Analysis of multiple scattering from two-dimensional dielectric sea surface with iterative Kirchhoff approximation

<正>An iterative method in the Kirchhoff approximation is proposed for high frequency multiple electromagnetic scattering from two-dimensional dielectric sea surface.The multiple interaction of the scattering field is characterized with the corrected electromagnetic currents of the wind-driven sea surface.The actual surface currents are approximated with the iterative solution of the corrected currents.A newly developed sea spectrum,Elfouhaily spectrum,is utilized to build the sea surface model.The shadowing correction is improved by the Depth-Buffer algorithm.The validity of the iterative Kirchhoff approximation is verified by the agreement of backscattering coefficients with the measured data.     

Performance analysis of multi‐input multi‐output systems with maximum likelihood detection over shadowed fading channels

Multiple‐input multiple‐output (MIMO) transmission techniques constitute an important technology in modern wireless communication. Hence, performance analysis methods for such systems are of considerable interest. This paper considers first the average pairwise error probability for uncoded MIMO systems employing maximum likelihood detection over a composite Rayleigh‐Lognormal fading channel with spatial correlation. It provides general results, applicable also to a wider class of shadowing models, concerning asymptotical diversity gains and shows that they are not changed by such shadowing. Then, analytical evaluation techniques for bit‐error‐rate (BER) over composite Rayleigh‐Lognormal fading channels, based on the truncated union bound and the transfer function, are considered. Furthermore, these techniques are modified for applications over spatially correlated channels. This paper shows that such performance evaluation techniques provide good approximations to BER of spatially uncorrelated MIMO systems and also in the presence of moderate spatial correlation, over Rayleigh‐Lognormal fading channels. Copyright © 2013 John Wiley & Sons, Ltd.     

Partial shadowing,MPPT performance and inverter configurations: observations at tracking PV plants

When analysing the influence of shade on photovoltaic (PV) systems, the intuitive assumption is that conversion architectures with more inverters, such as string‐ and module‐inverters, will have lower energy losses associated with partial shading of the generators. However, other phenomena which can affect a system's response to shade, for example, the way in which the inverter performs the maximum power point tracking (MPPT), mean that modular configurations are not always the least susceptible to shade effects. We present a case in which the general tendency of many of the currently available commercial inverters to remain in local power maxima results in a string‐inverter configuration behaving worse in response to shade than a central‐inverter configuration. Experimental data were collected throughout 2005 and 2006 from PV plants in Arguedas and Sesma (Spain). We interpret our observations with theoretical analysis based on the results of simulation experiments. Copyright © 2008 John Wiley & Sons, Ltd.     

发展中的三维成像合成孔径雷达

第１ 节简述了二维ＳＡＲ的方位和距离高分辨率的方法。第２ 节论述了用干涉仪法获得成像单元的相位差以及三维成像的基础干涉条纹图。由相位差值和其他可测知值推导出目标高度。机载ＳＡＲ通常采用双天线,因此它一次飞行即能三维成像,称为单航过法。星载ＳＡＲ采用双天线很困难,已进行过的三维成像均为单天线双航过法。第３ 节讨论了测高误差。第４ 节指出了测高中遮挡和重叠的影响。第５ 节论述了如何选择参数仪相位值不模糊以及差相位值模糊怎样解开相位重叠。第６ 节说明了机载干涉仪ＳＡＲ理论上虽能得到很好的测高精度,但气流使机身产生俯仰、横滚和偏转,因此必须设法解决气流影响问题。第７节讨论了差分干涉仪有可能对地震和火山喷发等重大灾害作出事前预报。第８节简述了发展趋势。第９ 节指出了三维成像的机理同样可在声纳上应用。     

Shadowing correlation assessment and modeling for satellite diversity in urban environments

Non‐geostationary orbit satellite networks have dynamic, yet deterministic topologies. This paper deals with the consequences of relying on the use of multiple visible satellites to improve availability with time/locations through satellite diversity techniques. The assumption of independent blockage events in two different satellite‐to‐mobile links is generally not accurate and information on shadowing correlation should be taken into account in the assessment of availability.In this paper a shadowing correlation study for urban environments is presented and a model for the real environments, as well as for a generic urban environment is inferred. The model proposed here is simple and can be run on a computer. It also relates urban and constellation geometries thus allowing the identification of those cases for which satellite diversity gain should be expected. As a result of this analysis and modelling, we present empirical analytical expressions describing positive correlation coefficient as a function of satellite angular separation (azimuth and elevation). We also show that an angle exists above which correlation can be negative and satellite diversity can sensibly improve link availability. Copyright © 2002 John Wiley & Sons, Ltd.     

三维合成孔径雷达的原理和实例

简单介绍机载合成孔径雷达用双天线干涉法测高得到三维SAR成像的原理并给出了实例。实例中选用英国Andover飞机在C波段获得的Malvern山的三维立体像和美国NASA／JPL设计的AIRSAR／TOPSAR三波段干涉测高在C波段洲得的玻利维亚Andes山的立体像。文中指出,航天飞机只给出了单天线双航过测高的实例。而干涉法有时套出现相位折叠,必须解开。文中给出了相位解开的参考文献。     

Effect of Microdiversity and Macrodiversity on Average Bit Error Probability in Gamma‐Shadowed Rician Fading Channels

In this letter, we analyze the error performance of a mobile communication system with microdiversity and macrodiversity reception in gamma‐shadowed Rician fading channels for a binary differential phase‐shift keying modulation scheme. Analytical expressions for the probability density function (PDF) and moment‐generating function (MGF) are derived. The average bit error probability can be calculated by averaging the conditional bit error probability over the PDF or using the MGF‐based approach. Numerical results are graphically presented to show the effects of macrodiversity, correlation, number of diversity branches, and severity of both fading and shadowing.     

一种室内无线网络多用户自适应定位及跟踪算法

室内移动网络中各用户的路由策略和其所在的位置紧密相关,所以为提供高效的路由方案,首先要实现准确的室内定位。同时,某些特定的部门,如警方、军方和消防等,更加迫切的需要实用的室内定位算法。但是由于室内环境复杂性的影响,手机和各接收机的距离估计可能存在严重误差。针对复杂的室内环境,提出了一种利用测量到用户之间的接收功率实现定位及跟踪的算法。仿真和模拟证明该方法是有效的。     

基尔霍夫近似下激光海面漫反射组网通信特性

针对激光点对点通信方式的不足,根据舰艇编队通信的实际需要,提出了利用海面作为激光漫反射媒介的一对多的组网通信方法,并且采用基尔霍夫近似的方法对激光海面漫反射通信的特性进行了研究。通过对激光光束入射海面后产生的散射场的分析计算,采用遮蔽函数对计算过程中的阴影效应加以修正,得出了较为准确的2维激光海面双站散射系数和后向散射系数,并进行了实验验证,说明了激光海面漫反射组网通信方法的可行性。