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IRS-aided Near-field Communication: Prospects and Challenges with Codebook Approach

Ryuhei Hibi, Hiroaki Hashida, Yuichi Kawamoto, Nei Kato

TL;DR

The paper addresses the near-field challenges of IRS-aided communication at high frequencies, where plane-wave-based beamforming becomes ineffective as IRS size grows. It advances a codebook-based beamtraining approach and introduces nonuniform 3D codebooks guided by a plane-wave approximation error analysis and a composite control accuracy index, supported by experiments and simulations. Key findings show that beamfocusing outperforms beamforming in the near-field, and that nonuniform 3D codebooks achieve higher SNR with fewer codewords compared to 2D or uniform 3D codebooks, while 2D codebooks can still be viable under strict overhead constraints. The work offers scalable, practical IRS control strategies for next-generation wireless systems, particularly for large-scale, millimeter-wave and terahertz deployments, enabling efficient near-field operation and paving the way for multiuser and mobile extensions.

Abstract

Intelligent reflecting surfaces (IRSs) are gaining attention as a low-cost solution to the coverage reduction in high-frequency bands used in next-generation communications. IRSs achieve low costs by controlling only the reflection of radio waves. However, to improve further the propagation environment, larger IRS sizes are required owing to their inability to amplify and retransmit signals. As the IRS size increases, the near-field region expands, requiring beamfocusing instead of beamforming, which is extensively used in existing research. This results in considerable overhead for IRS control decisions. To address this, constructing a codebook that achieves high communication quality with fewer IRS control patterns is effective. This article presents experimental results demonstrating the effectiveness of beamfocusing, construction policy for nonuniform three-dimensional codebooks, and simulation evaluation results of communication performance when operating IRSs with various codebooks. We believe these insights will foster further value for IRSs in next-generation communications.

IRS-aided Near-field Communication: Prospects and Challenges with Codebook Approach

TL;DR

The paper addresses the near-field challenges of IRS-aided communication at high frequencies, where plane-wave-based beamforming becomes ineffective as IRS size grows. It advances a codebook-based beamtraining approach and introduces nonuniform 3D codebooks guided by a plane-wave approximation error analysis and a composite control accuracy index, supported by experiments and simulations. Key findings show that beamfocusing outperforms beamforming in the near-field, and that nonuniform 3D codebooks achieve higher SNR with fewer codewords compared to 2D or uniform 3D codebooks, while 2D codebooks can still be viable under strict overhead constraints. The work offers scalable, practical IRS control strategies for next-generation wireless systems, particularly for large-scale, millimeter-wave and terahertz deployments, enabling efficient near-field operation and paving the way for multiuser and mobile extensions.

Abstract

Intelligent reflecting surfaces (IRSs) are gaining attention as a low-cost solution to the coverage reduction in high-frequency bands used in next-generation communications. IRSs achieve low costs by controlling only the reflection of radio waves. However, to improve further the propagation environment, larger IRS sizes are required owing to their inability to amplify and retransmit signals. As the IRS size increases, the near-field region expands, requiring beamfocusing instead of beamforming, which is extensively used in existing research. This results in considerable overhead for IRS control decisions. To address this, constructing a codebook that achieves high communication quality with fewer IRS control patterns is effective. This article presents experimental results demonstrating the effectiveness of beamfocusing, construction policy for nonuniform three-dimensional codebooks, and simulation evaluation results of communication performance when operating IRSs with various codebooks. We believe these insights will foster further value for IRSs in next-generation communications.

Paper Structure

This paper contains 12 sections, 6 figures.

Table of Contents

  1. Introduction
  2. Challenges of IRS-aided Near-field Communications
  3. Experimental Study
  4. Beamtraining Overhead
  5. Efficient Codebook Construction
  6. 2D Codebook
  7. 3D Codebook
  8. Nonuniform 3D Codebook Construction
  9. Plane-wave Approximation Error
  10. Control Accuracy Index
  11. Performance Evaluation
  12. Summary and Future direction

Figures (6)

  • Figure 1: Traditional and prospects of intelligent reflecting surface (IRS) control methods in the near-field.
  • Figure 2: Experimental environment for beamforming and beamfocusing by IRS.
  • Figure 3: Experimental results for beamforming and beamfocusing
  • Figure 4: Plane-wave approximation error for each angle vs. distance.
  • Figure 5: Control accuracy index and nonuniform three-dimensional codebook.
  • ...and 1 more figures