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Pinching-Antenna Systems (PASS): A Tutorial

Yuanwei Liu, Hao Jiang, Xiaoxia Xu, Zhaolin Wang, Jia Guo, Chongjun Ouyang, Xidong Mu, Zhiguo Ding, Arumugam Nallanathan, George K. Karagiannidis, Robert Schober

TL;DR

PASS introduces a meter-scale, reconfigurable antenna paradigm that couples dielectric waveguides with distributed pinching antennas to flexibly shape propagation, create LoS links, and enable near-field gains. The paper develops signal and hardware models, analyzes information-theoretic limits for uplink and downlink, and proposes single- and multi-waveguide beamforming strategies, including wideband OFDM considerations. It also covers practical CSI acquisition, machine-learning approaches for optimization and sensing, and potential applications in localization, ISAC, PLS, and UAV-enabled networks. Together, these contributions establish PASS as a scalable, low-cost path toward flexible aerial, terrestrial, and indoor wireless networks with enhanced reliability and spectral efficiency. The work highlights open challenges in multi-user, EM-coupling-aware analyses, continuous CSI, and robust, low-latency implementations for real-time PASS operation.

Abstract

Pinching antenna systems (PASS) present a breakthrough among the flexible-antenna technologies, and distinguish themselves by facilitating large-scale antenna reconfiguration, line-of-sight creation, scalable implementation, and near-field benefits, thus bringing wireless communications from the last mile to the last meter. A comprehensive tutorial is presented in this paper. First, the fundamentals of PASS are discussed, including PASS signal models, hardware models, power radiation models, and pinching antenna activation methods. Building upon this, the information-theoretic capacity limits achieved by PASS are characterized, and several typical performance metrics of PASS-based communications are analyzed to demonstrate its superiority over conventional antenna technologies. Next, the pinching beamforming design is investigated. The corresponding power scaling law is first characterized. For the joint transmit and pinching design in the general multiple-waveguide case, 1) a pair of transmission strategies is proposed for PASS-based single-user communications to validate the superiority of PASS, namely sub-connected and fully connected structures; and 2) three practical protocols are proposed for facilitating PASS-based multi-user communications, namely waveguide switching, waveguide division, and waveguide multiplexing. A possible implementation of PASS in wideband communications is further highlighted. Moreover, the channel state information acquisition in PASS is elaborated with a pair of promising solutions. To overcome the high complexity and suboptimality inherent in conventional convex-optimization-based approaches, machine-learning-based methods for operating PASS are also explored, focusing on selected deep neural network architectures and training algorithms. Finally, several promising applications of PASS in next-generation wireless networks are highlighted.

Pinching-Antenna Systems (PASS): A Tutorial

TL;DR

PASS introduces a meter-scale, reconfigurable antenna paradigm that couples dielectric waveguides with distributed pinching antennas to flexibly shape propagation, create LoS links, and enable near-field gains. The paper develops signal and hardware models, analyzes information-theoretic limits for uplink and downlink, and proposes single- and multi-waveguide beamforming strategies, including wideband OFDM considerations. It also covers practical CSI acquisition, machine-learning approaches for optimization and sensing, and potential applications in localization, ISAC, PLS, and UAV-enabled networks. Together, these contributions establish PASS as a scalable, low-cost path toward flexible aerial, terrestrial, and indoor wireless networks with enhanced reliability and spectral efficiency. The work highlights open challenges in multi-user, EM-coupling-aware analyses, continuous CSI, and robust, low-latency implementations for real-time PASS operation.

Abstract

Pinching antenna systems (PASS) present a breakthrough among the flexible-antenna technologies, and distinguish themselves by facilitating large-scale antenna reconfiguration, line-of-sight creation, scalable implementation, and near-field benefits, thus bringing wireless communications from the last mile to the last meter. A comprehensive tutorial is presented in this paper. First, the fundamentals of PASS are discussed, including PASS signal models, hardware models, power radiation models, and pinching antenna activation methods. Building upon this, the information-theoretic capacity limits achieved by PASS are characterized, and several typical performance metrics of PASS-based communications are analyzed to demonstrate its superiority over conventional antenna technologies. Next, the pinching beamforming design is investigated. The corresponding power scaling law is first characterized. For the joint transmit and pinching design in the general multiple-waveguide case, 1) a pair of transmission strategies is proposed for PASS-based single-user communications to validate the superiority of PASS, namely sub-connected and fully connected structures; and 2) three practical protocols are proposed for facilitating PASS-based multi-user communications, namely waveguide switching, waveguide division, and waveguide multiplexing. A possible implementation of PASS in wideband communications is further highlighted. Moreover, the channel state information acquisition in PASS is elaborated with a pair of promising solutions. To overcome the high complexity and suboptimality inherent in conventional convex-optimization-based approaches, machine-learning-based methods for operating PASS are also explored, focusing on selected deep neural network architectures and training algorithms. Finally, several promising applications of PASS in next-generation wireless networks are highlighted.

Paper Structure

This paper contains 66 sections, 1 theorem, 90 equations, 19 figures, 4 tables.

Table of Contents

  1. Introduction
  2. The Road to Flexible-Antenna Systems
  3. PASS: From "Last Mile" to "Last Meter" Communications
  4. Large-Scale Antenna Reconfiguration
  5. Line-of-Sight Creation
  6. Scalable Implementation
  7. Near-Field Advantage
  8. Motivations and Contributions
  9. Notations and Organization
  10. Fundamentals of PASS
  11. Signal Model
  12. Hardware and Power Radiation Model
  13. Directional Coupler-based Model
  14. Multiport Network-based Model
  15. Discussion on Uplink Signal Model
  16. ...and 51 more sections

Key Result

Theorem 1

(Maximum Receive Power ouyang2025array) With equal power radiation equal_power_radiation_rule and continuous activation continuous_activation_constraint, the maximum value of the receive power $P_r$ is tightly approximated by where $f_{\rm{ub}}(x)\triangleq\frac{\ln^2(\sqrt{1+x^2}+x)}{x}$.

Figures (19)

  • Figure 1: Illustration of signal propagation in PASS.
  • Figure 2: The ratio of power coupled by the PA versus (a) the spacing between waveguide and PA with a fixed coupling length of 5 mm and (b) the coupling lengths with a fixed spacing of 2 mm. The results are generated following 9310539.
  • Figure 3: Multiport network-based model for the PA.
  • Figure 4: Lumped equivalent circuit of the three-port PA based on directional coupler mongia1999rf.
  • Figure 5: Three practical activation methods of PASS.
  • ...and 14 more figures

Theorems & Definitions (5)

  • Remark 1
  • Remark 2
  • Remark 3
  • Theorem 1
  • Remark 4