Dynamic Metasurface-Enabled Generalized Pinching-Antenna Systems

Abstract

This article investigates dynamic metasurfaces as an electronic realization of generalized pinching antennas (GPA). By jointly optimizing the locations and radiation coefficients of activated elements, the dynamic metasurface-enabled GPA (DM-GPA) architecture exploits additional design flexibility to enhance spatial reconfigurability beyond that attainable through antenna placement in the conventional pinching-antenna system (PASS). Based on this architecture, we study weighted sum rate (WSR) maximization for multiuser downlink transmission. 1) For two-user transmission, the sum-rate improvement of DM-GPA over conventional PASS is quantified through a lower bound that reveals when the benefit of channel orthogonalization achieved by adjusting the radiation coefficients outweighs the channel power loss caused by the Lorentzian constraint. Furthermore, when conventional PASS yields a rank-deficient channel, DM-GPA is shown to achieve spatial multiplexing and transmit diversity, with a strict sum-rate advantage at sufficiently high signal-to-noise ratios. 2) For general multiuser transmission, a weighted minimum mean-square error (WMMSE)-based alternating optimization algorithm is developed for joint pinching beamforming and digital precoder design. A sequential element-wise search is developed to optimize the locations of the activated elements, with a closed-form solution for the radiation coefficient at each candidate location. Numerical results are provided to demonstrate that: (i) DM-GPA achieves higher WSR than other PASS architectures and fixed-array benchmarks, (ii) increasing the number of activated elements further improves the WSR of DM-GPA, and (iii) radiation coefficient adjustment is particularly beneficial when candidate activation locations are limited.