Movable Antenna Assisted Covert Communication with Wavelength-Scale Beamforming Resolution

It is challenging for a fixed-position antenna (FPA) system to achieve covert communication when the warden is in close proximity to the intended receiver due to limited beamforming resolution. This paper proposes a novel movable antenna (MA) assisted covert communication strategy, which can take full advantage of multi-path channels and achieve wavelength-scale beamforming resolution by adjusting antenna positions controllably. We formulate a covert rate maximization problem by jointly designing the antenna position and transmit beamforming of the MA system, and propose an alternating optimization algorithm to deal with it. Specifically, in the antenna position subproblem, the unit-modulus properties of the field-response vector are utilized to reconfigure the multi-path channel. Numerical results demonstrate the superiority of our proposed MA covert communication method, verifying its wavelength-scale beamforming resolution and showing that a two-antenna MA system can achieve 100% covert rate improvement compared with the FPA system.