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

TL;DR

This paper introduces a novel center-fed pinching antenna system (C-PASS), providing theoretical modeling, power scaling laws, and an optimized beamforming design that significantly enhances performance over existing systems.

Contribution

It presents a comprehensive framework for C-PASS, including closed-form expressions for DoF and power scaling, and develops an efficient optimization algorithm for joint beamforming design.

Findings

C-PASS achieves linear DoF scaling with input ports and receive antennas.

The system attains a power gain proportional to transmit power and number of ports.

Numerical results show C-PASS outperforms existing PASS systems, especially in high-attenuation scenarios.

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.