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Center-Fed Pinching Antenna System (C-PASS) Aided Wireless Communications

Xu Gan, Yuanwei Liu

TL;DR

Center-Fed PASS (C-PASS) doubles the available degrees of freedom by splitting the waveguide-fed signal into forward and backward directions. The paper proposes three operating protocols—Power Splitting (PS), Direction Switching (DS), and Time Switching (TS)—and develops corresponding joint transmit and pinching beamforming optimization frameworks, using WMMSE reformulation for PS, a penalty method for DS, and closed-form time allocation for TS. Across simulations, PS and DS achieve DoF of 2 in high-SNR scenarios while TS excels at low power, with PS/DS benefiting more from largerPA and M configurations, and TS leveraging time-domain separation. The results highlight the practical flexibility and performance gains of C-PASS for multi-user wireless downlink, guiding future explorations in uplink/downlink, channel estimation, and robust design in dense networks.

Abstract

The novel architecture of the center-fed pinching antenna system (C-PASS) is investigated, where the waveguide-fed signal is divided into two propagation directions through controllable power splitting. By doing so, a doubled degree of freedom (DoF) is achieved compared to conventional PASS. Based on the new designed basic signal model of C-PASS, three practical operating protocols for C-PASS are proposed, namely power splitting (PS), direction switching (DS), and time switching (TS). Then, the sum-rate maximization problem for the joint optimization of transmit and pinching beamforming is formulated for each of the proposed protocols. 1) For PS, the highly coupled non-convex problem is first transformed into a tractable form via the weighted minimum mean square error reformulation and solved using the alternating optimization framework; 2) For DS, the above approach is subsequently extended to solve the mixed-integer constraints inherent for DS via the penalty-based algorithm; 3) For TS, the optimization problem can be decomposed into two subproblems and solved using the similar iterative techniques, while its optimal time allocation ratio is derived in closed form. Finally, numerical results reveal that TS is superior in the low-power regime, while PS and DS achieve significantly higher rates in the high-power regime due to the enhanced DoF.

Center-Fed Pinching Antenna System (C-PASS) Aided Wireless Communications

TL;DR

Center-Fed PASS (C-PASS) doubles the available degrees of freedom by splitting the waveguide-fed signal into forward and backward directions. The paper proposes three operating protocols—Power Splitting (PS), Direction Switching (DS), and Time Switching (TS)—and develops corresponding joint transmit and pinching beamforming optimization frameworks, using WMMSE reformulation for PS, a penalty method for DS, and closed-form time allocation for TS. Across simulations, PS and DS achieve DoF of 2 in high-SNR scenarios while TS excels at low power, with PS/DS benefiting more from largerPA and M configurations, and TS leveraging time-domain separation. The results highlight the practical flexibility and performance gains of C-PASS for multi-user wireless downlink, guiding future explorations in uplink/downlink, channel estimation, and robust design in dense networks.

Abstract

The novel architecture of the center-fed pinching antenna system (C-PASS) is investigated, where the waveguide-fed signal is divided into two propagation directions through controllable power splitting. By doing so, a doubled degree of freedom (DoF) is achieved compared to conventional PASS. Based on the new designed basic signal model of C-PASS, three practical operating protocols for C-PASS are proposed, namely power splitting (PS), direction switching (DS), and time switching (TS). Then, the sum-rate maximization problem for the joint optimization of transmit and pinching beamforming is formulated for each of the proposed protocols. 1) For PS, the highly coupled non-convex problem is first transformed into a tractable form via the weighted minimum mean square error reformulation and solved using the alternating optimization framework; 2) For DS, the above approach is subsequently extended to solve the mixed-integer constraints inherent for DS via the penalty-based algorithm; 3) For TS, the optimization problem can be decomposed into two subproblems and solved using the similar iterative techniques, while its optimal time allocation ratio is derived in closed form. Finally, numerical results reveal that TS is superior in the low-power regime, while PS and DS achieve significantly higher rates in the high-power regime due to the enhanced DoF.
Paper Structure (36 sections, 2 theorems, 56 equations, 8 figures, 2 tables, 2 algorithms)

This paper contains 36 sections, 2 theorems, 56 equations, 8 figures, 2 tables, 2 algorithms.

Table of Contents

  1. Introduction
  2. Prior Works
  3. Studies on Single-Waveguide Aided Multi-User Communications
  4. Studies on Multi-Waveguide Aided Multi-User Communications
  5. Motivations and Contributions
  6. Organization and Notation
  7. Basic Signal Model and Practical Operating Protocols for C-PASS
  8. Basic Signal Model of C-PASS
  9. Three Practical Protocols for Operating C-PASS
  10. Power Splitting
  11. Direction Switching
  12. Time Switching
  13. System Model and Problem Formulation
  14. System Model
  15. Problem Formulation
  16. ...and 21 more sections

Key Result

Lemma 1

The sum-rate maximization function sec4_PS_o1 for PS is equivalent to the weighted error minimization function as shi2011iteratively where $\bm{\epsilon}=\left[\epsilon_{\text{FU}},\epsilon_{\text{BU}}\right]$, $\bm{\kappa}=\left[\kappa_{\text{FU}},\kappa_{\text{BU}} \right]$ and $\mathbf{t} = [t_{\text{FU}}, t_{\text{BU}}]$ are the auxiliary vectors, and the error is defined as

Figures (8)

  • Figure 1: Three practical protocols for operating C-PASS.
  • Figure 2: Illustration of a C-PASS aid downlink communications.
  • Figure 3: Coverage behaviors of the proposed algorithms.
  • Figure 4: Sum-rate comparison under different protocols.
  • Figure 5: Sum-rate comparison with baseline 1, $M=6$.
  • ...and 3 more figures

Theorems & Definitions (7)

  • Remark 1
  • Lemma 1
  • proof
  • Remark 2
  • Lemma 2
  • proof
  • Remark 3