改进的相控阵雷达信号检测方法

针对传统雷达信号检测方法对相控阵雷达信号检测概率较低的问题,提出了一种结合小波降噪和极值序列法的信号检测方法。该方法采用小波阈值降噪法对雷达信号进行预处理,以提高侦收信号的信噪比,利用极值序列法在高信噪比下检测精度较高的优势,完成对信号的准确检测和参数的精确估计。仿真结果表明,与传统检测方法相比,该方法在低信噪比下对相控阵雷达信号的检测概率平均提高21.8%。     

小波包变换及其在低信噪比雷达信号检测中的应用

雷达对目标进行检测之时，常常遇到目标回波信号被噪声污染的问题。为了把弱目标信号从强噪声背景中检测出来，对小波包变换良好的时频分析特性进行了分析，根据信号与噪声具有不同的Lipschitz指数，通过引入子频带∞-范数，对信号和噪声进行频谱分析，将最佳子空间的熵值及最佳子空间在完整二叉树中的位置参数作为特征量，应用浮动阈值去噪方法，解决了低信噪比情况下的雷达信号检测。最后，通过计算机的数值计算，模拟了小波包变换和小波变换在低信噪比雷达信号检测中的具体应用，得出了在低信噪比信号检测方面小波包变换优于小波变换的结论。     

不同小波基对探地雷达数据椒盐噪声处理分析

探地雷达因其无损性而广泛应用于工程结构体检测及异常体探测,但其信号易受干扰,常含大量的椒盐噪声,传统时域滤波的去噪效果难以保证,为此将时频域的小波变换应用于探地雷达信号的椒盐噪声去噪处理.通过在正演记录中添加高斯白噪,得到信噪比为1、2、5、10的探地雷达模拟记录.选用不同类型小波基进行滤波处理,并计算滤波后的峰值信噪比,结果显示紧支撑正交小波基去噪效果最好,信噪比为2的模拟记录峰值信噪比值增大至17.3663.进一步将该小波基用于实测记录的去噪处理,实测剖面中90％以上的椒盐噪声被滤除,有效反射得以突出.结果 表明:小波变换能应用于探地雷达数据中椒盐噪声的去除,但小波基的选择会对去噪效果产生显著影响,实际应用中值得关注.     

基于小波域KL变换的地质雷达信号处理技术研究

为了克服现有信号处理算法对地质雷达直耦波和噪声滤除的不足,基于KL变换和小波变换进行算法融合设计,提出一种适用于地质雷达信号滤波的小波域KL变换方法。采用电磁波时域有限差分法模拟雷达检测过程,并基于理想无噪声的雷达仿真信号设计验证实验,通过与KL变换方法、小波阈值去噪方法的对比,对小波域KL变换方法的滤波效果进行定量分析和评价。实验结果表明:小波域KL变换对于直耦波的辨识能力较强,用于地质雷达信号直耦波的去除可以取得理想的效果;在采用KL变换和小波变换滤除噪声时,去噪信号的信噪比分别为10.16和15.12,而小波域KL变换对应的结果为18.34,对于噪声的滤除具有更好的效果;同时,小波域KL变换滤波结果对小波函数和分解层数的敏感度较低,对于深部噪声信号的辨识能力亦较强。基于地质雷达实测数据的测试结果同样验证了小波域KL变换方法在实际工程应用中的良好性能。     

基于小波域KL变换的地质雷达信号处理技术

为了克服现有信号处理算法对地质雷达直耦波和噪声滤除的不足,基于KL变换和小波变换进行算法融合设计,提出一种适用于地质雷达信号滤波的小波域KL变换方法。采用电磁波时域有限差分法模拟雷达检测过程,并基于理想无噪声的雷达仿真信号设计验证实验,通过与KL变换方法、小波阈值去噪方法的对比,对小波域KL变换方法的滤波效果进行定量分析和评价。实验结果表明:小波域KL变换对于直耦波的辨识能力较强,用于地质雷达信号直耦波的去除可以取得理想的效果;在采用KL变换和小波变换滤除噪声时,去噪信号的信噪比分别为10.16和15.12,而小波域KL变换对应的结果为18.34,对于噪声的滤除具有更好的效果;同时,小波域KL变换滤波结果对小波函数和分解层数的敏感度较低,对于深部噪声信号的辨识能力亦较强。基于地质雷达实测数据的测试结果同样验证了小波域KL变换方法在实际工程应用中的良好性能。     

利用多尺度小波包变换和三阶谱对双模噪声去噪处理

文章为了改善信号检测性能,利用多尺度小波包变换良好的时频局部分析能力和三阶谱对有用信号中夹杂的双模噪声进行去噪。理论分析和仿真结果表明,该方法不仅具有算法比较简单和实时性较强的特点,而且大大提高了输出信噪比,比传统的小波包处理要优越。     

基于小波尺度相关的船舶轴频电场检测方法

为了提高低信噪比下对海水中被衰减的轴频电场信号的检测能力,提出一种基于小波尺度相关的船舶轴频电场检测算法.首先,使用小波变换对信号进行分解,并对噪声能量进行估计;然后,利用小波尺度相关对噪声和信号进行分离,并采用均值滤波降低小波系数平移的干扰;最后,提取最大尺度的相关系数作为特征值,对信号进行滑动检测.通过该算法和小波熵算法对实测数据和仿真数据进行处理和对比分析,结果表明:此算法在低信噪比情况下具有更高的稳定性和更好的检测效果.     

基于混沌理论和小波变换的微弱周期信号检测方法

根据小波变换具有多分辨率,混沌系统对噪声的强免疫力和对周期微弱信号的敏感性等特性,通过对小波阈值去噪方法和混沌Duffing振子方程的改进,提出小波阈值去噪和混沌系统相结合的微弱周期信号检测新方法.该方法利用小波变换的平滑作用对包含噪声的信号进行有限离散处理,并根据小波分解尺度确定阈值去噪深度,然后把重构的信号作为周期策动力的摄动并入混沌系统,采用混沌振子阵列实现在噪声背景下微弱信号的检测,并采用梅尔尼科夫方法作为混沌判据.该检测方法克服了以往小波分解对尺度确定的盲目性和阈值选择的不合理性以及对混沌临界状态与周期态区别的模糊性:同时能检测多种频率的信号.仿真测试表明:该方法直观、高效,检测精度高,检测的最低信噪比达到-100dB,频率误差为0.04％左右,改善了湮没在强噪声下的微弱信号检测技术.     

小波阈值降噪在岸桥小车轨道振动信号处理中的应用

针对测量时振动信号易受噪声干扰的特点,采用小波降噪法对原始信号进行降噪处理。小波具有“变焦距”、较好的时频局部分析能力等特性,适合非平稳信号振动噪声处理。分别通过小波阈值降噪法对仿真信号并口岸桥小车轨道铰点振动信号进行降噪处理。试验表明,小波阈值降噪法能够较好的消除噪声,能有效提高信噪比、降低均方误差,为进一步分析振动信号奠定了基础。     

应用小波变换进行信号消噪处理

小波分析在时域与频域同时具有良好的局部化性质,可以利用信息信号和噪声信号在小波变换下具有截然不同的奇异性来区分信息信号与噪声信号。根据信号与噪声在二进制小波变换随尺度参数减小时信息信号和白噪声信号的小波变换的模极大值点变化的不同性质做消噪处理,然后再重建消噪后的信号。采用本研究所给出的方法对实际数据进行处理,其结果表明应用小波分析可以明显地抑制噪声,提高信噪比。此方法具有很好的实用价值。     

An Index mechanism for multi-scale view in spatial databases

There are numerous geometric objects stored in the spatial databases. An importance function in a spatial database is that users can browse the geometric objects as a map efficiently. Thus the spatial database should display the geometric objects users concern about swiftly onto the display window. This process includes two operations:retrieve data from database and then draw them onto screen. Accordingly, to improve the efficiency, we should try to reduce time of both retrieving object and displaying them. The former can be achieved with the aid of spatial index such as R-tree, the latter require to simplify the objects. Simplification means that objects are shown with sufficient but not with unnecessary detail which depend on the scale of browse. So the major problem is how to retrieve data at different detail level efficiently. This paper introduces the implementation of a multi-scale index in the spatial database SISP (Spatial Information Shared Platform) which is generalized from R-tree. The difference between the generalization and the R-tree lies on two facets: One is that every node and geometric object in the generalization is assigned with a importance value which denote the importance of them, and every vertex in the objects are assigned with a importance value,too. The importance value can be use to decide which data should be retrieve from disk in a query. The other difference is that geometric objects in the generalization are divided into one or more sub-blocks, and vertexes are total ordered by their importance value. With the help of the generalized R-tree, one can easily retrieve data at different detail levels.Some experiments are performed on real-life data to evaluate the performance of solutions that separately use normal spatial index and multi-scale spatial index. The results show that the solution using multi-scale index in SISP is satisfying.     

Wuhan University Journal of Natural Sciences TOTAL CONTENTS

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Advances in broadband wireless communications under high-mobility scenarios

Future mobile communication systems aim at providing very high data transmission rates, even in high-mobility scenarios such as high-speed wheel-track trains, maglev trains, highway vehicles, airplanes, guided missiles or spacecraft. A particularly important commercial application is the strong and increasing worldwide demand for high- speed broadband wireless communications （up to 574.8 km/ h test speeds or 380 km/h commercial speeds） in railways, providing data, voice and video services for applications such as onboard entertainment services to passengers, train control, train dispatch, train sensor status handling and sur- veillance. In such high-mobility scenarios, there are a number of communication challenges, including fast hand- over, location updating, high-speed channel modeling, estimation and equalization, anti-Doppler spreading tech- niques, fast power control, and dedicated network architec- ture. Because signal transmission in very high-speed scenarios will inevitably experience serious deterioration, it is imperative to develop key broadband mobile communi- cation techniques for such high-speed vehicles.     

Perspherical Approaches for Electrons in Atoms and Charged Excitons in Quantum Wells

Instead of following Fock’s expansion,we solve the Schrodinger equation for some quantum mechanical manybody systems such as electrons in atoms and charged excitons in quantum wells in a similar way in hyperspherical coordinates by expanding the wave functions into orthonormal complete basis sets of the hyperspherical hannonics(HHs)of hyperangles and generalized Laguerre polynomials(GLPs)of the hyperradius.This leads the equation to     

Scale-based spatial data model for GIS

Being the primary media of geographical information and the elementary objects manipulated, almost all of maps adopt the layer-based model to represent geographic information in the existent GIS. However, it is difficult to extend the map represented in layer-based model. Furthermore, in Web-Based GIS, It is slow to transmit the spatial data for map viewing. In this paper, for solving the questions above, we have proposed a new method for representing the spatial data. That is scale-based model. In this model we represent maps in three levels: scale-view, block, and spatial object, and organize the maps in a set of map layers, named Scale-View, which associates some given scales.Lastly, a prototype Web-Based GIS using the proposed spatial data representation is described briefly.     

英文诗歌中的喻类修辞

为了有助于提高英文爱好者的个人情操、文化素养和学习兴趣,以及专业人员对英语学习和研究进行多途径的探索,本文通过一些精选诗歌的引证和分析,着重论述了喻类修辞法在英文诗歌中的运用其及效果。     

Man Is Unable to Change the Miserable Life——Analysis of the Arrangement of Four Characters in The Glass Menagerie

Tennessee Williams is considered as one of the most important American playwrights since World War II.The Glass Menagerie is his first successful drama,which describes a tragic situation of family and means to say that Man is unable to change the miserable life,no matter whatever means he try,This essay focuses on the analysis of the arrangement of the four main characters:Laura.Amanda,Jim and Tom to reveal the theme.Laura is fragile.Amanda is brave.Jim is vital.Tom is sensible.And all of them develop and try the different means to struggle against life,but fail tragically.With the evidence,the paper comes to conclusion naturally that Man is unable to change the miserable life,and he dooms to fail.     

Characterization of root-nodulating bacteria on Retama raetam in arid Tunisian soils

The aim of this study is to investigate the diversity of Retama raetam root-nodule bacteria isolated from arid regions of Tunisia. Twelve isolates, chosen as representative for different 16S rRNA gene patterns, were characterized by 16S rRNA gene sequencing and phenotypic analysis. Isolates were assigned to Sinorhizobium, Rhizobium and Agrobacterium. Symbiotic properties of Sinorhizobium and Rhizobium isolates showed a large diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Strain RK 22 identified as Rhizobium was the most effective isolate.     

An Affordable Accurate Evaluation of the Binding Conformations Predicted by Molecular Docking Studies in Bio-System

正Recently,docking has been widely used to predict the binding-modes of protein-inhibitors,when the crystal complexes structure was absent.Most docking algorithms are able to generate a large number of probable conformations,it,however,is difficult to effectively evaluate these docking poses and identify the most reasonable bindingmode.In the present study,on the basis of the crystallographic data of human 3-hydroxy-3-methylglutaryl coenzyme     

WIMAX与WI-FI技术分析及联合组网

介绍了WiMAX与Wi-Fi两种无线宽带接入技术,并对两者之间的关系及相互之间的影响做了对比及分析,并对WiMAX的关键技术进行了详细说明,最后对两者的联合组网方式做了简单的探讨。