In this paper, a multicast network in the presence of an untrusted relay is investigated.A three-phase AF-based cooperative jamming with power allocation is proposed to enhance the system secrecy rate.Based on time division based cooperative multicast (TDCM) protocol, the source uses part of its available power to broadcast pre-defined jamming signals in order to create interference at the untrusted relay, while the relay amplifies the linearly combined two received signals and then re-transmits it to the destination.Optimum power allocation policy involving the allocation between the information and jamming signals at the source and between two combined signal factors at the relay to maximize the achievable worse secrecy rate or sum-rate are derived and analyzed.Numerical results are provided to demonstrate our analytical results and reveal that compared with the two benchmarks schemes, the proposed scheme can obtain significantly higher positive secrecy rate for the same transmit power budget, especially in the case of maximizing secrecy sum-rate.
In this paper, a multicast network in the presence of an untrusted relay is investigated.A three-phase AF-based cooperative jamming with power allocation is proposed to enhance the system secrecy rate.Based on time division based cooperative multicast (TDCM) protocol, the source uses part of its available power to broadcast pre-defined jamming signals in order to create interference at the untrusted relay, while the relay amplifies the linearly combined two received signals and then re-transmits it to the destination.Optimum power allocation policy involving the allocation between the information and jamming signals at the source and between two combined signal factors at the relay to maximize the achievable worse secrecy rate or sum-rate are derived and analyzed.Numerical results are provided to demonstrate our analytical results and reveal that compared with the two benchmarks schemes, the proposed scheme can obtain significantly higher positive secrecy rate for the same transmit power budget, especially in the case of maximizing secrecy sum-rate.
The security of the three-phase two-way relaying system with an eavesdropper is investigated in this paper. A cooperative jamming and power allocation scheme is proposed to enhance the system secrecy capacity. When a source node transmits user signals to the relay node, the other source node interferes the relay node with pre-defined jamming signals simultaneously. Optimum power allocation between the user and jamming signals at each source node is analyzed. Our analytical results suggest that the proposed cooperative jamming scheme improves on the system secrecy capacity, especially when the channel gains of the two source-relay links are of large difference. Simulation results in close agreement with analytical results clearly demonstrate the advantage of the proposed cooperative jamming scheme.
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.
To improve physical (PHY) layer security of a wireless relay system in the presence of an eavesdropper, a two-phase cooperative relaying scheme is investigated in this paper. In phase I, the source transmits confidential message, simultaneously, it cooperates with the friendly jammers and destination to create jamming signal at the eavesdropper without affecting the forwarding relay which is preselected. In phase II, the forwarding relay retransmits the decoded signal, meanwhile, the particular relay cooperates with the friendly jammers to create jamming signal at the eavesdropper without affecting the destination. We focus on the investigation of optimal power allocation for maximizing achievable secrecy rate subject to a total power constraint. Optimal relay selection and suboptimal relay selection schemes are also proposed. It is shown that as the number of relays increases, both secrecy rate and the performance of suboptimal relay selection scheme improve significantly. Numerical results are presented to validate the derived analytical results and compare them to existing work.
In this paper, the security of two-phase relaying system with multiple intermediate nodes in the presence of a malicious eavesdropper is investigated. To enhance the secrecy, a joint cooperative beamforming and jamming combined with relay and jammer selection is proposed. First, the source broadcasts its signal to the relays that are located close to source in a cluster, i.e., the source node uses a small amount of power to broadcast its message locally to other nodes of the cluster, while destination and the eavesdropper are located outside this cluster. In the second phase, two relays transmit re-encoded signal with optimal beamforming such that the secrecy rate is maximized. Simultaneously, two other intermediate nodes (which act as friendly jammers) transmit random jamming signals to degrade the eavesdropper’s channel. Our goal in this paper is to maximize the secrecy rate by applying different methods such as cooperative beamforming, cooperative jamming and relay and jammer selection. To avoid operational complexity, we consider the minimum number of intermediate nodes needed for relaying and jamming without losing the performance, i.e., achieving a non-zero secrecy rate. Cooperative beamforming with multiple relays demands high amount of information exchange and therefore increases the operational complexity. Thus, we aim to reduce the number of relays which take part in cooperative beamforming. Limiting the number of relays may have a bad effect on the coding gain which we compensate it with a proposed selection gain scheme. Numerical results demonstrate the advantage of our proposed scheme compared to the scheme with no cooperative jamming. The main contribution of this work is combining cooperative beamforming and jamming with relay and jammer selection to enhance the physical layer security.
The security of the two-way relaying system with an eavesdropper is investigated in this paper. A cooperative jamming and power allocation scheme is proposed to enhance the system secrecy capacity. Both user and pre-defined jamming signals are transmitted by each source node simultaneously. The optimum power allocation between the user and jamming signals at each source node is derived. Our analytical results suggest that the proposed cooperative jamming scheme improves on the system secrecy capacity, especially when the channel gains of the two source-relay links are of large difference. Simulation results in close agreement with analytical results clearly demonstrate the advantage of the proposed cooperative jamming scheme.
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.