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| 1 | Geometric Mean Decomposition Based Hybrid Precoding for Millimeter-Wave Massive MIMO显示文摘Hybrid precoding can reduce the number of required radio frequency(RF)chains in millimeter-Wave(mmWave) massive MIMO systems. However, existing hybrid precoding based on singular value decomposition(SVD) requires the complicated bit allocation to match the different signal-to-noise-ratios(SNRs) of different sub-channels. In this paper,we propose a geometric mean decomposition(GMD)-based hybrid precoding to avoid the complicated bit allocation. Specifically,we seek a pair of analog and digital precoders sufficiently close to the unconstrained fully digital GMD precoder. To achieve this, we fix the analog precoder to design the digital precoder, and vice versa. The analog precoder is designed based on the orthogonal matching pursuit(OMP) algorithm, while GMD is used to obtain the digital precoder. Simulations show that the proposed GMD-based hybrid precoding achieves better performance than the conventional SVD-based hybrid precoding with only a slight increase in complexity. | Tian Xie Linglong Dai Xinyu Gao Muhammad Zeeshan Shakir Jianjun Li | 2018 | China Communications2018，15，5： | 17 |
| 2 | Codebook Design and Beam Training for Extremely Large-Scale RIS:Far-Field or Near-Field?显示文摘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 communications.Beam training is an effective way to acquire channel state information(CSI)for XL-RIS.Existing beam training schemes rely on the far-field codebook.However,due to the large aperture of XL-RIS,the scatters are more likely to be in the near-field region of XL-RIS.The far-field codebook mismatches the near-field channel model.Thus,the existing far-field beam training scheme will cause severe performance loss in the XL-RIS assisted nearfield communications.To solve this problem,we propose the efficient near-field beam training schemes by designing the near-field codebook to match the nearfield channel model.Specifically,we firstly design the near-field codebook by considering the near-field cascaded array steering vector of XL-RIS.Then,the optimal codeword for XL-RIS is obtained by the exhausted training procedure.To 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 size.Simulation results show the proposed near-field beam training schemes outperform the existing far-field beam training scheme. | Xiuhong Wei Linglong Dai Yajun Zhao Guanghui Yu Xiangyang Duan | 2022 | China Communications2022，19，6： | 3 |
| 3 | Wideband Channel Estimation for THz Massive MIMO显示文摘Terahertz(THz)communication is considered to be a promising technology for future 6G network.To overcome the severe attenuation and relieve the high power consumption,massive multipleinput multiple-output(MIMO)with hybrid precoding has been widely considered for THz communication.However,accurate wideband channel estimation,which is essential for hybrid precoding,is challenging in THz massive MIMO systems.The existing wideband channel estimation schemes based on the ideal assumption of common sparse channel support will suffer from a severe performance loss due to the beam split effect.In this paper,we propose a beam split pattern detection based channel estimation scheme to realize reliable wideband channel estimation in THz massive MIMO systems.Specifically,a comprehensive analysis on the angle-domain sparse structure of the wideband channel is provided by considering the beam split effect.Based on the analysis,we define a series of index sets called as beam split patterns,which are proved to have a one-to-one match to different physical channel directions.Inspired by this one-to-one match,we propose to estimate the physical channel direction by exploiting beam split patterns at first.Then,the sparse channel supports at different subcarriers can be obtained by utilizing a support detection window.This support detection window is generated by expanding the beam split pattern which is determined by the obtained physical channel direction.The above estimation procedure will be repeated path by path until all path components are estimated.Finally,the wideband channel can be recovered by calculating the elements on the total sparse channel support at all subcarriers.The proposed scheme exploits the wideband channel property implied by the beam split effect,i.e.,beam split pattern,which can significantly improve the channel estimation accuracy.Simulation results show that the proposed scheme is able to achieve higher accuracy than existing schemes. | Jingbo Tan Linglong Dai | 2021 | China Communications2021，18，5： | 3 |
| 4 | Positioning with OFDM signals for the next generation GNSS显示文摘 | DAI LINGLONG WANG ZHAOCHENG WANG JUN | 2010 | IEEE Transactions on Con- sumer Electronics2010，56，2： | 1 |
| 5 | Secure communication in TDS-OFDM system using constellation rotation and noise insertion显示文摘 | Ma Ruifeng Dai Linglong Wang Zhaocheng | | 0，，03： | 1 |
| 6 | Spectrally effi- cient time-frequency training OFDM for mobile large-scale MIMO system显示文摘 | Dai Linglong Wang Zhaocbeng Yang Zhixing | 2013 | IEEE Journal on Selected Areas in Commu- nications2013，31，2： | 1 |
| 7 | Secure communication in TDS- OFDM system using constellation rotation and noise insertion 显示文摘 | Ma Ruifeng Dai Linglong Wang Zhaocheng | 2010 | IEEE Transactions on Con- sumer Electronics2010，56，3： | 1 |
| 8 | Time-Frequency Training OFDM with High Spectral Efficiency and Reliable Performanc~ in High Speed Environments 显示文摘 | DAI Linglong WANG Zhaocheng YANG Zhixing | 2012 | IEEE Journal on Selected Areas in Commu- nications2012，20，4： | 1 |
| 9 | Time- Frequency Training OFDM with High Spectral Effi- ciency and Reliable Performance in High Speed Envi- ronments显示文摘 | Linglong Dai Zhaocheng Wang Zhixing Yang | 2012 | IEEE Journal on Selected Areas in Com- munications2012，，30： | 1 |
| 10 | Activity of Brucea javanica oil emulsion against gastric ulcers in rodents显示文摘The present study aims to investigate the gastroprotective effect of Brucea javanica oil emulsion(BJOE) in animals. Gastroprotective potential of BJOE was studied on absolute ethanol,aspirin, reserpine and restraint plus water immersion-induced gastric ulcers in mice as well as glacial acetic acid(GAA) and pyloric ligation(PL)-induced gastric ulcers in rats. Except for ulcer scores, total acidity as well as pepsin activity as for the PL-induced gastric ulcer model and ulcer incidence as for the GAA-induced gastric ulcer model were also determined. Histopathological evaluation as for aspirin, reserpine, PL-induced models was conducted. Results showed that BJOE significantly(P < 0.05) reduced ulcer index in the mouse and rat models in a dose-dependent manner. It had significant(P < 0.05) suppressive effect on total activity of gastric juice as well in PL-induced model. Histopathological examination for the stomach samples confirmed the findings in the aspirin, reserpine or PLinduced gastric lesion models, which showed relatively complete mucosa structure and less inflammation. It is concluded that BJOE could be effective on gastric ulcer in rodents and its gastroprotective activity might be related to antioxidant, anti-inflammatory ability and promote gastric mucus secreted. The results may provide beneficial basis for increasing BJOE's clinical indication in future. | Qian Li Linglong Yang Linlin Fan Chen Liang Qiujv Wang Huimin Wen Jinwei Dai Xin Li Yuyang Zhang | 2018 | Asian Journal of Pharmaceutical Sciences2018，13，3： | 1 |
| 11 | Next-generation digital television terrestrial broadcast-ing systems: Key technologies and research trends显示文摘 | DAI Linglong WANG Zhaocheng YANG Zhixing | 2012 | IEEE Communications Magazine2012，50，6： | 1 |
| 12 | Near-field wideband channel estimation for extremely large-scale MIMO显示文摘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. | Mingyao CUI Linglong DAI | 2023 | Science China(Information Sciences)2023，66，7： | 1 |
| 13 | Spectrally effi- cient time-frequency training OFDM for mobile large-scale MIMO systems 显示文摘 | Dai Linglong Wang Zhaocheng Yang Zhixing | 2013 | IEEE Journal on Selected Areas in Com- munications2013，31，2： | 1 |
| 14 | Secure communication in TDS-OFDM system using constellation rotation and noise insertion显示文摘 | Ma Ruifeng Dai Linglong Wang Zhaocheng | 2010 | IEEE Transactions on Con- sumer Electronics2010，，： | 1 |
| 15 | Editorial显示文摘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 communications.The basic idea of RIS is to deploy a reconfigurable passive array in the environment to manipulate the propagation of electron-magnetic waves.RIS 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 receiver.For 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 RIS.Although 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. | Linglong Dai Chan-Byoung Chae Shi Jin Marco Di Renzo Rui Zhang | 2022 | Intelligent and Converged Networks2022，3，1： | 0 |
| 16 | Joint Beamforming Design for RIS-Assisted Cell-Free Network with Multi-Hop Transmissions显示文摘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 communications.Similar 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 networks.In 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 improvement.Unfortunately,to the best of our knowledge,there is no work exploring the multi-hop transmission of RIS-assisted cell-free networks.To 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 design.Specifically,we propose a general multi-hop transmission model,which takes the direct links,single-reflecting links,and multi-hop links into account.Based 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 channels.To address the non-convexity of the formulated problem,a joint active and passive beamforming scheme is proposed to solve the problem.Particularly,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 sum-rate.Simulation 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. | Decai Shen Zijian Zhang Linglong Dai | 2023 | Tsinghua Science and Technology2023，28，6： | 0 |
| 17 | Reconfigurable Intelligent Surfaces for 6G:Nine Fundamental Issues and One Critical Problem显示文摘Thanks to the recent advances in metamaterials,Reconfigurable Intelligent Surface(RIS)has emergedas a promising technology for future 6G wireless communications.Benefiting from its high array gain,low cost,and low power consumption,RISs are expected to greatly enlarge signal coverage,improve system capacity,andincrease energy efficiency.In this article,we systematically overview the emerging RIS technology with the focuson its key basics,nine fundamental issues,and one critical problem.Specifically,we first explain the RIS basics,including its working principles,hardware structures,and potential benefits for communications.Based 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 literature.Then,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 links.To address this critical problem,a potential solution calledactive RISs is introduced,and its effectiveness is demonstrated by numerical simulations. | Zijian Zhang Linglong Dai | 2023 | Tsinghua Science and Technology2023，28，5： | 0 |
| 18 | Continuous-Time Channel Prediction Based on Tensor Neural Ordinary Differential Equation显示文摘Channel prediction is critical to address the channel aging issue in mobile scenarios.Existing 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 interpolation.However,these approaches suffer from a serious interpolation loss,especially for mobile millimeter-wave communications.To 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 channels.Specifically,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 channels.To 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 transform.Simulation results show that the proposed scheme is able to achieve higher intra-frame channel prediction accuracy than existing schemes. | Mingyao Cui Hao Jiang Yuhao Chen Yang Du Linglong Dai | 2024 | China Communications2024，21，1： | 0 |
| 19 | Transformer-based downlink precoding design in massive MIMO systems for 5G-advanced and 6G显示文摘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. | Hao JIANG Linglong DAI | 2023 | Science China(Information Sciences)2023，66，9： | 0 |
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