The benefits of Amplify-and-Forward (AF) and Decode-and-Forward (DF) cooperative relay for secure communication are investigated within Wyner's wiretap channel. We characterize the secrecy rate when source, destination, relay and eavesdropper all use single antenna and the channel conditions are fix. Both AF and DF cooperative strategies are proved theoretically to be able to facilitate secure communication. Detailed analysis of AF and DF scheme reveals a trade off between secrecy area and request secrecy rate. In addition, secrecy constraints in cooperative secure communication are discussed and are used to explain the differences in AF and DF scheme. Overall, our work establishes the utility of cooperation and compares each advantage of AF and DF scheme in facilitating secure communication over wireless channel.
The benefits of Amplify-and-Forward (AF) and Decode-and-Forward (DF) cooperative relay for secure communication are investigated within Wyner's wiretap channel. We characterize the secrecy rate when source, destination, relay and eavesdropper all use single antenna and the channel conditions are fix. Both AF and DF cooperative strategies are proved theoretically to be able to facilitate secure communication. Detailed analysis of AF and DF scheme reveals a trade off between secrecy area and request secrecy rate. In addition, secrecy constraints in cooperative secure communication are discussed and are used to explain the differences in AF and DF scheme. Overall, our work establishes the utility of cooperation and compares each advantage of AF and DF scheme in facilitating secure communication over wireless channel.
An amplify-and-forward(AF) dual-hop relay is proposed for secure communication within Wyner s wiretap channel.Based on an information-theoretic formulation,the average secrecy rate is characterized when two legitimate partners communicate over a quasi-static fading channel.Theoretical analysis and simulation results show that both cooperative strategies of average power scaling(APS) and instantaneous power scaling(IPS) are proved to be able to achieve information-theoretic security,and eavesdropper is unable to decode any information.
In wireless communication, physical layer security is widely used for secure communication between the transmitter and the receiver. In this paper, the secrecy performance of two cooperative schemes, decode-and-forward (DF) and amplify-and-forward (AF) relays is investigated in a single hop wireless relaying system. The achievable secrecy rate is investigated with these two types of relays under the constraint of total power transmitted. In the given jamming relay network, the relay transmits jamming signal while receiving data signal from the source. It is indicated by the resulting analysis that the AF relays have better secrecy rate as compared to the DF relays in the given condition. The secrecy rate of the AF relay is higher than that of the DF relay by 71.88% at a distance of 70 m between the relay and the eavesdropper in this jamming relay network.
Due to the character of low cost and easily to implemented, the cooperative communication is the future tendency. Three fundamental mode, Amplify-and-Forward (AF) mode, Decode-and-Forward (DF) mode and Compress and Forward (CF) mode are employed to the system. In the cooperative system, relays function to transmit the delivered signal to the destination. Each node in the system could play as the source station, the relay and the destination station. Currently, the issue of privacy and security are seriously requested in the communication. There could be the eavesdroppers pre-tend as the relay to steal the message. Hence, the secrecy protection becomes important. In the higher layer, the encryption scheme is applied to protect the message. However, it is difficult for those devices with low computing resources, the example of IoT (Internet of Things). With Shannon Theory, a secure communication could be supported with a positive secrecy rate. Hence, secure cooperative communication could be possible if there exist a positive secrecy rate between the two ends in the transmissions. Base on the secrecy rate analysis, the maximum secrecy rate is the initial step toward a secure communication. In the cooperative system, the delivered signal could be transmitted via relays. Hence, the path from the source to the destination could be a huge combination. With the exhaustive method to find the optimal secrecy rate could be realized. Hence, in this work, the numerical experiment, the AF and DF mode cooperative mode is adopted.
This paper studies different uses of two cooperating relays to improve the secrecy rate of a wiretap channel. These two relays are assumed to perform only simple functions: either amplify-and-forward (AF) or jamming. Complex functions such as decode-and-forward (DF) are not considered. We study three modes of cooperation: i) cooperative jamming (CJ), ii) AF-aided beamforming and iii) mixed AF-aided beamforming and CJ, all with individual relay power constraints. While i) is known in the literature, our efforts are spent on ii) and iii). In particular, for iii), we assume that the jamming signals in two communication stages are correlated, giving rise to improved performances. We also propose a heuristic approach for selecting the appropriate cooperating mode. Simulation results illustrate the performance gain of each scheme under different channel conditions and the effectiveness of the proposed mode selection method.
This paper addresses the physical layer security of a two-hop decode-and-forward (DF) wireless relay network in the presence of several eavesdroppers. The wiretap channel model consists of a source, several eavesdroppers, couples of trusted relays and a destination. For this DF based cooperative relay scheme, the relays use different code words independent of the source code words to transmit a weighted version of the recoded messages as with the source messages to the legitimate receiver and jam the eavesdropper. We fix the transmit power of the source ( Ps ) to obtain the weights for secrecy rate maximization, assuming that global channel state information (CSI) is available. The maximization problem can be made to a generalized eigenvector problem, and it is easy to obtain the corresponding eigenvector that is the optimal relay weight vector by using the matrix computations. The closed-form optimal solution is derived for the relay weights that maximize the achievable secrecy rate.
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.