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Pinching Antennas: Principles, Applications and Challenges
Zheng Yang, Ning Wang, Yanshi Sun, Zhiguo Ding, Robert Schober, George K. Karagiannidis, Vincent W. S. Wong, Octavia A. Dobre
TL;DR
Existing flexible antennas mainly address small-scale fading and have limited ability to create LoS links or flexibly scale antenna configurations. This article introduces pinching antennas, which use dielectric particles on waveguides, and surveys their systems, 6G applications, and research challenges. The paper presents adjustable LoS links, flexible antenna configurations, and communication designs spanning multiple waveguides, NOMA, ISAC, and related applications.
Problem
Existing flexible-antenna systems primarily address small-scale fading in NLoS conditions, while their limited movement and antenna flexibility restrict LoS establishment and straightforward antenna scaling.
Method
The article develops the principles of pinching antennas, surveys single- and multiple-waveguide system designs, and discusses 6G applications and future research directions.
Results
Pinching antennas provide strong LoS links and flexible antenna-array configurations, with discussed designs including joint beamforming, position optimization, and NOMA.
Takeaways & Limitations
Pinching antennas offer a flexible platform for communication systems and emerging 6G scenarios including ISAC, NGMA, SAGIN, and vehicular networks.
Abstract
from arXiv · showhide
Flexible-antenna systems, such as fluid antennas and movable antennas, have been recognized as key enabling technologies for sixth-generation (6G) wireless networks, as they can intelligently reconfigure the effective channel gains of the users and hence significantly improve their data transmission capabilities. However, existing flexible-antenna systems have been designed to combat small-scale fading in non-line-of-sight (NLoS) conditions. As a result, they lack the ability to establish line-of-sight links, which are typically 100 times stronger than NLoS links. In addition, existing flexible-antenna systems have limited flexibility, where adding/removing an antenna is not straightforward. This article introduces an innovative flexible-antenna system called pinching antennas, which are realized by applying small dielectric particles to waveguides. We first describe the basics of pinching-antenna systems and their ability to provide strong LoS links by deploying pinching antennas close to the users as well as their capability to scale up/down the antenna system. We then focus on communication scenarios with different numbers of waveguides and pinching antennas, where innovative approaches to implement multiple-input multiple-output and non-orthogonal multiple access are discussed. In addition, promising 6G-related applications of pinching antennas, including integrated sensing and communication and next-generation multiple access, are presented. Finally, important directions for future research, such as waveguide deployment and channel estimation, are highlighted.
I. INTRODUCTION
Existing flexible antennas reconfigure channels mainly against small-scale fading but have limited ability to restore LoS links or flexibly change antenna count. The article introduces pinching antennas and outlines their principles, system designs, applications, and research directions.
- Background: 6G networks require ultra-high-speed transmission, seamless connectivity, and massive device density across diverse wireless environments.Achievable data rate depends primarily on channel conditions between transceivers.
- Motivation: Existing fluid and movable antennas dynamically reconfigure channels affected by multipath fading but typically move only a few wavelengths.Such movement has little impact on large-scale path loss and may not restore blocked LoS links.
- Contribution: Pinching antennas activate adjustable radiation points along waveguides using small dielectric particles, enabling flexible placement without additional hardware.The approach is intended to establish adjustable LoS links in dynamic or obstructed locations.
- Article scope: The article examines pinching-antenna principles, different waveguide deployments, potential system designs, and future research directions.Its coverage includes basics, single- and multiple-waveguide communication scenarios, 6G applications, and open problems.
II. RADIO WAVE PROPAGATION AND WAVEGUIDES
Wireless links use direct LoS or obstructed NLoS paths, while waveguides confine electromagnetic propagation and modify the guided wavelength according to material properties.
- Radio channels: LoS paths are direct and unobstructed, whereas NLoS paths involve obstacles, reflection, or diffraction that produce signal degradation and multipath fading.At 28 GHz in outdoor microcellular scenarios, NLoS path loss is more than 20 dB higher than LoS path loss.
- Waveguides: A waveguide directs electromagnetic waves primarily along one direction while restricting propagation in others.A dielectric waveguide uses a higher-permittivity inner material surrounded by another dielectric material.
- Guided wavelength: The wavelength inside a dielectric waveguide is shorter than its free-space wavelength because the structure confines the wave.The supplied expression relates guided wavelength to free-space wavelength and inner-material relative permittivity.
C. Basics of Pinching Antennas
Pinching antennas use dielectric waveguides and localized dielectric pinches to create adjustable radiation sites, enabling nearby or newly established LoS links in obstructed environments.
- Operating principle: Pinching a dielectric waveguide with a different dielectric material creates radiating radio waves at selected points along the waveguide.The concept was experimentally verified using 60 GHz radio-frequency signals and can create communication zones around the waveguide.
- LoS enhancement: Placing a pinching antenna near a user reduces transmitter-user distance and strengthens an existing LoS link.This positioning is presented as a way to mitigate large-scale path loss.
- Blocked or NLoS users: Adjusting a pinching antenna can create an LoS link for a user whose conventional path is NLoS, where the expected gain follows the higher NLoS path loss.The passage states that NLoS path loss is much higher than LoS path loss.
- Extreme environments: In heavily obstructed environments, repositioning a pinching antenna can establish either an LoS or NLoS link where conventional systems may lack reliable transmission.The cited example includes tall buildings, enclosed spaces, and tunnels.
- Deployment scope: A single-waveguide deployment supports configurations with either one or multiple activated pinching antennas.The section introduces these configurations as separate application cases.
A. Single Waveguide with a Single Activated Pinching Antenna
With one waveguide and one activated pinching antenna, users can be served sequentially through OMA or simultaneously in groups, while adjustable locations create communication zones.
- Communication zones: Adjustable pinching-antenna locations create communication zones in the surrounding area and distinguish the system from conventional fixed-antenna arrangements.The figure contrasts conventional-antenna and pinching-antenna systems.
- OMA transmission: A single pinching antenna can serve N users through TDMA by activating at N different waveguide locations across N time slots.Separate dielectric pinches may be pre-deployed along a track parallel to the waveguide to simplify implementation.
- Grouped transmission: A pinching antenna positioned above a user group can serve multiple users simultaneously when fewer activation points are available than users.This configuration parallels the conventional situation in which the number of antennas is smaller than the number of users.
- Multiple access: For multicast, OMA can serve different groups in separate time slots, whereas unicast can use hybrid OMA with group-specific time slots and subcarriers.The schemes distinguish between serving identical information to a group and serving users individually.
B. Single Waveguide with Multiple Activated Pinching Antennas
With multiple activated pinching antennas on one waveguide, radiated signals form a single-stream architecture whose antenna positions dynamically tune beamforming coefficients and effective user channels.
- Architecture: SWMAP uses one feeder and one data stream while electromagnetic signals leak from multiple activated pinching antennas.Adjacent antennas radiate with propagation-induced phase shifts.
- Reconfigurable channels: Adjusting pinching-antenna positions dynamically tunes beamforming coefficients, free-space phase shifts, and large-scale path loss.This makes users’ effective channel gains reconfigurable.
- Multiple-waveguide extension: Multiple waveguides support MWSAP and MWMAP architectures, with each waveguide fed by a single RF chain.These architectures extend pinching-antenna systems beyond a single waveguide.
- Communication schemes: Pinching antennas can implement MIMO and NOMA through configurable waveguide and antenna arrangements.The paper presents these as innovative uses of multiple-waveguide systems.
A. New Forms of MIMO with Reconfigurable Channels
Multiple pinching antennas on multiple waveguides can reshape users’ channel space, increasing the possibility of jointly approaching interference suppression and intended-signal maximization.
- MIMO design challenge: Conventional ZF suppresses interference whereas MRC maximizes intended-signal strength, creating a design tension between the two goals.The ideal upper bound would achieve both simultaneously.
- Evaluation scenario: Three parallel waveguides, each with one optimized pinching antenna, are evaluated for three randomly distributed users.The scenario is illustrated in Fig. 3(a).
- Reconfigurable channels: Reconfiguring channel gains adjusts the structure of users’ channel space, increasing the possibility of approaching the ideal MIMO upper bound.This links antenna-location optimization with beamforming performance.
- Results: Pinching-antenna data rates are much higher than conventional-antenna rates and can exceed the conventional system’s upper limit.The comparison includes ZF and MRC beamforming results.
B. NOMA-Assisted Pinching-Antenna Systems
NOMA can complement pinching-antenna systems when available waveguides are fewer than users, while adjustable channel gains provide greater flexibility in user ordering and fairness.
- System design: NOMA is proposed when the number of waveguides is smaller than the number of users, with users grouped into clusters sharing beams.Signals within a cluster are separated through the power domain.
- Channel-gain control: Pinching-antenna systems can adjust users’ effective channel gains, unlike conventional systems with fixed channel gains.This creates additional flexibility for NOMA performance improvement.
- Fairness: Intelligently changing channel-gain ordering can provide more personalized service and improve user fairness.Conventional NOMA instead orders users by their fixed channel gains and allocates more power to weaker users.
B. Pinching-Antenna Assisted NGMA
Pinching antennas support NGMA by creating spatially distinct beams and controlling signal strength for nearby users, while related deployments can establish adaptable LoS links in integrated networks and vehicular environments.
- NGMA motivation: NGMA targets capacity and spectrum-efficiency limitations in high-density, large-scale, low-latency environments.It introduces innovative multiple-access methods beyond traditional approaches.
- Spatial separation: Flexible waveguide deployment and dynamic antenna positioning can create distinct spatial beams for users located close together.This helps differentiate users in challenging NOMA scenarios.
- Power control: Adjustable antenna placement and phase shifts provide control over signal strength, supporting power allocation for weaker-channel users.The text connects this control with efficient resource allocation.
- SAGIN applications: Waveguide-mounted pinching antennas can create strong satellite LoS links and dynamically adapt to changing SAGIN environments.The proposed placements include tall-building edges and unmanned aerial vehicles.
- Vehicular applications: Waveguides along roads and bridges can support stable, high-quality LoS links for vehicular networks despite obstacles.Dynamic radiation-point activation also supports real-time connections for autonomous driving.
E. Pinching-Antenna Assisted AI
Pinching antennas can dynamically direct resources toward data-intensive nodes and hotspot areas, supporting the low-latency, high-bandwidth demands of future AI applications. Their radiating points and paths can also be adjusted to maintain stable connectivity.
- Dynamic radiation positioning directs resources toward data-intensive nodes and hotspot areas.This enables pinching-antenna systems to respond to changing data demands.
- Pinching-antenna systems support the low-latency, high-bandwidth data showering required by future AI applications.
- Dynamically adjustable radiating points and paths help ensure stable and continuous connectivity for devices.
- The design of pinching-antenna systems remains in its early stages, leaving important open issues and challenges.
B. Topology and Network Optimization for Pinching-Antenna Systems
Future pinching-antenna systems require joint optimization of waveguide and antenna placement, robust phase-aware design, and efficient channel-estimation methods. Uplink development also remains constrained by phase alignment across waveguide and free-space propagation.
- Topology and Network Optimization: Multiple waveguides and pinching antennas can improve coverage, but their number and placement require joint optimization.Parallel, cross-pattern, and distributed layouts offer different coverage and management arrangements.
- Channel Estimation: Channel estimation must recover high-dimensional information from low-dimensional observations because each waveguide uses one RF chain for multiple pinching antennas.Unequal antenna spacing and dynamically adjusted activation locations also increase beam-training overhead.
- Uplink Transmission: Uplink transmission remains at an infancy stage, with accumulated waveguide and free-space phase shifts potentially misaligning multi-user signals.Accurate dynamic phase compensation is needed for effective signal power combining and demodulation at the base station.
E. Machine Learning (ML) for Pinching-Antenna Systems
Machine learning is proposed for difficult non-convex pinching-antenna placement problems, while combining pinching antennas with other flexible antennas could address dynamic, multipath-rich urban environments. The paper situates these approaches within broader 6G applications.
- Machine Learning for Pinching-Antenna Systems: Machine learning can seek sub-optimal solutions for non-convex pinching-antenna placement problems that are difficult for conventional methods.The non-convexity arises from phase shifts determined by pinching-antenna locations.
- Combining Flexible Antennas: Combining distributed pinching antennas with fluid or movable antennas could provide stable links while exploiting spatial diversity in dense urban environments.Pinching antennas contribute strong LoS capabilities, whereas user-side flexible antennas adjust location and direction.
- Applications and Outlook: The paper discusses pinching antennas for strong LoS links, flexible array configurations, joint beamforming and position optimization, NOMA, and emerging 6G applications.The listed applications include ISAC, NGMA, SAGIN, vehicular networks, and AI.