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Multi-Mode Pinching Antenna Systems Enabled Multi-User Communications

Xiaoxia Xu, Xidong Mu, Yuanwei Liu, Arumugam Nallanathan

TL;DR

This paper proposes a multi-mode PASS framework that enables mode-domain multiplexing to transmit multiple data streams within a single dielectric waveguide. A CMT-based physical model is derived to capture mode-selective PA radiation, and a PA-grouping scheme is developed to control power leakage across guided modes. For a two-PA non-leakage case, the authors formulate a channel-orthogonality problem that reduces to MRT with a Newton-based one-dimensional PA-placement search; for the general multi-PA case, a PSO-ZF algorithm is proposed to efficiently navigate a highly nonconvex, high-oscillatory design space. Numerical results show that multi-mode PASS outperforms TDMA-based single-mode PASS and fixed-antenna MISO across leakage regimes, demonstrating significant mode-domain multiplexing gains and robustness to practical constraints. The work provides a practical pathway to scalable, high-throughput downlink systems by leveraging guided-mode diversity within a single waveguide.

Abstract

This paper proposes a novel multi-mode pinching-antenna systems (PASS) framework. Multiple data streams can be transmitted within a single waveguide through multiple guided modes, thus facilitating efficient multi-user communications through the mode-domain multiplexing. A physic model is derived, which reveals the mode-selective power radiation feature of pinching antennas (PAs). A two-mode PASS enabled two-user downlink communication system is investigated. Considering the mode selectivity of PA power radiation, a practical PA grouping scheme is proposed, where each PA group matches with one specific guided mode and mainly radiates its signal sequentially. Depending on whether the guided mode leaks power to unmatched PAs or not, the proposed PA grouping scheme operates in either the non-leakage or weak-leakage regime. Based on this, the baseband beamforming and PA locations are jointly optimized for sum rate maximization, subject to each user's minimum rate requirement. 1) A simple two-PA case in non-leakage regime is first considered. To solve the formulated problem, a channel orthogonality based solution is proposed. The channel orthogonality is ensured by large-scale and wavelength-scale equality constraints on PA locations. Thus, the optimal beamforming reduces to maximum-ratio transmission (MRT). Moreover, the optimal PA locations are obtained via a Newton-based one-dimension search algorithm that enforces two-scale PA-location constraints by Newton's method. 2) A general multi-PA case in both non-leakage and weak-leakage regimes is further considered. A low-complexity particle-swarm optimization with zero-forcing beamforming (PSO-ZF) algorithm is developed, thus effectively tackling the high-oscillatory and strong-coupled problem. Simulation results demonstrate the superiority of the proposed multi-mode PASS over conventional single-mode PASS and fixed-antenna structures.

Multi-Mode Pinching Antenna Systems Enabled Multi-User Communications

TL;DR

This paper proposes a multi-mode PASS framework that enables mode-domain multiplexing to transmit multiple data streams within a single dielectric waveguide. A CMT-based physical model is derived to capture mode-selective PA radiation, and a PA-grouping scheme is developed to control power leakage across guided modes. For a two-PA non-leakage case, the authors formulate a channel-orthogonality problem that reduces to MRT with a Newton-based one-dimensional PA-placement search; for the general multi-PA case, a PSO-ZF algorithm is proposed to efficiently navigate a highly nonconvex, high-oscillatory design space. Numerical results show that multi-mode PASS outperforms TDMA-based single-mode PASS and fixed-antenna MISO across leakage regimes, demonstrating significant mode-domain multiplexing gains and robustness to practical constraints. The work provides a practical pathway to scalable, high-throughput downlink systems by leveraging guided-mode diversity within a single waveguide.

Abstract

This paper proposes a novel multi-mode pinching-antenna systems (PASS) framework. Multiple data streams can be transmitted within a single waveguide through multiple guided modes, thus facilitating efficient multi-user communications through the mode-domain multiplexing. A physic model is derived, which reveals the mode-selective power radiation feature of pinching antennas (PAs). A two-mode PASS enabled two-user downlink communication system is investigated. Considering the mode selectivity of PA power radiation, a practical PA grouping scheme is proposed, where each PA group matches with one specific guided mode and mainly radiates its signal sequentially. Depending on whether the guided mode leaks power to unmatched PAs or not, the proposed PA grouping scheme operates in either the non-leakage or weak-leakage regime. Based on this, the baseband beamforming and PA locations are jointly optimized for sum rate maximization, subject to each user's minimum rate requirement. 1) A simple two-PA case in non-leakage regime is first considered. To solve the formulated problem, a channel orthogonality based solution is proposed. The channel orthogonality is ensured by large-scale and wavelength-scale equality constraints on PA locations. Thus, the optimal beamforming reduces to maximum-ratio transmission (MRT). Moreover, the optimal PA locations are obtained via a Newton-based one-dimension search algorithm that enforces two-scale PA-location constraints by Newton's method. 2) A general multi-PA case in both non-leakage and weak-leakage regimes is further considered. A low-complexity particle-swarm optimization with zero-forcing beamforming (PSO-ZF) algorithm is developed, thus effectively tackling the high-oscillatory and strong-coupled problem. Simulation results demonstrate the superiority of the proposed multi-mode PASS over conventional single-mode PASS and fixed-antenna structures.
Paper Structure (32 sections, 3 theorems, 64 equations, 10 figures, 2 algorithms)

This paper contains 32 sections, 3 theorems, 64 equations, 10 figures, 2 algorithms.

Table of Contents

  1. Introduction
  2. Concept of Multi-Mode PASS
  3. Contributions
  4. CMT-Based Physic Model for Multi-Mode PASS
  5. Physic Model for Single PA
  6. Physic Model for Multiple PAs
  7. Signal Model and Problem Formulation
  8. Signal Model
  9. PA Grouping and Power Leakage Regimes
  10. Non-Leakage Regime
  11. Weak-Leakage Regime
  12. Problem Formulation
  13. Solution for Non-Leakage, Two-PA Case
  14. Channel Orthogonality Conditions
  15. Two-Scale Conditions
  16. ...and 17 more sections

Key Result

Proposition 1

Under mode-separation and weak inter-mode transfer assumptions, the multi-mode CME system eq:CME_env_A-eq:CME_env_B approximately decomposes into $M$ independent two-mode subsystems. Then, the power radiation coefficient in waveguide_to_PA_single is given by where $\phi_m\triangleq \sqrt{|\kappa_{m}|^2 + \Bigl(\frac{\Delta\beta_m}{2}\Bigr)^2}\in\mathbb{R}$ is the generalized coupling strength, $\

Figures (10)

  • Figure 1: The concept of single-mode and multi-mode waveguides.
  • Figure 2: Power radiation ratio $|\eta_m|^2$ for each guided mode $m$ versus the propagation constant $\beta^{\mathrm{PA}}$ of a PA. $\beta_1=638.8$ rad/m, $\beta_2=999.0$ rad/m, $\mu_1=1$, $\mu_{2}\in\{0.3,1\}$, and coupling strength $L=2$ cm. The PA can predominantly match with one guided mode $m$ at $\beta^{\mathrm{PA}}\approx \beta_{m}$ to radiate its signal power, while leaking a small amount of power from the unmatched mode, which indicates the mode selectivity.
  • Figure 3: The proposed multi-mode PASS framework.
  • Figure 4: Power leakage versus $\Delta \beta_{2,1}$.
  • Figure 5: Sum rate under different $P_{\max}$.
  • ...and 5 more figures

Theorems & Definitions (5)

  • Proposition 1: Decomposition into $M$ Two-Mode Subsystems
  • Remark 1
  • Corollary 1: Stationary points of $D(x)$
  • proof
  • Proposition 2: Piecewise monotonicity of $D(x)$