Directional Pinching-Antenna Systems

TL;DR

DiPASS addresses the gap between idealized PASS models and physical realism by introducing a directional, Gaussian-beam pinching-antenna channel that accounts for practical waveguide loss and stochastic LoS blockage. The authors propose equal quota division to fix coupling lengths and develop a scalable DiPASS optimization framework that converts joint design into a PA-user assignment problem, solved with a Hungarian-greedy approach and complemented by beamforming refinements. Key theoretical results include closed-form single-PA placement and orientation, a translation-invariant optimal offset, and guidelines showing waveguide diversity outperforms mere antenna density for capacity gains. Numerical results validate the model and demonstrate practical deployment insights, indicating that DiPASS can serve as a realistic benchmark for 6G PASS-enabled networks and guiding design principles for future directional PASS-enabled architectures.

Abstract

We propose a directional pinching-antenna system (DiPASS), a comprehensive framework that transitions PASS modeling from idealized abstraction to physical consistency. DiPASS introduces the first channel model that accurately captures the directional, pencil-like radiation of pinching antennas, incorporates a practical waveguide attenuation of 1.3 dB/m, and accounts for stochastic line-of-sight blockage. A key enabler of DiPASS is our new "equal quota division" power allocation strategy, which guarantees predetermined coupling lengths independent of antenna positions, thereby overcoming a critical barrier to practical deployment. Our analysis yields foundational insights: we derive closed-form solutions for optimal antenna placement and orientation in single-PA scenarios, quantifying the core trade-off between waveguide and free-space losses. For multi-PA systems, we develop a scalable optimization framework that leverages directional sparsity, revealing that waveguide diversity surpasses antenna density in enhancing system capacity. Extensive simulations validate our analysis and demonstrate that DiPASS provides a realistic performance benchmark, fundamentally reshaping the understanding and design principles for future PASS-enabled 6G networks.

Figures (8)

• Figure 1: Architecture of a typical PASS. The BS employs $N$ dielectric waveguides hosting a total of $NL$ PAs to serve $M$ single-antenna users.
• Figure 2: Radiation patterns for a set of antenna configurations with varying cross-sectional dimensions ($5\lambda \times 3\lambda$, $10\lambda \times 6\lambda$, and $20\lambda \times 12\lambda$) and elevation angles ($\theta = \pi$, $\tfrac{5}{6}\pi$, and $\tfrac{2}{3}\pi$): (a) spatial distribution of the power gain $|H|^2$ on the $z = 0$ plane; (b) variation of the power gain $|H|^2$ along the line aligned with the waveguide axis.
• Figure 3: Variation of the power gain $|H|^2$ with respect to the PA position $y^{(\text{P})}$ under different waveguide cross-sectional dimensions and user positions.
• Figure 4: Optimal $y^*$ under different combinations of $\alpha_{\text{W}}$ and $\alpha_{\text{L}}$, with simulation results, analytical solutions in \ref{['e:optimal_y']}, and simplified approximate expressions in \ref{['e:optimal_y_approx']}.
• Figure 5: Variation of $y^*$ under different deployment heights.

Theorems & Definitions (19)

• Definition 1: Equal Quota Division
• Proposition 1: Waveguide-to-PA Channel
• proof
• Remark 1
• Lemma 2: Coordinate Transformation
• proof
• Proposition 3: PA-to-User Channel
• proof
• Lemma 4: Optimal PA Orientation
• proof