The secrecy challenge of protecting a power domain non-orthogonal multiple access (NOMA) system is associated with the intrinsic superposition structure of the transmitted information. Because of this superposition operation, the interference generated by the other user's information must be first decoded by the receiver in order to allow the intended information to be acquired. Therefore, a robust secrecy solution for this type of channel access techniques must consider not only the existence of attacks coming from undetectable passive eavesdroppers located outside of the network, but also attacks carried out by eavesdroppers registered as legitimate users inside the system. In this work, a cooperative jamming technique is combined with a secure channel training solution in order to protect a two user power domain NOMA system against eavesdropping attacks coming simultaneously from inside and outside of the network. The proposed secrecy solution is evaluated numerically and the evaluation demonstrates that weak secrecy is achieved against the inside and outside eavesdroppers.
The secrecy challenge of protecting a power domain non-orthogonal multiple access (NOMA) system is associated with the intrinsic superposition structure of the transmitted information. Because of this superposition operation, the interference generated by the other user's information must be first decoded by the receiver in order to allow the intended information to be acquired. Therefore, a robust secrecy solution for this type of channel access techniques must consider not only the existence of attacks coming from undetectable passive eavesdroppers located outside of the network, but also attacks carried out by eavesdroppers registered as legitimate users inside the system. In this work, a cooperative jamming technique is combined with a secure channel training solution in order to protect a two user power domain NOMA system against eavesdropping attacks coming simultaneously from inside and outside of the network. The proposed secrecy solution is evaluated numerically and the evaluation demonstrates that weak secrecy is achieved against the inside and outside eavesdroppers.
This paper proposes a new design of non-orthogonal multiple access (NOMA) under secrecy considerations. We focus on a NOMA system, where a transmitter sends confidential messages to multiple users in the presence of an external eavesdropper. The optimal designs of decoding order, transmission rates, and power allocated to each user are investigated. Considering the practical passive eavesdropping scenario where the instantaneous channel state of the eavesdropper is unknown, we adopt the secrecy outage probability as the secrecy metric. We first consider the problem of minimizing the transmit power subject to the secrecy outage and quality of service constraints, and derive the closed-form solution to this problem. We then explore the problem of maximizing the minimum confidential information rate among users subject to the secrecy outage and transmit power constraints, and provide an iterative algorithm to solve this problem. We find that the secrecy outage constraint in the studied problems does not change the optimal decoding order for NOMA, and one should increase the power allocated to the user whose channel is relatively bad when the secrecy constraint becomes more stringent. Finally, we show the advantage of NOMA over orthogonal multiple access in the studied problems both analytically and numerically.
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.
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, secure communication in non-orthogonal multiple access (NOMA) downlink system is considered wherein two NOMA users with channel gain difference are paired in each transmission slot. The user with poor channel condition (weak user) is entrusted, while the user with good channel condition (strong user) is a potential eavesdropper. The weak user data can be intercepted by the strong user since the strong user needs to decode the weak user’s message for successive interference cancellation operation in NOMA. To impair strong user’s eavesdropping capability, weak user’s information-bearing signal is merged with an artificial signal (AS). Thus, the eavesdropping process requires extra decoding step at higher power level. The secrecy outage probability of the weak user is derived and provided in closed-form expression. The weak user faces a choice between transmitting the information-bearing signal with the total power and the deploying the AS technique, whereas the strong user can choose whether to eavesdrop the weak user’s message or not. To investigate users’ power-secrecy tradeoffs, their interactions are modeled as a non-cooperative zero-sum game. The existence of Nash equilibria (NEs) of the proposed game is first analyzed, and pure and mixed-strategy NE profiles are provided. In addition, numerical simulations are conducted to validate the analytical results and to prove that AS-Aided proposed scheme enhances the secrecy performance of NOMA systems while maintaining the NOMA superiority over OMA systems.
We have proposed and analyzed secrecy performance of a network architecture which contains a source, two destinations, a friendly jammer (FJ) and an eavesdropper (Eve). To jam the Eve in order to secure the confidential information of both users, the FJ sends a jamming signal while the source sends the combined information signal using non-orthogonal multiple access (NOMA) technique to both the users. A known jamming is considered which is known by both the users. Both the users subtract the known jamming from the received signal and then decode the information signal as per the NOMA technique. We analyzed the physical layer security of the network in terms of the secrecy outage probability (SOP) where the two users have different target secrecy rates. A closed form expression of the SOP is developed. We have analyzed the SOP under the impact of several numerical parameters such as: source transmit signal to noise ratio (SNR), FJ transmit SNR, fraction of source transmit power, and different target secrecy rates. For a fixed transmit SNR of the FJ, we obtain an optimal value of the source transmit SNR at which SOP is minimized. These analyzed results are also supported by the MATLAB based simulation results.
This work addresses the security of a two-user broadcast channel. The challenge of protecting a broadcast channel is associated with the necessity of securing the system, not only against eavesdropping attacks originating from external nodes, but also to ensure that the inside users do not eavesdrop on each other’s information. To address this issue, the present work proposes a cooperative jamming scheme that provides protection against eavesdropping attacks carried out simultaneously by inside users and external eavesdroppers. To achieve this goal, the developed scheme combines real interference alignment with a blind cooperative jamming technique defined in the literature. An information theoretical analysis shows that positive secure degrees of freedom are achievable using the proposed solution.