UAV Relay-Enabled THz Covert Communications Against Colluding Detection

Abstract

This paper investigates covert communications against colluding unmanned aerial vehicle (UAV) wardens in a UAV-assisted Terahertz (THz) relay system (UTRS), where a transmitter sends confidential signals to its intended receiver via a UAV relay, and two wardens attempt to detect the existence of two-hop transmissions. Considering a powerful adversary with colluding wardens, we examine the decision fusion (DF) and centralized testing (CT) schemes to characterize the colluding detection capabilities. We derive each warden's detection error probability (DEP) under Rician fading with atmospheric attenuation and establish the overall DEPs of two colluding schemes. We then formulate and solve a covert throughput maximization problem by jointly optimizing the transmission power and interference power, subject to the covertness and SINR constraints. Numerical results validate the theoretical analyses and illustrate the influence of key parameters on covert performance. In particular, the covert throughput against wardens under the DF scheme is lower than that under the CT scheme. This work sheds light on the covert communication design of UTRSs against colluding wardens in next-generation wireless communication networks.