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

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.