2-D SPATIAL-SPECTRUM ESTIMATION FORWIDE-BAND SOURCES BASED ON INTERPOLATED CIRCULAR ARRAYS

In array signal processing, 2-D spatial-spectrum estimation is required to determine DOA of multiple signals. The circular array of sensors is found to possess several nice properties for DOA estimation of wide-band sources. C. U. Padmini, et al.(1994) had suggested that the frequency-direction ambiguity in azimuth estimation of wide-baud signals received by a uniform linear array (ULA) can be avoided by using a circular array, even without the use of any delay elements. In 2-D spatial-spectrum estimation for wide-band signals, the authors find that it is impossible to avoid the ambiguity in source frequency-elevation angle pairs using a circular array. In this paper, interpolated circular arrays are used to perform 2-D spatial-spectrum estimation for wide-band sources. In the estimation, a large aperture circular array (Υ】λmin/2) is found to possess superior resolution capability and robustness.

A Virtual Walk along Street Based on View Interpolation

Image morphing is a powerful tool for visual effect. In this paper, a view interpolation algorithm is proposed to simulate a virtual walk along a street from start position to end position. To simulate a virtual walking view needs to create new appearing scene in the vision-vanishing point and disappearing scene beyond the scope of view. To attain these two aims we use two enhanced position parameters to match pixels of source images and target images. One enhanced position parameter is the angular coordinates of pixels. Another enhanced position parameter is the distances from pixels to the vision-vanishing point. According to the parameter values, pixels beyond the scope of view can be ＂moved＂ out in linear interpolation. Result demonstrates the validity of the algorithm. Another advantage of this algorithm is that the enhanced position parameters are based on real locations and walking distances, so it is also an approach to online virtual tour by satellite maps of virtual globe applications such as Google Earth.

Study on Solder Joint Reliability of Plastic Ball Grid Array Component Based on SMT Products Virtual Assembly Technology

Based on surface mount products virtual assembly technology,the solder joint reliability of plastic ball grid array (PBGA) was studied. Four process parameters,including the upper pad diameter,the stencil thickness,the chip weight on a single solder joint and the lower pad diameter were chose as four control factors. By using an L25(56) orthogonal array the PBGA solder joints which have 25 different process parameters’ levels combinations were designed. The numerical models of all the 25 PBGA solder joints were developed and the finite element analysis models were setup. The stress and strain distribution within the PBGA solder joints under thermal cycles were studied by finite element analysis,and the thermal fatigue life of PBGA solder joint was calculated using Coffin-Manson equation. Based on the calculated thermal fatigue life results,the range analysis was performed. The results of study show that that the impact sequence of the four factors from high to low on the fatigue life of PBGA solder joints are the stencil thickness,the upper pad diameter,the lower pad diameter and the chip weight on a single solder joint; the best level combination ofprocess parameters that results in the longest fatigue life is the lower pad diameter of 0.6 mm,the stencil thickness of 0.175 mm,the chip weight on asingle solder joint of 28×10 -5 N and the upper pad diameter of 0.5 mm.

DESIGN OF VIRTUAL UNIFORM LINEAR ARRAYS FOR EFFICIENT DIRECTION FINDING

The problem considered in this paper is to interpolate a virtual uniform array froma real two-dimensional array with arbitrary geometry via an interpolation matrix. The key to thisproblem is how to arrange these virtual sensors. It is shown that the virtual uniform linear arrayshould have the same main-lobe beam-pattern as the real array over an angular sector of interest.Simulation results are presented to illustrate the application of virtual array in direction finding.

A novel DOA estimation algorithm using directional antennas in cylindrical conformal arrays

In this paper, a novel direction of arrival(DOA) estimation algorithm using directional antennas in cylindrical conformal arrays(CCAs) is proposed. To eliminate the shadow effect, we divide the CCAs into several subarrays to obtain the complete output vector. Considering the anisotropic radiation pattern of a CCA, which cannot be separated from the manifold matrix, an improved interpolation method is investigated to transform the directional subarray into omnidirectional virtual nested arrays without non-orthogonal perturbation on the noise vector. Then, the cross-correlation matrix(CCM) of the subarrays is used to generate the consecutive co-arrays without redundant elements and eliminate the noise vector. Finally, the full-rank equivalent covariance matrix is constructed using the output of co-arrays,and the unitary estimation of the signal parameters via rotational invariance techniques(ESPRIT) is performed on the equivalent covariance matrix to estimate the DOAs with low computational complexity. Numerical simulations verify the superior performance of the proposed algorithm, especially under a low signal-to-noise ratio(SNR) environment.

MODE SPACE SMOOTHING ALGORITHM TO ESTIMATE DOA OF COHERENT SIGNALS IMPINGING ON UNIFORM CIRCULAR ARRAY

A novel method to estimate DOA of coherent signals impinging on a uniform circular array( UCA) is presented in this paper. A virtual uniform linear array (VULA) is first derived by using spatial DFT technique, transforming the UCA from element space to phase mode space to obtain the properties of ordinary ULA, and then the well known spatial smoothing technique is applied to the VULA so that the lost rank of covariance matrix due to signal coherence can be retrieved. This method makes it feasible to use the simple MUSIC algorithm to estimate DOA of coherent signals impinging on a UCA without heavy computation burden. Simulation results strongly verify the effectiveness of the algorithm.

Analysis and Comparison of Time Replica and Time Linear Interpolation for Pilot Aided Channel Estimation in OFDM Systems

This paper analyzes and compares two time interpolators, i.e., time replica and time linear interpolator, for pilot aided channel estimation in orthogonal frequency division multiplexing (OFDM) systems. The mean square error (MSE) of two interpolators is theoretically derived for the general case. The equally spaced pilot arrangement is proposed as a special platform for these two time interpolators. Based on this proposed platform, the MSE of two time interpolators at the virtual pilot tones is derived analytically;moreover, the MSE of per channel estimator at the entire OFDM symbol based on per time interpolator is also derived. The effectiveness of the theoretical analysis is demonstrated by numerical simulation in both the time-invariant frequency-selective channel and the time varying frequency-selective channel.

High-resolution bottom detection algorithm for a multibeam echo-sounder system with a U-shaped array

High-resolution approaches such as multiple signal classification and estimation of signal parameters via rotational invariance techniques（ESPRIT） are currently employed widely in multibeam echo-sounder（MBES）systems for sea floor bathymetry,where a uniform line array is also required.However,due to the requirements in terms of the system coverage/resolution and installation space constraints,an MBES system usually employs a receiving array with a special shape,which means that high-resolution algorithms cannot be applied directly.In addition,the short-term stationary echo signals make it difficult to estimate the covariance matrix required by the high-resolution approaches,which further increases the complexity when applying the high-resolution algorithms in the MBES systems.The ESPRIT with multiple-angle subarray beamforming is employed to reduce the requirements in terms of the signal-to-noise ratio,number of snapshots,and computational effort.The simulations show that the new processing method can provide better fine-structure resolution.Then a highresolution bottom detection（HRBD） algorithm is developed by combining the new processing method with virtual array transformation.The application of the HRBD algorithm to a U-shaped array is also discuss.The computer simulations and experimental data processing results verify the effectiveness of the proposed algorithm.

2D Augmented Coprime Array Geometry Based on the Difference and Sum Coarray Concept

The concept of difference and sum(diff-sum)coarray has attracted a lot of attentions in the estimation of direction-of-arrival(DOA)for the past few years,due to its high degrees-of-freedom(DOFs).A vectorized conjugate augmented MUSIC(VCA-MUSIC)algorithm is applied to generate an equivalent signal model which contains the virtual sensor positions of both the difference and sum of the physical sensors in the two-dimensional(2D)arrays,by utilizing both the spatial and temporal information.Besides,an augmented 2D coprime array configuration is presented with the basis on the concept of difference and sum coarray.By compressing the inter-element spacing of one subarray and introducing the proper separation between the two subarrays of 2D coprime array,the redundancy between the difference coarray and the sum one can be reduced so that more virtual sensors in both coarrays can make contributions to the DOFs.As a result,a much larger consecutive area in the diff-sum coarray can be achieved,which can significantly increase the DOFs.Numerical simulations verify the superiority of the proposed array configuration.

FAST ALGORITHM AND EFFICIENT HARDWARE ARCHITECTURE OF HALF-PIXEL INTERPOLATION UNIT FOR H.264/AVC

A fast half-pixel motion estimation algorithm and its corresponding hardware architecture are presented. Unlike three steps are needed in typical half-pixel motion estimation algorithm, the presented algorithm needs only two steps to obtain all the interpolated pixels of an entire 8′8 block. The proposed architecture works in a parallel way and is simulated by Modelsim 6.5 SE, synthesized to the Xilinx Virtex4 XC4VLX15 Field Programmable Gate Array(FPGA) device, and verified by hardware platform. The implementation results show that this architecture can achieve 190 MHz and 11 clock cycles are reduced to complete the entire interpolation process in comparison with typical half-pixel interpolation, which meets the requirements of real-time application for very high defination videos.

STUDY ON MONOPULSE ANGLE MEASUREMENT METHOD BASED ON VIRTUAL POLARIZATION MATCHING

A monopulse angle measurement method for polarization array radar is studied in this paper.The receiving signal model is established and then a monopulse angle measurement method based on virtual polarization matching is proposed.To analyze the estimation performance,the Cramer-Rao Lower Bound(CRLB)of angle estimation is derived.Both theoretical analysis and simulation show that:firstly,the proposed method is superior to the traditional angle measurement methods based on the single polarization.Secondly,the performance of the new method is unrelated to the echo polarization.Thirdly,angle estimation of this method is asymptotically optimal.The results show that this method has great potential to be used in polarization array radar.

Direction Finding Using Cumulant in Multipath Environment with an Arbitrary Array

In this paper, the problem of estimating the direction of arrival of signals of which some may be perfectly correlated is considered. This method can be applied in the situation that the non-Gaussian independent and coherent signals coexist with unknown Gaussian noise. In this method at first via mappings, the virtual uniform linear array (ULA) and also the shifted versions of this virtual ULA by assuming that all the DOAs are located in one section are constructed. In order to avoid coloring the noise because of these mappings we use a cumulant matrix instead of a covariance ones. In this method since we construct all the subarrays virtually for detection of coherent signals we do not need the array with regular configuration. The advantages of this method are: increasing the array aperture, having the ability to find the DOAs with fewer sensors and also avoiding the coupling between sensors as much as possible in contrast to conventional spatial smoothing.

基于协方差矩阵加权截断核范数的DOA估计

针对互质阵列通过差联合处理得到具有高自由度的虚拟阵列存在空洞位置,导致子空间类算法不适用、阵元利用率不足等问题,文中提出了一种基于加权截断核范数的协方差矩阵重构的波达方向(DOA)估计算法。该算法首先根据虚拟域信号表达式和空洞位置构建待填充矩阵;然后,利用最小化加权截断核范数实现阵列插值;最后,迭代重构接收信号协方差矩阵得到角度功率谱估计。仿真结果表明:所提算法可快速准确地实现DOA参数估计,相比基于最小化核范数和截断核函数正则化的DOA估计算法,该算法具有良好的鲁棒性,在快拍数小和信噪比低的情况下均具有较高的估计精度。

基于RFID虚拟标签的室内停车场车辆定位算法

在室内停车场中应用基于RFID的LANDMARC算法进行车辆定位时,由于室内停车场的复杂结构以及多径效应的影响,车辆定位精度不能通过增加参考标签数目或均匀规则的部署参考标签等方式来提升。提出了一种基于虚拟RFID标签的室内定位算法(location algorithm based on virtual tag,LAVT)。该算法通过近邻标签确定车辆的近邻区域,计算出近邻区域的外心并插入虚拟参考标签;通过虚拟参考标签替换原近邻标签、缩小近邻区域面积,使新近邻标签更临近待定位车辆,从而更精确地计算出车辆的位置。仿真实验表明:LAVT算法在室内停车场环境中将车辆定位精度提升了19.03%。LAVT算法应用于室内停车场环境中的车辆定位具有更好的适用性,能满足室内停车场车辆定位的基本需求。

基于Karnopp模型和数据驱动的虚拟针灸手法力建模

针灸学是一门实践性学科,操作训练的经验对针灸医学生掌握针灸技术十分重要。本文针对传统训练方法准确性和真实感低的问题,基于Touch X和unity搭建了虚拟针灸训练平台,并通过采集针刺猪肉的数据建立提插和捻转手法力模型。针对提插手法可分为刺入力和提插力两部分,在刺入力模型中增加了衰减力建模,使刺入的分层感更加真实;借鉴Karnopp模型建立不同组织层的单位长度阻尼函数,结合刺入力和提插力建立完整的提插手法力模型。针对捻转手法采用数据驱动建模,分为动态捻转和静态衰减两部分,两者测试集准确率分别为0.98508和0.99249。最后通过左右手对比实验和用户使用感受对模型进行评估,结果表明,本文建立的两种针灸手法力模型准确度高,真实性强,可扩展性好。

基于几何细分的三维地质模型自适应精细化构建方法

为钻孔采样数据设计的广义三棱柱体元是地质建模中的常用方法,它利用相邻的三棱柱体元表达地层空间分布情况,而通常相邻钻孔采样间隔较大,导致这些区域模型的精度较低,地层面不光滑。基于此提出了三棱柱三维地质模型的插值平滑的理论和方法,在不该变模型数据结构的情况可以自适应地细分三棱柱模型实现高精度插值。①提出了三棱柱三维地质模型几何平滑度的定义与计算方法,用于判断一个三棱柱体元是否需要插值。②详细讨论了基于三棱柱几何平滑度的三维地质模型插值虚拟钻孔设计与计算方法。③基于虚拟钻孔设计计算和基于现有三棱柱体元的三维地质模型自适应平滑插值方法研究。

基于虚拟现实的多彩UI界面分块布局方法

由于传统方法忽略了用户视觉与UI界面之间的关系,导致分块过密、色彩不够显著。因此研究基于虚拟现实的多彩UI界面分块布局方法。预先明确用户视觉与UI界面之间的关系,利用灰度线性插值法,定位UI界面分块布局边缘点。引入图像尺度空间理论,匹配UI界面分块,基于虚拟现实技术,渲染UI分块界面色彩,实现对多彩UI界面的分块布局。实验结果表明,与传统布局方法相比,所研究的方法的分块密度更合适,分块之间、分块与界面背景之间的色彩差异更显著。可见所研究的分块布局方法可以提升多彩UI界面分块布局视觉增强效果。

一种基于互质线阵的改进空间平滑信源角度估计算法

本文针对互质阵列产生的虚拟阵列不连续,导致部分信息损失问题,提出一种基于阵列插值的改进空间平滑算法。该算法充分利用了虚拟域阵列的全部信息。首先将互质阵列导出至虚拟域,形成一个非均匀的虚拟阵列;然后通过插值虚拟阵元的方式,将其转变为一个连续均匀的虚拟阵列;最后利用空间平滑算法,实现了信源角度的超分辨估计。仿真结果表明:与截取最大连续虚拟阵元的算法相比,有效提升了阵列自由度和信源角度估计性能。

基于光流改进的视频虚拟试衣

随着计算机视觉的发展,基于图像的虚拟试衣方法已经取得了很大的进展,但是,直接将此方法应用到视频虚拟试穿的任务时,由于缺乏时空一致性,会导致视频帧之间的不一致和不连贯,会对视频的视觉效果产生很大的影响,为了解决上述问题,本文提出了一种基于光流改进的视频虚拟试穿模型。首先使用正则化校正损失的薄板样条插值变换方法对服装进行扭曲,然后使用一个U-Net网络进行服装试穿,同时使用原视频服装区域的光流监督,合成视频服装区域的光流。实验结果表明,本文基于光流改进的视频虚拟试衣方法能很好解决虚拟试衣视频时空一致性问题。

基于虚拟仪器的平方检测法电压闪变测量实现

电压闪变已成为电力系统的重要污染,为实现闪变测量,简化了IEC推荐的平方检测法电压闪变测量过程,提出并建立了一种计算量小的基于Blackman窗插值FFT的平方检测法电压闪变测量算法,通过对离散的电压均方根值进行加窗插值FFT分解,求得电压均方根值的离散频谱数列Uf(j),对Uf(j)进行视感度加权处理,得到电压均方根值数列对应的瞬时闪变量p,进一步统计排序求得短时间闪变值Pst和长时间闪变值Plt。仿真实验验证了算法的可行性和准确性,在此基础上研制了基于虚拟仪器的电压闪变测量仪,给出了仪器构成与主框图程序,检验与运行证明了仪器的准确性。