Yujie Ling

This letter investigates multi-user covert communications. Specifically, we propose an intelligent spectrum control (ISC) scheme that employs spectrum sensing-assisted dynamic control to generate time-frequency resource occupation matrices for multiple legitimate users. Guided by these matrices, the users can occupy different frequency slots irregularly for covert data transmission. By performing spectrum sensing in advance, the proposed scheme can also proactively avoid external interference and co-channel collisions among users. In addition, we consider an eavesdropper with wideband detection capability and derive the closed-form expressions for the minimum detection error probability (DEP) of the eavesdropper and the reliable transmission probability (RTP) of the legitimate users. We then optimize the transmit power to maximize the covert rate (CR), and further characterize the maximum number of legitimate users that can access the network covertly and concurrently. Simulation results demonstrate the superiority of the proposed ISC scheme in terms of covertness, reliability, and user capacity.

Integrated air-ground communication (IAGC) has emerged as a promising solution to deliver seamless wireless coverage and high-data-rate services. However, potential malicious eavesdroppers pose a serious threat to the confidential transmission in IAGC due to their non-cooperative behaviors and the inherent openness of communication channels. To tackle this problem, a dynamic spectrum control (DSC)-based transmission scheme is proposed to enhance covert performance and communication reliability in IAGC. With the proposed scheme, we apply the principles of block cryptography, perform adaptive iterative and orthogonal transformations to generate sequence sets that drive transmission decisions. Guided by these sequences, multiple legitimate users can dynamically occupy different frequency slots and transmit data simultaneously. In addition, we analyze the probability of frequency slot multiplexing when several data groups occupy the same frequency slot in a time slot, resulting in the closed-form expression for the detection error probability. We then derive the maximum reliable transmission probability and ergodic rate subject to the covert communication constraints. Simulation results demonstrate that the proposed scheme can achieve superior covert performance compared with benchmark schemes. Furthermore, we evaluate and discuss the effects of key parameters in the proposed DSC-based transmission scheme on communication security and reliability.