The advancement of industrial Internet of Things (IIoT) networks has brought challenges in terms of connectivity, efficient spectrum usage, and low latency. To tackle these challenges, advanced multiple access techniques have been developed. Non-orthogonal multiple access (NOMA) is a promising multiple access technique due to its high energy efficiency and fairness for devices. However, NOMA has inherent security issues due to wireless transmission and complex successive interference cancellation (SIC) based decoding, which can negatively impact system performance. Furthermore, achieving perfect SIC is also a challenging task due to implementation complexity. This study investigates the effects of imperfect SIC in a dual-device cooperative NOMA system. Our system includes direct links between the source and devices and uses both decode-and-forward and amplify-and-forward relays. The overall objective is to optimize decoding order and power allocation coefficients in order to maximize the near or priority device’s secrecy rate while meeting the quality-of-service (QoS) requirements of the far or normal device. Observing the underlying optimization problems to be non-convex, a low-complexity algorithm yielding optimal solutions is developed. Our findings reveal how imperfect SIC can impact massive access systems and secrecy performance. Extensive simulations provide novel design insights into the achievable secrecy rate and optimal power allocation coefficients. We also explore the trade-off between the priority device’s secrecy rate and the normal device’s rate, along with the impact of residual interference. Finally, our proposed solution has been shown to significantly improve the QoS-constrained secrecy rate of priority devices when compared to relevant benchmarks.

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.

Non-orthogonal multiple access (NOMA) has emerged as an enabling solution for 5th generation and beyond networks, but the often-neglected issues due to successive interference cancellation (SIC) based decoding might seriously hamper its performance. In this paper, we study a downlink NOMA system with cooperative half-duplex relaying with imperfect SIC, where the base station is communicating with two untrusted users with the aid of a trusted decode-and-forward relay while also considering the availability of direct links from the source. An optimization problem is formulated for maximizing the secrecy rate of the near user while fulfilling the quality-of-service requirements of the far user. The optimal power allocation solution is derived while considering the impact of SIC error. The simulation results illustrate the exactness of the theoretical analysis alongside insightful discussions to investigate the impact of imperfect SIC.

Non-orthogonal multiple access (NOMA) has been considered as a promising solution to provide spectrally efficient communications in the 5th generation and beyond networks. Cooperative communication, on the other hand, helps in improving the coverage and reliability of the communications. In this paper, we consider a cooperative NOMA communication system with two untrusted users and a trusted amplify-and-forward relay. Maximization of the secrecy rate of the near user while considering the service requirements of the far user is tackled. Closed-form expressions are obtained for the optimal power sharing between the source and the relay, along with the optimal power allocation for both users. Numerical results are also provided, which verify the exactness of the theoretical analysis and provide insights on the design of secure NOMA-based cooperative communication networks.