Near-Field Terahertz Covert Communications With Noise Uncertainty

We devise a cutting-edge near-field terahertz (THz) covert communication strategy with noise uncertainty where the beam is focused at a specific location, defined by both distance and direction. Leveraging unique near-field properties, the strategy combats eavesdroppers by increasing the capacity gap between legitimate and eavesdropping channels. We first develop a novel performance analytical framework for the near-field THz covert communication system, based on which we derive closed-form expressions for key performance metrics and thresholds, including the average covert probability, covert outage probability, covert rate, optimal detection threshold, and received power threshold of the eavesdropper. To further improve the secrecy performance, we design a new true-time-delay (TTD)-based piecewise approximation hybrid beamforming scheme for maximizing the covert rate, while effectively mitigating the negative impact caused by the beam split effect. Our numerical results demonstrate that the near-field THz covert communication strategy effectively combats eavesdroppers at all distances in the sector covering the main beam, demonstrating its practical significance for future wireless networks.