This paper investigates covert communication in spectrum-sharing Internet of Things (IoT) device-to-device (D2D) networks assisted by unmanned aerial vehicles equipped with intelligent reflecting surfaces (UAV-IRS). Existing schemes assume known or deterministic eavesdropper locations, which limits their effectiveness in the presence of spatially random adversaries in IoT environments. They also often neglect severe interference in spectrum-sharing environments and lack effective protection mechanisms for cellular links, resulting in degraded covert reliability and cellular performance. To address these challenges, we propose a UAV–IRS-assisted D2D covert communication scheme for spectrum-sharing networks, where a full-duplex base station simultaneously receives cellular signals and generates artificial noise (AN) to combat spatially random eavesdroppers. The spatial uncertainty is characterized by modeling three representative configurations between the eavesdroppers’ surveillance regions and the guard zone of the cellular link, i.e., disjoint, overlapping, and contained. Meanwhile, the average minimum detection error probability is derived as the covertness requirement. A two-layer optimization framework is then designed to jointly optimize D2D and AN transmit powers, UAV location, and IRS phase shifts, while ensuring cellular reliability. Simulation results demonstrate the effectiveness of the proposed scheme in enhancing the covert rate in IoT spectrum-sharing networks.

This article proposes an energy-efficient covert offloading scheme for blockchain-enabled Internet of Things (IoT), allowing sensors to upload tasks undetected by adversaries while ensuring satisfaction in paid computation offloading. Covert communication conceals the existence of transmitted signals or links. However, existing schemes primarily rely on artificial noise (AN) or wireless channel uncertainty, resulting in low covert rates for IoT offloading scenarios. Additionally, blockchain-enabled IoT, being value-oriented, necessitates consideration of sensors’ satisfaction during covert offloading. To tackle these challenges, the proposed scheme combines the adversary’s channel estimation errors with AN to enhance the covert rate, while also matching sensors’ satisfaction with the computation resources of mobile edge servers. Notably, a closed-form expression of the average minimum error detection probability is derived to maximize the effective covert rate. Furthermore, an integrated algorithm combining the Kuhn-Munkres (KM) algorithm with two bubble sort algorithms is designed to minimize energy consumption. Both analytical and simulation results demonstrate that the proposed scheme significantly reduces energy consumption compared to existing solutions.

For the sake of enhancing the covertness and sensing performance in the integrated sensing and covert communications (ISCC) system, we design a beamforming framework for reconfigurable intelligence surface (RIS) assisted ISCC. Specifically, the system intends to transmit information to a legitimate receiver (Bob) covertly and sense the target simultaneously while avoiding being detected by a warden (Willie). RIS can be applied to both traditional single-connected networks and a broad fully-connected networks. By jointly optimizing the beamforming vector of the communication and the autocorrelation matrix of the sensing, and the phase shift matrix of the RIS, both the convert rate and the target’s probing power are maximized. And the covertness and the constant-mode constraints are considered. A multi-strategy alternate optimization (MSAO) algorithm is proposed to solve the optimization problem based on quadratic constraint quadratic programming (QCQP) and semidefinite relaxation (SDR). Furthermore, we consider a more realistic application scenario where the legal party has imperfect channel state information of Willie. Simulation results show that deploying RIS in a generalized fully-connected mode can achieve better transmission of beampatterns and increase upper limit of covert communications rate than conventional single-connected mode.

Physical layer covert communication is a crucial secure communication technology that enables a transmitter to convey information covertly to a recipient without being detected by adversaries. Unlike typical cryptography and physical layer security systems that concentrate on protecting the sent signal content, covert communications seek to conceal the existence of legitimate transmission. Thus, with beyond fifth-generation (B5G) wireless communications, covert communications can operate in tandem or as a supplement to conventional security techniques. We provide an extensive overview of the basic theories and several strategies in physical layer covert communications in this article. In particular, we go into great detail about the basic theories of physical layer covert communications, such as channel models, codes, secret keys, and covertness metrics, as well as various covert schemes in progressively more complicated scenarios, such as covert communications in single-antenna and multiantenna three-node systems and covert communications in jammer-and relay-aided systems. In addition, we identify the challenges and future directions for research on covert communications in B5G wireless networks.

Wireless energy harvesting (WEH) enabled Device-to-Device (D2D) communication emerges as an effective technique to improve spectral and energy efficiencies. However, D2D users are usually power-constrained devices that may be monitored or attacked by adversaries easily. To confuse randomly distributed adversaries in WEH-enabled D2D underlaying cellular networks, power beacons (PBs) can be used to send jamming signals in idle time slots. A time slot is divided into two sub-slots, i.e., WEH sub-slot and covert transmission sub-slot. The energy collected by a D2D transmitter in the first sub-slot is used to support possible covert transmission in the second sub-slot. The performance of the proposed scheme is measured by covert throughput, which is defined as D2D communication rate with several constraints, e.g., wireless energy harvesting, covertness, and cellular link communication requirements. The closed-form expressions of energy outage probability, covert probability, and desired link connection outage probabilities are derived. The minimum covert probability is used to measure covertness. Moreover, an alternating optimization algorithm is adopted to maximize covert throughput. The analytical results are compared with Monte-Carlo simulation results to verify the analytical approach. In addition, the impacts of different parameters (e.g., density of PBs and covert signal transmit power) on covert performance are evaluated.