Near-Field Terahertz Covert Communications Against Randomly Distributed Eavesdroppers

We study the near-field Terahertz (THz) covert communications against a randomly distributed eavesdropper with unbounded noise uncertainty. First, we model the eavesdropper as randomly and uniformly distributed in a disc centered on the transmitter. Then, we derive a closed-form expression of the eavesdropper's received power by leveraging Fresnel integrals to approximate near-field phase variations. Furthermore, we analyze the system performance metrics, including the average covert probability, average covert outage probability, and covert rate. Numerical results demonstrate the accuracy of our analysis and reveal a non-monotonic relationship between the average covert outage probability and the radius of the eavesdropping area, further indicating that an optimal communication distance exists to minimize the average outage probability for each specific radius of the eavesdropping area, thereby providing guidelines for secure wireless networks deployment.