Beam Squint Assisted Near-Field Covert Communication

In the near-field extremely large-scale multiple-input multiple-output (XL-MIMO) systems, the large bandwidth and massive antenna arrays lead to a significant beam-squint effect, causing subcarriers at different frequencies to focus on distinct locations and resulting in severe array gain loss. However, this effect can be leveraged to enable rapid near-field beam training. Based on this, we propose a joint optimization solution for location estimation (LE) and data transmission (DT) based on extremely large antenna array (ELAA) and true-time-delay lines (TTDs) to address the challenges of near-field covert communication. Specifically, with the help of TTDs, the transmitter Alice leverages the beam-squint effect for rapid localization of the legitimate receiver Bob in the LE phase, then suppresses the effect in the DT phase to concentrate energy, thereby minimizing the detection probability at the warden Willie. Theoretical analysis and simulation show that the proposed scheme maximizes the effective covert rate (ECR) by balancing the number of subcarriers and the transmit power while meeting covertness constraints.