In order to improve the security performance of multiuser visible light communication (VLC) and facilitate the secure application of optical wireless communication technology in Internet-of-Things, we investigate the physical-layer security in a multiuser VLC system with non-orthogonal multiple access (NOMA). When the light-emitting diode (LED) transmitter communicates with multiple legitimate users by downlink NOMA, both single eavesdropper and multi-eavesdropper scenarios are considered. In the presence of single eavesdropper, based on transmission characteristics of the optical wireless channel, with known instantaneous channel state information (CSI) of the NOMA legitimate channels and statistical CSI of the eavesdropper channel, an exact expression of secrecy outage probability (SOP) is derived, which acts as a benchmark of the security performance to guide selecting or optimizing parameters of the LED transmitter and the photodiode receiver of NOMA legitimate users. In the multi-eavesdropper case, based on the spatial distribution of legitimate users and eavesdroppers, the SOP is obtained via a stochastic geometry theory, so as to guide the NOMA legitimate users to keep away from the area with high eavesdropper density. For typical parameters of the indoor LED transmitter and the PD receiver, simulation results show that the SOP performance improves with the increasing of LED transmission power or transmission signal-to-noise ratio (SNR) in both scenarios. Specifically, in the single eavesdropper case, enlarging the channel condition difference of user groups or deviating the eavesdropper from the given user group can improve the SOP performance, and for a given NOMA legitimate user, the SOP eventually settles around 0.2 while the semiangle at half illuminance of the LED varies between 15° to 60°. In the multi-eavesdropper case, we can get a better SOP performance when reducing the eavesdropper density or the semi-angle at half illuminance of the LED for a given eavesdropper density.

In view of the secrecy requirements of visible light communication (VLC) and the massive connectivity demand of future communication, this work investigates physical-layer security (PLS) for a VLC network based on nonorthogonal multiple access (NOMA). To date, however, research on PLS in NOMA-enabled VLC networks considers only users in a static state. The movements of users make it imperative to dynamically allocate optical access points (OAPs) and transmit power to mobile users (MUs). Such a resource allocation problem is transformed into the problem of dynamically allocating power in this paper. Thus, joint secure communication and power allocation optimization is formulated to maximize the network secrecy performance in each time frame subject to the constraint of the maximum power of OAPs and the constraint of power allocation based on NOMA among the associated MUs at each OAP. The formulated joint optimization problem is generally nonconvex because the logarithmic subtraction operation exists in the secrecy capacity, and we cannot directly find the optimal solution. A hierarchical power allocation algorithm is naturally proposed based on an iterative security-aware water-filling approach and the optimality conditions of Karush-Kuhn-Tucker. Convergence and effectiveness are investigated for the presented power allocation algorithms through simulations. The simulation results show that the network sum secrecy capacity depends on the number of MUs, the characteristics of the optical transceiver, and the number of OAPs deployed in the room.

Hybrid power line communication (PLC)/visible light communication (VLC) networks have been demonstrated to be crucial for indoor practical communications and have attracted widespread attention. However, most current research in hybrid PLC/VLC networks focus mainly on communication reliability and resource allocation, and little has been carried on physical layer security. In this paper, we investigate the secure communication of a hybrid PLC/VLC network with two non-orthogonal multiple access legitimate users. During the two-hop PLC and VLC transmission, two eavesdroppers attempt to wiretap the confidential information from the PLC link via power line, and from the VLC link via visible light, respectively. Based on the randomness of the impulsive noise arriving at the PLC link, and the randomness of users’ positions covered by the VLC link, the channel statistical characteristics of the PLC and VLC links are derived, respectively. Furthermore, the approximate closed-form expressions of secrecy outage probability (SOP) are determined. Simulations are performed to validate the effectiveness of theoretical results, and simulation results show that to get a high-level secrecy outage performance, the parameters of both the PLC and VLC links should be jointly designed. Furthermore, with regard to SOP, it is the worst case for both the PLC and VLC links eavesdropping, as compared to only PLC link eavesdropping or only VLC link eavesdropping.

In the visible light communication (VLC) for parallel vehicles, the light emitted by the headlamps cannot reach the photodiode (PD), which is the receiver installed on another vehicle. To solve this problem, the mirror array-based intelligent reflecting surface- (IRS-) aided VLC system is designed for parallel vehicles, and the system performance with different number of mirrors and transmission distance is analyzed. The maximum distance between adjacent IRSs is calculated via the exhaustive method, and the nearest neighbor iterative search (NNIS) algorithm is proposed for IRS node selection. Numerical results show that the SNR increases with the number of mirrors increasing. If the number of mirrors is in the IRS, the maximum distance between adjacent IRSs is 37 meters. When the interval between adjacent IRSs is 32 meters, the required BER can be satisfied with merely three IRSs working together according to the NNIS algorithm.

The ability to ensure covert unmanned aerial vehicle (UAV) communications is imperative in critical missions such as military surveillance and emergency response. In this paper, a multi-UAV covert communication system with informed jammers is investigated. To increase ground wardens’ detection uncertainty, we propose a joint dynamic scheduling and sensing jamming (DSSJ) scheme. Unlike existing approaches with fixed UAV roles and non-informed jamming, DSSJ dynamically schedules UAVs across adjacent time slots (TSs), while the jamming UAV performs sensing-based informed jamming per TS. Closed-form expressions are derived for the covert rate and minimum detection error probability (MDEP) under the worst-case scenario with optimal warden detection. An optimization problem is formulated to maximize the normalized weighted sum of covert rate and MDEP, subject to multiple constraints, including scheduling, sensing ratio, and other key factors. To solve this mixed-integer non-convex problem, we design a double deep Q-network (DDQN)-DSSJ algorithm, integrating DSSJ within a deep reinforcement learning framework, accelerated by experience replay and dynamic exploration, achieving real-time covert decision-making with polynomial complexity. Simulations demonstrate that DDQN-DSSJ achieves 25% faster convergence, enhanced stability, and superior covertness compared to proximal policy optimization and deep Q-network. Additionally, DDQN-DSSJ improves the covert rate by over 4× and MDEP by up to 28.3%, outperforming state-of-the-art schemes.

An intelligent reflecting surface (IRS)‐assisted wireless communication system with user mobility following random waypoint (RWP) model is investigated, where the user receives the reflection signal from the IRS controlled by the access point (AP) via a programmable controller, and the IRS is mounted on an unmanned aerial vehicle which is only an auxiliary device to enable IRS reflection communication at a certain altitude. As user moves, the AP makes the reflected beamforming of the IRS following with the user through coding the unit‐element of the IRS. To investigate the effect of joint IRS feature and user mobility on the outage performance, the cumulative distribution function of the received signal‐to‐noise ratio of the mobile user is first derived and then the close‐form expression for the outage probability is obtained. Numerical simulations are performed to validate the accuracy of the analytical results. The solutions are also compared with that for conventional amplify‐and‐forward relay system. Insights are drawn related to the number of meta‐surface elements, and the maximum activity radius of mobile user.