一种滤除周期性信号中畸点的方法

在周期性工程测量信号中常会出现许多畸点。目前去除畸点的方法都有其局限和不足之处。为此,本文提出了一种快速衰减畸点值而不会带来其它误差的畸点衰减法,通过对带有大量畸点的模拟和实测周期性信号进行的处理表明,本方法滤除畸点效果良好且计算迅速,可应用于工程实际。     

A phase tracking system for three phase utility interface inverters

The analysis and design of the phase-locked loop (PLL) system is presented for the phase tracking system of the three phase utility interface inverters. The dynamic behavior of the closed loop PLL system is investigated in both continuous and discrete-time domains, and the optimization method is considered for the second order PLL system. In particular, the performance of the three phase PLL system is analyzed in the distorted utility conditions such as the phase unbalancing, harmonics, and offset caused by the nonlinear load conditions and measurement errors. The tracking errors under these distorted utility conditions are also derived. The phase tracking system is implemented in a digital manner using a digital signal processor (DSP) to verify the analytic results. The design considerations for the phase tracking system are deduced from the analytic and experimental results     

表面误差对双弯曲反射面天线副瓣的影响

天线反射面的表面误差会引起反射面天线的副瓣发生变化。为确定赋形波束双弯曲反射面天线反射面的表面误差与反射面天线副瓣最大值变化之间的关系,采用数理统计的方法,对受到随机表面误差影响的面电流积分,得到天线辐射场。随机表面误差用相关半径和Z向随机误差两个参量表示。根据随机表面误差求出其天线最大副瓣样本分布函数,较好地展现了表面误差引起的副瓣最大值变化,使得反射面天线表面误差引起的副瓣变化可预测,为天线反射面加工的精度要求提供了理论依据。     

天线表面误差的精确计算方法及电性能分析

提出一种天线表面误差的计算方法,用来精确计算变形表面法向、径向及轴向误差,并推导了相应的计算公式.通过分析某工程7.3m圆抛物面天线在多种工况下的表面误差,及其与ANSYS软件计算结果的比较,证明了该方法的正确性,且计算结果仅为ANSYS软件分析结果的三分之一左右.实验结果说明此方法能够更准确地分析变形天线的表面误差及电性能.在工程中应用此方法分析大型空间天线与地面天线,可明显降低天线设计成本,缩短天线设计周期,并为电气设计人员提供准确的天线变形反射面信息.     

基于FPGA的三相电网故障环境下锁相技术分析

为使三相光伏并网逆变器在各种电网环境下准确、快速地锁定基波相位。利用三相锁相环基本结构,提出了一种在FPGA上的数字锁相环设计。通过流水线结构编写Verilog HDL硬件描述语言对dq坐标变换、PI控制器和数控振荡器在FPGA模块化实现锁相算法。并以FPGA为验证平台,分析了三相锁相环在电网故障环境中,即三相不平衡、频率突变、相位突变和电网谐波干扰等对三相锁相环技术分析得出误差。利用Matlab模拟电网故障Modelsim进行系统仿真,仿真结果验证了该锁相环能够快速准确地锁定电网基波相位,并对畸变电压具有较强的抑制作用。     

基于最小二乘法的天线变形反射面的拟合

面天线变形反射面表达式的确立是计算其电性能的重要基础 ,提出的拟合方法就是用来精确确定变形反射面的数学方程的。其基本原理是通过分析天线结构 ,根据反射面节点位移 ,最小化整个曲面上采样型值点的轴向误差的均方根 ,从而求出用来确定变形抛物面几何位置的 6个参数 ,同时也就得到了基于最小二乘法的变形反射面方程。该拟合方法简单实用 ,易于程序实现 ,能够对天线机械结构设计人员提供了理论指导与帮助。     

Series resistance effects in semiconductor CV profiling

The effects of series resistance on semiconductor doping profiles obtained by conventional CV analysis are discussed, and it is shown that this resistance can cause extremely large errors in the profiles. It is demonstrated that the existence of such errors can be inferred from suitable RF phase angle measurements obtained during the CV profiling process, and that this information can be used to correct distorted profiles. A theoretical analysis and several computer simulations are presented in order to illustrate the nature of the problem and the methods by which accurate profiles can be obtained. All of the behavior predicted by computer simulations is verified by experimental examples.     

Simulation for capacitance correction from Nyquist plot of complex impedance–voltage characteristics

The impression of series resistance on unipolar semiconductor device’s capacitance–voltage spectrum is discussed by conventional impedance and admittance analysis, and it is shown that series resistance may cause large errors in capacitance–voltage data. It is shown that the existence of such errors can be deduced from suitable complex impedance measurement obtained during the capacitance–voltage measurement process and this information can be used to correct the distorted capacitance values. A theoretical analysis and computer simulation are presented in order to illustrate the nature of the problem and the technique by which accurate depletion region capacitance can be obtained.     

Carrier and Clock Recovery from Transversal Equalizer Tap Settings for a Partial Response System

A general expression is derived for the tap settings of a linear transversal equalizer using the minimum mean-square error (MMSE) criterion when the class-4 partial-response (PR) signal is distorted by noise as well as carrier phase and timing errors. The values of the tap settings are used to reduce the carrier and timing phase errors.     

Restoration of differently blurred versions of an image withmeasurement errors in the PSF''s

Restoration of an object from T observations is considered. Each image is distorted by a different deterministic blur and additive noise. The point spread function (PSF) for each observation is unknown; however, a noisy measurement of it is available. Taking the errors in measurements of the PSFs into consideration, the maximum-likelihood and Wiener filters are derived. It is shown that these filters give better results when the regression filter and the conventional Wiener filter, i.e., the one which ignores the presence of the noise in the PSFs. The consistency and the ill-conditioning characteristics of the filters are discussed. Regularized forms for these filers are obtained.     

Beamforming for Phased Arrays on Vibrating Apertures

A beamforming approach for phased arrays on vibrating apertures is proposed. The essence is to dynamically calibrate the antenna element position errors due to aperture vibrations. This is achieved by estimating element positions through the aid of a few near field reference sources attached to the antenna. The reference sources need to be mounted on rigid frames and be impervious to vibrations. The estimated position information is then substituted into the beamforming process to correct the distorted pattern of the antenna array. To validate the proposed concept, a 5.8 GHz eight-element array with artificially displaced element positions is built to emulate the vibration effect. The proposed calibration approach gives, a close estimate of position errors with deviations under 4% of the free space wavelength. Based on the estimated information, an array pattern with desired features is constructed.     

OCT图像畸变的消除--相关峰值扫描重定位算法

分析了 OCT系统中某些导致图像畸变的因素 ,提出了相应的补偿算法——“相关峰值扫描重定位算法”。从图像的相关峰值位置函数中 ,将样品本身灰度特征的变化规律和畸变特征用数字滤波的方法分离开来。分析了噪声对相关运算的影响及用灰度门限抑制噪声的措施。讨论了算法的容错性 ,通过对重定位量加以限制 ,避免了严重错位引起的重定位阶跃失真。对算法存在的累积误差等局限性提出了改进建议。给出了畸变图像的恢复实例。     

Influence of coding and hardware imperfections on the bit errorstructure of multilevel QAM systems

When putting together 140-Mb/s 16-ary quadrature amplitude modulation (16-QAM) modems, radio-relay sets, and the appertaining total multiplex/demultiplex equipment, different and even higher bit error rates (BERs) have been measured at the primary low-level 64-kb/s outputs as compared to that at 140 Mb/s. The authors show that this error multiplex effect is mainly caused by the coding of signal points and by hardware imperfections such as carrier and clock phase jitter, nonideal regenerator threshold voltages, etc. They derive the mathematical tools necessary for calculation of the bit error structure at the modem output under optimum and nonoptimum receiver conditions. It is shown how the errors are distributed among the demultiplexer channels. QAM space diagrams of distorted signals are used for calculation of the BERs in the subsystems. Some experimental results emphasize the fact that the multiplex equipment must not be excluded from design considerations for QAM modems. The 16- and 64-QAM systems are compared with respect to their susceptibility to the error multiplex effect, and a scrambling technique is proposed as a possible means to reduce the BER differences     

The Mean-Square Error of SSBAM Class 4 Partial Response Data Signals Distorted by Parabolic Group Delay

An expression is derived for the mean-square error of an SSBAM multilevel class 4 partial response data signal when distorted by a channel with parabolic group delay with the minimum value centered in the signal spectrum. The optimum carrier phase and sampling times are also determined. Numerically evaluated results indicate that the approximation errors made in the derivation are not significant in the regions of practical interest.     

Intelligent Neural Network-Based Fast Power System Harmonic Detection

Nowadays, harmonic distortion in power systems is attracting significant attention. Traditional technical tools for harmonic distortion analysis using either fast Fourier transform or discrete Fourier transform are, however, susceptible to the presence of noise in the distorted signals. Harmonic detection by using Fourier transformation also requires input data for more than one cycle of the current waveform and requires time for the analysis in the next coming cycle. In this paper, an alternative method using neural network algorithm has achieved satisfactory results for fast and precise harmonic detection in noisy environments by providing only 1/2 cycle sampled values of distorted waveforms to neural network. Sensitivity considerations are conducted to determine the key factors affecting the performance efficiency of the proposed model to reach the lowest errors of testing patterns     

Detection of nonlinear distortion in audio signals

Nonlinear distortion of a signal passing through a system may be caused by a number of factors. One of those factors, a limiter like transfer function, is considered. The nonlinear distortion causes a change in the probability density function (PDF) of the signal. The PDF of the signal can be characterized by the coefficients of a fifth-order polynomial fitted to the PDF curve. The coefficients are used as a vector input to an artificial neural network trained to classify the vector as belonging to a distorted or undistorted audio signal. Results show that the artificial neural network is able to classify signals, with PDFs indicating the presence of significant high amplitude components, into distorted or undistorted. A low amplitude signal will not be distorted during its passage through a nonlinear system and therefore the output will be classified as "not distorted". This gives rise to, what seem to be, errors in the classification of signals. However, the technique developed identifies distortion in the signal and not in the system through which the signal has passed.     

基于人类视觉的感知立体图像质量评价方法

为了实现对不同失真类型的立体图像进行质量评 价,提出了一种基于人类视觉的立体图像 质量客观评价方法,分别从图像清晰度与立体感两方面进行评价。图像清晰度方面,将原始 与失真立体图 像分解为5个带通图像后利用对比度敏感度函数(CSF)优化各失真带通图像,并模拟掩 盖效应,通过整合各原始 带通图像,综合感知误差,构造信噪比(SNR)作为评价图像 清晰度的性能指标;立体感方面,对绝对差值图像进 行视觉感知模拟,建立SNR指标评价立体感的优劣。实验结 果表明,对不同失真类型立体图像的评价 结果表明,Pearson线性相关系数(PLCC)与Spearman等级 相关系数(SRCC)均优于现有评价方法。     

弹载SAR图像几何失真校正误差分析

该文主要讨论了弹载侧视合成孔径雷达(SAR)在导弹下降飞行过程中所获取图像的几何失真校正及其误差分析问题。由于要求成像的过程中,弹体的高度在不断减小,SAR图像存在严重的几何失真,该文根据成像过程中的几何关系,说明了采用子孔径RD算法获得的SAR图像几何失真的校正方法,着重对校正后图像的几何失真误差进行了分析,通过成像处理仿真试验验证了几何校正方法以及误差分析的正确性。     

Relation of User-Perceived Response Time to Error Measurements on ISDN Data Links

The LAPD link-level protocol was used to interchange messages on a computer-simulated link. The link was subjected to random errors generated with the Gilbert error-producing model. Tabulations were made of the delays encountered in sending and acknowledging messages, and of facility statistics such as error-free seconds. Objectives are 1) provide quantitative relationships between facility measurements and user-perceived performance on a data circuit, and 2) determine which measurements correlate best with observed performance. Major conclusions include: an interval of one second is recommended for facility measurements, as shorter interval measurements such as bit-error ratio are strongly distorted by certain types of errors; error-free seconds (EFS) correlates poorly with link response time performance; a new measure, the sum of squares of errored-second sequences (SQUESS), yields better correlation,     

Array pattern distortion and remedies in space-time adaptiveprocessing for airborne radar

Space-time adaptive processing (STAP) for airborne early warning radar has been a very active area of research since the late 1980's. An airborne rectangular planar array antenna is usually configured into subarrays and then partial adaptive processing is applied to the outputs of these subarrays. In practice, three kinds of errors are often encountered: the array gain and phase errors existing in each element, the channel gain and phase errors, and the clutter covariance matrix estimation errors due to insufficient secondary data samples. These errors not only degrade the clutter suppression performance, but also cause the adapted array patterns to suffer much distortion (high sidelobes and distorted mainbeams), which may result in the rise of false-alarm probability and make the adaptive monopulse tracking and sidelobe blanketing more difficult. In this paper, the causes of the above three kinds of errors to array pattern distortion are discussed and a novel quadratic soft constraint factored approach is proposed to precisely control the peak sidelobe level of adapted patterns. The soft constraint factor can be determined explicitly according to the peak sidelobe level desired and the known or desired tolerant error standard deviations. Numerical results obtained by using high-fidelity simulated airborne radar clutter data are provided to illustrate the performance of the proposed approach. Although the method is presented for STAP, it can be directly applied to the conventional adaptive beamforming for rectangular planar arrays used to suppress jammers