基于太赫兹智能反射面波束色散和分裂的快速感知方法

郝万明; 杨兰; 朱政宇; 李兴旺

doi:10.11999/JEIT240789

基于太赫兹智能反射面波束色散和分裂的快速感知方法

doi: 10.11999/JEIT240789

郝万明^{1, 2, ,},
杨兰¹,
朱政宇¹,
李兴旺³

1.
郑州大学电气与信息工程学院郑州 450001
2.
东南大学移动通信全国重点实验室南京 210096
3.
河南理工大学物理与电子信息学院焦作 454000

基金项目: 国家自然科学基金(62471440)，东南大学移动通信全国重点实验室开放研究基金(2024D12)

详细信息

作者简介:
郝万明：男，副教授，研究方向为毫米波通信、太赫兹通信、大规模MIMO技术、物理层安全技术、智能超表面技术等

杨兰：女，硕士生，研究方向为太赫兹通信、智能反射面技术等

朱政宇：男，副教授，研究方向为智能反射面技术、物理层安全技术、无线通信与信号处理等

李兴旺：男，副教授，研究方向为非正交多址接入(NOMA)、智能反射面通信、物理层安全、无线信息与能量协同传输等

通讯作者:
郝万明　iewmhao@zzu.edu.cn

中图分类号: TN92
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出版历程
- 收稿日期: 2024-09-12
- 修回日期: 2025-02-17
- 网络出版日期: 2025-02-26

Fast Sensing Method Based on Beam Squint and Beam Split of Terahertz Reflective Intelligent Surfaces

1.
School of Electrical and Information Engineering, Zhengzhou University, Zhengzhou 450001, China
2.
National Mobile Communications Research Laboratory, Southeast University, Nanjing 210096, China
3.
School of Physics and Electronic Information Engineering, Henan Polytechnic University, Jiaozuo 454000, China

Funds: The National Natural Science Foundation of China (62471440), The Open Research Fund of the National Mobile Communications Research Laboratory, Southeast University (2024D12)

摘要

摘要: 针对太赫兹智能反射面(RIS)系统中基于波束扫描感知耗时较长问题，该文提出一种基于太赫兹RIS波束色散和分裂的快速感知方法。通过在每个RIS元件处部署实时延(TTD)以动态调整波束色散程度，设置大阵列RIS单元间距以形成波束分裂效应，进而联合波束色散和分裂实现目标区域快速感知。具体地，将感知区域分为多个子区域，并基于RIS波束色散优化TTD和RIS反射元件相移，以覆盖单一子区域。同时，利用波束分裂无缝覆盖多个子区域，相比使用单一波束扫描感知显著降低了时间开销。而后，为减少回波信号路径损耗，在RIS处配置主动感知元件，用于直接接收并分析回波信号。在此基础上，推导出感知目标角度估计值及其均方根误差(RMSE)。仿真结果表明了所提快速感知方案的有效性。
- 太赫兹 /
- 智能反射面 /
- 波束色散 /
- 波束分裂 /
- 快速感知
Abstract: Objective Reﬂecting Intelligent Surface (RIS)-aided Terahertz (THz) communications are considered a key technology for future Sixth-Generation (6G) mobile communication systems addressing issues such as signal attenuation and Line-of-Sight (LoS) link blockage issues, due to their ultra-large bandwidth and low power consumption. However, the frequency independent characteristics of RIS elements can cause beam squint effects, where beams of different carriers are directed at different angles. Although this reduces the beam gain received by users, it can be leveraged to enhance sensing capabilities in sensing applications. Specifically, beam squint allows for simultaneous sensing of a target using multiple carrier beams directed in different directions. Existing studies have explored beam squint for beam training. For example, by studying near-field beam squint and True Time Delay (TTD) to generate beams that focus at multiple positions across different frequencies, enabling rapid beam training with reduced overhead. Additionally, combining TTD with beam squint and beam split for sensing extends the beam coverage area and enables the quick acquisition of user locations through feedback. However, there is no research on jointly utilizing beam squint and beam split for sensing in RIS-assisted THz systems, thus understanding the full potential of beam squint in sensing. This paper aims to conduct detailed research on the use of beam squint for sensing in such systems. Methods To address the time-consuming issue of beam scanning in RIS-assisted THz systems, a fast sensing method based on RIS beam squint and split effects is proposed. Each RIS element is equipped with a TTD mechanism to dynamically adjust the degree of beam squint, while the large array RIS units are spaced to induce the beam split effect. By combining beam quint and beam split, the method enables rapid sensing of the target area. Specifically, the sensing area is divided into multiple sub-areas, with the TTD and the phase shift at the RIS elements optimized to cover each sub-area based on beam squint. The beam split effect is then used to seamlessly cover multiple sub-areas, significantly reducing time overhead compared to single beam scanning. To further mitigate echo signal path loss, active sensing elements are configured at the RIS for direct reception and analysis of the echo signals. The estimation of the sensing target’s angle, along with its root mean square error (RMSE), is derived based on this approach. Results and Discussions Consider the RIS-assisted THz sensing system model (Fig. 1). By deriving the channel and beam gain expressions, the beam patterns under the beam squint effect are analyzed (Fig. 2). Based on the internal structural diagram of the RIS (Fig. 4), the beam split effect is examined by varying the spacings between RIS elements (Fig. 5), with corresponding beam patterns (Fig. 3) presented for different spacings. Next, the RIS structure utilizing TTD (Fig. 6) allows for flexible adjustment of the beam squint and split degrees, significantly expanding the beam coverage area compared to traditional beam squint and split methods (Fig. 7, Fig. 8). Additionally, to fine-tune the gaps between adjacent split beams, the ATDS method is proposed. By combining beam squint and beam split, this method achieves near-seamless coverage of all subareas (Fig. 9). Finally, the target direction is estimated by analyzing the echo signals received at the RIS-SE, based on the RSME. The simulation results demonstrate the relationship between sensing accuracy and the number of carriers (Fig.10, Fig. 11), confirming the effectiveness and feasibility of the rapid sensing method combining beam squint and split. Conclusions This paper investigates the issues of beam squint and beam split in RIS-assisted THz systems and proposes a rapid sensing method that combines both effects. Specifically, TTD is used to adjust the direction of subcarrier beams based on beam squint. To expand the sensing area, the combined effects of beam squint and beam split, divide the sensing area into multiple subareas, which are simultaneously covered by multiple carrier beams within a single OFDM block. The target direction is then estimated based on echo signals received at the RIS-SE, with sensing error measured using the RMSE between the true and estimated values. Simulation results demonstrate the feasibility and effectiveness of the proposed rapid sensing method. However, it is found that while the beam squint effect significantly reduces beam gain and communication performance, it expands the beam coverage area and enhances sensing capabilities. Therefore, in an integrated sensing and communication system, the impact of beam squint should be considered at different stages. Future research will focus on improving the performance of such integrated systems.
- Terahertz (THz) /
- Reflecting Intelligent Surface (RIS) /
- Beam squint /
- Beam split /
- Fast sensing

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图 1 RIS辅助太赫兹感知系统模型

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图 2 波束色散效应下的波束图样

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图 3 波束分裂效应下的波束图样($P = 3$)

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图 4 RIS元件中有关二极管结构电路图

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图 5 RIS元件不同间距的阵列图

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图 6 基于TTD的RIS元件结构图

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图 7 基于TTD的波束色散

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图 8 基于TDS的联合RIS波束色散和分裂 (P=2)

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图 9 基于ATDS的联合RIS波束色散和分裂 ($P = 2$)

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图 10 基于TDS的RMSE与载波数目之间的关系

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图 11 基于ATDS的RMSE与载波数目之间的关系

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