The integration of simultaneous wireless information and power transfer (SWIPT) with backscatter and reconfigurable intelligent surface (RIS)-aided communication provides a promising paradigm to reduce the energy consumption. In this paper, we propose a RIS-enhanced hybrid backscatter and wireless-powered transmission scheme in the symbiotic radio network. Under this setting, we formulate the throughput maximization problem by jointly optimizing the transmit beamforming, passive beamforming, transmit power, backscatter coefficient, and slot allocation. Due to the coupled variables, the formulated optimization is non-convex. To solve it, an iterative algorithm is developed to decompose it into multiple subproblems. Specifically, we obtain the closed-form solutions for those variables in the single-user system. For the multi-user system, we solve the problem via the second-order cone programming (SOCP) and semi-definite programming (SDP) methods. Numerical simulations show that the proposed hybrid transmission scheme can effectively improve the network throughput.

This letter makes a first attempt to design a cooperative relay scheme to secure wireless communications by adopting a fast-forward full-duplex (F3D) node. Different from the conventional full-duplex relay, the F3D node could process and forward the received signal immediately. With such forwarding, the forwarded signal of F3D could enhance the signal to interference plus noise ratio (SINR) of the receiver while weaken that of the eavesdropper and thus build up a secure channel. Beyond the proposed scheme, we move forward to optimize the signal processing design of the F3D node with the target of maximizing the secrecy capacity. The formulated optimization problem is non-convex and challenging to deal with. We then design an iterative algorithm based on generalized fractional programming to solve it. One key step in the iterative algorithm involves another non-convex optimization and we decompose it into a two-level optimization. Simulation results validate the effectiveness of our designed secure cooperative relay scheme and show that adopting F3D node for physical-layer security has good performance in terms of achievable secrecy capacity compared with the scheme without F3D node.

Accurately identifying optical fiber vibration signals is crucial for ensuring the proper operation of optical fiber perimeter security warning systems. To enhance the recognition accuracy of intrusion events detected by the distributed acoustic sensing system (DAS) based on phase-sensitive optical time-domain reflectometer (φ-OTDR) technology, we propose an identification method that combines empirical mode decomposition (EMD) with convolutional neural networks (CNNs) and long short-term memory (LSTM) networks. First, the EMD algorithm decomposes the collected original optical fiber vibration signal into several intrinsic mode functions (IMFs), and the correlation coefficient between each IMF and the original signal is calculated. The signal is then reconstructed by selecting effective IMF components based on a suitable threshold. This reconstructed signal serves as the input for the network. CNN is used to extract time-series features from the vibration signal and LSTM is employed to classify the reconstructed signal. Experimental results demonstrate that this method effectively identifies three different types of vibration signals collected from a real-world environment, achieving a recognition accuracy of 97.3% for intrusion signals. This method successfully addresses the challenge of φ-OTDR pattern recognition and provides valuable insights for the development of practical engineering products.

This paper investigates physical layer secure communication in a wideband wireless system, where a base station (BS) equipped with an extremely large scale antenna array (ELAA) transmits confidential information to a legitimate receiver under the threat of a potential eavesdropper. Due to the high carrier frequency and large antenna aperture, both the receiver and eavesdropper lie in the near-field region of the BS. In order to mitigate the beam split effect and reduce the hardware cost, a true-time delayer-based hybrid beamfocusing architecture is designed. Then, a nonconvex sum secrecy capacity maximization problem (SSCM) is formulated for securing wideband communications. Based on alternating optimization, the SSCM is decomposed into three subproblems solved iteratively for designing the digital beamfocusing vectors, time delay matrices, and phase shift matrices on each subcarrier, respectively. Simulation results show that the proposed scheme yields significantly high secrecy capacity compared to benchmarks, which validates the effectiveness of our scheme in enhancing secure wideband communications and mitigating the beam split effects.

This letter attempts to design a surveillance scheme by adopting an active reconfigurable intelligent surface (RIS). Different from the conventional passive RIS, the active RIS could not only adjust the phase shift but also amplify the amplitude of the reflected signal. With such reflecting, the reflected signal of active RIS could jointly adjust the signal to noise ratio (SNR) of the suspicious receiver and the legitimate monitor, hence the proactive eavesdropping at the physical layer could be effectively realized. We formulate the optimization problem with the target of maximizing the eavesdropping rate to obtain the optimal reflecting coefficient matrix of the active RIS. The formulated optimization problem is nonconvex fractional programming and challenging to deal with. We then solve the problem by approximating it as a series of convex constraints. Simulation results validate the effectiveness of our designed surveillance scheme and show that the proposed active RIS aided surveillance scheme has good performance in terms of eavesdropping rate compared with the scheme with passive RIS.

This paper investigates the physical-layer security in a Virtual Antenna Array (VAA)-aided Device-to-Device Multicast (D2DM) communication system, where the User Equipments (UEs) who cache the common content will form a VAA system and cooperatively multicast the content to UEs who desire it. Specifically, with the target of securing the VAA-aided D2DM communication under the threat of multiple eavesdroppers, we propose a secure beamforming scheme by jointly considering the formed VAA and the Base Station (BS). For obtaining the optimal beamforing vectors, a nonsmooth and nonconvex Weight Sum Rate Maximization Problem (WRMP) is formulated and solved using Successive Convex Approximation (SCA) approach. Furthermore, we consider the worst case that eavesdroppers cooperatively form a eavesdrop VAA to enhance the overhearing capacity. In the worst case, we modify the securing beamforming scheme, formulate the corresponding WRMP and solve it using a two-level optimization. Simulation results validate the improvements of the VAA-aided D2DM scheme in terms of communication security compared with conventional D2DM schemes.