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Wave effect of gravitational waves intersected with a microlens field Ⅱ:An adaptive hierarchical tree algorithm and population study

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Science China(Physics,Mechanics & Astronomy) 2025年第1期Mechanics & Astronomy) .卷 241-254页

作者： Xikai Shan Guoliang Li Xuechun Chen Wen Zhao Bin Hu Shude Mao Department of Astronomy Tsinghua University purple mountain Observatory Chinese Academy of Sciences Institute for Frontier in Astronomy and Astrophysics Beijing Normal University School of Physics and Astronomy Beijing Normal University School of Astronomy and Space Science University of Science and Technology of China CAS Key laboratory for Researches in Galaxies and Cosmology Department of Astronomy University of Science and Technology of ChinaChinese Academy of Sciences

The gravitational lensing wave effect generated by a microlensing field embedded in a lens galaxy is an inevitable phenomenon in strong lensed gravitational waves （SLGWs）.This effect presents both challenges and opportunities for the detection and application of ***,investigating this wave effect requires computing a complete diffraction integral over each microlens in the *** is extremely time-consuming due to the large number of microlenses （10～3-10～6）.Therefore,simply adding all the microlenses is ***,the complexity of the time delay surface makes the lens plane resolution a crucial factor in controlling numerical *** this paper,we propose a trapezoid approximation-based adaptive hierarchical tree algorithm to meet the challenges of calculation speed and *** find that this algorithm accelerates the calculation by four orders of magnitude compared to the simple adding method and is one order of magnitude faster than the fixed hierarchical tree algorithm proposed for electromagnetic *** importantly,our algorithm ensures controllable numerical errors,increasing confidence in the *** with our previous work （***.66,239511,2023）,this paper addresses all numerical issues,including integral convergence,precision,and computational time1).Finally,we conducted a population study on the microlensing wave effect of SLGWs using this algorithm and found that the microlensing wave effect cannot be ignored,especially for Type II SLGWs （from saddle position of the time delay surface） due to their intrinsic geometric structures and their typical intersection with a denser microlensing ***,more than 33%（11%） of SLGWs have a mismatch larger than 1%（3%） compared to the unlensed ***,we found that the mismatch between signal pairs in a doubly imaged GW is generally larger than 10-3,and 61%（25%） of signal pairs have a mismatch larger than 1%（3%）.Therefo

关键词： gravitational lensing diffractional integral algorithm gravitational wave

When AI meets sustainable 6G

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Science China(Information Sciences) 2025年第1期 4-22页

作者： Xiaohu YOU Yongming HUANG Cheng ZHANG Jiaheng WANG Hao YIN Hequan WU National Mobile Communications Research laboratory Southeast University purple mountain Laboratories Chinese Academy of Military Science China Information Communication Technologies Group

Sixth-generation(6G) networks are anticipated to achieve transformative advancements, characterized by extreme connectivity, deep integration with artificial intelligence(AI) and sensing, and airground integration. The evolution of 6G exhibits two major trends: ubiquitous intelligence and sustainability. The former aims to embed state-of-the-art AI technology into the 6G network, from the physical layers to applications, while the latter emphasizes reducing energy consumption while enhancing network performance to address environmental concerns. Despite the amazing progress in recent years, AI advancements come with substantial increases in data and computational overhead, posing critical challenges for integrating AI into sustainable 6G networks. First, high energy consumption from large datasets and heavyweight AI models contradicts6G's green goals. Second, the precise collection of large datasets, message delivery latency, and inference delays in AI models pose challenges for real-time tasks in 6G. Third, the uninterpretability and unpredictability of AI models complicate meeting the stringent requirements for controllable transmission in dynamic wireless environments. Addressing these challenges and achieving sustainable 6G with ubiquitous intelligence calls for a revolutionary design of 6G architecture and AI frameworks. To this end, this paper introduces a novel and practical methodology for green, real-time, and controllable 6G native intelligence,starting with knowledge graph(KG) analysis to extract small but critical datasets, followed by the development of distributed lightweight AI models, and the use of digital twins(DTs) to create precise replicas of physical 6G networks. This leads to a pervasive multi-level(PML)-AI framework supported by a task-centric, three-layer 6G architecture. The AI framework operates through non-real-time and real-time cycles, leveraging three key technologies: wireless data KGs for efficient data management,lightweight AI mode

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Density-based user clustering in downlink NOMA systems

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Science China(Information Sciences) 2022年第5期65卷 196-204页

作者： Hanliang YOU Yaoyue HU Zhiwen PAN Nan LIU National Mobile Communication Research laboratory Southeast University purple mountain Laboratories

Non-orthogonal multiple access(NOMA) technology, which can effectively improve the bandwidth utilization, is one of the key technologies in the next-generation wireless communication systems. In the downlink multiple antenna NOMA systems, user clustering is one of the problems that must be *** this paper, we focus on the user clustering that maximizes the system sum rate. First, a user clustering method based on the density-based spatial clustering of applications with noise(DBSCAN) algorithm is proposed for static user scenarios. Then an improved low-complexity dynamic clustering method is further developed for dynamic user scenarios. Simulation results show that compared with existing clustering methods, the DBSCAN-based method has better clustering performance in complex static user scenarios, and the proposed dynamic clustering method performs close to completely re-executing the DBSCAN-based method but with lower complexity.

关键词： NOMA user clustering machine learning DBSCAN dynamic clustering

An overview on integrated localization and communication towards 6G

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Science China(Information Sciences) 2022年第3期65卷 5-50页

作者： Zhiqiang XIAO Yong ZENG National Mobile Communications Research laboratory Southeast University purple mountain Laboratories

While the fifth generation(5 G) cellular system is being deployed worldwide, researchers have started the investigation of the sixth generation(6 G) mobile communication networks. Although the essential requirements and key usage scenarios of 6 G are yet to be defined, it is believed that 6 G should be able to provide intelligent and ubiquitous wireless connectivity with Terabits per second(Tbps) data rate and submillisecond(sub-ms) latency over three-dimensional(3 D) network coverage. To achieve such goals, acquiring accurate location information of the mobile terminals is becoming extremely useful, not only for locationbased services but also for improving wireless communication performance in various ways such as channel estimation, beam alignment, medium access control, routing, and network optimization. On the other hand, the advancement of communication technologies also brings new opportunities to greatly improve the localization performance, as exemplified by the anticipated centimeter-level localization accuracy in 6 G by extremely large-scale multiple-input multiple-output(MIMO) and millimeter wave(mm Wave) *** this regard, a unified study on integrated localization and communication(ILAC) is necessary to unlock the full potential of wireless networks for dual purposes. While there are extensive studies on wireless localization or communications separately, the research on ILAC is still in its infancy. Therefore, this article aims to give a tutorial overview on ILAC towards 6 G wireless networks. After a holistic survey on wireless localization basics, we present the state-of-the-art results on how wireless localization and communication inter-play with each other in various network layers, together with the main architectures and techniques for localization and communication co-design in current two-dimensional(2 D) and future 3 D networks with aerial-ground integration. Finally, we outline some promising future research directions for ILAC.

关键词： wireless localization integrated localization and communication cellular networks B5G 6G

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Performance analysis of full-duplex densely distributed MIMO with wireless backhaul

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Science China(Information Sciences) 2023年第6期66卷 186-203页

作者： Ziqian WAN Qijun PAN Jiamin LI Pengcheng ZHU Dongming WANG National Mobile Communications Research laboratory Southeast University purple mountain Laboratories

In this paper, the spectral efficiency of a full-duplex(FD)densely distributed multi-input multioutput(MIMO)system with wireless backhaul is considered. In-band full-duplex(IBFD)backhauling, in which the backhaul and access transmissions take place on the same spectrum, is exploited for wireless backhauling to enable an efficient spectrum reuse. However, the severe cross-tier interference and crosslink interference reduce the gains of IBFD backhauling. To evaluate the achievable spectral efficiency with imperfect channel state information(CSI), we propose a two-phase channel estimation scheme to estimate the CSI for two wireless links, and the scheme estimates an effective interference CSI between access points(APs)based on beamforming training to perform interference cancelation at APs. Given the estimated CSI,the closed-form expressions of the uplink and downlink achievable rates with maximum ratio transmission beamforming and maximum ratio combining receivers, respectively, are derived with Gamma *** results verify the accuracy of the derived closed-form expressions and the effectiveness of the twophase channel estimation scheme for interference cancelation. Moreover, compared with half-duplex densely distributed MIMO systems, FD systems with interference cancelation have a better performance.

关键词： full-duplex wireless backhaul performance analysis beamforming training interference cancelation

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Joint optimization of spectral efficiency and energy efficiency with low-precision ADCs in cell-free massive MIMO systems

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Science China(Information Sciences) 2022年第5期65卷 169-183页

作者： Han WANG Chang SUN Jiamin LI Pengcheng ZHU Dongming WANG Xiaohu YOU National Mobile Communications Research laboratory Southeast University purple mountain Laboratories

In cell-free massive multiple-input multiple-output(MIMO) systems, it is beneficial to apply low-precision analog-to-digital converters(ADCs) to reduce power consumption, hardware cost, and the load on backhaul link. However, low-precision ADCs will result in serious degradation in spectral efficiency(SE). It is important to achieve a good tradeoff between SE and energy efficiency(EE) for cell-free massive MIMO systems with low-precision ADCs. In this paper, we first derive the closed-form expressions of uplink achievable rates with maximal ratio combining(MRC) receiver and zero-forcing(ZF) receiver in cell-free massive MIMO systems. Then we analyze the EE model of cell-free massive MIMO systems. Based on the above analysis, the tradeoff between SE and EE is studied. Moreover, we propose two quantization bit allocation algorithms to optimize the SE and EE jointly from the perspective of multi-objective *** algorithm is based on the deep Q-network(DQN) and the other one is based on the non-dominated sorting genetic algorithm Ⅱ(NSGA-Ⅱ). The proposed algorithms provide more feasible solutions and achieve better system performance than equal quantization bit allocation algorithm. Numerical results verify the accuracy of the derived closed-form expressions and the effectiveness of the proposed optimization algorithms.

关键词： cell-free massive MIMO low-precision ADC spectral efficiency energy efficiency multi-objective optimization

Robust online energy efficiency optimization for distributed multi-cell massive MIMO networks

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Science China(Information Sciences) 2023年第3期66卷 239-252页

作者： Li YOU Yufei HUANG Wen ZHONG Wenjin WANG Xiqi GAO National Mobile Communications Research laboratory Southeast University purple mountain Laboratories

This paper studies the energy efficiency(EE) oriented precoding design in multi-cell massive multiple-input multiple-output(MIMO) systems, with only statistical channel state information(CSI) at the transmitter. During the transmission, as the channel varies dynamically with time and the previously obtained CSI becomes outdated, the base stations must adjust their transmit policies accordingly. To tackle this issue, we propose an online EE maximization algorithm that can achieve a no-regret transmission; i.e.,the performance of this online method gradually approaches that of the fixed offline method which has full knowledge of the future CSI. Specifically, we first construct the online EE optimization problem in a distributed way to reduce the information required to be exchanged between cells. Then, we apply the largedimensional random matrix theory to lower the calculation complexity, and the Charnes-Cooper transform to address the nonconvexity of the problem, respectively. The online gradient ascent method is utilized to perform this no-regret power allocation strategy based on all past CSI. We also assess the robustness of the algorithm to estimation error of statistical CSI under some mild conditions which can usually be satisfied in practice. Numerical results demonstrate the no-regret property and the robustness of the proposed online algorithm for energy efficient multi-cell massive MIMO transmission.

关键词： energy efficiency statistical CSI multi-cell MIMO massive MIMO online gradient ascent distributed processing robust transmission

Coordinated multicast and unicast transmission in V2V underlay massive MIMO

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Science China(Information Sciences) 2022年第3期65卷 235-245页

作者： Xinxin NIU Li YOU Xiqi GAO National Mobile Communications Research laboratory Southeast University purple mountain Laboratories

This paper investigates coordinated multicast and unicast transmission for vehicle-to-vehicle(V2 V) underlay massive multiple-input multiple-output(MIMO). First, the achievable ergodic multicast rate for the cellular link and the achievable ergodic unicast rate for all the V2 V links are summed with weight to formulate the rate optimization problem, with the assumption that the statistical channel state information(CSI) is known at the base station and the transmitters of the V2 V communication pairs. We then derive the optimal transmitting directions in closed-form for the cellular link and all the V2 V links,respectively, which converts the original optimal problem to a simpler power allocation problem in the beam domain. Via invoking the concave-convex procedure, an efficient iterative algorithm with guaranteed convergence is proposed for the power allocation problem. Furthermore, we replace the objectives which contain high-complex expectation operations with their deterministic equivalents in each iteration of the proposed algorithm to achieve lower algorithm complexity. Simulation results show the fast convergence speed of the proposed power allocation algorithm and the significant performance gains of the proposed transmission design for V2 V underlay massive MIMO.

关键词： coordinated multicast and unicast transmission V2V underlay massive MIMO statistical CSI

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Blockchain-enabled wireless communications: a new paradigm towards 6G

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National Science Review 2021年第9期8卷 167-191页

作者： Jiaheng Wang Xintong Ling Yuwei Le Yongming Huang Xiaohu You National Mobile Communications Research laboratory Southeast University purple mountain Laboratories

With the deployment of fifth-generation(5 G) wireless networks worldwide, research on sixth-generation(6 G) wireless communications has commenced. It is expected that 6 G networks can accommodate numerous heterogeneous devices and infrastructures with enhanced efficiency and security over diverse,e.g. spectrum, computing and storage, resources. However, this goal is impeded by a number of trust-related issues that are often neglected in network designs. Blockchain, as an innovative and revolutionary technology that has arisen in the recent decade, provides a promising solution. Building on its nature of decentralization, transparency, anonymity, immutability, traceability and resiliency, blockchain can establish cooperative trust among separate network entities and facilitate, e.g. efficient resource sharing,trusted data interaction, secure access control, privacy protection, and tracing, certification and supervision functionalities for wireless networks, thus presenting a new paradigm towards 6 G. This paper is dedicated to blockchain-enabled wireless communication technologies. We first provide a brief introduction to the fundamentals of blockchain, and then we conduct a comprehensive investigation of the most recent efforts in incorporating blockchain into wireless communications from several aspects. Importantly, we further propose a unified framework of the blockchain radio access network(B-RAN) as a trustworthy and secure paradigm for 6 G networking by utilizing blockchain technologies with enhanced efficiency and *** critical elements of B-RAN, such as consensus mechanisms, smart contract, trustworthy access,mathematical modeling, cross-network sharing, data tracking and auditing and intelligent networking, are elaborated. We also provide the prototype design of B-RAN along with the latest experimental results.

关键词： blockchain wireless communication 6G