We investigate the problem of optimizing the secrecy rate of a link between a single source and a single destination in the presence of multiple relays and multiple eavesdroppers. Multiple relays assist the source by either retransmitting a weighted version of the source signal in a decode-and-forward (DF) fashion, or by performing cooperative jamming (CJ) i.e., transmitting weighted noise in order to confound the eavesdropper. In each protocol, the relay weights are designed to maximize the secrecy rate subject to a total power constraint. For the case of a single eavesdropper we obtain expressions for the optimal weights under both protocols in closed form, or propose the algorithms to research for the solution. For the DF protocol with multiple eavesdroppers we propose an algorithm to search for the solution. Numerical results illustrate that cooperation can significantly improve the system performance as compared to direct transmission.
We investigate the problem of optimizing the secrecy rate of a link between a single source and a single destination in the presence of multiple relays and multiple eavesdroppers. Multiple relays assist the source by either retransmitting a weighted version of the source signal in a decode-and-forward (DF) fashion, or by performing cooperative jamming (CJ) i.e., transmitting weighted noise in order to confound the eavesdropper. In each protocol, the relay weights are designed to maximize the secrecy rate subject to a total power constraint. For the case of a single eavesdropper we obtain expressions for the optimal weights under both protocols in closed form, or propose the algorithms to research for the solution. For the DF protocol with multiple eavesdroppers we propose an algorithm to search for the solution. Numerical results illustrate that cooperation can significantly improve the system performance as compared to direct transmission.
We consider a cooperative wireless network in the presence of one or more eavesdroppers, and exploit node cooperation for achieving physical (PHY) layer based security. Two different cooperation schemes are considered. In the first scheme, cooperating nodes retransmit a weighted version of the source signal in a decode-and-forward (DF) fashion. In the second scheme, referred to as cooperative jamming (CJ), while the source is transmitting, cooperating nodes transmit weighted noise to confound the eavesdropper. We investigate two objectives: i) maximization of the achievable secrecy rate subject to a total power constraint and ii) minimization of the total power transmit power under a secrecy rate constraint. For the first design objective, we obtain the exact solution for the DF scheme for the case of a single or multiple eavasdroppers, while for the CJ scheme with a single eavesdropper we reduce the multivariate problem to a problem of one variable. For the second design objective, existing work introduces additional constraints in order to reduce the degree of difficulty, thus resulting in suboptimal solutions. Our work raises those constraints, and obtains either an analytical solution for the DF scheme with a single eavesdropper, or reduces the multivariate problem to a problem of one variable for the CJ scheme with a single eavesdropper. Numerical results are presented to illustrate the proposed results and compare them to existing work.
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.
In this paper, we consider decode-and-forward (DF) relay beamforming for secrecy with cooperative jamming (CJ) in the presence of multiple eavesdroppers. The communication between a source-destination pair is aided by a multiple-input multiple-output (MIMO) relay. The source has one transmit antenna and the destination and eavesdroppers have one receive antenna each. The source and the MIMO relay are constrained with powers PSand PR, respectively. We relax the rank-1 constraint on the signal beamforming matrix and transform the secrecy rate max-min optimization problem to a single maximization problem, which is solved by semidefinite programming techniques. We obtain the optimum source power, signal relay weights, and jamming covariance matrix. We show that the solution of the rank-relaxed optimization problem has rank-1. Numerical results show that CJ can improve the secrecy rate.
We consider a cooperative wireless network, and exploit node cooperation for achieving physical layer based security. The case of one source, multiple cooperating nodes and one eavesdropper is considered. Two different cooperation schemes are considered. In the first scheme, cooperating nodes transmit a weighted version of the source signal in a decode and forward fashion (DF). In the second scheme, while the source is transmitting, cooperating nodes transmit weighted noise to confound the eavesdropper (cooperative jamming (CJ)). The objective is to select the node weights and the source transmit power so that the total transmit power (source transmission power plus cooperating nodes power) under a secrecy capacity constraint is minimized. Previous works related to this problem introduced additional constraints in order to reduce the degree of difficulty, thus resulting in suboptimal solutions. In this paper, the optimal solution is considered. In particular, the closed form solution is obtained for the DF scheme, while for the CJ scheme, the problem is reduced to a univariate optimization one. For the latter problem a convergent algorithm for obtaining the solution is provided.
In this paper, we study robust joint beamforming and cooperative jamming (CJ) in a secure decode-and-forward (DF) relay system in the presence of multiple eavesdroppers, in which a multi-antenna DF relay employs transmit beamforming to help the source deliver information to the destination and simultaneously generates Gaussian artificial noise to confuse these eavesdroppers. We assume that all the channel state information (CSI) is imperfectly known at the relay subject to norm-bounded CSI errors. Our objective is to maximize the achievable secrecy rate at the destination by jointly optimizing the transmit beamforming vector of information signals and the covariance matrix of jamming signals at the relay subject to its total transmit power constraint. Although this problem is non-convex and in general difficult to be solved, we obtain its optimal solution via the technique of semi-definite relaxation (SDR) together with a one-dimensional (1-D) search. Specifically, we prove that the SDR is tight for the problem of our interest. Finally, numerical results are provided to validate our proposed scheme.
In a cooperative wireless network, we exploited node cooperation for achieving physical layer based security. In this paper, the case of one source-destination pair with the help of multiple cooperating nodes(relay nodes and jamming nodes) in the presence of one eavesdropper was considered to improve the performance of secure wireless communications. A novel cooperative scheme joint decode-and-forward and cooperative jamming(JDFCJ) was proposed. In this scheme, the relay nodes transmit a weighted version of the source signals and the jamming nodes just transmit a common weighted jamming signal to confound the eavesdropper. The novel system design is proposed to minimize the transmit power subject to a secrecy rate constraint. For JDFCJ, the optimal power allocation is obtained in closed-form in the condition of the complete nulling of jamming signals at the destination. The numerical evaluation of the transmit power results shows that the proposed scheme can significantly improve the performance of secure wireless communications, as compared to the DF scheme.