The Physical Layer Security (PLS) technology has been proved to be an effective way to reduce information leakage in wireless communication networks. This paper discusses the problem of secure transmission for Amplify-and-Forward (AF) cooperative network which contains both an external eavesdropper and some untrusted relays at the same time, where each relay acts as a helper of transmitting information and a potential eavesdropper. We adopt the technology of Cooperative Jamming (CJ), which yields a significant performance in terms of providing a better level of security against eavesdropping and improving the secure transmission performance of the system. First we discuss the security performance of this new system model, give the secrecy rate in theory and derive a tight lower bound of this secrecy rate. Then we propose a relay selection scheme, which avoids using the channel state information (CSI) of external eavesdropper, to transmit information. Afterward, we also discuss the problem of power allocation in order to maximize the secrecy rate.
The Physical Layer Security (PLS) technology has been proved to be an effective way to reduce information leakage in wireless communication networks. This paper discusses the problem of secure transmission for Amplify-and-Forward (AF) cooperative network which contains both an external eavesdropper and some untrusted relays at the same time, where each relay acts as a helper of transmitting information and a potential eavesdropper. We adopt the technology of Cooperative Jamming (CJ), which yields a significant performance in terms of providing a better level of security against eavesdropping and improving the secure transmission performance of the system. First we discuss the security performance of this new system model, give the secrecy rate in theory and derive a tight lower bound of this secrecy rate. Then we propose a relay selection scheme, which avoids using the channel state information (CSI) of external eavesdropper, to transmit information. Afterward, we also discuss the problem of power allocation in order to maximize the secrecy rate.
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.
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.
We study a relay and user selection scheme to improve the secrecy performance of cooperative multi-user multiple amplify-and-forward (AF) relay network. Nevertheless, relay transmission is highly susceptible to eavesdropping since confidential information is broadcasted twice, i.e., by the source and the relay. In particular, we propose a cooperative jamming aided secure transmission through the relay path. Furthermore, with the presence of the direct path, a transmission mode selection scheme is elaborated in such a way to reduce the amount of information leaked to non-selected users in the system, who may overhear the source message as eavesdroppers. Specifically, the selected relay is only activated when it has better secrecy performance than the source. We study the impact of outdated channel state information (CSI) on the system by deriving a closed-form lower bound for the secrecy outage probability (SOP). By investigating the effect of the jamming power level and the correlation coefficients imbalance, a comparison reveals that the proposed scheme outperforms the fixed transmission modes and its signal-to-noise ratio based counterpart. It is shown that the secrecy outage probability can be decreased as the number of destinations grows unless the number of relays is small. Importantly, optimal relay location and jamming power allocation significantly enhance the secrecy performance.
Cooperative communication in wireless relay systems can improve the physical layer security, and the relay selection has great impacts on the security performances. In this paper the relay selection in Amplify-and-Forward (AF) cooperative networks is investigated. The system model constitutes of a source, an eavesdropper, a destination, and a number of intermediate nodes with secrecy constraints. The proposed optimal selection (OS) algorithm is based on the instantaneous channel state information (CSI) of two hops, jointly protects the target destination against eavesdropping and interference. To simplify the complexity of OS, the suboptimal selection (SS) algorithm is also presented, which is based on the instantaneous of the first hop and the statistical CSI of the second hop respectively. The secrecy capacity and secrecy outage probability of these two relay selection algorithms are analyzed. Simulation results of OS and SS validate our theoretical analysis and show enhancement in the secrecy rate over the direct transmission.
The physical layer security technology is an effective way to reduce information leakage in a wireless communication system. In this paper, we study the physical-layer security of one-way wiretap channel which contains a source-destination pair, an eavesdropper and multiple cooperating relay nodes. What's more, in this channel, there exists direct link between the source and the destination (eavesdropper) and lacks he eavesdropper's channel state information (ECSI). To address its physical-layer security, we proposed a scheme which combines amplify-and-forward (AF)-based relay beamforming and cooperation jamming (CJ) technology. We aim at minimizing the power available for transmitting desired information in relays and optimizing the relay weights under the scenario of limiting the signal to ratio at the destination to a given range, which can be solved by convex optimization techniques. After that, we prove that the optimization results are unique and globally optimum. And the numerical results show that the proposed design can effectively enhance secure transmission rate.
In this paper, we propose a destination-assisted jamming and beamforming (DAJB) scheme for physical layer security in a one-way cooperative amplify-and-forward (AF) relay communication system. The system model consists of one source, one destination, one eavesdropper, and N relay nodes, with the individual power constraint of each relay node and the destination-assisted jamming node as well as unknown instantaneous channel state information (CSI) of the eavesdropper. Due to the half-duplex constraint of the relay nodes, there are two phases in our proposed DAJB scheme. In the first phase, the source node broadcasts information signal and all N relay nodes listen simultaneously. In the meantime, the destination node transmits the jamming signal to confuse the potential eavesdropper. In the second phase, all N relay nodes amplify and forward the received signals, covered by the artificial noise (AN), to the destination using the distributed beamforming technology. The optimal beamformer weights and power allocation are obtained by solving the second-order convex cone programming (SOCP) together with a linear programming (LP) problem. Furthermore, the performance of the DAJB scheme is analyzed in terms of the achievable secrecy rate. Compared with the scheme that selects a relay node as the jammer, we obtain larger power gain to achieve higher secrecy rates. Finally, the simulation results verify that the DAJB scheme greatly improves the secrecy rate of a one-way cooperative AF relay communication system.