Multigroup Multicast Design for Pinching-Antenna Systems: Waveguide-Division or Waveguide-Multiplexing?

TL;DR

This paper proposes new multigroup multicast transmission frameworks for pinching-antenna systems, optimizing beamforming and power allocation for waveguide-division and waveguide-multiplexing architectures, leading to significant rate improvements.

Contribution

It introduces novel optimization strategies for PASS-enabled multigroup transmission, including element-wise sequential optimization and MM-based frameworks for both WD and WM architectures.

Findings

Both WD and WM architectures significantly improve multicast rates over traditional MIMO.

WM is more robust in dense deployments, WD performs better with spatially separated groups.

Proposed algorithms achieve efficient beamforming and power allocation with low complexity.

Abstract

This article addresses the design of multigroup multicast communications in the pinching-antenna system (PASS). A PASS-enabled multigroup transmission framework is proposed to maximize multicast rates under a couple of transmission architectures: waveguide-division (WD) and waveguide-multiplexing (WM). 1) For WD, an element-wise sequential optimization strategy is proposed for pinching beamforming, i.e., optimizing the activated positions of pinching antennas along dielectric waveguides. Meanwhile, a log-sum-exp projected gradient descent algorithm is proposed for transmit power allocation across waveguides. 2) For WM, a majorization-minimization (MM)-based framework is proposed to tackle the problem's non-smoothness and non-convexity. On this basis, a low-complexity element-wise sequential optimization method is developed for pinching beamforming using the MM surrogate objective. Furthermore, the optimal transmit beamformer structure is derived from the MM surrogate objective using the Lagrange duality, with an efficient transmit beamforming algorithm proposed using projected adaptive gradient descent. Numerical results demonstrate that: i) both WD and WM architectures in PASS achieve significant multicast rate improvements over conventional MIMO techniques, especially for systems with large service areas; ii) WM is more robust than WD in dense deployments, while WD excels when user groups are spatially separated.