Holographic multiple-input multiple-output (HMIMO) systems deploy ultra-dense antennas in confined spaces, yet spatial degrees of freedom (DoF) fail to scale with element count. Only by harnessing evanescent waves can the potential gains of ultra-dense arrays be unlocked. However, in practical scenarios, antenna apertures are typically too small relative to communication distances to generate significant near-field effects for capturing these evanescent waves. This paper proposes a method to alter the dispersion relation via locally resonant metamaterials (LRM), thereby enabling the radiation of near-field evanescent wave components into the far field. This approach leverages the DoF gains offered by ultra-dense elements within a confined aperture. Full-wave simulations validate the effectiveness of the evanescent-propagating wave conversion method, demonstrating an increase in the spatial DoF radiated into the far field by the HMIMO system even with a limited aperture.

A distributed acoustic sensing (DAS) system is proposed and a data processing method for vibration is designed in this paper. The proposed DAS system is based on the Rayleigh scattering signal and utilizes phase-sensitive optical time-domain reflectometry ( ? -OTDR) to demodulate the environmental vibration. It can collect the vibration information in railways and implement vibration classification based on the feature of sensed vibration signals. This system has been deployed in Guangzhou Shenzhen High-Speed Railway, and the experimental results validate its effectiveness.

Intelligent transportation system (ITS) is proposed as the most effective way to improve road safety and traffic efficiency. However, the future of ITS for large scale transportation infrastructures deployment highly depends on the security level of vehicular communication systems (VCS). Security applications in VCS are fulfilled through secured group broadcast. Therefore, secure key management schemes are considered as a critical research topic for network security. In this paper, we propose a framework for providing secure key management within heterogeneous network. The security managers (SMs) play a key role in the framework by retrieving the vehicle departure information, encapsulating block to transport keys and then executing rekeying to vehicles within the same security domain. The first part of this framework is a novel Group Key Management (GKM) scheme basing on leaving probability (LP) of vehicles to depart current VCS region. Vehicle's LP factor is introduced into GKM scheme to achieve a more efficient rekeying scheme and less rekeying costs. The second component of the framework using the blockchain concept to simplify the distributed key management in heterogeneous VCS domains. Extensive simulations and analysis are provided to show the effectiveness and efficiency of the proposed framework: Our GKM results demonstrate that probability-based BR reduces rekeying cost compared to the benchmark scheme, while the blockchain decreases the time cost of key transmission over heterogeneous networks.