In the conventional directional modulation (DM) system without relay aiding, when the eavesdropper locates within the main-beam of the desired direction, it can intercept the confidential message from source Alice. In this paper, we propose a strategy to enhance physical-layer security of direction modulation in wireless transmission with the help of multi-relay cooperation. In this scenario, the confidential messages are forwarded to the desired destination receiver, and the artificial noise (AN) is enforced to the eavesdroppers with the aid of multi-relays and direction modulation such that the eavesdropper can not successfully recover the useful information from its received signals. The simulation results show that the proposed method achieves a significantly higher signal-to-interference-plus-noise ratio (SINR) peak at the destination position than at other positions outside the main-beam of the desired position and its secrecy rate performance at undesired position is so poor that the secure transmission is guaranteed.
In the conventional directional modulation (DM) system without relay aiding, when the eavesdropper locates within the main-beam of the desired direction, it can intercept the confidential message from source Alice. In this paper, we propose a strategy to enhance physical-layer security of direction modulation in wireless transmission with the help of multi-relay cooperation. In this scenario, the confidential messages are forwarded to the desired destination receiver, and the artificial noise (AN) is enforced to the eavesdroppers with the aid of multi-relays and direction modulation such that the eavesdropper can not successfully recover the useful information from its received signals. The simulation results show that the proposed method achieves a significantly higher signal-to-interference-plus-noise ratio (SINR) peak at the destination position than at other positions outside the main-beam of the desired position and its secrecy rate performance at undesired position is so poor that the secure transmission is guaranteed.
In this paper, a practical wireless transmission scheme is proposed to transmit confidential messages to the desired user securely and precisely by the joint use of multiple techniques including artificial noise (AN) projection, phase alignment (PA)/beamforming, and random subcarrier selection (RSCS) based on OFDM, and directional modulation (DM), namely RSCS-OFDM-DM. This RSCS-OFDM-DM scheme provides an extremely low-complexity structures for the transmitter and desired receiver and makes the secure and precise wireless transmission realizable in practice. For illegal eavesdroppers, the receive power of confidential messages is so weak that their receivers cannot intercept these confidential messages successfully once it is corrupted by AN. In such a scheme, the design of phase alignment/beamforming vector and AN projection matrix depend intimately on the desired direction angle and distance. It is particularly noted that the use of RSCS leads to a significant outcome that the receive power of confidential messages mainly concentrates on the small neighboring region around the desired receiver and only small fraction of its power leaks out to the remaining large broad regions. This concept is called secure precise transmission. The probability density function of real-time receive signal-to-interference-and-noise ratio (SINR) is derived. Also, the average SINR and its tight upper bound are attained. The approximate closed-form expression for average secrecy rate is derived by analyzing the first-null positions of SINR and clarifying the wiretap region.
The broadcast nature of wireless communications makes the propagation medium vulnerable to security attacks such as eavesdropping and jamming from adversarial or unauthorized users. Applying physical layer secrecy approaches will enable the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, without using any secret keys. However, physical layer security approaches are typically feasible only when the source-eavesdropper channel is weaker than the source-destination channel. Cooperative jamming can be used to overcome this challenge and increase the secrecy rate. In this paper, the security of two-phase relaying system with multiple intermediate nodes and in the presence of an eavesdropper is investigated. To enhance the system secrecy rate, a joint cooperative beamforming and jamming combined with relay and jammer selections is proposed. In phase I, the source node broadcasts a signal to relays while three intermediate nodes (which act as jammers) help the source node by transmitting random jamming signals to confuse the eavesdropper. Since the friendly (cooperative) jammers create interference for both the intended relays and the eavesdropper, optimal beamforming is applied such that no interference is caused at two preselected desired relays (that are going to receive the confidential massage in phase I). In phase II, two preselected relays transmit the source message with beamforming coefficients such that the received signal at the eavesdropper is completely nulled out. Our goal in this paper is to minimize the received SNR at the eavesdropper while increasing it at the destination as much as possible by applying different methods such as cooperative beamforming, cooperative jamming and relay selection. To avoid operational complexity, we consider the minimum number of intermediate nodes that are necessary without losing the performance. Numerical results demonstrate the advantage of our proposed scheme compared with the scheme with no cooperative jamming.
In this paper, a practical wireless transmission scheme is proposed to transmit confidential messages to the desired user securely and precisely by the joint use of multiple techniques, including artificial noise (AN) projection, phase alignment/beamforming, and random subcarrier selection (RSCS) based on orthogonal frequency division multiplexing (OFDM), and directional modulation (DM), namely RSCS-OFDM-DM. This RSCS-OFDM-DM scheme provides an extremely low-complexity structure for the desired receiver and makes the secure and precise wireless transmission realizable in practice. For illegal eavesdroppers, the receive power of confidential messages is so weak that their receivers cannot intercept these confidential messages successfully once it is corrupted by AN. In such a scheme, the design of phase alignment/beamforming vector and AN projection matrix depends intimately on the desired direction angle and distance. It is particularly noted that the use of RSCS leads to a significant outcome that the receive power of confidential messages mainly concentrates on the small neighboring region around the desired receiver and only small fraction of its power leaks out to the remaining large broad regions. This concept is called secure precise transmission. The probability density function of real-time receive signal-to-interference-and-noise ratio (SINR) is derived. Also, the average SINR and its tight upper bound are attained. The approximate closed-form expression for average secrecy rate is derived by analyzing the first-null positions of the SINR and clarifying the wiretap region. Simulation and analysis show that the proposed scheme actually can achieve a secure and precise wireless transmission of confidential messages in line-of-propagation channel, and the derived theoretical formula of average secrecy rate is verified to coincide with the exact results well for medium and large scale transmit antenna array or in the low and medium SNR regions.
In this paper, the physical-layer security of a cooperative wireless system with multi-antenna full-duplex (FD) destination is examined. More specifically, we consider a cooperative transmission scenario in which a source communicates with a destination through a relay in the presence of an eavesdropper. In order to degrade the wiretap channel, the FD destination simultaneously transmits an interference signal towards the eavesdropper, while receiving information from the relay. A joint transmit and receive beamformer design is proposed to maximize the signal-to-interference-plus-noise ratio (SINR) at the destination, while guaranteeing that the SINR at the eavesdropper is below a certain threshold. We reformulate the optimization problem as a semidefinite relaxation problem in terms of a transmit beamforming matrix. To balance the performance and system complexity, we investigate suboptimum beamforming designs based on zero-forcing criterion. We derive exact closed-form expressions for the average secrecy rates of the proposed suboptimum designs. Our results reveal that optimum and suboptimum beamforming schemes along with friendly jamming significantly improve the secrecy performance. Moreover, simulation results demonstrate that the optimum scheme outperforms suboptimum schemes, especially in high transmit power regimes.
The communication process of a secure relay system usually has two stages: source to relay, relay to destination. When the source is only equipped with one antenna, the information transmission is not secure during the first stage. In this paper, we propose a novel three-stage scheme to transmit confidential messages in an amplify-and-forward (AF) relay system. In the proposal, during the additional stage all the relays independently send artificial interference signals to the source. Then in the next stage, the sending signals of the source node are mixed with both the confidential messages and the interference signals received in the first stage. Finally the relays forward the hybrid signals to the destination node, and cancel the interference signals simultaneously. Since the sending signals are hybrid, all the three stages are secure in the proposed scheme, even when the eavesdropper is located very close to the source, positive secrecy rate of the system can still be achieved. Simulation results verify that the proposed scheme has much better near-field performance than the traditional secure relay communication schemes.
In this paper, we investigate a security transmission scheme at the physical layer for cooperative wireless relay networks in the presence of a passive eavesdropper.While the security scheme has been previously investigated with perfect channel state information(CSI) in the presence of a passive eavesdropper, this paper focuses on researching the robust cooperative relay beamforming mechanism for wireless relay networks which makes use of artificial noise (AN) to confuse the eavesdropper and increase its uncertainty about the source message.The transmit power used for AN is maximized to degrade the signal-to-interference-plus-noise-ratio (SINR) level at the eavesdropper, while satisfying the individual power constraint of each relay node and worst-case SINR constraint at the desired receiver under a bounded spherical region for the norm of the CSI error vector from the relays to the destination.Cooperative beamforming weight vector in the security scheme can be obtained by using S-Procedure and rank relaxation techniques.The benefit of the proposed scheme is showed in simulation results.