Multiuser Covert Terahertz Communication With Outdated CSI and Data Exception

Abstract

This article investigates a multiuser covert terahertz communication system with a warden, Willie, and a legitimate receiver, Bob, under the constraint of outdated channel state information (CSI) and data exception. Outdated CSI, caused by feedback delays, introduces uncertainty in channel conditions and severely degrades the system performance. In addition, data exceptions are taken into account, which arise when certain data packets cannot be transmitted due to factors such as interference or transmission errors, further complicating the communication process and disrupting the reliability of covert transmissions. To tackle these issues, we propose a joint optimization framework for the beamforming vectors at Alice, designed to maximize the covert rate to Bob while minimizing the detection probability at Willie. By formulating the problem as a trade-off between the two objectives, we derive an optimal beamforming strategy that accounts for both the statistical properties of outdated CSI and the occurrence of data exceptions. Numerical simulations validate the effectiveness of the proposed approach, demonstrating significant performance improvement over conventional schemes. Specifically, for the transmit power $$ dBm and channel correlation coefficient $$, the proposed scheme achieves a 25% higher received signal-to-noise ratio (SNR) at Bob compared to traditional beamforming schemes. In addition, when $$ and the covertness parameter $$, the proposed scheme reduces Willie's detection probability by 30%, ensuring robust covert communication.