基于FrFT和RVM的变压器局部放电模式识别

快速准确识别局部放电类型对于保证变压器安全稳定运行具有重要意义。针对局部放电信号模式识别中面临的最优特征参数提取和分类器设计难题,提出一种基于分数阶傅里叶变换(fractional Fourier transform,FrFT)和相关向量机(relevance vector machine,RVM)的局部放电模式识别方法。首先将FrFT引入局部放电信号分析领域,利用FrFT将局部放电信号转换至分数域并对其进行多尺度分析,在扩充信息提取维度的同时,提取可反映不同局部放电信号波形差异的14维特征构成特征向量;然后将特征向量作为输入,建立RVM模型进行最优特征选择和分类判决函数的联合优化,从而实现对不同局部放电信号的分类识别。建立电晕放电、沿面放电和气隙放电试验模型并采集局部放电超声信号开展试验,结果表明所提方法对于每种局部放电信号均能获得较高的识别精度,平均正确识别率相对于常规支持向量机(support vector machine,SVM)分类方法提升超过2.7%。

基于FrFT-FH架构LPD通信波形设计与性能分析

针对Chirp基调制信号在分数阶傅里叶变换域特征明显,信号周期易被检测等问题,提出一种能够实现多域隐蔽的低检测概率(low probability of detection,LPD)波形构造方法。该方法采用分数阶傅里叶变换跳频(fractional Fourier transform-frequency hopping,FrFT-FH)架构,在不改变Chirp信号扩频增益的前提下,通过时宽分割和重组(time width division and reorganization,TDR),降低信号在分数阶傅里叶变换域和周期域的能量聚敛特性。仿真结果表明,相较于现有LPD波形只能实现单一特征域隐蔽的问题,所提波形在不影响系统通信性能的前提下,面对频域检测、分数阶傅里叶变换域检测、周期域检测多种检测手段,在10 dB信噪比条件下的信号检测概率均低于0.2,满足系统在不同特征域下的LPD需求。

基于FRFT的低信噪比LFM信号参数快速估计算法

基于分数阶傅里叶变换(Fractional Fourier Transform,FRFT)对线性调频(Linear Frequency Modulated,LFM)信号参数进行估计,问题关键是确定FRFT最佳阶数,根据误差迭代思想提出新的参数估计算法,该算法利用归一化带宽和旋转角的转化关系,由估计误差推算角度差值,有效降低了运算量,不需要调频斜率正负的先验信息,改进的对数搜索算法可以进一步提高参数估计结果的稳定性和可靠性。仿真结果表明,信噪比在-8 dB以上时该方法在高效率的前提下仍具有良好的参数估计性能,平均估计误差在1%以内,估计结果接近Cramer-Rao下限,满足工程实时处理需求。

基于FrFT-Keystone运动补偿的OFDM声纳高速微弱目标相参积累检测算法

针对水下目标探测中使用的正交频分复用信号,提出了一种针对高速微弱目标的相参积累算法,以解决多脉冲积累下由目标机动引起的较大相位变化和由水下环境中信噪比低导致的相参积累增益不足的问题。所提算法利用分数阶傅里叶变换来估计目标的运动参数并进行补偿,并结合Keystone变换,实现对高速微弱目标的多脉冲相参积累。理论推导和仿真实验结果表明,所提算法能够有效补偿高速目标脉冲间的相位移动,并在低信噪比环境下取得较好的能量积累效果。

基于FrFT的组合预测模型在地铁基坑沉降监测中的应用

针对极限学习机(ELM)模型在地铁基坑沉降预测领域存在的参数选取困难问题,本文引入粒子群(PSO)算法对ELM模型的关键参数进行寻优,结合分数阶傅里叶变换(FrFT),提出一种基于FrFT与PSO-ELM模型的地铁基坑沉降组合预测模型。首先,采用FrFT对地铁基坑沉降数据进行多尺度分解,得到若干结构简单的子序列;其次,引入粒子群算法对ELM模型进行全局寻优,提升ELM预测性能,对于各子序列,使用提出的PSO-ELM模型分别进行建模预测;最后,叠加各子序列结果作为预测结果。使用某地铁基坑沉降监测数据进行预测实验,对比GM(1,1)模型、ELM网络模型、长短期记忆(LSTM)模型与本文组合预测模型的实验结果,证明本文提出的组合预测模型的预测精度较对比模型明显提升,从而验证了本文模型能够有效挖掘数据中存在的规律性与趋势性信息,同时解决参数选取困难的问题,为相关结构变形监测与预测提供了一定借鉴。

PCG-Based Exercise Fatigue Detection Method Using FRFT-Based Fusion Model

Accurate detection of exercise fatigue based on physiological signals is vital for reason-able physical activity.As a non-invasive technology,phonocardiogram(PCG)signals possess arobust capability to reflect cardiovascular information,and their data acquisition devices are quiteconvenient.In this study,a novel hybrid approach of fractional Fourier transform(FRFT)com-bined with linear and discrete wavelet transform(DWT)features extracted from PCG is proposedfor PCG multi-class classification.The proposed system enhances the fatigue detection performanceby combining optimized FRFT features with an effective aggregation of linear features and DWTfeatures.The FRFT technique is employed to convert the 1-D PCG signal into 2-D image which issent to a pre-trained convolutional neural network structure,called VGG-16.The features from theVGG-16 were concatenated with the linear and DWT features to form fused features.The fusedfeatures are sent to support vector machine(SVM)to distinguish six distinct fatigue levels.Experi-mental results demonstrate that the proposed fused features outperform other feature combinationssignificantly.

基于FRFT与盲分离的扩频通信网络跳频信号时差估计

针对扩频通信网络跳频信号时差估计结果误差过高,导致信号定位追踪能力下降,多领域内信号传播停滞的问题,为增强扩频通信网络跳频信号的传播效率,提高辐射源跟踪和定位系统的信号探测能力,提出基于分数阶傅立叶变换(FRFT:Fractional Fourier Transform)与盲分离的扩频通信网络跳频信号时差估计算法的方法。采用盲分离方法获取满足跳频信号时差估计条件的两条信道,即平坦衰落信道和频率选择性衰落信道,利用FRFT估计两条信道特征,分别将平坦衰落信道特征和频率选择性衰落信道特征与最大似然块检测算法结合,实现扩频通信网络跳频信号的时差估计。实验结果表明,该方法无论是在正常环境中,还是在噪声干扰环境中,其均方根误差均处于较低水平、估计成功率均处于较高水平。

一种新的基于FrFT的动目标测速和定位方法

使用分数阶傅里叶变换(FrFT)进行SAR动目标测速的传统计算方式是二维搜索,即遍历所有的旋转角度进行FrFT计算,在二维平面内搜索峰值获得最优解。该方法需要在计算精度和计算量之间权衡。提出一种基于时频平面几何信息的动目标测速和定位方法,首先计算两个不同角度下的FrFT及其投影长度;然后利用时频平面内的几何关系,计算动目标的最优旋转角;最后计算最优旋转角下的FrFT,并对动目标测速和定位。值得注意的是,通过选择关于π对称的两个旋转角度,可以进一步抑制杂波。综上,该方法具有速度快、参数估计精度高的优点。通过仿真实验和真实数据实验,验证了提出方法的有效性和优越性。

基于FRFT-RBF网络的船舶电网故障定位方法

为了解决大规模船舶电网在运行中的单相接地故障无法快速精准定位问题,提高船舶电网运行可靠性和生命力,针对船舶电网故障信号具有非平稳性的特点,通过对分数阶傅立叶变换(FRFT)基本理论、最优阶次确定方法、滤波去噪方法,以及功率谱和能量率理论的研究,提出了基于FRFT的电网故障特征提取方法和实现步骤;并针对船舶电网故障特性具有非规律性特点,通过对径向基神经网络算法(RBF)的研究,结合故障特征提取的方法,提出了基于FRFT-RBF网络的船舶电网故障定位方法和实现步骤。通过开展电网故障定位的仿真实验,验证了方法的可行性,为解决大规模船舶电网故障定位问题提供了可行的工程应用方法。

基于FRFT的单基地MIMO雷达稳健波束形成算法

以单基地多输入多输出(multiple input multiple output,MIMO)雷达系统为研究对象,针对线性调频(linear frequency modulation,LFM)形式的正交频分复用(orthogonal frequency division multiplexing,OFDM)信号,提出了一种新的稳健自适应波束形成算法。所提算法首先利用LFM信号的特性,对匹配滤波后的雷达回波信号进行分数阶傅里叶变换(fractional Fourier transform,FRFT),经化简得到峰值点作为阵列的观测值。而后,利用观测值构建接收信号的协方差矩阵,并使用Capon谱估计方法重构干扰加噪声数据协方差矩阵。最后,通过求解优化问题估计实际导向矢量,从而得到阵列的最优权值。通过计算机仿真实验,验证了所提算法的有效性。

A fine acquisition algorithm based on fast three-time FRFT for dynamic and weak GNSS signals

As high-dynamics and weak-signal are of two primary concerns of navigation using Global Navigation Satellite System(GNSS)signals,an acquisition algorithm based on threetime fractional Fourier transform(FRFT)is presented to simplify the calculation effectively.Firstly,the correlation results similar to linear frequency modulated(LFM)signals are derived on the basis of the high dynamic GNSS signal model.Then,the principle of obtaining the optimum rotation angle is analyzed,which is measured by FRFT projection lengths with two selected rotation angles.Finally,Doppler shift,Doppler rate,and code phase are accurately estimated in a real-time and low signal to noise ratio(SNR)wireless communication system.The theoretical analysis and simulation results show that the fast FRFT algorithm can accurately estimate the high dynamic parameters by converting the traditional two-dimensional search process to only three times FRFT.While the acquisition performance is basically the same,the computational complexity and running time are greatly reduced,which is more conductive to practical application.

Solving a Nonlinear Multi-Order Fractional Differential Equation Using Legendre Pseudo-Spectral Method

In this paper, we apply the Legendre spectral-collocation method to obtain approximate solutions of nonlinear multi-order fractional differential equations (M-FDEs). The fractional derivative is described in the Caputo sense. The study is conducted through illustrative example to demonstrate the validity and applicability of the presented method. The results reveal that the proposed method is very effective and simple. Moreover, only a small number of shifted Legendre polynomials are needed to obtain a satisfactory result.

Multi-Order and Multi-Center Metallogenic Zoning of Yinshan Cu-Au Polymetallic Ore Deposit,Jiangxi Province,China

Yinshan anticline is the product of tectono-dynamic deformation - metamorphism .Along the axis of the anticline exists a brittle-ductile shearing zone which obviously controls the ore-formation . Mineralization occurs along the axis of the anticline in a width of about 1000m .In the mining area .volcano- subvolcanic rocks of Early Yanshan period are divided into three cycles :Ⅰ intermediate acidic dacite lava and dacite porphyry ;Ⅱ acidic amphibole liparite and quartz porphyry;Ⅲ intermediate andesite porphyrite . Among them activities of ⅠandⅡ cycles are more intensive and are intimately related to the mineralization . Yinshan ore deposit is the result of combinative processes of tectono -dynamic and volcano -magmatic hydrothermal fluids, so that mere are two centers of metallogenic zoning, one being the axial strain zone of Yinshan anticline which is the center of first order, and the other being porphyry stock , 2nd order.

Multi-Order Intermittent Chaotic Synchronization of Closed Phase Locked Loop

For the model of a Closed Phase Locked Loop (CPLL) communication System consists of both the transmission and receiver ends. This model is considered to be in a multi-order intermittent chaotic state. The chaotic signals are then synchronized along side with our system. This chaotic synchronization will be demonstrated and furthermore, a modulation will be formed to examine the system if it will perfectly reconstruct or not. Finally we will demonstrate the synchronization conditions of the system.

3D Target Localization Based on FrFT from Spaceborne Curve SAR

Synthetic aperture radar(SAR)three-dimensional(3D)imaging technology can reconstruct the complete structure of observed targets and has been a hot topic.Compared with tomographic SAR,array interferometric SAR,and circular SAR,curve SAR can use less data to achieve 3D positioning of targets.Most existing algorithms for estimating Doppler frequency modulation(FM)rate are based on sub aperture partitioning,resulting in low computational efficiency.To address this,this article establishes a target height estimation model,which reflects the relation-ship between the height and the residual Doppler FM rate for spaceborne curve SAR.Then,a fast SAR 3D localization processing flow based on fractional Fourier transform(FrFT)is proposed.Experimental verification demonstrates that this method can estimate the Doppler FM of the target column by column,and the 3D position error for non-overlapping targets is controlled within 1 m.For overlapping points with an intensity ratio greater than 1.5,the root mean square error(RMSE)of the estimation results is around 5 m.If the separation between overlapping points is greater than 35 m,the RMSE decreases to approximately 2 m.

A Study of Multi-order Semidifferential Oscillographic Chronopotentiometry

By applying the convolution technique to the treatment of oscillographic signal, a new electroanalytical method, 0.5-3.5 order differential A.C. oscillographic chronopotentiometry is presented. This note represents the experimental circuits, principle and characteristics of the method.

基于海杂波FRFT谱多尺度Hurst指数的目标检测方法

本文主要研究海杂波分数阶Fourier变换(FRFT)谱的扩展自相似特性及FRFT域多尺度Hurst指数在海杂波目标检测中的应用.鉴于扩展自相似过程的描述参数——多尺度Hurst指数可以描述分形信号在各尺度下的细节信息,本文基于实测雷达数据研究海杂波FRFT谱的扩展自相似性以及影响参数,并利用最优FRFT域尺度下多尺度Hurst指数对目标较敏感的特点设计海杂波中目标的恒虚警检测方法.经实测数据验证,海杂波FRFT谱的多尺度Hurst指数比时域单一Hurst指数、时域多尺度Hurst指数具有更好的海杂波与目标区分能力,并且由于FRFT可以很好地积累匀加速类目标回波的能量,有效提升信杂比,因此该检测方法具有检测海杂波中微弱运动目标的潜力.

海杂波FRFT域分形特征判别及动目标检测方法

该文研究了海杂波在分数阶Fourier变换(FRFT)域的分形特征,提出了一种基于分形特征差异的联合动目标检测方法。首先,分析了海杂波数据在FRFT域的统计特性,通过对不同极化方式下分形曲线的仿真分析,得到海杂波在FRFT域满足自相似性。其次,给出了分形参数的提取方法和无标度区间,并分析了变换阶数对分形参数估计的影响。最后,利用临近距离单元或临近时刻的雷达回波信号在FRFT域的分形维数和斜距的差值作为检测统计量,经不同极化方式下的海杂波数据验证,表明算法不仅具有良好的微弱动目标检测能力,而且能够准确估计目标的运动状态。

盲分离算法和FRFT联合抗雷达主瓣干扰技术研究

压制干扰信号从天线主瓣进入雷达接收机,会严重影响雷达的性能,通常的旁瓣抗干扰技术难以奏效。而基于盲源分离算法(BSS)的抗主瓣干扰技术在低信噪比条件下性能恶化,因此本文提出了BSS和分数阶傅里叶变换(FRFT)联合抗主瓣干扰的技术。文章首先利用经典的BSS算法分离接收到的主瓣干扰混合信号,然后对有线性调频(LFM)信号特征的分离信号进行FRFT变换处理,并在FRFT域滤波去除大部分噪声的能量,最后FRFT逆变换恢复出目标信号。仿真实验表明,新算法相比BSS的抗主瓣干扰算法对脉冲压缩以后的峰值信噪比有较大的改善,较大地提高了脉冲压缩雷达的检测性能,具有良好的应用前景。

海杂波FRFT谱的近似分形特性与目标检测

主要介绍了海杂波分数阶Fourier变换(FRFT)谱的近似分形特性及其在海杂波目标检测中的应用。根据FRFT的尺度变换性质,研究了自相似过程FRFT谱的近似分形特性,然后将近似分形分析方法引入到实测海杂波FRFT谱分析中,发现在特定变换阶数下得到的海杂波FRFT谱间存在近似分形特性,且目标回波可使近似分形特性描述参数——FRFT域Hurst指数发生变化。因此,可利用FRFT域Hurst指数设计恒虚警率(CFAR)检测方法。经X波段和C波段雷达实测数据验证,所提方法的检测性能明显优于经典的利用时域Hurst指数的目标检测方法。