The ultimate objective of cooperative communication is to secure data transmitted from source to destination against eavesdropper attacks. The paper compares different power optimization algorithms for cooperative jamming schemes to improve the secrecy performance of a four-node Amplify and Forward (AF) relay network. The main focus of the work is on the investigation of Optimal Power Allocation (OPA) for maximizing the secrecy rate subject to a total power constraint using two cooperative jamming schemes, Source and Relay Based Jamming (SRBJ) and Source Based Jamming (SBJ). The secrecy performance of SBJ is evaluated for trusted and untrusted relaying scenarios. In the untrusted case, the situation in which an external eavesdropper and untrusted relay exist simultaneously is analyzed. The iterative algorithms such as the Nelder-Mead technique (N-M), the Broyden - Fletcher – Goldfarb - Shanno (BFGS) algorithm and the Conjugate-Gradient (CG) methods are used for power optimization and, consequently, for secrecy rate maximization. Both symmetric and asymmetric relay positions are subjected to the secrecy analysis. A comparison is conducted using the equal power Allocation (EPA) approach and the Exhaustive Search (ES) algorithm. The paper also studies the complexity of different algorithms and jamming methods based on the average number of iterations required for system convergence. It was found that the iterative algorithms provide better secrecy than the conventional methods. Experimental results reveal a trade-off between the iterative algorithms' convergence and complexity. The gradient-based BFGS and CG algorithms are less complex than the gradient-free N-M method. When assessing all jamming schemes, the N-M method is a good choice for convergence, whereas the BFGS is the best choice for lesser complexity.
The ultimate objective of cooperative communication is to secure data transmitted from source to destination against eavesdropper attacks. The paper compares different power optimization algorithms for cooperative jamming schemes to improve the secrecy performance of a four-node Amplify and Forward (AF) relay network. The main focus of the work is on the investigation of Optimal Power Allocation (OPA) for maximizing the secrecy rate subject to a total power constraint using two cooperative jamming schemes, Source and Relay Based Jamming (SRBJ) and Source Based Jamming (SBJ). The secrecy performance of SBJ is evaluated for trusted and untrusted relaying scenarios. In the untrusted case, the situation in which an external eavesdropper and untrusted relay exist simultaneously is analyzed. The iterative algorithms such as the Nelder-Mead technique (N-M), the Broyden - Fletcher – Goldfarb - Shanno (BFGS) algorithm and the Conjugate-Gradient (CG) methods are used for power optimization and, consequently, for secrecy rate maximization. Both symmetric and asymmetric relay positions are subjected to the secrecy analysis. A comparison is conducted using the equal power Allocation (EPA) approach and the Exhaustive Search (ES) algorithm. The paper also studies the complexity of different algorithms and jamming methods based on the average number of iterations required for system convergence. It was found that the iterative algorithms provide better secrecy than the conventional methods. Experimental results reveal a trade-off between the iterative algorithms' convergence and complexity. The gradient-based BFGS and CG algorithms are less complex than the gradient-free N-M method. When assessing all jamming schemes, the N-M method is a good choice for convergence, whereas the BFGS is the best choice for lesser complexity.
Physical (PHY) layer security approaches for wireless communications can prevent eavesdropping without upper layer data encryption. However, they are hampered by wireless channel conditions: absent feedback, they are typically feasible only when the source-destination channel is better than the source-eavesdropper channel. Node cooperation is a means to overcome this challenge and improve the performance of secure wireless communications. This paper addresses secure communications of one source-destination pair with the help of multiple cooperating relays in the presence of one or more eavesdroppers. Three cooperative schemes are considered: decode-and-forward (DF), amplify-and-forward (AF), and cooperative jamming (CJ). For these schemes, the relays transmit a weighted version of a reencoded noise-free message signal (for DF), a received noisy source signal (for AF), or a common jamming signal (for CJ). Novel system designs are proposed, consisting of the determination of relay weights and the allocation of transmit power, that maximize the achievable secrecy rate subject to a transmit power constraint, or, minimize the transmit power subject to a secrecy rate constraint. For DF in the presence of one eavesdropper, closed-form optimal solutions are derived for the relay weights. For other problems, since the optimal relay weights are difficult to obtain, several criteria are considered leading to suboptimal but simple solutions, i.e., the complete nulling of the message signals at all eavesdroppers (for DF and AF), or the complete nulling of jamming signal at the destination (for CJ). Based on the designed relay weights, for DF in the presence of multiple eavesdroppers, and for CJ in the presence of one eavesdropper, the optimal power allocation is obtained in closed-form; in all other cases the optimal power allocation is obtained via iterative algorithms. Numerical evaluation of the obtained secrecy rate and transmit power results show that the proposed design can significantly improve the performance of secure wireless communications.
Summary Cooperative communication based on relaying nodes has been considered as a promising technique to increase the physical layer security (PLS) performance in wireless communications. In this paper, an optimal power allocation (OPA) scheme based on Nelder‐Mead (NM) algorithm is proposed for improving the secrecy rate of amplify‐and‐forward (AF) cooperative relay networks employing cooperative jamming (CJ) scheme. The proposed hybrid jamming scheme allows the source and selected relay to transmit the jamming signal along with the information to confound the eavesdropper. The path selection probability of ant colony optimization (ACO) algorithm is used for selecting the relay for transmission. The performance based on secrecy rate is evaluated for “n” trusted relays distributed dispersedly between the source and destination. Gradient‐based optimization and three‐dimensional exhaustive search methods are used as benchmark schemes for comparison of the proposed power optimization algorithm. The secrecy performance is also compared with conventional AF scheme and CJ scheme without power optimization (EPA). The impact of single and multiple relays on secrecy performance is also evaluated. Numerical results reveal that, compared with the gradient method and exhaustive search algorithm, the proposed power allocation strategy achieves optimal performance. Also, the derived OPA results show a significantly higher secrecy rate than the EPA strategy for both CJ and AF schemes.
In this paper, a power optimized source-based-jamming scheme is proposed for secure communication in a two-hop amplify-and-forward relaying network with multiple trusted relays and a passive eavesdropper. The proposed transmission scheme employs a single jamming signal, which is transmitted from the source node along with the information to degrade the eavesdropper. The power optimization is done by means of Nelder-Mead algorithm. The conventional transmission schemes and optimization methods, jamming scheme without optimization are derived for performance comparison. Simulation results show that the secrecy performance of the proposed power optimized scheme outperforms other schemes.
In this paper, we investigate the cooperative jamming (CJ) strategy in a three-node cooperative system, where the relay, which forwards the received signals in a amplify-and-forward (AF) protocol, is untrusted, furthermore, there is an external malicious eavesdropper. A two-phase CJ scheme, which merely using internal nodes of the cooperative system without the help of external nodes, is proposed to enhance the secrecy information transmission against the malicious eavesdropper and the untrusted relay. And then, we provide the optimal power allocation with maximum instantaneous secrecy rate (OPA-MISR) and the suboptimal power allocation with max-min instantaneous secrecy rate (SPA-MMISR). Finally, the simulation results show that the cooperative jamming proposed is effective to improve the achievable instantaneous secrecy rate and to resist both internal untrusted relay and external malicious eavesdropper.
Abstract—In this paper, the problem of secure transmission in two-hop amplify-and-forward (AF) systems with an untrusted relay is investigated. To prevent the untrusted relay from intercepting the source message and to achieve positive secrecy rate, the destination-based cooperative jamming (DBCJ) technique is used. In this method the destination sends an intended jamming signal to the relay. This jamming signal helps protecting the source message from being captured reliably at the untrusted relay, while the destination cancels itself intended jamming signal. The optimal power allocation (OPA) technique is considered for the presented system. It is observed that the objective function is a quasiconcave function at high signal-to-noise-ratio (SNR) regimes. Based on this OPA technique, we study the ergodic secrecy rate (ESR) and the secrecy outage probability (SOP) of the system when the source and relay are equipped with a single antenna while the destination is equipped with largescale antenna arrays (LSA). Using the achieved closed-form expressions, one can evaluate the performance of the secure system easily and fast and also, they provide significant insight for system design. Finally, simulation results indicate the accuracy of the derived expressions.
The inherent broadcast characteristics of wireless medium make wireless data transmission difficult to be shielded from unintended recipients. As such, secure communication over wireless channels becomes a critical issue in the design of wireless networks. In this study, the authors study cooperative jamming and power optimisation in untrusted relay networks to improve physical layer security. By exploiting the direct link, a source‐based jamming (SBJ) scheme is proposed to hinder the untrusted relay from intercepting the confidential message. Considering the total power budget, a power allocation strategy is also proposed to optimally determine the power of source and untrusted relay as well as the power of information and jamming signals. Furthermore, to evaluate the secrecy performance of the proposed SBJ scheme with the power allocation strategy, tight lower bound of ergodic secrecy capacity and asymptotic secrecy outage probability are derived in closed form. Simulation verifies the advantages of the proposed SBJ scheme and the power allocation strategy.