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Continuous-Time Channel Prediction Based on Tensor Neural Ordinary Differential Equation

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China Communications 2024年第1期21卷 163-174页

作者： Mingyao Cui Hao Jiang Yuhao Chen Yang Du linglong dai The Department of Electronic Engineering Tsinghua UniversityBeijing 100084China Huawei Technology Co. Ltd.Chengdu Research InstituteChengdu 611730China

Channel prediction is critical to address the channel aging issue in mobile *** channel prediction techniques are mainly designed for discrete channel prediction,which can only predict the future channel in a fixed time slot per frame,while the other intra-frame channels are usually recovered by ***,these approaches suffer from a serious interpolation loss,especially for mobile millimeter-wave *** solve this challenging problem,we propose a tensor neural ordinary differential equation(TN-ODE)based continuous-time channel prediction scheme to realize the direct prediction of intra-frame ***,inspired by the recently developed continuous mapping model named neural ODE in the field of machine learning,we first utilize the neural ODE model to predict future continuous-time *** improve the channel prediction accuracy and reduce computational complexity,we then propose the TN-ODE scheme to learn the structural characteristics of the high-dimensional channel by low-dimensional learnable *** results show that the proposed scheme is able to achieve higher intra-frame channel prediction accuracy than existing schemes.

关键词： channel prediction massive multipleinput-multiple-output millimeter-wave communications ordinary differential equation

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Reconfigurable Intelligent Surfaces for 6G:Nine Fundamental Issues and One Critical Problem

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Tsinghua Science and Technology 2023年第5期28卷 929-939页

作者： Zijian Zhang linglong dai Department of Electronic Engineering Tsinghua Universityand also with Beijing National Research Center for Information Science and Technology(BNRist)Beijing 100084China

Thanks to the recent advances in metamaterials,Reconfigurable Intelligent Surface(RIS)has emergedas a promising technology for future 6G wireless *** from its high array gain,low cost,and low power consumption,RISs are expected to greatly enlarge signal coverage,improve system capacity,andincrease energy *** this article,we systematically overview the emerging RIS technology with the focuson its key basics,nine fundamental issues,and one critical ***,we first explain the RIS basics,including its working principles,hardware structures,and potential benefits for *** on thesebasics,nine fundamental issues of RISs,such as“What’s the differences between RISs and massive MIMO?”and“Is RIS really intelligent?”,are explicitly addressed to elaborate its technical features,distinguish it from existingtechnologies,and clarify some misunderstandings in the ***,one critical problem of RISs is revealedthat,due to the“multiplicative fading”effect,existing passive RISs can hardly achieve visible performance gains inmany communication scenarios with strong direct *** address this critical problem,a potential solution calledactive RISs is introduced,and its effectiveness is demonstrated by numerical simulations.

关键词： Reconfigurable Intelligent Surface(RIS) sixth generation mobile system(6G) wireless communications

Near-field wideband channel estimation for extremely large-scale MIMO

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Science China(Information Sciences) 2023年第7期66卷 283-296页

作者： Mingyao CUI linglong dai Department of Electronic Engineering Tsinghua University Beijing National Research Center for Information Science and Technology(BNRist)

Extremely large-scale multiple-input-multiple-output(XL-MIMO) at millimeter-wave(mm Wave)and terahertz(THz) bands plays an important role in supporting extreme high beamforming gain as well as ultra-wideband spectrum resources. Unfortunately, accurate wideband XL-MIMO channel estimation suffers from a new challenge called the near-field beam split effect. Prior studies either neglect the accurate nearfield channel model or fail to exploit the beam split effect, resulting in poor channel estimation accuracy for wideband XL-MIMO. To tackle this problem, this paper proposes a bilinear pattern detection(BPD)-based approach to accurately recover the wideband XL-MIMO channel. Specifically, by analyzing the characteristics of near-field wideband channels, we first reveal the bilinear pattern of the near-field beam split effect, which implies that the sparse support set of near-field channels in both the angle and the distance domains can be regarded as a linear function against frequency. Then, inspired by the classical simultaneously orthogonal matching pursuit technique, we use the bilinear pattern to estimate the angle-of-arrival(Ao A) and distance parameters of each near-field path component at all frequencies. In this way, the entire wideband XL-MIMO channel can be recovered by compressed sensing algorithms. Moreover, we provide the computational complexity of the proposed algorithm compared with existing algorithms. Finally, simulation results demonstrate that our scheme can achieve the accurate estimation of the near-field wideband XL-MIMO channel in the presence of near-field beam split effect.

关键词： XL-MIMO wideband near-field beam split channel estimation

面向6G的信息超材料和智能超表面通信与感知技术

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无线电通信技术 2024年第2期50卷 219-223页

作者：李廉林戴凌龙崔铁军北京大学电子学院北京100871 琶洲实验室(黄埔) 广东广州510555 清华大学电子工程系北京100084 东南大学毫米波国家重点实验室江苏南京210096

目前,信息超材料和智能超表面(Reconfigurable Intelligent Surface, RIS)已经在全球范围内受到了产业界与学术界的广泛关注,在5G和未来6G网络中具有重要机遇和应用前景。针对信息超材料和智能超表面在6G时代通信和感知的需求,分析与阐... 详细信息

目前,信息超材料和智能超表面(Reconfigurable Intelligent Surface, RIS)已经在全球范围内受到了产业界与学术界的广泛关注,在5G和未来6G网络中具有重要机遇和应用前景。针对信息超材料和智能超表面在6G时代通信和感知的需求,分析与阐述了基于信息超材料和RIS的通信与感知理论、基本算法和系统设计,并对信息超材料和RIS的进一步发展进行了展望。

关键词： 5G/6G网络信息超材料智能超表面通信感知

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Joint Beamforming Design for RIS-Assisted Cell-Free Network with Multi-Hop Transmissions

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Tsinghua Science and Technology 2023年第6期28卷 1115-1127页

作者： Decai Shen Zijian Zhang linglong dai Department of Electronic Engineering Tsinghua UniversityBeijing 100084China Beijing National Research Center for Information Science and Technology(BNRist) Beijing 100084China

The collaboration of multiple Reconfigurable Intelligent Surfaces(RISs)and Access Points(APs)enjoys advantages of capacity enhancement,power saving,etc.,making the RIS-assisted cell-free network an important architecture for future *** to most existing works on RIS-assisted communications,the multi-hop link among RISs,i.e.,the reflecting link including more than one RISs,is usually ignored in RIS-assisted cell-free *** these scenarios,however,since multiple RISs are closely deployed,we find that the multi-hop channels should not be simply ignored due to their potential for capacity ***,to the best of our knowledge,there is no work exploring the multi-hop transmission of RIS-assisted cell-free *** fill in this blank,we investigate the multi-hop transmission of RIS-assisted cell-free networks,including the multi-hop channel model and the corresponding beamforming ***,we propose a general multi-hop transmission model,which takes the direct links,single-reflecting links,and multi-hop links into *** on this model,we formulate a beamforming design problem in an RIS-assisted cell-free network,which allows us to maximize the multi-user sum-rate with considering the impact of multi-hop *** address the non-convexity of the formulated problem,a joint active and passive beamforming scheme is proposed to solve the ***,by utilizing fractional programming,we decouple the coupled beamforming parameters in the problem,and then these parameters are alternately optimized until the convergence of the *** results verify that the consideration for multi-hop links is necessary,and the capacity performance of the proposed scheme is 20%higher than those of the existing schemes.

关键词： Reconfigurable Intelligent Surface(RiS) cell-free network multi-hop transmissions beamforming

Transformer-based downlink precoding design in massive MIMO systems for 5G-advanced and 6G

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Science China(Information Sciences) 2023年第9期66卷 303-304页

作者： Hao JIANG linglong dai Department of Electronic Engineering Tsinghua University Beijing National Research Center for Information Science and Technology(BNRist)

Massive multiple-input multiple-output(MIMO) with a larger number of base station(BS) antennas has been regarded as a key technique to support digital twins and the metaverse in future 5G-Advanced and 6G [1]. To realize the expected high-speed transmission, the channel information state(CSI) is required to design the precoding in BS.

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Fusion of electromagnetic world and digital world through information metasurface: an interview with Tie Jun Cui

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National Science Review 2023年第8期10卷 64-67页

作者：戴凌龙 Tsinghua University

Metasurfaces consist of subwavelength artificial elements(also called meta-atoms) arranged in a two-dimensional fashion. Through careful design of these elements, the metasurfaces can control the amplitude, phase, fre...

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Codebook Design and Beam Training for Extremely Large-Scale RIS:Far-Field or Near-Field?

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China Communications 2022年第6期19卷 193-204页

作者： Xiuhong Wei linglong dai Yajun Zhao Guanghui Yu Xiangyang Duan Beijing National Research Center for Information Science and Technology(BNRist)as well as the Department of Electronic Engineering Tsinghua UniversityBeijing 100084China ZTE Corporation Shenzhen 518038China

Reconfigurable intelligent surface(RIS)is more likely to develop into extremely large-scale RIS(XL-RIS)to efficiently boost the system capacity for future 6 G *** training is an effective way to acquire channel state information(CSI)for *** beam training schemes rely on the far-field ***,due to the large aperture of XL-RIS,the scatters are more likely to be in the near-field region of *** far-field codebook mismatches the near-field channel ***,the existing far-field beam training scheme will cause severe performance loss in the XL-RIS assisted nearfield *** solve this problem,we propose the efficient near-field beam training schemes by designing the near-field codebook to match the nearfield channel ***,we firstly design the near-field codebook by considering the near-field cascaded array steering vector of ***,the optimal codeword for XL-RIS is obtained by the exhausted training *** reduce the beam training overhead,we further design a hierarchical nearfield codebook and propose the corresponding hierarchical near-field beam training scheme,where different levels of sub-codebooks are searched in turn with reduced codebook *** results show the proposed near-field beam training schemes outperform the existing far-field beam training scheme.

关键词： extremely large-scale RIS near-field codebook design beam training

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Editorial

Intelligent and Converged Networks 2022年第1期3卷 I0001-I0003页

作者： linglong dai Chan-Byoung Chae Shi Jin Marco Di Renzo Rui Zhang Beijing National Research Center for Information Science and Technology(BNRist)and the Department of Electronic Engineering Tsinghua UniversityBeijing 100084China School of Integrated Technology Yonsei Institute of Convergence TechnologyYonsei UniversityIncheon 406-840Republic of Korea. National Mobile Communications Research Laboratory Southeast UniversityNanjing 210096China. the UniversitéParis-Saclay CNRSCentraleSupélecLaboratoire des Signaux et Systèmes3 Rue Joliot-Curie91192 Gif-sur-YvetteFrance. Department of Electrical and Computer Engineering National University of SingaporeSingapore 117583Singapore

Reconfigurable Intelligent Surface(RIS),also known as intelligent reflecting surface or large intelligent surface,is an emerging new physical-layer technology in the field of wireless *** basic idea of RIS is to deploy a reconfigurable passive array in the environment to manipulate the propagation of electron-magnetic *** promises a new design paradigm for wireless communications,where the wireless propagation environment can be dynamically controlled,which is substantially different from the conventional design that focuses only on the transmitter and *** RIS-aided wireless communications,some of the current methodologies in conventional communication systems need to be revised,and some novel solutions are required to realize the potential benefits of the *** the number of publications about RIS has recently sharply increased,there are still many challenging issues to be extensively investigated,such as the RIS channel modeling,fundamental performance limits,the system design,joint optimization of the RIS and the transceivers,channel state information acquisition,and interdisciplinary applications.

关键词： passive sharply revised