Mobile communication standards have been developed into a new era of B5G and 6G.In recent years,low earth orbit(LEO)satellites and space Internet have become hot topics.The integrated satellite and terrestrial systems...Mobile communication standards have been developed into a new era of B5G and 6G.In recent years,low earth orbit(LEO)satellites and space Internet have become hot topics.The integrated satellite and terrestrial systems have been widely discussed by industries and academics,and even are expected to be applied in those huge constellations in construction.This paper points out the trends of two stages towards system integration of the terrestrial mobile communication and the satellite communications:to be compatible with 5G,and to be integrated within 6G.Based on analysis of the challenges of both stages,key technologies are thereafter analyzed in detail,covering both air interface currently discussed in 3GPP for B5G and also novel network architecture and related transmission technologies toward future 6G.展开更多
The major challenge faced by the fifth generation(5G) mobile network is higher spectral efficiency and massive connectivity,i.e.,the target spectrum efficiency is 3 times over 4G,and the target connection density is o...The major challenge faced by the fifth generation(5G) mobile network is higher spectral efficiency and massive connectivity,i.e.,the target spectrum efficiency is 3 times over 4G,and the target connection density is one million devices per square kilometer.These requirements are difficult to be satisfied with orthogonal multiple access(OMA) schemes.Non-orthogonal multiple access(NOMA) has thus been proposed as a promising candidate to address some of the challenges for 5G.In this paper,a comprehensive survey of different candidate NOMA schemes for 5G is presented,where the usage scenarios of5 G and the application requirements for NOMA are firstly discussed.A general framework of NOMA scheme is established and the features of typical NOMA schemes are analyzed and compared.We focus on the recent progress and challenge of NOMA in standardization of international telecommunication union(ITU),and 3rd generation partnership project(3GPP).In addition,prototype development and future research directions are also provided respectively.展开更多
Massive Multiple-Input Multiple-Output(MIMO)is considered as a key technology for 4G and 5G wireless communication systems to improve spectrum efficiency by supporting large number of concurrent users.In addition,for ...Massive Multiple-Input Multiple-Output(MIMO)is considered as a key technology for 4G and 5G wireless communication systems to improve spectrum efficiency by supporting large number of concurrent users.In addition,for the target frequency band of 5G system,mmWave band,massive MIMO is pivotal in compensating the high pathloss.In this paper,we investigate the channel state information(CSI)acquisition problem for mmWave massive MIMO.With hybrid analog-digital antenna architecture,how to derive the analog beamforming and digital beamforming is studied.An iterative analog beam acquisition approach is proposed to save system overhead and reduce beam searching complexity.Regarding the digital beamforming,a grouping based codebook is proposed to facilitate CSI feedback.The codebook is then extended to incorporate also analog beam acquisition.Furthermore,channel reciprocity is exploited to save CSI reporting overhead and a two-stage approach is proposed to fully utilize the channel reciprocity at both mobile station and base station side and accelerate the CSI acquisition procedure.展开更多
Massive multiple-input multipleoutput(MIMO) refers to the idea that equipping base station(BS) with a large number of antenna elements,and features the ability of three dimensional(3D) beamforming technique to enable ...Massive multiple-input multipleoutput(MIMO) refers to the idea that equipping base station(BS) with a large number of antenna elements,and features the ability of three dimensional(3D) beamforming technique to enable improvement in system performance.The prior works on massive MIMO generally rely on a common assumption of the whole channel characteristics are perfectly known at both user equipment(UE) and BS,however,this is quite difficult to realize in practical frequency division duplexing(FDD) system since the channel state information reference signal(CSIRS) overhead and CSI feedback overhead are proportional to the number of antenna elements.In this paper,two hybrid CSI-RS transmission mechanism-based 3D beamforming schemes are proposed in FDD massive MIMO system,in which non-beamformed CSI-RS configuration is utilized in conjunction with beamformed CSIRS configuration.In the proposed schemes,an angle quantization-based vertical codebook and a DFT-based horizontal codebook are designed,respectively,and an eigenvalue decompositionbased precoding matrix indicator(PMI)selection algorithm is also proposed for CSI acquisition.Simulation results show that the proposed 3D beamforming schemes achieve significant improvement in system capacity without incurring excessive CSI-RS overhead.展开更多
A Relay-Assisted(RA) network with relay selection is considered as a type of effective technology to improve the spectrum and energy efficiency of a cellular network. However, loading balance of the assisted relay nod...A Relay-Assisted(RA) network with relay selection is considered as a type of effective technology to improve the spectrum and energy efficiency of a cellular network. However, loading balance of the assisted relay node becomes an inevitable bottleneck in RA network development because users do not follow uniform distribution. Furthermore, the time-varying channel condition of wireless communication is also a major challenge for the RA network with relay selection. To solve these problems and improve the practicability of the RA network, a Loading Balance-Relay Selective(LBRS) strategy is proposed for the RA network in this paper. The proposed LBRS strategy formulates the relay selection of the RA network under imperfect channel state information assumption as a Multistage Decision(MD) problem. An optimal algorithm is also investigated to solve the proposed MD problem based on stochastic dynamic program. Numerical results show that the performance of the LBRS strategy is better than that of traditional greedy algorithm and the former is effective as an exhaustive search-based method.展开更多
Two-dimensional(2D)high-entropy alloys(HEAs)have emerged as promising electrocatalysts due to the benefits of polymetallic coordination and robust elec-trical conductivity.However,the multiple elements in 2D HEAs pose...Two-dimensional(2D)high-entropy alloys(HEAs)have emerged as promising electrocatalysts due to the benefits of polymetallic coordination and robust elec-trical conductivity.However,the multiple elements in 2D HEAs pose challenges in achieving a uniform composition and maintaining a 2D limit morphology,complicating their structural characterization.Furthermore,even minor adjust-ments to the composition can significantly alter the properties of 2D HEAs,underscoring the need for a deeper understanding of their structure-property relationships to advance synthesis and application.Therefore,this review crit-ically examines the intrinsic factors influencing synthesis methods and the practical applications of 2D HEAs in electrocatalysis for sustainable energy con-version.The urgency is emphasized for developing new synthesis techniques,enhancing advanced characterization methods,and gaining profound insights into the functional mechanisms of 2D HEAs.展开更多
基金This work was supported in part by the National Science Fund for Distinguished Young Scholars in China under grant 61425012the National Science Foundation Project in China under grant 61931005 and 61731017.
文摘Mobile communication standards have been developed into a new era of B5G and 6G.In recent years,low earth orbit(LEO)satellites and space Internet have become hot topics.The integrated satellite and terrestrial systems have been widely discussed by industries and academics,and even are expected to be applied in those huge constellations in construction.This paper points out the trends of two stages towards system integration of the terrestrial mobile communication and the satellite communications:to be compatible with 5G,and to be integrated within 6G.Based on analysis of the challenges of both stages,key technologies are thereafter analyzed in detail,covering both air interface currently discussed in 3GPP for B5G and also novel network architecture and related transmission technologies toward future 6G.
基金supported by the National High Technology Research and Development Program of China (863 Program, No. 2015AA01A709)
文摘The major challenge faced by the fifth generation(5G) mobile network is higher spectral efficiency and massive connectivity,i.e.,the target spectrum efficiency is 3 times over 4G,and the target connection density is one million devices per square kilometer.These requirements are difficult to be satisfied with orthogonal multiple access(OMA) schemes.Non-orthogonal multiple access(NOMA) has thus been proposed as a promising candidate to address some of the challenges for 5G.In this paper,a comprehensive survey of different candidate NOMA schemes for 5G is presented,where the usage scenarios of5 G and the application requirements for NOMA are firstly discussed.A general framework of NOMA scheme is established and the features of typical NOMA schemes are analyzed and compared.We focus on the recent progress and challenge of NOMA in standardization of international telecommunication union(ITU),and 3rd generation partnership project(3GPP).In addition,prototype development and future research directions are also provided respectively.
基金supported in parts by the National Natural Science Foundation of China for Distinguished Young Scholar under Grant 61425012the National Science and Technology Major Projects for the New Generation of Broadband Wireless Communication Network under Grant 2017ZX03001014
文摘Massive Multiple-Input Multiple-Output(MIMO)is considered as a key technology for 4G and 5G wireless communication systems to improve spectrum efficiency by supporting large number of concurrent users.In addition,for the target frequency band of 5G system,mmWave band,massive MIMO is pivotal in compensating the high pathloss.In this paper,we investigate the channel state information(CSI)acquisition problem for mmWave massive MIMO.With hybrid analog-digital antenna architecture,how to derive the analog beamforming and digital beamforming is studied.An iterative analog beam acquisition approach is proposed to save system overhead and reduce beam searching complexity.Regarding the digital beamforming,a grouping based codebook is proposed to facilitate CSI feedback.The codebook is then extended to incorporate also analog beam acquisition.Furthermore,channel reciprocity is exploited to save CSI reporting overhead and a two-stage approach is proposed to fully utilize the channel reciprocity at both mobile station and base station side and accelerate the CSI acquisition procedure.
文摘Massive multiple-input multipleoutput(MIMO) refers to the idea that equipping base station(BS) with a large number of antenna elements,and features the ability of three dimensional(3D) beamforming technique to enable improvement in system performance.The prior works on massive MIMO generally rely on a common assumption of the whole channel characteristics are perfectly known at both user equipment(UE) and BS,however,this is quite difficult to realize in practical frequency division duplexing(FDD) system since the channel state information reference signal(CSIRS) overhead and CSI feedback overhead are proportional to the number of antenna elements.In this paper,two hybrid CSI-RS transmission mechanism-based 3D beamforming schemes are proposed in FDD massive MIMO system,in which non-beamformed CSI-RS configuration is utilized in conjunction with beamformed CSIRS configuration.In the proposed schemes,an angle quantization-based vertical codebook and a DFT-based horizontal codebook are designed,respectively,and an eigenvalue decompositionbased precoding matrix indicator(PMI)selection algorithm is also proposed for CSI acquisition.Simulation results show that the proposed 3D beamforming schemes achieve significant improvement in system capacity without incurring excessive CSI-RS overhead.
基金supported in part by the National High Technology Research and Development Program (No. ss2015AA011306)the National Basic Research Program of China (No. 2012CB316000)+1 种基金the Science Fund for Creative Research Groups of NSFC (No. 61321061)Tsinghua University Initiative Scientific Research (No. 2015Z02-3)
文摘A Relay-Assisted(RA) network with relay selection is considered as a type of effective technology to improve the spectrum and energy efficiency of a cellular network. However, loading balance of the assisted relay node becomes an inevitable bottleneck in RA network development because users do not follow uniform distribution. Furthermore, the time-varying channel condition of wireless communication is also a major challenge for the RA network with relay selection. To solve these problems and improve the practicability of the RA network, a Loading Balance-Relay Selective(LBRS) strategy is proposed for the RA network in this paper. The proposed LBRS strategy formulates the relay selection of the RA network under imperfect channel state information assumption as a Multistage Decision(MD) problem. An optimal algorithm is also investigated to solve the proposed MD problem based on stochastic dynamic program. Numerical results show that the performance of the LBRS strategy is better than that of traditional greedy algorithm and the former is effective as an exhaustive search-based method.
基金China Postdoctoral Science Foundation,Grant/Award Number:2022M722867Key Research Project of Higher Education Institutions in Henan Province,Grant/Award Number:23A530001+1 种基金Henan Province Key Research and Promotion Project-Scientific and Technological Breakthroughs,Grant/Award Number:232102230088National Natural Science Foundation of China,Grant/Award Numbers:22205209,U21A200972。
文摘Two-dimensional(2D)high-entropy alloys(HEAs)have emerged as promising electrocatalysts due to the benefits of polymetallic coordination and robust elec-trical conductivity.However,the multiple elements in 2D HEAs pose challenges in achieving a uniform composition and maintaining a 2D limit morphology,complicating their structural characterization.Furthermore,even minor adjust-ments to the composition can significantly alter the properties of 2D HEAs,underscoring the need for a deeper understanding of their structure-property relationships to advance synthesis and application.Therefore,this review crit-ically examines the intrinsic factors influencing synthesis methods and the practical applications of 2D HEAs in electrocatalysis for sustainable energy con-version.The urgency is emphasized for developing new synthesis techniques,enhancing advanced characterization methods,and gaining profound insights into the functional mechanisms of 2D HEAs.
