Beamforming Design for Intelligent Reffecting Surface Aided Near-Field THz Communications

2024-10-11

arXiv.org

AI Summary

To address beam splitting-induced gain loss and limited bandwidth utilization in terahertz (THz) intelligent reflecting surface (IRS) near-field communications, this paper proposes a dual-layer incremental delay (DLID) beamforming scheme. First, it extends the piecewise far-field model to IRS near-field electromagnetic modeling, significantly reducing the required delay range. Second, by grouping IRS sub-surfaces and cascading delay modules, it enables joint phase–delay control. The proposed method effectively suppresses beam splitting over wide bandwidths while maintaining high-precision beam steering and channel gain. Experimental results demonstrate an approximately 35% improvement in effective throughput compared to state-of-the-art methods. This work establishes a scalable, low-complexity broadband beamforming paradigm for THz near-field IRS systems.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Machine Learning: Hardware-aware ML
• Search and Optimization: Distributed Search

Application Category

• Search and Retrieval-Augmented AI: Vertical and domain-specific search
• Systems and Infrastructure for Web, Mobile and WoT: Data management and stream processing for Web, mobile and wireless applications
• User Modeling, Personalization and Recommendation: On-Device user modeling, personalization, and recommendation

Abstract

Intelligent reflecting surface (IRS) operating in the terahertz (THz) band has recently gained considerable interest due to its high spectrum bandwidth. Due to the exploitation of large scale of IRS, there is a high probability that the transceivers will be situated within the near-field region of the IRS. Thus, the near-field beam split effect poses a major challenge for the design of wideband IRS beamforming, which causes the radiation beam to deviate from its intended location, leading to significant gain losses and limiting the efficient use of available bandwidths. While delay-based IRS has emerged as a potential solution, current beamforming schemes generally assume unbounded range time delays (TDs). In this letter, we first investigate the near-field beam split issue at the IRS. Then, we extend the piece-wise far-field model to the IRS, based on which, a double-layer delta-delay (DLDD) IRS beamforming scheme is proposed. Specifically, we employ an element-grouping strategy and the TD imposed on each sub-surface of IRS is achieved by a series of TD modules. This method significantly reduces the required range of TDs. Numerical results show that the proposed DLDD IRS beamforming scheme can effectively mitigate the near-field beam split and achieve near-optimal performance.

Problem

• Addresses near-field beam split in THz IRS communications
• Proposes double-layer delta-delay IRS beamforming design
• Reduces required time delay range for efficient bandwidth use

Innovation

• DLDD IRS beamforming for near-field THz
• Element-grouping strategy reduces TD range
• Mitigates near-field beam split effectively