such as the maximized artificial jamming power scheme, the maximized artificial jamming power scheme with artificial jamming beamforming design and maximized secrecy sum rate scheme without artificial jamming beamforming design.
Non-orthogonal multiple access (NOMA) is envisioned as a promising technology for achieving both high spectral efficiency and massive connectivity in emerging wireless networks. While the massive connectivity powered by NOMA grants mobile devices more opportunities for access, it also renders the network vulnerable to be intercepted. In this article, the application of full-duplex relaying/jamming technology to NOMA-based cooperative networks against eavesdropping is investigated. Adopting the full-duplex technique, the intermediate node plays two roles in the secure network: 1) coordinates the NOMA transmission and enhances link reliability for legitimate users; 2) emits artificial noise in addition to multi-user interference to deteriorate the received signal quality of any potential eavesdropper. From the perspective of signal processing, we concentrate on the NOMA signal designs, decoding strategies, interference management, and power allocation to improve the secrecy performance under different eavesdropping manners. Moreover, we also discuss some future research directions on this topic.