Reconfigurable intelligent surface(RIS)is a promising candidate technology of the upcoming Sixth Generation(6G)communication system for its ability to provide unprecedented spectral and energy efficiency increment thr...Reconfigurable intelligent surface(RIS)is a promising candidate technology of the upcoming Sixth Generation(6G)communication system for its ability to provide unprecedented spectral and energy efficiency increment through passive beamforming.However,it is challenging to obtain instantaneous channel state information(I-CSI)for RIS,which obliges us to use statistical channel state information(S-CSI)to achieve passive beamforming.In this paper,RIS-aided multiple-input single-output(MISO)multi-user downlink communication system with correlated channels is investigated.Then,we formulate the problem of joint beamforming design at the AP and RIS to maximize the sum ergodic spectral efficiency(ESE)of all users to improve the network capacity.Since it is too hard to compute sum ESE,an ESE approximation is adopted to reformulate the problem into a more tractable form.Then,we present two joint beamforming algorithms,namely the singular value decomposition-gradient descent(SVD-GD)algorithm and the fractional programming-gradient descent(FP-GD)algorithm.Simulation results show the effectiveness of our proposed algorithms and validate that 2-bits quantizer is enough for RIS phase shifts implementation.展开更多
Since the implementation of the reform and opening-up policy,China has undergone a period of rapid development.However,this urban expansion has been accompanied by significant ecological challenges.Therefore,understan...Since the implementation of the reform and opening-up policy,China has undergone a period of rapid development.However,this urban expansion has been accompanied by significant ecological challenges.Therefore,understanding the relationship between urban expansion and ecological sustainability is crucial for future urban planning.This study analyzes land use data to investigate the spatiotemporal dynamics of urban agglomeration expansion from 2000 to 2020.Using MODIS satellite data,this study constructs a Remote Sensing Ecological Index(RSEI)model to assess ecological quality changes over the past two decades.Additionally,an improved coupling coordination model is applied to examine the interaction between urban expansion and ecological quality and to evaluate the spatiotemporal trends of their coordination.The results indicate that:①From 2000 to 2020,urban expansion in the Henan section of the Yellow River Basin followed a pattern of“growth-growthdecline”.Pattern recognition analysis indicated that both urban agglomerations and individual cities primarily expanded through edge extension and infill development,while enclave-style expansion occurred in only a small portion of the region.②Between 2000 and 2020,the ecological quality of urban agglomerations in the Henan section of the Yellow River Basin showed a slight improvement.RSEI values ranged from 0.4 to 0.7,indicating moderate ecological quality.Ecological quality exhibited a spatial pattern of being higher in the southwest and lower in the northeast.Significant declines in ecological quality were primarily concentrated in urban built-up areas,forming a patch-like distribution.Conversely,notable improvements in ecological quality occurred mainly in the mountainous regions of the southwest and north.③Between 2000 and 2020,the coupling coordination level of urban agglomerations showed an increasing trend.Coupling coordination values ranged from 0.248 to 0.734.Most cities were near an imbalance between urban expansion and ecological quality,while Zhengzhou was the only city to consistently maintain coordinated development over two decades.Spatially,highly imbalanced areas were mainly concentrated in the western and southern Henan sections,particularly in Sanmenxia and Luoyang.Conversely,areas with high coupling coordination were centered around Zhengzhou,showing a radial expansion pattern in recent years.展开更多
为揭示中国西部地区旅游经济韧性的动态演变规律及其驱动机制,提升西部地区旅游业应对外部冲击的适应能力和恢复能力,从抵御力、恢复力、重构力和创新力等4个维度构建旅游经济韧性指标体系,以2011—2022年中国西部地区除西藏自治区外的1...为揭示中国西部地区旅游经济韧性的动态演变规律及其驱动机制,提升西部地区旅游业应对外部冲击的适应能力和恢复能力,从抵御力、恢复力、重构力和创新力等4个维度构建旅游经济韧性指标体系,以2011—2022年中国西部地区除西藏自治区外的11个省(自治区、直辖市)为研究对象,运用熵权TOPSIS法(Technique for Order Preference by Similarity to Ideal Solution,TOPSIS)、探索性空间数据分析和地理探测器模型,深入分析西部地区的旅游经济韧性水平和影响因素。研究结果表明:1) 2011—2022年,中国西部地区11个省(自治区、直辖市)的旅游经济韧性总体呈现持续上升态势,表现出较强的抗冲击和恢复能力。2)研究期内,西部地区的旅游经济韧性未呈现显著空间自相关,空间分异呈现“南热北冷”鲜明格局,南部区域长期处于旅游经济高韧性区和热点区,北部区域则持续处于旅游经济低韧性区和冷点区。3)西部地区的旅游经济韧性受到多重因素的综合影响,其中科技创新水平、旅游消费水平和政府支持力度是旅游经济韧性空间分异的关键影响因子,旅游产业结构合理化水平、旅游产业集聚水平和城市舒适度等因素虽对空间分异存在一定解释力,但相对较弱,且不同因子交互作用对旅游经济韧性的空间分异影响显著,驱动作用远超单一因子。研究成果为中国西部地区旅游产业转型及韧性提升提供了重要的理论依据与政策参考方向。展开更多
基金partially supported by the National Key Research and Development Project under Grant 2020YFB1806805Science and Technology on Communication Networks Laboratorysupported by China Scholarship Council.
文摘Reconfigurable intelligent surface(RIS)is a promising candidate technology of the upcoming Sixth Generation(6G)communication system for its ability to provide unprecedented spectral and energy efficiency increment through passive beamforming.However,it is challenging to obtain instantaneous channel state information(I-CSI)for RIS,which obliges us to use statistical channel state information(S-CSI)to achieve passive beamforming.In this paper,RIS-aided multiple-input single-output(MISO)multi-user downlink communication system with correlated channels is investigated.Then,we formulate the problem of joint beamforming design at the AP and RIS to maximize the sum ergodic spectral efficiency(ESE)of all users to improve the network capacity.Since it is too hard to compute sum ESE,an ESE approximation is adopted to reformulate the problem into a more tractable form.Then,we present two joint beamforming algorithms,namely the singular value decomposition-gradient descent(SVD-GD)algorithm and the fractional programming-gradient descent(FP-GD)algorithm.Simulation results show the effectiveness of our proposed algorithms and validate that 2-bits quantizer is enough for RIS phase shifts implementation.
基金State Key Laboratory of Spatial Datum(No.SKLSD2025-ZZ-17)National Natural Science Foundation of China(No.U21A2014)+2 种基金High-Resolution Satellite Project of the State Administration of Science,Technology,and Industry for National Defense of the PRC(No.80Y50G19-9001-22/23)National Science and Technology Platform Construction Project(No.2005DKA32300)Major Research Projects of the Ministry of Education(No.16JJD770019).
文摘Since the implementation of the reform and opening-up policy,China has undergone a period of rapid development.However,this urban expansion has been accompanied by significant ecological challenges.Therefore,understanding the relationship between urban expansion and ecological sustainability is crucial for future urban planning.This study analyzes land use data to investigate the spatiotemporal dynamics of urban agglomeration expansion from 2000 to 2020.Using MODIS satellite data,this study constructs a Remote Sensing Ecological Index(RSEI)model to assess ecological quality changes over the past two decades.Additionally,an improved coupling coordination model is applied to examine the interaction between urban expansion and ecological quality and to evaluate the spatiotemporal trends of their coordination.The results indicate that:①From 2000 to 2020,urban expansion in the Henan section of the Yellow River Basin followed a pattern of“growth-growthdecline”.Pattern recognition analysis indicated that both urban agglomerations and individual cities primarily expanded through edge extension and infill development,while enclave-style expansion occurred in only a small portion of the region.②Between 2000 and 2020,the ecological quality of urban agglomerations in the Henan section of the Yellow River Basin showed a slight improvement.RSEI values ranged from 0.4 to 0.7,indicating moderate ecological quality.Ecological quality exhibited a spatial pattern of being higher in the southwest and lower in the northeast.Significant declines in ecological quality were primarily concentrated in urban built-up areas,forming a patch-like distribution.Conversely,notable improvements in ecological quality occurred mainly in the mountainous regions of the southwest and north.③Between 2000 and 2020,the coupling coordination level of urban agglomerations showed an increasing trend.Coupling coordination values ranged from 0.248 to 0.734.Most cities were near an imbalance between urban expansion and ecological quality,while Zhengzhou was the only city to consistently maintain coordinated development over two decades.Spatially,highly imbalanced areas were mainly concentrated in the western and southern Henan sections,particularly in Sanmenxia and Luoyang.Conversely,areas with high coupling coordination were centered around Zhengzhou,showing a radial expansion pattern in recent years.
文摘为揭示中国西部地区旅游经济韧性的动态演变规律及其驱动机制,提升西部地区旅游业应对外部冲击的适应能力和恢复能力,从抵御力、恢复力、重构力和创新力等4个维度构建旅游经济韧性指标体系,以2011—2022年中国西部地区除西藏自治区外的11个省(自治区、直辖市)为研究对象,运用熵权TOPSIS法(Technique for Order Preference by Similarity to Ideal Solution,TOPSIS)、探索性空间数据分析和地理探测器模型,深入分析西部地区的旅游经济韧性水平和影响因素。研究结果表明:1) 2011—2022年,中国西部地区11个省(自治区、直辖市)的旅游经济韧性总体呈现持续上升态势,表现出较强的抗冲击和恢复能力。2)研究期内,西部地区的旅游经济韧性未呈现显著空间自相关,空间分异呈现“南热北冷”鲜明格局,南部区域长期处于旅游经济高韧性区和热点区,北部区域则持续处于旅游经济低韧性区和冷点区。3)西部地区的旅游经济韧性受到多重因素的综合影响,其中科技创新水平、旅游消费水平和政府支持力度是旅游经济韧性空间分异的关键影响因子,旅游产业结构合理化水平、旅游产业集聚水平和城市舒适度等因素虽对空间分异存在一定解释力,但相对较弱,且不同因子交互作用对旅游经济韧性的空间分异影响显著,驱动作用远超单一因子。研究成果为中国西部地区旅游产业转型及韧性提升提供了重要的理论依据与政策参考方向。
