In this paper, we consider a cooperative non-orthogonal multiple access (NOMA) system with two untrusted users and a trusted decode-and-forward (DF) relay. We formulate two optimization problems to maximize the secrecy rate of near user under two scenarios, namely joint and individual power budget constraints on source and relay. Closed-form expressions are obtained for power sharing between source and relay, along with energy-efficient power allocation coefficients for both the users. Numerical results are provided, which verify the exactness of the theoretical analysis and present insights on the design of a secure cooperative communication network.
In this paper, we consider a cooperative non-orthogonal multiple access (NOMA) system with two untrusted users and a trusted decode-and-forward (DF) relay. We formulate two optimization problems to maximize the secrecy rate of near user under two scenarios, namely joint and individual power budget constraints on source and relay. Closed-form expressions are obtained for power sharing between source and relay, along with energy-efficient power allocation coefficients for both the users. Numerical results are provided, which verify the exactness of the theoretical analysis and present insights on the design of a secure cooperative communication network.
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.
In this work, the secrecy of a typical wireless cooperative dual-hop non-orthogonal multiple access (NOMA)-enabled decode-and-forward (DF) relay network is investigated with the impact of collaborative and non-collaborative eavesdropping. The system model consists of a source that broadcasts the multiplexed signal to two NOMA users via a DF relay, and information security against the eavesdropper nodes is provided by a helpful jammer. The performance metric is secrecy rate and ergodic secrecy capacity is approximated analytically. In addition, a differential evolution algorithm-based power allocation scheme is proposed to find the optimal power allocation factors for relay, jammer, and NOMA users by employing different jamming schemes. Furthermore, the secrecy rate analysis is validated at the NOMA users by adopting different jamming schemes such as without jamming (WJ) or conventional relaying, jamming (J), and with control jamming (CJ). Simulation results demonstrate the superiority of CJ over the J and WJ schemes. Finally, the proposed power allocation outperforms the fixed power allocation under all conditions considered in this work.
We investigate a secrecy-enhancing design for cooperative downlink and uplink non-orthogonal multiple access (NOMA) transmissions with an untrusted relay. A source uses the NOMA principle to have downlink and uplink transmissions with a near user and a far user, and the communications between the source and the far user are aided by an untrusted relay. To minimize information leakage at the untrusted relay and achieve secure NOMA communications, adaptive downlink and uplink cooperative jamming schemes are proposed, where the far user in downlink and the near user in uplink adaptively emit a jamming signal to the untrusted relay to impair its eavesdropping capability. Both downlink and uplink jamming power are optimized to fully exploit the benefits of the proposed schemes for security enhancement. Then, for each scheme, we quantify the secrecy performance by deriving the ergodic secrecy sum rate lower bound and its scaling law. Finally, computer simulation is used to demonstrate the effectiveness of the proposed adaptive downlink and uplink cooperative jamming schemes and verify the accuracy of the derived analytical results.
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.
In this paper, we study the secrecy outage probability (SOP)and the strictly positive secrecy capacity (SPSC)of cooperative non-orthogonal multiple access (NOMA)system with a single antenna over Rayleigh fading channel in which there are a source, a relay node, two destinations and one eavesdropper. The relay adopts amplify-and-forward (AF)and decode-and-forward (DF)relaying schemes. The SOP and SPSC performance are analyzed to evaluate the level of security granted to legitimate users for both AF and DF protocols. The effects of the optimal power allocation value on system performance are also discussed and provided through numerical results.
The application of successive interference cancellation (SIC) introduces critical security risks to cooperative non-orthogonal multiple access (NOMA) systems in the presence of untrustworthy network nodes, referred to as internal eavesdroppers. To address this potential security and reliability flaw, by assuming all users are untrusted, this letter investigates the effective secrecy throughput (EST) for a cooperative NOMA system, where a near user serves as an amplify-and-forward relay to help forward the information of a far user. Considering the inverse power allocation and SIC decoding order, a novel jamming strategy is proposed to enhance the security performance of the far user. Gauss-Chebyshev approximations of ESTs over Nakagami-mchannels are derived. Asymptotic EST expressions are proposed to provide further insights. Numerical results demonstrate that the proposed jamming strategy and the inverse power allocation and SIC decoding order are both essential for achieving positive secrecy rates for both users.