Intermittent Clutter Removal Approac for wind Profiler Data Based on Fractional Fourier Transform

Through the analysis of the target characteristics and according to the intermittent clutter bursting and short duration characteristics, a new method for the clutter recognition based on the fractional Fourier transform (FRFT) is proposed. This method is predicated on the fact that the FRFT perfectly localizes a chirp signal as an impulse when the angle parameter of the transform matches the chirp rate of the chirp signal. The method involves detecting the presence of the intermittent clutter and correctly estimating its orientation in the time-frequency plane, removing the intermittent clutter in the fractional domain, and completing wind estimation by the power spectrum. By testing the artificial WPR-like signal and data measured from the field, we verify that the FRFT-based method is very effective.     

基于分数阶Fourier变换的水声通信多普勒系数估计技术研究

本文基于传统多普勒系数估计方法,提出一种基于分数阶Fourier变换的多普勒系数估计方法,该方法利用分数阶Fourier变换估计得到经过信道后LFM信号调频斜率的变化量值,进而得到多普勒系数的估计。通过计算机仿真研究验证了该方法的有效性与稳健性。     

Detection of T-wave Alternans in ECG Signals Using FRFT and Tensor Decomposition

T-wave alternans(TWA) refers to the periodic beat-to-beat variation in the amplitude of T-wave in the electrocardiogram(ECG) signal in an ABAB-pattern. TWA has been proven to be a very important indicator of malignant arrhythmia risk stratification. A new method to detect TWA by combining fractional Fourier transform(FRFT) and tensor decomposition is proposed.First, the T-wave vector is extracted from the ECG of each heartbeat, and its FRFT amplitudes at multiple orders are arranged to form a T-wave matrix. Then, a third-order tensor is composed of Twave matrices of several consecutive heart beats. After tensor decomposition, projection matrices are obtained in three dimensions. The complexity of the projection matrix is measured by Shannon entropy to obtain feature vector to detect the presence of TWA. Results show that the sensitivity,specificity, and accuracy of the algorithm on the MIT-BIH database are 91.16%, 94.25%, and92.68%, respectively. This method effectively utilizes the fractional domain information of ECG,and shows the promising potential of the FRFT in ECG signal processing.     

基于延时相关和FRFT的编队目标架次分辨方法

为较好满足窄带雷达的防空作战需求,提出了一种基于延时相关和分数阶傅里叶变换(FRFT)的空中编队目标架次分辨方法.该方法首先利用延时相关法粗略估计出回波信号的多普勒调频斜率,依据调频斜率和FRFT阶次的对应关系,获得最优变换阶次的粗略值;然后以FRFT后信号的熵值为最小化目标函数,提出一种精确搜索最优变换阶次算法,并以...     

Novel LFM Jammer Suppression Algorithm for DSSS in FRFT Domain

A novel algorithm is proposed to resolve the defects in the traditional linear frequency modulation (LFM) jamming suppression algorithm in the fractional Fourier transform (FRFT) domain. The traditional LFM jamming suppression algorithm in the FRFT domain has some defects. For example, the exact threshold is difficult to set and both the signal-to-noise ratio (SNR) loss and spectrum leakage are serious in strong jamming-to-signal ratio (JSR) situations. Windowing, overlapping and inverse windowing techniques are used in the FRFT domain to reduce the spectrum leakage and the SNR loss. Under the condition that only the direct sequence spread spectrum (DSSS) signal and white Gaussian noise are present, the amplitude of the received signal after FRFT is assumed to be Rayleigh distributed. Based on the distribution characteristic, hypothesis testing is used to suppress the jamming spectrum using the algorithm. Simulation results show that the performance of proposed algorithm is better than that of the conventional algorithms, especially in a strong jamming and multi component LFM jamming environment.     

基于DPCA-FrFT算法的SAR运动目标参数估计

在双通道的工作模式下,结合DPCA技术和分数阶傅立叶变换实现了对SAR运动目标的定位和两个方向(方位向和地面距离向)上速度的估计。首先建立了双通道SAR系统对运动目标的回波信号模型,阐述了动目标DPCA信号为线性调频信号这个特点,并且根据这个特点采用了分数阶傅立叶变换对其进行检测和参数估计。由于DPCA技术具有良好的杂波对消功能以及FrFT对chirp信号的良好检测效果,在不同信噪比情况下,DPCA-FrFT算法都能有效地抑制静止背景、获得良好的测速和定位效果。仿真结果证明了该算法的正确性和有效性。     

基于FRFT滤波的SNCK通信系统接收方法

正弦型非线性切普键控（sine non linear chirp keying,SNCK）作为一种非线性调频方法,其已调信号缺乏有效的滤波技术,针对此问题,提出了一种将SNCK已调信号波形样本近似为分段线性调频信号进行分数阶傅里叶变换的处理方法.推导了采用SNCK调制参数计算相应FRFT变换阶数的公式,并给出了通信系统采用SNCK信号进行传输时,接收端采用FRFT方法进行前置滤波的框图.通过数值仿真分析验证了该方法对SNCK各调制参数的普遍适用性,能有效提高接收信号的信噪比改善因子,降低通信误码率.     

基于FRFT的对流层散射Chirp信号重构方法

针对对流层散射的辐射源信号侦察中提取低信噪比信号特征难的问题,采用分数阶傅里叶变换（FRFT）提取了对流层散射线性调频信号的调频斜率与载频;在低信噪比条件下,给出了信号初步检测及采用FRFT、滤波和反FRFT进行信号特征估计与重构的方法．实测数据的处理结果证明了该方法的有效性,为脉宽测量和脉内调制特征分析提供了高信噪比基础．     

基于广义随机共振的Chirp信号检测性能分析

为便于提取多个chirp信号叠加噪声模型中目标chirp信号的参数信息,本文研究了该混合信号激励过阻尼双稳系统的随机共振现象。但由于chirp信号在频域能量的非聚焦性,传统刻画随机共振的信噪比指标失效。因此,基于chirp信号在分数阶傅里叶变换域上的能量分布特性,对非线性随机动力系统的畸变输出信号进行变换域上的最优滤波,给出最优分数阶傅里叶变换域上的信干比定义形式,并以此作为目标chirp信号经过系统后的性能增益的度量和广义随机共振现象的判别依据。数值仿真结果表明,在存在多个chirp信号驱动的过阻尼双稳系统中,当目标chirp信号或噪声能量不足以激发粒子跃迁时,干扰chirp信号能在一定程度上协助粒子发生跃迁,产生协同随机共振现象,从而提高对目标chirp信号的检测性能。     

Improved Spectral Representation for Birdcall Based on Fractional Fourier Transform

A novel spectral representation based on fractional Fourier transform (FrFT) is proposed and applied to birdcall analysis. The FrFT-based spectrogram of a signal is derived and compared with its FT-based counterpart,and the spectrum gathering method is used to show the energy distribution related to the pitch frequency. The fixed transform order and adaptive orders for FrFT are tested. The fixed order can be obtained empirically or calculated according to the known chirp rate. The adaptive optimal orders are determined by using ambiguity function. Experimental results with birdcalls show that the FrFT-based spectrogram with an optimal transform order has higher resolution than its STFT-based counterpart,and the better performance can be achieved if adaptive orders are used.     

采用chirp信号调制的中压配电线通信系统

针对中压配电线信道特性,提出了一种基于分数阶Fourier变换(FRFT)的通信方法。以线性调频信号(chirp)作为调制信号,利用线性调频信号在分数阶傅里叶变换域的能量聚焦特性,提高系统的抗噪声干扰和频率选择性衰减的能力。建立了系统的仿真模型,仿真结果证明了方法的可行性。     

存在相位抖动下 Chirp-UWB信号零中频处理研究

Chirp-UWB通信技术作为WPAN的无线接人标准而倍受关注,为降低采样率与技术成本,接收时常将GHz频段的Chirp-UWB信号搬移到基带进行匹配滤波或分数阶傅立叶变换(FRFT)处理.通过Chirp信号匹配滤波和FRFT能量聚集效能的简洁推导,分析了零中频变换存在的随机相位抖动对检测性能的影响.为消除频差,提出了...     

基于WVHT 的合成孔径雷达运动目标检测与成像

目的针对合成孔径雷达（ＳＡＲ）的运动目标检测和成像提出了一种通用、完整的ＷｉｇｎｅｒＶｉｌｅＨｏｕｇｈ变换（ＷＶＨＴ）．方法基于线积分,将ＷＶＤ和Ｈｏｕｇｈ变换结合起来,推导出ＷＶＨ变换,并利用计算机仿真的ＳＡＲ回波数据对该新ＷＶＨ变换作了验证．结果与结论计算机仿真结果证明了该变换的正确性和有效性．和传统的ＷＶＤＨＴ方法相比,这种基于ＷＶＨＴ的ＳＡＲ运动目标检测和成像的新方法,可以将多目标回波的ｃｈｉｒｐ信号从时间域直接转换到参数域,同时完成了ＷＶＤＨＴ方法中的交叉项抑制和运动参数的估计,进而对多目标成像,简化了处理过程．这种新ＷＶＨ变换还可以应用于其它场合的ｃｈｉｒｐ信号检测中．     

线性调频分数傅立叶变换理论及应用

基于普通傅立叶变换(FT)的特征函数,本文给出了一种连续时间信号的线性调频分数傅立叶变换(CFRFT)的表达方式,在此基础上,分析了CFRFT包括时移特性、展缩特性、反褶特性、时域微分特性、分数域频移特性、时域斜变信号相乘特性和Parseva l定理等变换性质,得出一些常用连续时间信号的CFRFT的变换表达式,说明了傅立叶变换可视为分数傅立叶变换(FRFT)的一个特例,对应用分数傅立叶变换分析系统具有启发作用。作为分数傅立叶变换的应用,解决了傅立叶变换不能有效分析时变系统的问题。     

基于MPDFRFT的数字水印算法

基于多参量离散分数阶Fourier变换(MPDFRFT)理论提出了一种数字水印算法,该算法首先将水印经Arnold变换进行置乱,然后根据分数阶Fourier变换具有空域和频域双域信息表达能力,分别对载体图象和所加水印进行不同阶次向量的多参量分数阶Fourier变换;将变换后的水印信息直接叠加到载体图象的特征区域内,然后进行反变换得到水印图象。在噪声、滤波、剪切和JPEG压缩等攻击方式下,对算法进行了鲁棒性分析,仿真实验结果表明该算法具有较强的鲁棒性和安全性。     

基于FRFT的LFM信号的检测及其参数估计

针对LFM信号的检测及参数估计等问题,先对现有的检测方法如Wigner-Ville、FRFT等进行研究,在FRFT变换的基础上提出基于预判法与FRFT变换相结合的算法。通过仿真分析,验证了该方法能有效对L F M信号的参数进行估计,同时降低了计算量。     

基于调频率调制的雷达通信共享信号研究

雷达通信一体化可有效提高电子系统的资源共享,是实现电子装备多功能综合一体化的一个重要方向。本文根据Chirp信号的调频率与分数阶傅里叶变换的阶数之间的关系,提出了一种基于Chirp信号调频率的雷达通信共享波形,固定调频率的主载波实现雷达功能,副载波由通信码元键控得到调频率从而实现通信信息调制;主载波与副载波的叠加形式使此共享信号能在不影响雷达性能的前提下实现单脉冲多比特的数据传输,而且利用不同阶数的分数阶傅里叶变换的解调过程具有多普勒稳健性。     

基于FRFT的小波包调制信号的识别研究

该文基于正交频分复用调制和小波包调制信号的调制原理,利用分数阶傅立叶变换的时频旋转特性,探讨了在高斯信道、瑞利信道和频率选择信道下小波包调制信号的识别.仿真实验结果表明,该方法具有良好的识别性能,不需要任何信道参数,能较好的实现盲信道的小波包调制识别.     

基于时频分析的LFM信号检测与参数估计

基于Radon Wigner变换、分数阶Fourier变换与时频分布的关系,利用其对线性调频(linearityfrquencymodulation,LFM)信号良好的时频聚集性,通过计算Radon Wigner变换或分数阶Fourier变换,对线性调频信号LFM信号进行检测和参数估计。理论分析和计算机仿真证明:2种方法对于LFM信号的分析好于Wigner Ville变换等常用的时频变换。     

Rejection of Linear FM Interference in DSSS System Based on Fractional Fourier Transform

A new method for the rejection of linear frequency modulation (LFM) interference in direct sequence spread spectrum (DSSS) system based on the fractional Fourier transform is proposed, and the configuration of the receiver with an interference exciser is also presented. Based on the property that the fractional Fourier transform of a signal is equivalent to rotating the signal in the time-frequency plane, the received signal is transform into a certain fractional Fourier domain, this transform will result in the least spectrum overlap between the signal and interference. Then, a narrowband filter is exploited to extract most of the interference energy. The performance analyses show that remarkable improvements in signal-to-noise ratio (SNR) and biterror-ratio (BER) are obtained.