TIME DOMAIN PROCESSING MODE SPREAD SPECTRUM SYSTEM

The construction and specifications of a surface acoustic wave storage correlator are described. A time domain processing mode spread spectrum system is presented. An analysis of the interference rejection for this system is provided. The formula for calculating the probability of error of the system is given. The experimental results agree with the theoretical analysis.

Direction-of-arrival estimation based on direct data domain (D3) method

A direction-of-arrival （DOA） estimation algorithm based on direct data domain （D3） approach is presented. This method can accuracy estimate DOA using one snapshot modified data, called the temporal and spatial two-dimensional vector reconstruction （TSR） method. The key idea is to apply the D3 approach which can extract the signal of given frequency but null out other frequency signals in temporal domain. Then the spatial vector reconstruction processing is used to estimate the angle of the spatial coherent signal source based on extract signal data. Compared with the common temporal and spatial processing approach, the TSR method has a lower computational load, higher real-time performance, robustness and angular accuracy of DOA. The proposed algorithm can be directly applied to the phased array radar of coherent pulses. Simulation results demonstrate the performance of the proposed technique.

3D prestack reverse time migration of ground penetrating radar data based on the normalized correlation imaging condition

The reverse time migration(RTM)of ground penetrating radar(GPR)is usually implemented in its two-dimensional(2D)form,due to huge computational cost.However,2D RTM algorithm is difficult to focus the scattering signal and produce a high precision subsurface image when the object is buried in a complicated subsurface environment.To better handle the multi-off set GPR data,we propose a three-dimensional(3D)prestack RTM algorithm.The high-order fi nite diff erence time domian(FDTD)method,with the accuracy of eighth-order in space and second-order in time,is applied to simulate the forward and backward extrapolation electromagnetic fi elds.In addition,we use the normalized correlation imaging condition to obtain pre-stack RTM result and the Laplace fi lter to suppress the low frequency noise generated during the correlation process.The numerical test of 3D simulated GPR data demonstrated that 3D RTM image shows excellent coincidence with the true model.Compared with 2D RTM image,the 3D RTM image can more clearly and accurately refl ect the 3D spatial distribution of the target,and the resolution of the imaging results is far better.Furthermore,the application of observed GPR data further validates the eff ectiveness of the proposed 3D GPR RTM algorithm,and its fi nal image can more reliably guide the subsequent interpretation.

Analysis of the Frequency Domain Water-level Deconvolution Method Based on Reservoir Airgun Source Data

Based on the 2016 airgun experimental data of the Fujian Nanyi reservoir,we adopted the frequency domain water-level deconvolution method and cross-correlation time delay detection technique to study the influence of level scaling factor and the background noise level of the station on deconvolution calculation results, and analyze the effect of deconvolution on eliminating the influence of the source caused by different air-gun pressures. The results show that:( 1) When the level scaling factor is smaller,the signal to noise ratio of the waveform after the deconvolution is smaller,and when the level scaling factor is over smaller,the identification error of travel time is greater.( 2) When the SNR of the station record is higher,the recognition accuracy of travel time is higher,the influence of SNR on the reference station record is far greater than the far station,when the SNR of the far station record is more than 10,the error of travel time is within6 ms,but when the SNR of the reference station record is 30,the travel time error may reach to 20 ms.( 3) When the airgun source difference is big,the frequency domain waterlevel deconvolution method has better effect on eliminating the source influence,but the method error may be introduced when the source difference is small.

基于时序Q-learning算法的主网变电站继电保护故障快速定位方法

主网变电站继电保护故障通常是突发性的,不会持续一段时间,暂态性质不明显,快速定位效果受限,基于此,提出基于时序Q-learning算法的故障快速定位方法。在时序Q-learning中,使用不同多项式函数参数表示不同主网变电站继电保护动作,采用贪婪策略选择主网变电站继电保护动作,根据继电保护状态反馈结果更新权重,使用时序Q-learning算法进行参数训练。构建故障暂态网络的节点导纳矩阵,计算支路电压、电流,确定故障关联域。按照拓扑图论方式时序Q-learning算法搭建快速定位拓扑结构,通过分析支路电流与故障电流之间距离,计算故障相关度,完成故障快速定位。由实验结果可知,该方法故障相序与实际一致,可以分析主网变电站继电保护暂态性质,适用于复杂多变的继电保护装置。

基于Bagging集成高斯过程回归模型的刀具寿命预测

提出了一种集成高斯过程回归(Gaussian process regression,GPR)模型的预测方法,首先将信号进行时域和频域分析,提取信号时频域特征,再结合距离相关系数(distance correlation,DC)进行特征筛选;为了提高模型的预测精度,采用Bagging算法对多个基学习器进行GPR集成,最大限度地降低噪声信号的影响;最后根据贝叶斯后验概率计算得到各子模型的权重,对子模型的输出进行融合,得到全局预测值。进行对比分析实验,验证了该方法的有效性,较之人工神经网络和支持向量机,该方法预测精度更好,具有一定的工程实用意义。

A modified algorithm for SAR parallel imaging

Synthetic aperture radar can provide two dimension images by converting the acquired echoed SAR signal to target’s coordinate and reflectivity. With the advancement of sophisticated SAR signal processing, more and more SAR imaging methods have been proposed for synthetic aperture radar which works at near field and the Fresnel approximation is not appropriate. Time domain correlation is a kind of digital reconstruction method based on processing the synthetic aperture radar data in the two-dimensional frequency domain via Fourier transform. It reconstructs SAR image via simply correlation without any need for approximation or interpolation. But its high computational cost for correlation makes it unsuitable for real time imaging. In order to reduce the computational burden a modified algorithm about time domain correlation was given in this paper. It also can take full advantage of parallel computations of the imaging processor. Its practical implementation was proposed and the preliminary simulation results were presented. Simulation results show that the proposed algorithm is a computationally efficient way of implementing the reconstruction in real time SAR image processing.

基于频域阈值处理广义互相关和空间筛选的多源局部放电定位方法

该文针对电力设备的多源局部放电定位问题,提出了基于频域阈值处理广义互相关(frequency domain threshold processing generalized cross-correlation,FDTP-GCC)和空间筛选的多源局部放电定位方法。为实现多源局部放电超声信号的同源时间差提取问题,该文提出了FDTP-GCC算法,该算法直接应用于超声传感设备采集的原始信号,在频域内通过设置幅度谱阈值排除干扰频段,幅度谱归一化突出多源信号时间差的冲激函数特征,直接得到对应同源信号的时间差。通过仿真证明了FDTP-GCC算法进行时间差估计的高准确性、高稳定性、高抗噪能力。为解决FDTP-GCC算法带来的同源时间差分离的问题,该文提出了基于空间筛选的多源局部放电定位方法,并分析了采用基于解析解的算法和智能算法进行空间筛选的定位性能。最后采用双局部放电源进行了定位试验,试验结果表明该文方法提取的时间差误差均在1μs以内,两个局部放电源的定位误差为20.53cm和4.93cm。

常规直流逆变站交流送出线路距离保护适应性分析与对策

常规直流逆变站交流送出线路故障通常会引发换相失败,存在故障电压和电流波形畸变等问题,可能导致工频相量距离保护性能劣化。首先,分析了工程中广泛应用的正序电压极化距离保护在常规直流逆变站交流送出线路中的适应性,分析结果表明,当逆变站运行于单回交流出线工况时,传统正序电压极化距离保护不再适用;然后,基于交流线路的RL模型,提出了基于波形相关系数的时域距离元件,可以不受逆变站非线性输出特性的影响,并针对时域距离元件存在的出口近区故障方向判别问题,利用电流畸变程度判断故障方向;最后,通过仿真验证了时域距离保护方案的有效性。

基于时域曲线相关性鉴别的分布式光纤扰动定位算法研究

针对瑞利散射信号的随机性以及光纤衰减导致分布式光纤传感系统扰动定位困难、事件误报率高的问题,根据瑞利散射曲线的时域相关性,提出了基于滑动窗的相关系数的扰动事件校验与定位算法。该算法根据在发生扰动事件时相邻周期的光时域反射曲线、扰动点及后续位置相关性骤降的特征,在相邻两周期的光时域反射曲线末端设置数据窗并计算相关系数,设定相关系数的阈值校验有无扰动事件发生。若判别存在扰动事件,则向前滑动数据窗并计算相关系数,然后与定位阈值对比从而定位事件。文中搭建了分布式光纤振动传感系统,在25 km长的光纤范围内实现了±3 m的定位误差、±5 m的空间分辨率,系统响应时间仅为0.15 s。

基于改进TFDR法的核电站仪控电缆断裂缺陷检测

时频域反射(time-frequency domain reflectometry,TFDR)法具有成熟便捷、分辨率较高的特点,广泛应用于各类电缆的故障测距。为了有效判别和精确定位核电站仪控电缆绝缘屏蔽层断裂缺陷,文中通过介入热应力,提出一种改进TFDR法。对50 m多芯仪控电缆进行不同程度的断裂破损模拟,并使用传统TFDR法和改进TFDR法进行检测实验验证。检测结果显示,改进TFDR法对弱断裂缺陷的定位峰峰值为0.2,是传统TFDR法的2.5倍,且不同程度断裂缺陷下定位误差率均小于2.5%。可得出如下结论:相较于传统TFDR法,改进TFDR法使用热应力浮动方差曲线作为缺陷判别的依据,可显著提高对弱断裂缺陷的判别能力;改进TDFR法通过对原定位距离进行修正,进一步提高了对弱断裂破损的定位精准度,可实现对微弱缺陷的有效识别定位。

Phase-coded time-domain holography in persistent hole burning materials

The possible application of the spectral hole burning in the optical storage field has attracted scientists’ attention due to its high density storage which increases 3 orders of magnitude more than that of the present conventional optical disk. By adding a frequency space to the optical storage the storage density can break through the limitation exerted by the fight spot diffraction in the three-dimensional space. The holographically optical

Dielectric properties of benzylamine in 1,2,6-hexanetriol mixture using time domain reflectometry technique

The dielectric properties of binary mixtures of benzylamine-1,2,6-hexantriol mixtures at different volume fractions of 1,2,6-hexanetriol have been measured using Time Domain Reflectometry(TDR)technique in the frequency range of 10 MHz to 30 GHz.Complex permittivity spectra were fitted using Havriliak-Negami equation.By using least square fit method the dielectric parameters such as static dielectric constant(ε_(0)),dielectric constant at high frequency(ε_(∞)),relaxation time
τ(ps)and relaxation distribution parameter(β)were extracted from complex permittivity spectra at 25℃.The intramolecular interaction of different molecules has been discussed using the Kirkwood correlation factor,Bruggeman factor.The Kirkwood correlation factor(gf)and effective Kirkwood correlation factor(g^(eff))indicate the dipole ordering of the binary mixtures.

Complex permittivity spectra of binary polar liquids using time domain reflectometry

The study of complex properties in a binary mixture of polar liquids has been carried out in the frequency range of 10 MHz to 30 GHz at 293 K and 298 K temperatures using time domain reflectometry.The complex properties of polar liquids in binary mixture give information about the frequency dispersion in the dielectric permittivity(ε')and dielectric loss(ε").The information regarding the orientation of electric dipoles in a polar liquid mixture is given by Kirkwood parameters.The Bruggeman parameters are used as the indicator of liquid1 and liquid2 interaction.Molar entropy(ΔS)and molar enthalpy(ΔH)are also discussed at the end of the paper.

车辆四轮相关时域随机输入通用模型的研究

在分析单轮时域随机输入模型产生机理基础上,建立了车辆四轮相关随机输入的滤波模型。在模型中根据各向同性假设直接得到了与车辆轮距有关的左右轮相干函数而无需实测相干函数,因此该模型适合各种车辆,通用性好,计算方便。所得路面功率谱与理论功率谱吻合很好,相关性也得到验证。该模型对车辆四轮相关频域随机输入模型也有一定的参考作用。

时间-小波能量谱在滚动轴承故障诊断中的应用

为滚动轴承故障诊断提供了一种新途径 ,针对滚动轴承故障振动信号的特点 ,构造脉冲响应小波 ,采用连续小波变换的方法来提取滚动轴承故障振动信号的特征 ,在此基础上提出了一种滚动轴承故障诊断方法 :时间 -小波能量谱自相关分析法。通过对滚动轴承具有外圈缺陷、内圈缺陷的情况下振动信号的分析 ,说明时间 -小波能量谱自相关分析法不仅能检测到滚动轴承故障的存在 ,而且能有效地识别滚动轴承的故障模式。

适用于风电接入系统的时域模型识别纵联保护新原理

为适应风电系统弱馈、高谐波、频率偏移等故障特征,提出一种基于时域模型识别的纵联保护新原理。根据线路两端差动电压电流在区外故障时符合电容模型、区内故障时不符合电容模型的特点,利用相关系数对电容模型进行描述,若由差动电压电流计算得到的电容模型符合度接近于1则判为区外故障,否则判为区内故障,并给出了保护判据。该保护判据在时域中实现;不受风电系统弱馈、高谐波、频率偏移等特征的影响,采用故障全量,不受风电系统阻抗不稳定的影响。利用PSCAD建立了风电接入系统模型,仿真验证了所提原理的有效性。

时空相关路面不平度时域模型仿真研究

路面不平度时域模型对现代汽车理论研究意义重要。应用谐波叠加法建立单轮路面不平度输入模型,提出两种不同轮辙路面空间相关模型,并结合同轮辙路面不平度输入时间延迟关系,将单轮模型拓展为四轮路面不平度时域模型。仿真分析显示,该两种方法建立的路面不平度模型,其功率谱与理论功率谱基本吻合,异轮辙输入相干函数符合理论规律。与其它方法相比,该模型建模效率高。

车辆四轮相关路面非平稳随机输入通用时频模型

车辆非匀速行驶时路面的随机输入模型是汽车非平稳动力学分析研究的重要基础。首先应用等效协方差方法建立了单轮随机输入非平稳时域模型。根据时间-空间一、二阶微分关系,成功地解决了前后轮变时差相关的问题,并由各向同性假设直接得到了与车辆轮距有关的左右轮相干函数,无需实测相干函数,因此适合各种车辆。本文还应用Wigner-Ville谱分析了路面非平稳随机输入的瞬时功率谱。分析表明Wigner-Ville谱很好地反映了频率特征和路面波形特征。

车辆非匀速行驶时路面随机输入的时频研究

首先应用协方差等效方法建立了单轮随机输入非平稳时域模型。根据时间-空间一、二阶微分关系,给出了前后轮变时差相关的问题,较好地解决了非平稳路面时域研究中的低速大幅值波动问题。并由各向同性假设直接得到了车辆左右轮的相关关系,因此适合各种车辆。分析表明Wigner-Ville谱很好地反映了频率特征和路面波形特征。