Center-Fed Pinching Antenna System (C-PASS): Modeling, Analysis, and Beamforming Design

TL;DR

This work introduces a generalized Center-Fed Pinching Antenna System (C-PASS) to overcome the DoF bottleneck in single-waveguide PASS by distributed center-fed feeding, enabling $DoF = \min\{M,K\}$ and a linear power gain $\mathcal{O}(P_T M)$. It develops a joint transmit and pinching beamforming framework and solves the resulting non-convex problem via a WMMSE reformulation and alternating optimization, updating $\mathbf{W}$, power-splitting ratios, PA positions, and radiation coefficients, with efficient subroutines including grid search and Brent’s method. Theoretical results are validated numerically, showing superior DoF and PSL performance relative to conventional PASS, and concrete gains (e.g., over $10$ dB in high-attenuation settings) when serving multiple users. The approach offers practical, scalable improvements for B6G systems, and the linear DoF scaling with $M$ suggests strong potential when extending to multi-waveguide configurations.

Abstract

A generalized framework for the novel center-fed pinching antenna system (C-PASS) is proposed. Within this framework, closed-form expressions for the degree of freedom (DoF) and power scaling law of the proposed C-PASS are first derived. These theoretical results reveal that the achievable DoF scales linearly with the number of input ports, $M$, and the number of receive antennas, $K$. Furthermore, the derived power scaling laws demonstrate that the C-PASS achieves a power gain of order $\mathcal{O}(P_T M)$, where $P_T$ denotes the transmit power. Based on the proposed C-PASS modeling, a sum-rate maximization problem for the joint optimization of transmit and pinching beamforming is then formulated. To solve this highly coupled non-convex problem, an efficient alternating optimization algorithm is developed. More particularly, the transmit precoding and power splitting ratios are updated via derived closed-form solutions, while the pinching antenna positions and radiation coefficients are optimized using block coordinate descent (BCD) methods. Finally, our numerical results reveal that the single-waveguide C-PASS: 1) achieves superior DoF and power scaling laws compared to the single-waveguide PASS; and 2) outperforms the multi-waveguide PASS in high-attenuation regimes, yielding a substantial gain exceeding $10$ dB.

Figures (9)

• Figure 1: Illustration of a C-PASS architecture.
• Figure 2: Illustration of a C-PASS aided communications.
• Figure 3: DoF characterization of C-PASS.
• Figure 4: Power scaling law characterization of C-PASS.
• Figure 5: Convergence behavior of the proposed algorithm.

Theorems & Definitions (7)

• Theorem 1
• proof
• Remark 1
• Theorem 2
• proof
• Lemma 1
• proof