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Pinching-Antenna Systems (PASS): Power Radiation Model and Optimal Beamforming Design

Xiaoxia Xu, Xidong Mu, Zhaolin Wang, Yuanwei Liu, Arumugam Nallanathan

TL;DR

PASS addresses the joint design of discrete pinching-antenna activation and beamforming in a PASS downlink by introducing an adjustable power radiation model that tunes radiation ratios through antenna-spacing. The work delivers both globally optimal (BnB) solutions for single- and multi-user cases and a low-complexity welfare-driven many-to-many matching approach to reduce complexity while maintaining near-optimal performance; the matching step uses SOCP for beamforming given a fixed activation pattern. Theoretical guarantees include convergence and epsilon-optimality for the BnB algorithms and stability and local optimality for the welfare-based matching, with simulations showing substantial power savings and improved coverage over conventional MIMO, especially as user counts and spatial range grow. Code for reproduce is provided at https://github.com/xiaoxiaxusummer/PASS_Discrete, highlighting the practical potential of PASS for next-generation wireless systems.

Abstract

Pinching-antenna systems (PASS) improve wireless links by configuring the locations of activated pinching antennas along dielectric waveguides, namely pinching beamforming. In this paper, a novel adjustable power radiation model is proposed for PASS, where power radiation ratios of pinching antennas can be flexibly controlled by tuning the spacing between pinching antennas and waveguides. A closed-form pinching antenna spacing arrangement strategy is derived to achieve the commonly assumed equal-power radiation. Based on this, a practical PASS framework relying on discrete activation is considered, where pinching antennas can only be activated among a set of predefined locations. A transmit power minimization problem is formulated, which jointly optimizes the transmit beamforming, pinching beamforming, and the numbers of activated pinching antennas, subject to each user's minimum rate requirement. (1) To solve the resulting highly coupled mixed-integer nonlinear programming (MINLP) problem, branch-and-bound (BnB)-based algorithms are proposed for both single-user and multi-user scenarios, which is guaranteed to converge to globally optimal solutions. (2) A low-complexity many-to-many matching algorithm is further developed. Combined with the Karush-Kuhn-Tucker (KKT) theory, locally optimal and pairwise-stable solutions are obtained within polynomial-time complexity. Simulation results demonstrate that: (i) PASS significantly outperforms conventional multi-antenna architectures, particularly when the number of users and the spatial range increase; and (ii) The proposed matching-based algorithm achieves near-optimal performance, resulting in only a slight performance loss while significantly reducing computational overheads. Code is available at https://github.com/xiaoxiaxusummer/PASS_Discrete

Pinching-Antenna Systems (PASS): Power Radiation Model and Optimal Beamforming Design

TL;DR

PASS addresses the joint design of discrete pinching-antenna activation and beamforming in a PASS downlink by introducing an adjustable power radiation model that tunes radiation ratios through antenna-spacing. The work delivers both globally optimal (BnB) solutions for single- and multi-user cases and a low-complexity welfare-driven many-to-many matching approach to reduce complexity while maintaining near-optimal performance; the matching step uses SOCP for beamforming given a fixed activation pattern. Theoretical guarantees include convergence and epsilon-optimality for the BnB algorithms and stability and local optimality for the welfare-based matching, with simulations showing substantial power savings and improved coverage over conventional MIMO, especially as user counts and spatial range grow. Code for reproduce is provided at https://github.com/xiaoxiaxusummer/PASS_Discrete, highlighting the practical potential of PASS for next-generation wireless systems.

Abstract

Pinching-antenna systems (PASS) improve wireless links by configuring the locations of activated pinching antennas along dielectric waveguides, namely pinching beamforming. In this paper, a novel adjustable power radiation model is proposed for PASS, where power radiation ratios of pinching antennas can be flexibly controlled by tuning the spacing between pinching antennas and waveguides. A closed-form pinching antenna spacing arrangement strategy is derived to achieve the commonly assumed equal-power radiation. Based on this, a practical PASS framework relying on discrete activation is considered, where pinching antennas can only be activated among a set of predefined locations. A transmit power minimization problem is formulated, which jointly optimizes the transmit beamforming, pinching beamforming, and the numbers of activated pinching antennas, subject to each user's minimum rate requirement. (1) To solve the resulting highly coupled mixed-integer nonlinear programming (MINLP) problem, branch-and-bound (BnB)-based algorithms are proposed for both single-user and multi-user scenarios, which is guaranteed to converge to globally optimal solutions. (2) A low-complexity many-to-many matching algorithm is further developed. Combined with the Karush-Kuhn-Tucker (KKT) theory, locally optimal and pairwise-stable solutions are obtained within polynomial-time complexity. Simulation results demonstrate that: (i) PASS significantly outperforms conventional multi-antenna architectures, particularly when the number of users and the spatial range increase; and (ii) The proposed matching-based algorithm achieves near-optimal performance, resulting in only a slight performance loss while significantly reducing computational overheads. Code is available at https://github.com/xiaoxiaxusummer/PASS_Discrete
Paper Structure (30 sections, 9 theorems, 75 equations, 10 figures, 3 algorithms)

This paper contains 30 sections, 9 theorems, 75 equations, 10 figures, 3 algorithms.

Table of Contents

  1. Introduction
  2. System Model and Problem Formulation
  3. Adjustable Power Radiation Model
  4. PASS Signal Model
  5. Signal Radiation within Waveguides
  6. Signal Radiation in Free Space
  7. Problem Formulation
  8. BnB-Based Globally Optimal Beamforming
  9. Optimal Solution for Single-User Scenario
  10. BnB Principles
  11. Convex Relaxation
  12. BnB Algorithm
  13. Optimal Solution for Multi-User Scenario
  14. Convex Relaxation
  15. BnB Algorithm
  16. ...and 15 more sections

Key Result

Proposition 1

The coupling coefficient $\kappa_{l,n}$ in CMT_intgeral can be modelled as a function of coupling spacing $S_{l,n}$ as followsAs proven in Appendix proof:proposition:coupling_strength, eq:coupling_coefficient provides a tractable approximation, where $\Omega_{0}$ reflects geometry/material factors a where coefficient $\Omega_{0}$ captures electric distribution and modal normalization, and the clad

Figures (10)

  • Figure 1: PASS enabled downlink MISO communication with discrete pinching antenna activation.
  • Figure 2: The proposed adjustable power radiation model with a local Cartesian coordinate system. The power radiation ratio of each pinching antenna is decided by adjustable spacing $S_{l,n}$.
  • Figure 3: Coupling effects versus waveguide-antenna spacing.
  • Figure 4: Convergence of BnB for single-user scenario.
  • Figure 5: Performance comparisons in single-user scenario.
  • ...and 5 more figures

Theorems & Definitions (24)

  • Proposition 1
  • proof
  • Lemma 1: Element-Wise Adjustable Power Radiation Model
  • Lemma 2: Special Case: Equal-Power Radiation
  • proof
  • Definition 1
  • Remark 1
  • Proposition 2
  • Lemma 3
  • proof
  • ...and 14 more