Designing a secure non-orthogonal multiple access (NOMA) system has recently sparked a lot of interest among researchers due to its competency over bandwidth utilization. This paper addresses the critical security issue that arises from the adoption of successive interference cancellation based decoding approach in a two-user untrusted NOMA scenario. With the objective of maximizing secrecy fairness between users, a joint optimization problem of power allocation and decoding order is investigated to maximize the minimum ergodic secrecy rate between users. The optimized solutions are obtained by proposing a low computational complexity iterative method. In addition, closed-form optimal solutions based on a tight approximation are presented. Finally, numerical simulations validate the key nontrivial analytical claims and demonstrate that substantial performance gain is achieved over existing benchmark schemes.
Designing a secure non-orthogonal multiple access (NOMA) system has recently sparked a lot of interest among researchers due to its competency over bandwidth utilization. This paper addresses the critical security issue that arises from the adoption of successive interference cancellation based decoding approach in a two-user untrusted NOMA scenario. With the objective of maximizing secrecy fairness between users, a joint optimization problem of power allocation and decoding order is investigated to maximize the minimum ergodic secrecy rate between users. The optimized solutions are obtained by proposing a low computational complexity iterative method. In addition, closed-form optimal solutions based on a tight approximation are presented. Finally, numerical simulations validate the key nontrivial analytical claims and demonstrate that substantial performance gain is achieved over existing benchmark schemes.
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) is a wireless communication technique that uses the Successive Interference Cancellation (SIC) strategy to achieve high efficiency. However, SIC can pose security risks in an untrusted NOMA environment where users can suffer from internal eavesdropping. In this research paper, we propose security solutions for downlink NOMA transmission involving two untrusted user terminals and imperfect SIC. Specifically, we investigate the ergodic secrecy rate performance in NOMA for two user terminals against mutual eavesdropping. To achieve the maximum weighted ergodic sum secrecy rate of the system while meeting the quality of service (QoS) requirements of both user terminals, we formulate an optimization problem for power allocation. Our solution approach considers a decoding order that yields the best possible outcome and employs an iterative method to obtain the optimal power allocation. Simulation results confirm the analytical claims and provide key insights on the optimal design parameters. Lastly, we numerically demonstrate that our proposed power control and decoding order design outperforms the benchmark schemes in terms of weighted ergodic sum secrecy rate performance.
The amalgamation of non-orthogonal multiple access (NOMA) and physical layer security is a significant research interest for providing spectrally-efficient secure fifth-generation networks. Observing the secrecy issue among multiplexed NOMA users, which is stemmed from successive interference cancellation based decoding at receivers, we focus on safeguarding untrusted NOMA. Considering the problem of each user’s privacy from each other, the appropriate secure decoding order and power allocation (PA) for users are investigated. Specifically, a decoding order strategy is proposed which is efficient in providing positive secrecy at all NOMA users. An algorithm is also provided through which all the feasible secure decoding orders in accordance with the proposed decoding order strategy can be obtained. Further, in order to maximize the sum secrecy rate of the system, the joint solution of decoding order and PA is obtained numerically. Also, a sub-optimal decoding order solution is proposed. Lastly, numerical results present useful insights on the impact of key system parameters and demonstrate that average secrecy rate performance gain of about 27 dB is obtained by the jointly optimized solution over different relevant schemes.
Non-orthogonal multiple access (NOMA) has been recognized as a promising multiple access technique for enhanced spectral efficiency in the current and next-generation wireless networks. In this paper, we examine a realistic NOMA model where users, assisted by a regenerative relay, cannot be fully trusted. We address the challenge of ensuring secure access for these users while accounting for the error propagation in successive interference cancellation (SIC) during the decoding process. For such, we formulate and solve two optimization problems, viz. maximizing the minimum secrecy rate of the users and maximizing the sum secrecy rate of the users, while accounting for SIC errors and the constraint on the power budget. For each case, we derive the optimal power allocation solution to achieve positive secrecy rates despite imperfect SIC. Simulation results provide key insights on the obtained secrecy rates and power allocations, factoring in residual interference. The joint optimal solution for the decoding order and power allocation is compared with different benchmark schemes: optimal decoding order and equal power allocation, fixed decoding order and equal power allocation, fixed decoding order and optimal power allocation, and optimal decoding order and channel-based power allocation. Our proposed framework demonstrates average performance gains of about 47.62 dB, 50.79 dB, 54.02 dB and 39.83 dB over these schemes and, hence, the fact that the proposed framework can substantially improve the secrecy performance.
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.
Observing the significance of spectrally-efficient secure non-orthogonal multiple access (NOMA), this paper proposes a novel quality of service (QoS) aware secure NOMA protocol that maximizes secrecy fairness among untrusted users. Considering a base station (BS) and two users, a novel decoding order is designed that provides security to both users. With the objective of ensuring secrecy fairness between users, while satisfying their QoS requirements under BS transmit power budget constraint, we explore the problem of minimizing the maximum secrecy outage probability (SOP). Closed-form expression of pair outage probability (POP) and optimal power allocation (PA) minimizing POP are obtained. To analyze secrecy performance, analytical expressions of SOP for both users are derived, and individual SOP minimization problems are solved using concept of generalized-convexity. High signal-to-noise ratio approximation of SOP and asymptotically optimized solution minimizing this approximation is also found. Furthermore, global-optimal solution from secrecy fairness standpoint is obtained at low computational complexity, and tight approximation is derived to get analytical insights. Numerical results present useful insights on globally optimized PA which ensure secrecy fairness and provide performance gain of about 55.12%, 69.30%, and 19.11%, respectively, compared to fixed PA and individual users' optimal PAs. Finally, a tradeoff between secrecy fairness performance and QoS demands is presented.