基于图形电磁学的雷达散射截面计算方法改进

图形电磁学(GRECO)可以高效计算电大目标雷达散射截面(RCS)。但传统GRECO算法无法直接计算双站RCS和仿真多次反射,存在计算精度依赖屏幕分辨率的缺点。文中提出了基于渲染后的像素信息还原目标几何信息的方法,使其能够计算双站RCS,并结合弹跳射线法(SBR)计入多次反射的影响。同时,研究基于帧缓存对象(FBO)的离屏GRECO方法,克服了其计算精度依赖屏幕分辨率的缺点。     

飞行器座舱RCS可视化计算方法研究

根据分层媒质理论和图形电磁学理论,得到并验证了一种新的分析和计算座舱ＲＣＳ的方法,低ＲＣＳ座舱罩表面的散射场利用图形电磁学计算方法（ＧＲＥＣＯ）求解,其中边缘效应利用增量长度ＩＬＤＣ方法估算;舱内结构散射分析,应用分层媒质理论得到介质舱罩反射系数的传输系数,同时采用能量分布调制和随机相位加权的方法计算舱内结构散射,在本文的最后给出了数据分析结果。     

基于图形电磁学的近场角闪烁预估方法研究

角闪烁的研究大多基于远场条件的假设,但是近场条件下,角闪烁对雷达的跟踪误差产生更大影响,近场角闪烁的研究更加具有学术和实际工程应用意义。该文推导了近场条件下角闪烁线偏差的解析计算方法,并将图形电磁学(GRECO)应用到近场角闪烁的预估中,使其具有实时性强、电大目标计算的能力且不需要散射中心的提取过程。雷达波束不完全覆盖目标的情况被首次考虑,使得全程估计目标的雷达跟踪误差成为可能。通过不同模型的仿真计算结果与理论计算结果比较,验证了计算方法的正确性。     

基于图形电磁学雷达散射截面计算方法之改进

图形电磁学（GRaphical Electromagnetic COmputing,GRECO）利用图形加速卡和Z-Buffer技术可较为有效地解决传统电磁计算方法中存在的消隐困难和非可视化难题,是求解高频电大尺寸目标特性最有效的方法之一。但传统GRECO算法存在着无法精确提取目标法矢信息、计算精度依赖屏幕分辨率和多次反射计算困难等缺点,限制了这种方法的使用。本文针对GRECO方法就精确提取像素几何信息方法进行了简要改进,将其与基于帧缓存对象（Frame-Buffer Object,FBO）的离屏渲染技术相结合,提出了改进的GRECO算法,克服了传统GRECO算法无法精确提取像素法矢信息和计算精度依赖屏幕分辨率的缺点。进而,采用AP／PO（Area Projection／Physical Optics）法,并对传统的多次散射面元对判别方法进行了适当改进,实现了对产生多次反射目标的雷达截面计算。     

复杂目标的太赫兹波近场RCS快速计算

在太赫兹频段,散射目标大部分处于近场区域,远场计算方法已经不再适用,为此该文推导了近场雷达散射截面(RCS)的计算公式。针对太赫兹频段近场条件下,物理光学法(PO)由于面元数量巨大引起的遮挡判断耗时过长,以及图形电磁学(GRECO)以像素为计算单位计算误差过大的问题,该文提出一种以面元为计算单位,以像素为遮挡判断单位的复杂目标太赫兹波近场RCS的快速计算方法,该方法在保证计算精度的基础上,大大降低了遮挡判断的计算复杂度和时间。最后,以标准目标体平板、球体以及复杂目标体卫星在不同距离下的雷达散射截面的计算为例,验证了该方法的有效性和准确性。     

一体化双站散射图形算法

研究了图形算法计算双站RCS的方法，并将RCS分析与目标外形设计相结合，提出了一种一体化方法，将图形算法集成到CAD造型软件中，能够在目标外形设汁阶段随时分析其双站散射特性。计算实例说明．这种方法不但能够满足计算精度要求，而且可以简化RCS的前处理工作，提高目标设计的总体效率。     

雷达目标角闪烁预估计算

介绍了目标角闪烁的计算方法。利用SCTE预估系统对目标雷达散射截面预估后，对其中的相位进行求导从而实现雷达目标角闪烁的预估计算。文中选用三球目标模型进行了理论和预估计算，两结果非常一致，验证了SCTE预估系统能够对雷达目标角闪烁准确预估。     

计算电磁学的进展与展望

本文对计算电磁学的发展现状作了总结，对常用的电磁计算方法作了必要的分类，重点介绍了目前计算电磁学领域出现的颇有应用前景的新方法和新观点，并以今后该领域的发展方向提出了若干建议。     

Matlab GUI在电磁学可视化教学中的应用

针对电磁学课程内容理论性强、概念抽象的特点,利用Matlab强大的数值计算和图形绘制功能,文章以电粒子在均匀电磁场中的运动和平面电磁波的传播为例,制作了Matlab图形用户界面,动态展示了带电粒子的运动和平面电磁波的传播,解决了传统教学方式在可视化环节上难以实现动态性的问题,展现了Matlab的图形用户界面在电磁学可视化教学方面的优越性。     

准八木型相控阵天线模式项散射特性研究

采用工程预估方法对大规模相控阵天线模式项散射特性进行分析,考虑了均匀矩形阵列相控阵天线在不同波束扫描角度下的散射特性.实测相控阵为40×50准八木型均匀矩形阵列天线,工作在X波段,中心频率为10 GHz,峰值增益为37.421 33 dBi,运用HFSS阵列综合预估技术给出了数学近似公式和近似综合2种近似方法计算天线模式项雷达散射截面.仿真结果表明相对于传统预估技术,近似方法计算精度虽有所下降,但效率很高,大大提高了对天线阵列散射预估的速度.     

混合树估计算法及其应用

提出一种混合树分布估计算法,将一种新的图形模式,混合树图形模式纳入了分布估计算法框架中。算法在进化过程中以选择得到的中间群体为数据集,自动学习混合树模型以描述中间群体中各基因之间复杂依赖关系,并从该模型中抽样得到新一代群体。算法具有更强的自适应性,对进化方向也具有更好的指导作用,模型所具有的聚类特性使得算法能够很好的求解多模态优化问题。将算法实际应用于求解多目标图像识别问题,表现出了良好的优化性能。     

Synthesis of Embedded Software from Synchronous Dataflow Specifications

The implementation of software for embedded digital signal processing (DSP) applications is an extremely complex process. The complexity arises from escalating functionality in the applications; intense time-to-market pressures; and stringent cost, power and speed constraints. To help cope with such complexity, DSP system designers have increasingly been employing high-level, graphical design environments in which system specification is based on hierarchical dataflow graphs. Consequently, a significant industry has emerged for the development of data-flow-based DSP design environments. Leading products in this industry include SPW from Cadence, COSSAP from Synopsys, ADS from Hewlett Packard, and DSP Station from Mentor Graphics. This paper reviews a set of algorithms for compiling dataflow programs for embedded DSP applications into efficient implementations on programmable digital signal processors. The algorithms focus primarily on the minimization of code size, and the minimization of the memory required for the buffers that implement the communication channels in the input dataflow graph. These are critical problems because programmable digital signal processors have very limited amounts of on-chip memory, and the speed, power, and cost penalties for using off-chip memory are often prohibitively high for embedded applications. Furthermore, memory demands of applications are increasing at a significantly higher rate than the rate of increase in on-chip memory capacity offered by improved integrated circuit technology.     

Direct blind multiuser detection for CDMA in multipath withoutchannel estimation

We consider the blind multiuser detection problem for asynchronous DS-CDMA systems operating in a multipath environment. Using only the spreading code of the desired user, we first estimate the column vector subspace of the channel matrix by multiple linear prediction. Then, zero-forcing detectors and MMSE detectors with arbitrary delay can be obtained without explicit channel estimation. This avoids any channel estimation error, and the resulting methods are therefore more robust and more accurate. Corresponding batch algorithms and adaptive algorithms are developed. The new algorithms are extremely near-far resistant. Simulations demonstrate the effectiveness of these methods     

基于复杂网络的Psor链路预测算法

复杂网络领域中,链路预测在网络演化规律的研究中被广泛应用,具有巨大的实际应用价值。针对现有的基于网络拓扑的链路预测方法存在预测精度偏低的问题,提出了一种基于复杂网络的Psor链路预测算法。该算法综合节点自身和邻居节点的度,定义了节点的Psor指数和Psor相似性指标进行链路预测。该算法能够全面考虑复杂网络的局部结构信息,更加准确地对复杂网络链路进行预测。仿真结果表明,Psor链路预测算法的预测精度相比8种经典的相似性算法的预测精度最高提升了37.96%。     

High-frequency RCS of complex radar targets in real-time

This paper presents a new and original approach for computing the high-frequency radar cross section (RCS) of complex radar targets in real time with a 3-D graphics workstation. The aircraft is modeled with I-DEAS solid modeling software using a parametric surface approach. High-frequency RCS is obtained through physical optics (PO), method of equivalent currents (MEC), physical theory of diffraction (PTD), and impedance boundary condition (IBC). This method is based on a new and original implementation of high-frequency techniques which the authors have called graphical electromagnetic computing (GRECO). A graphical processing approach of an image of the target at the workstation screen is used to identify the surfaces of the target visible from the radar viewpoint and obtain the unit normal at each point. High-frequency approximations to RCS prediction are then easily computed from the knowledge of the unit normal at the illuminated surfaces of the target. The image of the target at the workstation screen (to be processed by GRECO) can be potentially obtained in real time from the I-DEAS geometric model using the 3-D graphics hardware accelerator of the workstation. Therefore, CPU time for RCS prediction is spent only on the electromagnetic part of the computation, while the more time-consuming geometric model manipulations are left to the graphics hardware. This hybrid graphic-electromagnetic computing (GRECO) results in real-time RCS prediction for complex radar targets     

New efficient LS and SVD based techniques for high-resolutionfrequency estimation

New least squares and singular value decomposition based methods for the estimation of the frequencies of complex sinusoids in white noise are presented. The methods are based on a new symmetric prediction problem that has some very useful properties leading to algorithms that have considerably reduced complexity. The new symmetric predictor is superior in performance as compared to the well known symmetric Smoother and has a performance comparable to other well known methods. Finally a new LS based method, which combines the new prediction technique with the FBLP method is proposed. This method performs slightly better than the FBLP offering at the same time a significant computational saving. As a by-product in the derivation of the new methods is the establishment of some useful properties concerning the eigenstructure of Hermitian and Persymmetric matrices     

Algorithmically engineered fast multichannel adaptive filter basedon QR-RLS

A fast version of the multichannel QR algorithm for RLS adaptive filtering, with channel filters of unequal length, is derived. This is achieved by applying the techniques of algorithmic engineering to a signal flow graph representation of the basic QR RLS algorithm. By virtue of this graphical approach, the derivation is relatively straightforward and circumvents the complex and notationally verbose matrix algebra usually involved in the derivation of fast RLS algorithms in general and the previously published, unequal-length, multichannel RLS lattice algorithm in particular     

自由空间复杂导体目标的太赫兹RCS高频分析方法

研究了自由空间复杂导体目标的太赫兹（THz）雷达散射截面（RCS）的高频求解方法。将并矢格林函数引入物理光学方法中,对自由空间环境进行考虑,推导出自由空间物理光学分析方法,并结合图形电磁计算（GRECO）方法,采用分区显示算法改进后,在Visual C++ 2010 程序中实现目标的OpenGL 显示,对自由空间复杂导体目标进行消隐判断,提取像素面元法矢量和深度缓存等有效信息,计算了自由空间复杂导体目标的THz RCS。最后,将程序计算结果与FEKO 软件仿真结果进行比较,结果证明该方法的有效性和准确性。该研究结果为THz 雷达未来在军事、天文和遥感等领域的应用提供了重要依据和方法。     

Improved spectral resolution

Two new methods are presented for the estimation of the frequencies of closely spaced complex valued sinusoidal signals in the presence of noise. The most effective method is a computationally efficient method for realization of maximum likelihood or maximum posterior probability estimates of the frequencies. The second method is a class of algorithms for removing some of the deficiencies of present adaptive filtering and correlation-estimation approaches to estimation of frequencies, such as the forward-backward linear prediction method. In both of these new methods one is fitting a signal model to data. In method 1 the data are the observed samples of two complex sinusoids plus noise. In the second method the data are elements of an estimated correlation matrix, or of some of its eigenvectors, obtained from the observed samples.     

Watermarking mesh-based representations of 3-D objects using local moments.

A new methodology for fingerprinting and watermarking three-dimensional (3-D) graphical objects is proposed in this paper. The 3-D graphical objects are described by means of polygonal meshes. The information to be embedded is provided as a binary code. A watermarking methodology has two stages: embedding and detecting the information that has been embedded in the given media. The information is embedded by means of local geometrical perturbations while maintaining the local connectivity. A neighborhood localized measure is used for selecting appropriate vertices for watermarking. A study is undertaken in order to verify the suitability of this measure for selecting vertices from regions where geometrical perturbations are less perceptible. Two different watermarking algorithms, that do not require the original 3-D graphical object in the detection stage, are proposed. The two algorithms differ with respect to the type of constraint to be embedded in the local structure: by using parallel planes and bounding ellipsoids, respectively. The information capacity of various 3-D meshes is analyzed when using the proposed 3-D watermarking algorithms. The robustness of the 3-D watermarking algorithms is tested to noise perturbation and to object cropping.