Wireless systems are of paramount importance in enabling ubiquitous data transmission for various Internet of Things (IoT) applications. However, due to the broadcast nature and openness of wireless channels, such systems face inherent security challenges. Covert communication is an enabling technology for secure wireless communications while the Unmanned Aerial Vehicle (UAV)-assisted covert communication is particularly promising for enhancing covert performance. This paper investigates joint covert and secure communications in a two-hop UAV-assisted wireless system, where a source S transmits a covert message to a destination D with the help of an untrusted UAV, while being subject to detection by a warden W. We first design a covert transmission scheme for the proposed system with the considerations of both covert and secure constraints. We then develop theoretical models for the warden1detection error probability and the covert-and-secure rate (CSR) from S to D. Based on these models, we further explore the optimal power control for CSR maximization under both covertness and security constraints. Finally, numerical results are presented to validate the theoretical models and demonstrate the performance of covert and secure communications in the UAV-assisted system.

This article investigates covert communications in a multirelay Internet of Things (IoT) system with multiple energy harvesting jammers, where a transmitter (Alice) attempts to covertly transmit confidential messages to its destination (Bob) through relay forwarding, while a warden (Willie) detects the existence of Alice’s transmission. Specifically, we employ a harvesting-then-jamming protocol with which the jammers first harvest energy from Alice and then send jamming signals to interfere with Willie’s detection. We propose a relay and jammer selection strategy, namely quality of service (QoS)-aware selection, and use the random selection strategy as a comparison strategy. Under these two selection strategies, we derive the optimal detection threshold and minimum detection error probability at Willie, respectively. We then model the covert throughput performance and obtain the maximum covert throughput by jointly optimizing covert transmit power and jamming transmit power. Extensive numerical results are provided to illustrate the impacts of system parameters on covert throughput performance.

Wireless connectivity in smart cities relies on widely deployed Internet of Things (IoT) systems. However, the broadcast and open nature of wireless channels in such systems also raise serious security concerns. Covert communication technology presents a promising solution for tackling these challenges. In the multi-relay assisted wireless systems where the warden acts as a jammer, this paper investigates the performance of covert communication. First, the transmission model is introduced and the warden behavior is defined, which will perform detection and jamming throughout the covert communication process. Due to the warden’s jamming, the transmitter must increase its transmit power in order to ensure successful decoding, which increases the risk of detection. To explore this tradeoff in depth, this paper proposes a new theoretical framework to analyze the performance metrics of covert communication. These performance metrics are analyzed and derived under two relay selection schemes, i.e., random selection scheme and superior-link selection scheme. The maximum covert rate is optimized by power control under the condition that the covertness and outage requirements are satisfied. Finally, the results of simulations and numerical experiments confirm the theoretical analysis and visualize the performance of covert communication in systems with active warden.

This paper investigates the covert communications via cooperative jamming and relay selection in a wireless relay system, where a source intends to transmit a message to its destination with the help of a selected relay, and a warden attempts to detect the existence of wireless transmissions from both the source and relay, while friendly jammers send jamming signals to prevent warden from detecting the transmission process. To this end, we first propose two relay selection schemes, namely random relay selection (RRS) and max-min relay selection (MMRS), as well as their corresponding cooperative jamming (CJ) schemes for ensuring covertness in the system. We then provide theoretical modeling for the covert rate performance under each relay selection scheme and its CJ scheme and further explore the optimal transmit power controls of both the source and relay for covert rate maximization. Finally, extensive simulation/numerical results are presented to validate our theoretical models and also to illustrate the covert rate performance of the relay system under cooperative jamming and relay selection.

Internet of Things (IoT) systems are of paramount importance to provide ubiquitous wireless connectivity for smart cities. However, such systems are facing security challenges due to the broadcast and openness nature of wireless channels. This article studies the performance of covert communication under a scenario consisted of a source-destination pair, a passive warden, and multiple relays. We first propose two relay selection schemes, one is random selection and another is superior-link selection. Based on these two schemes, we then examine the transmission strategy design for the source and thus define the necessary condition that the source can transmit covert messages. We further derive the detection error probability of warden and covert capacity based on two relay selection schemes and also explore the covert capacity maximization through efficient numerical searches. Finally, numerical results are provided to illustrate our theoretical findings and the performance of covert communication in such systems. Remarkably, the superior-link selection scheme has 108% improved to the random selection scheme for the maximum covert capacity performance under the same transmission power at the source.