Dual Image Cryptosystem Using Henon Map and Discrete Fourier Transform

This paper introduces an efficient image cryptography system.The pro-posed image cryptography system is based on employing the two-dimensional(2D)chaotic henon map(CHM)in the Discrete Fourier Transform(DFT).The proposed DFT-based CHM image cryptography has two procedures which are the encryption and decryption procedures.In the proposed DFT-based CHM image cryptography,the confusion is employed using the CHM while the diffu-sion is realized using the DFT.So,the proposed DFT-based CHM image crypto-graphy achieves both confusion and diffusion characteristics.The encryption procedure starts by applying the DFT on the image then the DFT transformed image is scrambled using the CHM and the inverse DFT is applied to get the final-ly encrypted image.The decryption procedure follows the inverse procedure of encryption.The proposed DFT-based CHM image cryptography system is exam-ined using a set of security tests like statistical tests,entropy tests,differential tests,and sensitivity tests.The obtained results confirm and ensure the superiority of the proposed DFT-based CHM image cryptography system.These outcomes encourage the employment of the proposed DFT-based CHM image cryptography system in real-time image and video applications.

基于DFT的旋转变压器信号偏差矫正方法研究

解码芯片在对旋转变压器输出的位置信号做处理的过程中,芯片在采样时容易产生各种非理想偏差,这会造成转子位置估算精度的急剧下降。针对该问题,分析了电压信号中的幅值偏差和正交偏差会对旋转变压器解码的输出角度叠加一个2倍频的波动,直流偏差会叠加一个同频波动的问题,提出了一种基于离散傅里叶变换(DFT)的输入矫正法用于实现旋转变压器输出信号的偏差矫正,同时有效降低一次二次波动。该方法首先离散采样信号,通过DFT公式提取旋转变压器输出信号的直流信号和基频信号;然后基于直流信号和基频信号先后计算直流偏差、幅值偏差和正交偏差,通过控制器实现偏差值矫正。最后,仿真和试验结果表明,在芯片采样产生偏差时,所提出的偏差提取方法有效,试验中相应的正余弦输出信号指定阶次的波动更小。

分数阶Fourier变换的测不准原理

该文参考Fourier变换的性质研究了离散分数阶Fourier变换的测不准原理以及连续分数阶Fourier变换在Lebesgue测度下的测不准原理,使得分数阶Fourier变换的测不准原理性质更一般化.

Authentication and Secret Message Transmission Technique Using Discrete Fourier Transformation

In this paper a novel technique, Authentication and Secret Message Transmission using Discrete Fourier Transformation (ASMTDFT) has been proposed to authenticate an image and also some secret message or image can be transmitted over the network. Instead of direct embedding a message or image within the source image, choosing a window of size 2 x 2 of the source image in sliding window manner and then con-vert it from spatial domain to frequency domain using Discrete Fourier Transform (DFT). The bits of the authenticating message or image are then embedded at LSB within the real part of the transformed image. Inverse DFT is performed for the transformation from frequency domain to spatial domain as final step of encoding. Decoding is done through the reverse procedure. The experimental results have been discussed and compared with the existing steganography algorithm S-Tools. Histogram analysis and Chi-Square test of source image with embedded image shows the better results in comparison with the S-Tools.

基于滑窗DFT算法的新能源直流并网逆变器协调控制方法

当前的并网逆变器协调控制结构一般设置为独立形式,整体协调控制效率较低,导致周期逆变器的畸变率增加,为此提出基于滑窗离散傅里叶变换(Discrete Fourier Transform,DFT)算法的新能源直流并网逆变器协调控制方法。根据现有的测定需求和标准,先进行畸变电流测定,采用多目标的方式提高整体的协调控制效率。设计多目标交叉协调控制结构,构建滑窗DFT测算并网逆变器协调控制模型,采用三相平衡控制实现逆变器协调控制处理。测试结果表明,与传统带输出LC滤波器辅助逆变器协调控制方法和传统光伏处理逆变器协调控制方法相比,本次设计的基于滑窗DFT算法的逆变器协调控制方法最终得出的周期逆变器畸变率均被控制在0.2%以下,大幅提升了变网逆变器的协调控制效率,控制针对性增强,具有较好的实际应用价值。

基于DFT-SWOMP的OFDM系统信道估计方法

基于压缩感知的OFDM信道估计方案中,分段弱正交匹配追踪(SWOMP)算法具有不需要预知信道稀疏度的优点,但其信道估计精度受输入的门限参数和迭代次数的影响较大。针对这一问题,提出一种基于DFT-LS算法的门限自适应的SWOMP算法改进方案。考虑到在OFDM系统中,保护间隔长度外的信道时域响应都可以视为噪声,因此该方案的核心思想是利用DFT-LS算法预估出噪声水平,并用此预估值来动态设置SWOMP算法的门限参数。同时,该方案还使用DFT-LS算法预估出的信道频域响应作为SWOMP算法的迭代停止条件。仿真结果表明,这种SWOMP算法的改进方案可以有效地估计出信道参数,并且相比SWOMP算法,其估计结果的MSE值在不同信噪比下都有不同程度的提升。

Fractal Surface Synthesis Based on Two Dimensional Discrete Fourier Transform

The discrete Fourier transform（DFT） is used for fractional Brownian motion（FBM） surface synthesis in tribology（i.e., contact, sliding, and sealing, etc）. However, the relationship between fractal parameters（fractal dimension and scale factor） and traditional parameters, the influence of fractal parameters on surface appearance, have not been deeply discussed yet. These lead to some kind of difficulty to ensure the synthesized surfaces with ideal fractal characteristic, required traditional parameters and geometric appearance. A quantitative relationship between fractal parameters and the root mean square deviation of surface （Sq） is derived based on the energy conservation property between the space and frequency domain of DFT. Under the stability assumption, the power spectrum of a FBM surface is composed of concentric circles strictly, a series of FBM surfaces with prescribed Sq could be synthesized with given fractal dimension, scale factor, and sampling numbers, but the ten-point height（Sz）, the skewness（Ssk） and the kurtosis（Sku） are still in random, where the probability distributions of Sz and Ssk are approximately normal distribution. Furthermore, by iterative searching, a surface with desired Abbott-Firestone curve could be obtained among those surfaces. An intuitive explanation for the influence of fractal dimension and scale factor on surface appearance is obtained by discussing the effects on the ratio of energy between high and low frequency components. Based on the relationship between Sq and surface energy, a filtering method of surface with controllable Sq is proposed. The proposed research ensures the synthesized surfaces possess ideal FBM properties with prescribed Sq, offers a method for selecting desired Abbott-Firestone curve of synthesized fractal surfaces, and makes it possible to control the Sq of surfaces after filtering.

Digital watermarking for still image based on discrete fractional fourier transform

Presents a digital watermarking technique based on discrete fractional Fourier transform (DFRFT), discusses the transformation of the original image by DFRFT, and the modification of DFRFT coefficients of the original image by the information of watermark, and concludes from experimental results that the proposed technique is robust to lossy compression attack.

Theory and algorithms for two-dimensional warped discrete Fourier transform

In this paper, the two-dimensional Warped Discrete Fourier Transform （2-D WDFT） is developed based on the concept of the 1-D WDFT. An exact computation algorithm is developed for 2-D WDFT based on matrix factorizing with special structure. A fast algorithm is then proposed to reduce greatly the computational complexity of the inverse 2-D WDFT. Finally, numerical examples are given to show the efficiency of the proposed approach.

A Matrix Formulation of Discrete Chirp Fourier Transform Algorithms

This work presents a computational matrix framework in terms of tensor signal algebra for the formulation of discrete chirp Fourier transform algorithms. These algorithms are used in this work to estimate the point target functions （impulse response functions） of multiple-input multiple-output （MIMO） synthetic aperture radar （SAR） systems. This estimation technique is being studied as an alternative to the estimation of point target functions using the discrete cross-ambiguity function for certain types of environmental surveillance applications. The tensor signal algebra is presented as a mathematics environment composed of signal spaces, finite dimensional linear operators, and special matrices where algebraic methods are used to generate these signal transforms as computational estimators. Also, the tensor signal algebra contributes to analysis, design, and implementation of parallel algorithms. An instantiation of the framework was performed by using the MATLAB Parallel Computing Toolbox, where all the algorithms presented in this paper were implemented.

Generalized Parseval’s Theorem on Fractional Fourier Transform for Discrete Signals and Filtering of LFM Signals

This paper investigates the generalized Parseval’s theorem of fractional Fourier transform (FRFT) for concentrated data. Also, in the framework of multiple FRFT domains, Parseval’s theorem reduces to an inequality with lower and upper bounds associated with FRFT parameters, named as generalized Parseval’s theorem by us. These results theoretically provide potential valuable applications in filtering, and examples of filtering for LFM signals in FRFT domains are demonstrated to support the derived conclusions.

基于TS-DFT高速光谱解调的FBG温度分布检测

基于时间拉伸-色散傅里叶变换(time-stretch dispersive Fourier transformation,TS-DFT)技术实现了光纤布拉格光栅反射谱高速解调。解调系统由锁模激光器、环行器、色散补偿光纤、参考光栅、传感光栅以及数据采集和处理模块组成。实验得到了传感光栅在不同温度场下的时域映射光谱,通过与光谱仪测量光谱对比,验证了系统高速光谱解调能力,解调速率为51.2 MHz。结合光谱反演算法得到了沿光栅轴向的温度分布,空间分辨率为200µm,实现了传感光栅高速、高空间分辨率温度传感。

A WEIGHTED GENERAL DISCRETE FOURIER TRANSFORM FOR THE FREQUENCY-DOMAIN BLIND SOURCE SEPARATION OF CONVOLUTIVE MIXTURES

This letter deals with the frequency domain Blind Source Separation of Convolutive Mixtures (CMBSS). From the frequency representation of the "overlap and save", a Weighted General Discrete Fourier Transform (WGDFT) is derived to replace the traditional Discrete Fourier Transform (DFT). The mixing matrix on each frequency bin could be estimated more precisely from WGDFT coefficients than from DFT coefficients, which improves separation performance. Simulation results verify the validity of WGDFT for frequency domain blind source separation of convolutive mixtures.

Numerical Approximation of Real Finite Nonnegative Function by the Modulus of Discrete Fourier Transform

The numerical algorithms for finding the lines of branching and branching-off solutions of nonlinear problem on mean-square approximation of a real finite nonnegative function with respect to two variables by the modulus of double discrete Fourier transform dependent on two parameters, are constructed and justified.

基于迭代修正DFT的车轮多边形磨耗状态识别

受车辆变速运行、轨道随机不平顺等因素的影响,轨道车辆的运行过程为典型的非平稳过程。由于传统方法对于非平稳信号的处理不理想,使得车轮多边形磨耗阶次与幅值的准确识别比较困难。为提高车轮多边形磨耗状态的识别准确度,提出了一种基于迭代修正离散傅里叶变换(discrete Fourier transform,简称DFT)的动态识别方法,采用车辆处于相对稳定速度运行时产生的轴箱垂向振动加速度信号进行分析。首先,通过设定适当的平稳性检验条件,从样本信号中抽取出部分相对平稳的短时信号;其次,对所抽取的短时信号进行频域分析与迭代计算,获得各阶车轮多边形的振动频率与振动周期;然后,根据振动周期的长度对所抽取的短时信号进行二次截断,获得代表各阶车轮多变形振动周期整数倍长度的新短时信号;最后,结合车轮多边形的几何特征与动态特性,对抽取的新短时信号再次进行频域分析与磨耗参数(阶次、幅值)计算,进而实现对车轮多边形磨耗状态的准确识别。分析表明,该识别方法有效减少了传统分析方法中因栅栏效应和频谱泄漏等固有缺陷导致的识别误差,可消除大部分非平稳因素的干扰,为轨道车辆的安全运行维护提供理论支持和方法参考。

Quantum Discrete Fourier Transform in an Ion Trap System

<正> We propose two schemes for the implementation of quantum discrete Fourier transform in the ion trap sys-tem.In each scheme we design a tunable two-qubit phase gate as the main ingredient.The experimental implementationof the schemes would be an important step toward complex quantum computation in the ion trap system.

Detection Algorithm for LFM Echo of Underwater Moving Targets Based on Discrete Fractional Fourier Transform

The mismatch between echo and replica caused by underwater moving target(UMT)'s radial velocity degrades the detection performance of the matched filter(MF)for the linear frequency modulation(LFM)signal.By using the focusing property of fractional Fourier transform(FRFT)to that signal,a detection algorithm for UMT's LFM echo based on the discrete fractional Fourier transform(DFRFT)is proposed.This algorithm is less affected by the target's radial velocity compared with the other MF detection algorithm utilizing zero radial velocity replica(ZRVR),and the mathematical relation between the output peak positions of these two algorithms exists in the case of existence of target echo.The algorithm can also estimate the target distance by using this relation.The simulation and experiment show that this algorithm'sdetection performance is better than or equivalent to that of the other MF algorithm utilizing ZRVR for the LFM echo of UMT with unknown radial velocity under reverberation noise background.

CONCURRENT SPEECHES SEPARATION USING WRAPPED DISCRETE FOURIER TRANSFORM

This letter proposes a new method for concurrent voiced speech separation. Firstly the Wrapped Discrete Fourier Transform (WDFT) is used to decompose the harmonic spectra of the mixed speeches. Then the individual speech is reconstructed by using the sinusoidal speech model. By taking advantage of the non-uniform frequency resolution of WDFT, harmonic spectra parameters can be estimated and separated accurately. Experimental results on mixed vowels separation show that the proposed method can recover the original speeches effectively.

Improved Speech Denoising Algorithm Based on Discrete Fractional Fourier Transform

The speech signal and noise signal are the typical non-stationary signals,however the speech signa is short-stationary synchronously.Presently,the denoising methods are always executed in frequency domain due to the short-time stationarity of the speech signal.In this article,an improved speech denoising algorithm based on discrete fractional Fourier transform（DFRFT）is pre sented.This algorithm contains linear optimal filtering and median filtering.The simulation shows that it can easily eliminate the noise compared to Wiener filtering improve the signal to noise ratio（SNR）,and enhance the original speech signal.

基于DFT的旋变软件解码非理想偏差标定方法

针对目前旋变软件解码中的采样包络面存在非理想偏差问题,从理论推导了幅值偏差、直流偏差会对旋变软件解码的输出角度叠加一个2倍频波动,正交偏差会叠加一个同频波动。提出了基于离散傅里叶变换(DFT)的矫正方法,利用该方法实现了幅值偏差、直流偏差和正交偏差的提取,并对这3种偏差设计了相应的矫正环节。同时又推导了存在转速误差条件下使用DFT方法提取到的幅值偏差、直流偏差存在一个和旋变包络面初始相位相关的波动误差,并通过取一段时间内波动平均值的方法解决了该误差对提取结果的影响。最后通过仿真试验验证了推导的正确性,搭建了拖台架并进行旋变标定试验,对比标定前后数据,表明偏差矫正后的锁相环输出的角度线性度更好,转速波动更小,相应的dq轴电流的指定阶次波动也更小。