基于联合检测在时分同步码分多址技术中的多径干扰分析

针对商用3G移动通信系统中,特别是成熟度缺陷的时分同步码分多址技术系统中多径干扰问题,提出一种新的联合检测技术。通过理论分析和系统仿真分析,新的联合检测抗多径干扰技术可以直接对系统终端和中心设备进行固件或软件版本升级完成优化,并可以根据系统中的设备不同性能配置,采用自适应算法以匹配。     

CRLS算法在智能天线中的应用

提出一种应用于窄带自适应波束形成的约束递归最小二乘算法.通过最小化阵列的输出功率,算法根据环境能有效的实现自适应,并且维持可视方向的频率响应.这种主瓣对准用户和旁瓣对准干扰的能力对当前和未来传感器网络有很大影响.递归最小二乘优势在于不需要对大量相关矩阵求逆,递归方程使相关矩阵的逆容易更新.通过matlab进行了仿真,给出了以改变天线数目和改变阵元间距的方向图以及跟踪能力比较图.仿真结果表明,递归最小二乘算法不仅有较好的稳定性,而且算法有较强的跟踪能力.     

CRLS算法在智能天线中的应用

提出一种应用于窄带自适应波束形成的约束递归最小二乘算法。通过最小化阵列的输出功率,算法根据环境能有效的实现自适应,并且维持可视方向的频率响应。这种主瓣对准用户和旁瓣对准干扰的能力对当前和未来传感器网络有很大影响。递归最小二乘优势在于不需要对大量相关矩阵求逆,递归方程使相关矩阵的逆容易更新。通过matlab进行了仿真,给出了以改变天线数目和改变阵元间距的方向图以及跟踪能力比较图。仿真结果表明,递归最小二乘算法不仅有较好的稳定性,而且算法有较强的跟踪能力。     

基于LMS滤波的地基增强系统电离层异常检测

针对地基增强系统(GBAS)中传统电离层异常检测方法无法同时兼顾检测精度与灵敏度的问题,通过构造单通道变步长最小均方(LMS)自适应滤波器以抑制伪码-载波偏离度高频噪声。单通道LMS自适应滤波器是在标准双通道LMS自适应滤波器的基础上,利用被检测信号短时相关性及其量化噪声的非相关性,构造一个采用被检测信号延时量作为参考输入的自适应滤波器,同时对Sigmoid函数进行改进,使得自适应滤波器在前期收敛速度快,且待滤波器收敛后保持较高稳定性。实验结果表明,在相同卫星仰角与电离层时间梯度值下,采用LMS自适应滤波器后电离层异常检测时间缩短,且当电离层时间梯度较小时,该方法也能够实现异常检测,验证了其有效性。     

数据分辨率对最小二乘配置解的影响

数据分辨率是影响地球重力场建模和大地水准面精度的重要因素。基于最小均方误差准则的频域形式探讨了最小二乘配置与数据分辨率之间的关系,给出了依赖数据分辨率的最优线性估计及其误差的一般公式。算例表明,该公式与传统配置公式的结果是一致的。     

基于参数约束的隧道断面抗差拟合研究

城市地铁建设过程中,测量隧道断面并进行椭圆拟合,可得到断面中心坐标和收敛数据,进一步指导施工.隧道施工现场具有干扰多、遮挡多的特点,导致测量数据易出现粗差和数据缺失,进而影响椭圆拟合的准确性.针对隧道断面拟合的难点,本文提出一种基于参数约束的抗差拟合方法:通过最小平方中值方法剔除数据粗差,再利用附带参数约束的最小二乘拟...     

基于导频序列的OFDM信道估计性能分析

正交频分复用(OFDM)作为一种可以有效对抗符号间干扰(ISI)的高速传输技术,得到了广泛的应用,而信道估计技术作为其重要技术之一得到了很大的发展.信道估计分为盲信道估计、半盲信道估计和基于导频的信道估计.主要研究基于导频的最小平方(LS)信道估计和线性最小均方误差(LMMSE,Linear Minimum Mean Square Error)信道估计,在不同的信道环境和不同的循环前缀(CP)和导频子载波数下的性能比较并得出结论.     

基于卡方检验的抗差自适应Kalman滤波在变形监测中的应用

在抗差Kalman滤波的基础上引入双自适应因子,分别对动态模型不准确和观测模型存在粗差进行调节,构建双自适应因子滤波模型。针对抗差自适应Kalman滤波效率较低的缺点,通过构建基于卡方检验的抗差自适应Kalman滤波,先用卡方检验对粗差进行检验,再调用抗差自适应Kalman滤波进行处理。工程实例表明,双自适应因子滤波模型可以很好地抵御粗差,并减弱模型不精确的影响。基于卡方检验的抗差自适应Kalman滤波不仅可以削弱粗差对滤波估值的影响,而且可以提高数据处理的效率。     

直接序列扩频通信中的抗窄带干扰非线性自适应滤波器

分析用于直接序列扩频通信中窄带干扰抑制的几种非线性自适应滤波器,提出了一种称为非线性LTJ(Lattice and Transversal Joint)滤波器的新型非线性抗干扰滤波器.对比几种滤波器的信噪比改善性能、收敛速度以及计算复杂度,发现非线性LTJ滤波器具有收敛速度快的优点,并且在干扰强度较大时,其抗干扰性能要比非线性Lattice滤波器好.     

ICA在合成孔径雷达抗噪声干扰中的应用研究

将ICA（Independence Component Analysis）消噪原理应用于合成孔径雷达抗噪声干扰技术中,用噪声信号和受到干扰的SAR回波数据作为扩展的虚拟观测信号,对扩展的多维加噪观测信号进行分离, 得到源雷达回波信号, 从而实现噪声的有效消除.通过对条带式SAR点目标成像进行仿真试验, 结果表明这种消噪方法在消除SAR噪声干扰中是有效的.     

Comparison on soil carbon stocks between urban and suburban topsoil in Beijing,China

The urban population and urbanized land in China have both increased markedly since the 1980s. Urban and suburban developments have grown at unprecedented rates with unknown consequences for ecosystem functions. In particular, the effect of rapid urbanization on the storage of soil carbon has not been studied extensively. In this study, we compared the soil carbon stocks of different land use types in Beijing Municipality. We collected 490 top-soil samples （top 20 cm） from urban and suburban sites within the Sixth Ring Road of Beijing, which cover approximately 2400 km2, and the densities of soil organic carbon （SOC）, soil inorganic carbon （SIC）, and total carbon （TC） were analyzed to determine the spatial distribution of urban and suburban soil carbon characteristics across seven land use types. The results revealed significant differences in soil carbon densities among land use types. Additionally, urban soil had significantly higher SOC and SIC densities than suburban soil did, and suburban shelterbelts and productive plantations had lower SIC densities than the other land use types. The comparison of coefficients of variance （CVs） showed that carbon content of urban topsoil had a lower variability than that of suburban topsoil. Further findings revealed that soil carbon storage increased with built-up age. Ur- ban soil built up for more than 20 years had higher densities of SOC, SIC and TC than both urban soil with less than 10 years and sub- urban soil. Correlation analyses indicated the existence of a significantly negative correlation between the SOC, SIC, and TC densities of urban soil and the distance to the urban core, and the distance variable alone explained 23.3% of the variation of SIC density and 13.8% of the variation of TC density. These results indicate that SOC and SIC accumulate in the urban topsoil under green space as a result of the conversion of agricultural land to urban land due to the urbanization in Beijing.     

Distribution of soil carbon in different grassland types of the Qinghai-Tibetan Plateau

Accurate estimate of soil carbon storage is essential to reveal the role of soil in global carbon cycle. However, there is large uncertainty on the estimation of soil organic carbon (SOC) storage in grassland among previous studies, and the study on soil inorganic carbon (SIC) is still lack. We surveyed 153 sites during plant peak growing season and estimated SOC and SIC for temperate desert, temperate steppe, alpine steppe, steppe meadow, alpine meadow and swamp, which covered main grassland in the Qinghai Plateau during 2011 to 2012. The results showed that the vertical and spatial distributions of SOC and SIC varied by grassland types. The SOC amount mainly decreased from southeast to northwest, whereas the SIC amount increased from southeast to northwest. The magnitude of SOC amount in the top 50 cm across grassland types ranked by: swamp > alpine meadow > steppe meadow > temperate steppe > alpine steppe > temperate desert, while the SIC amount showed an opposite order. There was a great deal of variation in proportion of SOC and SIC among different grassland types (from 55.17 to 94.59 for SOC and 5.14 to 44.83 for SIC). The total SOC and SIC storage was 5.78 Pg and 1.37 Pg, respectively, in the top 50 cm of soil in Qinghai Province. The mixed linear model revealed that grassland types was the predominant factor in spatial variations of SOC amount while grassland types and soil pH accounted for those of SIC amount. Our results suggested that the community shift of alpine meadow towards alpine grassland induced by climate warming would decrease carbon sequestration capacity by 6.0 kg C m².     

The New Minimum of Sea Ice Concentration in the Central Arctic in 2016

In view of the extremely low sea ice concentration(SIC) appeared at high latitudes of the Arctic in the summer of 2010, the changes of SIC in the central Arctic from 2010 to 2017 were investigated in this paper based on the AMSR-E/AMSR-2 SIC products retrieved by the NT2 algorithm. The results show that the extremely low sea ice concentration in the central Arctic not only occurred in 2010 but also occurred again in 2016, and the daily average sea ice concentration(ASIC) reached a minimum of 0.70, which was significantly lower than the value of 0.78 in 2010 and became a new historical low record. A large area of sea ice in the sector 150°E–180° in 2010 disappeared in 2016, which was the most important difference to produce the new minimum. Also, the ice edge in 2016 retreated into the 85°N circle, whereas in 2010 it was far from the central Arctic. In 2010 and 2016, there were high correlations between the wind stress curl and the relative variation rate of ASIC, which indicates that wind stress curl(WSC) drove the divergence of sea ice. It directly leads to the decrease in the SIC and is the main cause of the extremely low SIC events. The results in this paper show that the decline of Arctic sea ice is represented by not only the reduction of sea ice coverage but also the reduction of SICs. The central Arctic has always been covered by large amount of sea ices, so the drastic reduction of SIC will not only change the structure of the ice field, but also lead to critical climatic effects that deserve further attention.     

Dominant modes of geopotential height in the northern hemisphere in summer on interdecadal timescales

Empirical orthogonal function(EOF) analysis is performed on the field of the northern hemisphere geopotential height at 200-hPa using a 54-year(1958-2011) record of summer data on an interdecadal time scale.The first dominant mode,which shows smooth semi-hemispheric variation with maximum action centers in the western hemisphere in the mid-latitudes over the eastern Pacific,North America,and the North Atlantic,is related to global warming.The second mode,which has a pronounced tropical-extratropical alternating pattern with active centers located over the eastern hemisphere from Western Europe across East Asia to the western Pacific,has a close relationship with the Arctic Oscillation.Further analysis results indicate that the two dominant modes show good correlation with the Arctic sea ice concentration(SIC),with correlation coefficients between these two modes and the first two EOF modes of the Arctic SIC reaching 0.88 and 0.86,respectively.     

Satellite-observed trends in the Arctic sea ice concentration for the period 1979–2016

Arctic sea ice cover has decreased dramatically over the last three decades. This study quanti?es the sea ice concentration(SIC) trends in the Arctic Ocean over the period of 1979–2016 and analyzes their spatial and temporal variations. During each month the SIC trends are negative over the Arctic Ocean, wherein the largest(smallest) rate of decline found in September(March) is-0.48%/a(-0.10%/a).The summer(-0.42%/a) and autumn(-0.31%/a) seasons show faster decrease rates than those of winter(-0.12%/a) and spring(-0.20%/a) seasons. Regional variability is large in the annual SIC trend. The largest SIC trends are observed for the Kara(-0.60%/a) and Barents Seas(-0.54%/a), followed by the Chukchi Sea(-0.48%/a), East Siberian Sea(-0.43%/a), Laptev Sea(-0.38%/a), and Beaufort Sea(-0.36%/a). The annual SIC trend for the whole Arctic Ocean is-0.26%/a over the same period. Furthermore, the in?uences and feedbacks between the SIC and three climate indexes and three climatic parameters, including the Arctic Oscillation(AO), North Atlantic Oscillation(NAO), Dipole anomaly(DA), sea surface temperature(SST), surface air temperature(SAT), and surface wind(SW), are investigated. Statistically, sea ice provides memory for the Arctic climate system so that changes in SIC driven by the climate indices(AO, NAO and DA) can be felt during the ensuing seasons. Positive SST trends can cause greater SIC reductions, which is observed in the Greenland and Barents Seas during the autumn and winter. In contrast, the removal of sea ice(i.e., loss of the insulating layer) likely contributes to a colder sea surface(i.e., decreased SST), as is observed in northern Barents Sea. Decreasing SIC trends can lead to an in-phase enhancement of SAT, while SAT variations seem to have a lagged in?uence on SIC trends. SW plays an important role in the modulating SIC trends in two ways: by transporting moist and warm air that melts sea ice in peripheral seas(typically evident inthe Barents Sea) and by exporting sea ice out of the Arctic Ocean via passages into the Greenland and Barents Seas, including the Fram Strait, the passage between Svalbard and Franz Josef Land(S-FJL),and the passage between Franz Josef Land and Severnaya Zemlya(FJL-SZ).     

Transition Periods Between Sea Ice Concentration and Sea Surface Air Temperature in the Arctic Revealed by an Abnormal Running Correlation

This study used the synthetic running correlation coefficient calculation method to calculate the running correlation coefficients between the daily sea ice concentration(SIC) and sea surface air temperature(SSAT) in the Beaufort-Chukchi-East Siberian-Laptev Sea(BCEL Sea), Kara Sea and southern Chukchi Sea, with an aim to understand and measure the seasonally occurring changes in the Arctic climate system. The similarities and differences among these three regions were also discussed. There are periods in spring and autumn when the changes in SIC and SSAT are not synchronized, which is a result of the seasonally occurring variation in the climate system. These periods are referred to as transition periods. Spring transition periods can be found in all three regions, and the start and end dates of these periods have advancing trends. The multiyear average duration of the spring transition periods in the BCEL Sea, Kara Sea and southern Chukchi Sea is 74 days, 57 days and 34 days, respectively. In autumn, transition periods exist in only the southern Chukchi Sea, with a multiyear average duration of only 16 days. Moreover, in the Kara Sea, positive correlation events can be found in some years, which are caused by weather time scale processes.     

Ecological impact assessment method of highways in Tibetan Plateau:A Case study of Gonghe-Yushu Expressway

In recent years,the ecological environment along highways in Tibetan Plateau has been severely affected due to the rapid construction of highways.In order to solve the problems of multiple indicators and inconsistent criteria in the ecological impact assessment of highways,and to scientifically screen assessment indicators,the paper proposes a multi-round indicator screening method,which combines literature analysis,expert rating,and statistical analysis.Based on this screening method,normalized difference vegetation index,land surface temperature,elevation,and normalized difference soil index are screened out.Combined with multiple linear regression,an ecological impact assessment model is established and applied to ecological impact assessment of Gonghe-Yushu Expressway.The results show that the expressway construction is the first driving force for the deterioration of the ecological environment along the roadside,and its interference range on the desert grassland ecosystem is greater than that on the agroforestry system.The ecological environment within 150 m on both sides of the expressway should be protected.     

气象因素对倾斜仪观测干扰特征分析

采用常熟台水管仪与垂直摆2009～2015年观测数据,研究了气压、降雨、气温、洞温等因素对地倾斜观测的影响特征。结果表明,降雨对地倾斜观测数据干扰最为显著,表现为NS分量发生南倾,EW分量发生西倾,量级上NS分量受干扰程度比EW分量大,垂直摆受干扰程度比水管仪大;气压变化影响表现为短周期扰动,并导致日值曲线出现短时间畸变;气温及洞温变化影响观测值出现明显的年变规律和年变幅变化,对日观测值影响不明显。     

Detection of PPM acoustic Pulse in shallow sea channels

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