Pinching-Antenna System (PASS)-Enhanced Covert Communications

A Pinching-Antenna SyStem (PASS)-assisted covert communication framework is proposed. PASS utilizes dielectric waveguides with freely positioned pinching antennas (PAs) to establish strong line-of-sight links. Capitalizing on the high reconfigurable flexibility of waveguides, the potential of PASS for covert communications is investigated. 1) For the single-waveguide single-PA (SWSP) scenario, a closed-form optimal PA position that maximizes the covert rate is first derived. Subsequently, a one-dimensional search is performed to obtain the optimal transmit power, while a truncation method is applied simultaneously to reduce the search region. With antenna mobility on a scale of meters, PASS can deal with the challenging situation of the eavesdropper enjoying better channel conditions than the legal user. 2) For the multi-waveguide multi-PA (MWMP) scenario, the positions of multiple PAs are optimized to enable effective pinching beamforming, thereby enhancing the covert rate. In particular, an upper bound on the malicious user’s beam gain over its position-uncertainty region is first derived. Building on this, the original optimization can be converted into an equivalent problem determined solely by the PA positions. To address this problem, a particle swarm optimization (PSO)–based method is devised to solve it efficiently. Numerical results demonstrate that: i) the proposed approaches can effectively resolve the optimization problems; ii) PASS achieves a higher covert rate than conventional fixed-position antenna architectures; and iii) with enhanced flexibility, the MWMP setup outperforms the SWSP counterpart.