We investigate the physical-layer security problems of two-way relay networks in this paper. The whole network consists of two legitimate users and one eavesdropper, where the legal users need the help of some intermediate nodes to exchange information. We propose joint jamming and relaying mechanism, where a jamming node is selected from all intermediate nodes, to create interference upon eavesdropper, while other nodes are used to relay data for two users. All intermediate nodes are subjected to per-node power constraints. Based on null-space beamforming, we propose two different transmission schemes when the number of relay nodes is large enough. One scheme is designed to maximize the secrecy sum rate (MSSR) of the network, and the other is designed to maximize the minimum secrecy rate (MMSR) between two users. In the MMSR scheme, a series of semi-definite programming problems with a rank-1 constraint needs to be solved. We prove that this rank-1 constraint does not affect the solutions of original problems. In addition, we propose two modified secure transmission schemes when the number of relay nodes is less abundant. In short, no matter how many intermediate nodes in the communication networks, one can find suitable transmission schemes to ensure communication security.
We investigate the physical-layer security problems of two-way relay networks in this paper. The whole network consists of two legitimate users and one eavesdropper, where the legal users need the help of some intermediate nodes to exchange information. We propose joint jamming and relaying mechanism, where a jamming node is selected from all intermediate nodes, to create interference upon eavesdropper, while other nodes are used to relay data for two users. All intermediate nodes are subjected to per-node power constraints. Based on null-space beamforming, we propose two different transmission schemes when the number of relay nodes is large enough. One scheme is designed to maximize the secrecy sum rate (MSSR) of the network, and the other is designed to maximize the minimum secrecy rate (MMSR) between two users. In the MMSR scheme, a series of semi-definite programming problems with a rank-1 constraint needs to be solved. We prove that this rank-1 constraint does not affect the solutions of original problems. In addition, we propose two modified secure transmission schemes when the number of relay nodes is less abundant. In short, no matter how many intermediate nodes in the communication networks, one can find suitable transmission schemes to ensure communication security.
In this paper, we investigate physical-layer transmission security problem of a two-way relay wireless network consisting of two legitimate terminal nodes who wants to communicate with each other in presence of one eavesdropper, with help of N intermediate nodes. We propose a cooperative relaying and jamming strategy, which selecting one intermediate node to create intentional interference upon the eavesdropper, while other K = N -1 intermediate nodes operating in relay mode and assisting the source nodes to deliver data to their corresponding destinations using an amplify-and-forward (AF) protocol. All N intermediate nodes in this system are under a per-node power constraint. When K ≥ 3, we propose two different system design criteria based on null-space beamforming, to maximize secrecy sum rate by rate-splitting method with a bisection numerical algorithm iteratively getting the maximal secrecy sum rate, or to maximize the minimum rate between the two terminals. And we also propose the modified security schemes when the number of intermediate nodes is not enough for the previously mentioned schemes (K <; 3).
Cooperative relaying and jamming are two efficient schemes to improve the physical-layer security of a wireless transmission in the presence of an eavesdropper. In this paper, we propose a hybrid cooperative relaying and jamming mechanism to enhance the security of a two-way relay network, where some intermediate nodes adopt distributed beamforming to improve the channel quality to legitimate terminals and others jam the eavesdropper, simultaneously. Subjected to the more practical per-node power constraint of each cooperative node, we propose a secrecy scheme to maximize the secrecy sum rate of the two terminals. It is shown that the problem can be transformed into a semi-definite programming (SDP) problem with an additional rank-1 constraint. We then propose a penalty function method and an iterative algorithm to solve such a problem efficiently, instead of the popular semi-definite relaxation (SDR) and randomization technique in the previous literature. Simulations show that the proposed hybrid schemes greatly improve the security of the two-way relay networks.
Exploiting the idea of cooperative communications is an efficient way to improve the physical-layer security of a wireless transmission in the presence of passive eavesdroppers. In this paper, we propose a hybrid cooperative relaying and jamming scheme to enhance the security of a two-way relay network, where some intermediate nodes help to relay the signal to the legitimate terminals via distributed beamforming and the others jam the eavesdropper simultaneously. In such a way, both two cooperative phases of the data transmission are protected. Subjected to the more practical per-node power constraint of each node and without the channel state information (CSI) of the eavesdropper, we propose a scheme to enhance the secrecy of the two terminals. It is shown that the problem can be transformed into a semidefinite programming (SDP) problem with an additional rank-1 constraint. We then develop a penalty function method and an iterative algorithm to solve such a problem efficiently, instead of the popular semi-definite relaxation (SDR) and randomization techniques proposed in the previous literatures. Simulations show that the proposed hybrid scheme greatly improves the security of the two-way relay networks.
In this paper, we investigate joint relay and jammer selection in two-way cooperative networks, consisting of two sources, a number of intermediate nodes, and one eavesdropper, with the constraints of physical layer security. Specifically, the proposed algorithms select two or three intermediate nodes to enhance security against the malicious eavesdropper. The first selected node operates in the conventional relay mode and assists the sources to deliver their data to the corresponding destinations using an amplify-and-forward protocol. The second and third nodes are used in different communication phases as jammers in order to create intentional interference upon the eavesdropper node. Firstly, we find that in a topology where the intermediate nodes are randomly and sparsely distributed, the proposed schemes with cooperative jamming outperform the conventional non-jamming schemes within a certain transmitted power regime. We also find that, in the scenario in which the intermediate nodes gather as a close cluster, the jamming schemes may be less effective than their non-jamming counterparts. Therefore, we introduce a hybrid scheme to switch between jamming and non-jamming modes. Simulation results validate our theoretical analysis and show that the hybrid switching scheme further improves the secrecy rate.
In this paper, we investigate joint relay and jammer selection in two-way cooperative networks, consisting of two sources, a number of intermediate nodes, and one eavesdropper, with the constraints of physical-layer security. Specifically, the proposed algorithms select two or three intermediate nodes to enhance security against the malicious eavesdropper. The first selected node operates in the conventional relay mode and assists the sources to deliver their data to the corresponding destinations using an amplify-and-forward protocol. The second and third nodes are used in different communication phases as jammers in order to create intentional interference upon the malicious eavesdropper. First, we find that in a topology where the intermediate nodes are randomly and sparsely distributed, the proposed schemes with cooperative jamming outperform the conventional nonjamming schemes within a certain transmitted power regime. We also find that, in the scenario where the intermediate nodes gather as a close cluster, the jamming schemes may be less effective than their nonjamming counterparts. Therefore, we introduce a hybrid scheme to switch between jamming and nonjamming modes. Simulation results validate our theoretical analysis and show that the hybrid switching scheme further improves the secrecy rate.
In this paper, we propose a hybrid cooperative beamforming and jamming scheme to enhance the physical-layer security of a single-antenna-equipped two-way relay network in the presence of an eavesdropper. The basic idea is that in both cooperative transmission phases, some intermediate nodes help to relay signals to the legitimate destination adopting distributed beamforming, while the remaining nodes jam the eavesdropper, simultaneously, which takes the data transmissions in both phases under protection. Two different schemes are proposed, with and without the instantaneous channel state information of the eavesdropper, respectively, and both are subjected to the more practical individual power constraint of each cooperative node. Under the general channel model, it is shown that both problems can be transformed into a semi-definite programming (SDP) problem with an additional rank-1 constraint. A current state of the art technique for handling such a problem is the semi-definite relaxation (SDR) and randomization techniques. In this paper, however, we propose a penalty function method incorporating the rank-1 constraint into the objective function. Although the so-obtained problem is not convex, we develop an efficient iterative algorithm to solve it. Each iteration is a convex SDP problem, thus it can be efficiently solved using the interior point method. When the channels are reciprocal such as in TDD mode, we show that the problems become second-order convex cone programming ones. Numerical evaluation results are provided and analyzed to show the properties and efficiency of the proposed hybrid security scheme, and also demonstrate that our optimization algorithms outperform the SDR technique.