Joint Transmit and Pinching Beamforming for Multiuser 2D Pinching-Antenna Systems

Abstract

Conventional line-shaped pinching-antenna systems (PASS) provide a flexible antenna architecture for highfrequency communications, but their one-dimensional deployment limits the spatial degrees of freedom available for multiuser beamforming. This paper investigates a multiuser downlink system enabled by two-dimensional PASS (2D-PASS), where multiple dielectric waveguide planes are deployed to serve several single-antenna users. To enhance the weighted sum-rate (WSR), we formulate a joint transmit and pinching beamforming problem by optimizing the digital transmit beamforming matrix and the positions of pinching antennas (PAs), subject to the transmit power and minimum PA-distance constraints. The formulated problem is highly nonconvex due to the strong coupling between the transmit beamforming and PA positions. To address this issue, we propose a two-loop iterative algorithm, where the inner loop employs the fractional programming plus (FP+) method to optimize transmit beamforming for given PA positions, while the outer loop adopts particle swarm optimization (PSO) with a penalty mechanism to search for feasible PA configurations. Simulation results show that the proposed algorithm achieves stable convergence and that 2D-PASS provides considerable WSR gains over conventional line-shaped PASS. The results also demonstrate the benefits of exploiting 2D PA position adjustment for multiuser beamforming in high-frequency indoor wireless systems.