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Pinching-Antenna System Design under Random LoS and NLoS Channels

Yanqing Xu, Yang Lu, Zhiguo Ding, Tsung-Hui Chang

TL;DR

<p>The paper addresses multiuser wireless downlink performance when the pinching-antenna system operates under a realistic composite LoS/NLoS channel. It develops two complementary design frameworks: (i) an average-SNR-based max-min optimization to enhance long-term throughput and fairness via a monotonic, bisection-enabled solution, and (ii) an outage-constrained optimization guaranteeing a target SNR with specified reliability using a CCDF-based monotone approach. The authors reveal structural properties that render the nonconvex problems globally solvable with low computational complexity, and they provide a closed-form two-user solution as well as extensive simulations showing sizable gains over fixed-antenna deployments, especially in larger regions and under stringent reliability requirements. The results demonstrate the practical potential of pinching antennas for robust and adaptable wireless connectivity in dynamic, obstacle-rich environments.</p>

Abstract

Pinching antennas, realized through position-adjustable radiating elements along dielectric waveguides, have emerged as a promising flexible-antenna technology thanks to their ability to dynamically reshape large-scale channel conditions. However, most existing studies focus on idealized LoS-dominated environments, overlooking the stochastic nature of realistic wireless propagation. This paper investigates a more practical multiuser pinching-antenna system under a composite probabilistic channel model that captures distance-dependent LoS blockage and NLoS scattering. To account for both efficiency and reliability aspects of communication, two complementary design metrics are considered: an average signal-to-noise ratio (SNR) metric characterizing long-term throughput and fairness, and an outage-constrained metric ensuring a prescribed reliability level. Based on these metrics, we formulate two optimization problems: the first maximizes the max-min average SNR across users, while the second maximizes a guaranteed SNR threshold under per-user outage constraints. Although both problems are inherently nonconvex, we exploit their underlying monotonic structures and develop low-complexity, bisection-based algorithms that achieve globally optimal solutions using only simple scalar evaluations. Extensive simulations validate the effectiveness of the proposed methods and demonstrate that pinching-antenna systems significantly outperform conventional fixed-antenna designs even under random LoS and NLoS channels.

Pinching-Antenna System Design under Random LoS and NLoS Channels

TL;DR

<p>The paper addresses multiuser wireless downlink performance when the pinching-antenna system operates under a realistic composite LoS/NLoS channel. It develops two complementary design frameworks: (i) an average-SNR-based max-min optimization to enhance long-term throughput and fairness via a monotonic, bisection-enabled solution, and (ii) an outage-constrained optimization guaranteeing a target SNR with specified reliability using a CCDF-based monotone approach. The authors reveal structural properties that render the nonconvex problems globally solvable with low computational complexity, and they provide a closed-form two-user solution as well as extensive simulations showing sizable gains over fixed-antenna deployments, especially in larger regions and under stringent reliability requirements. The results demonstrate the practical potential of pinching antennas for robust and adaptable wireless connectivity in dynamic, obstacle-rich environments.</p>

Abstract

Pinching antennas, realized through position-adjustable radiating elements along dielectric waveguides, have emerged as a promising flexible-antenna technology thanks to their ability to dynamically reshape large-scale channel conditions. However, most existing studies focus on idealized LoS-dominated environments, overlooking the stochastic nature of realistic wireless propagation. This paper investigates a more practical multiuser pinching-antenna system under a composite probabilistic channel model that captures distance-dependent LoS blockage and NLoS scattering. To account for both efficiency and reliability aspects of communication, two complementary design metrics are considered: an average signal-to-noise ratio (SNR) metric characterizing long-term throughput and fairness, and an outage-constrained metric ensuring a prescribed reliability level. Based on these metrics, we formulate two optimization problems: the first maximizes the max-min average SNR across users, while the second maximizes a guaranteed SNR threshold under per-user outage constraints. Although both problems are inherently nonconvex, we exploit their underlying monotonic structures and develop low-complexity, bisection-based algorithms that achieve globally optimal solutions using only simple scalar evaluations. Extensive simulations validate the effectiveness of the proposed methods and demonstrate that pinching-antenna systems significantly outperform conventional fixed-antenna designs even under random LoS and NLoS channels.

Paper Structure

This paper contains 22 sections, 3 theorems, 61 equations, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Contributions
  3. System Mode and Channel Model
  4. System Model
  5. Channel Model with Random LoS and NLoS Components
  6. Probabilistic LoS Channel Component
  7. NLoS Channel Component
  8. Composite Channel Model
  9. Signal Model and Performance Metrics
  10. Signal Model
  11. Performance Metrics
  12. Average-SNR-based Pinching-Antenna System Design
  13. Per-User Average SNR Derivations
  14. Max--Min Average SNR Maximization Problem Formulation and Analysis
  15. Solving Problem \ref{['p: max min epigraph']} via the Monotonicity of $\mathcal{F}(t)$
  16. ...and 7 more sections

Key Result

Proposition 1

For each user $m$ and any given target SNR level $t>0$, the feasibility set is either a closed interval or an empty set. Consequently, the global feasibility set is also either a closed interval or empty. Moreover, $\mathcal{F}(t)$ monotonically shrinks as $t$ increases, i.e.,

Figures (8)

  • Figure 1: A geometric illustration of a two-user pinching-antenna system under (a) small and (b) large horizontal distances, showing the feasible antenna position regions and optimal deployment strategy.
  • Figure 2: Max–min average SNR comparison between pinching-antenna and fixed-antenna designs versus $D_x$ and $\beta$.
  • Figure 3: Max–min average SNR comparison between pinching-antenna and fixed-antenna designs versus $D_x$ and $M$.
  • Figure 4: CDF of the max-min average SNR for pinching- and fixed-antenna systems with different numbers of users $M$.
  • Figure 5: CCDF of the instantaneous SNR $\Gamma(t)$ for different LoS blockage coefficients $\beta$ with $D_x = 30$ m.
  • ...and 3 more figures

Theorems & Definitions (6)

  • Proposition 1
  • Remark 1
  • Lemma 1
  • Remark 2
  • Proposition 2
  • Remark 3