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1.
We present a fractional Gabor expansion on a non-rectangular time-frequency lattice. Sinusoidal analysis used in the traditional Gabor expansion is not appropriate for a compact representation for chirp-type signals. Basis functions of the proposed expansion are obtained via fractional Fourier basis. Completeness and biorthogonality conditions of the new expansion are derived. 相似文献
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多时相AVHRR数据的傅立叶分析 总被引：10，自引：0，他引：10
傅立叶分析(FourierAnalysis)是一种常用的信号处理方法.将中国全年 36旬的NOAA AVHRR的 1km数据采用最大值合成法获得 1 2个月的NDVI时间序列数据,然后运用离散傅立叶变换检测该时间信号的频率分布状况.结果各频率分量与NDVI的累加值及不同周期的季节性变化等生物学特征相关.其中零频率分量为均值NDVI,而 1/1 2频率分量最大程度概括了中国地表覆盖类型的全年季节性变化模式.将提取出的这些生物学特征引入到地表覆盖分类的特征空间中,提高了类别间的可分性.这些研究表明了傅立叶变换是分析多时相AVHRR数据及提取植被的生物学特征的有用工具 相似文献
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针对常见的雷达脉冲信号（常规信号（NS）,线性调频信号（LFM）,双线性调频信号（DLFM）运用时频工具对调制方式的识别进行研究。运用两种时频分析方法1.短时傅里叶变换2.相位展开算法.通过这两种算法对雷达信号的调制方式进行分析,并通过仿真得到雷达信号的时--频分布以及时—频,时—相曲线,对仿真结果进行研究。通过仿真实验表明,雷达信号调制方式识别算法是可行的,有效的,而且具有良好的性能。 相似文献
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基于中心类型DFT矩阵特征分解的MA-CDFRFT(Multiangle Centered Discrete Fractional Fourier Transform)算法在计算一组离散分数阶傅立叶变换DFRFT(Discrete Fractional Fourier Transform)时充分利用FFT运算来减小运算量。结合偶数点离散傅立叶变换DFT(Discrete Fourier Transform)运算的对称性原理，通过数学推导将MA-CDFRFT算法中的一维对称性扩展到频率和变换阶数的二维平面上。利用这个二维对称性原理，改进算法将原算法的主要计算量减小了一半左右。仿真测试结果证明了改进算法的正确性。 相似文献
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本文将边界序列的多尺度描述和傅里叶描述符结合起来,得到闭合边界的多尺度傅里叶描述符。该方法先将边界序列呈现到不同的尺度空间,然后进行傅里叶变换,得到了不同尺度空间的傅里叶描述符。分类实验表明,该方法提取的特征具有较好的分类特性。 相似文献
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Martin J. Bastiaans 《Journal of The Franklin Institute》2011,348(9):2670-2673
It is shown that the recently introduced T-class of time-frequency distributions is a subclass of the S-method distributions. From the generalization of the S-method distribution by rotating it in the time-frequency plane, a similar generalization of the T-class distribution follows readily. The generalized T-class distribution is then applicable to signals that behave chirp like, with their instantaneous frequency slowly varying around the slope of the chirp; this slope needs no longer be zero, as is the case for the original T-class distribution, but may take an arbitrary value. 相似文献
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The chaotic behaviors in the fractional order unified system are numerically investigated. By utilizing the fractional calculus techniques, we found that chaos exists in the fractional order unified system with order less than 3. The lowest order we found to have chaos in this system is 2.76. Chaos synchronization of the fractional order unified system is theoretically and numerically studied using the one-way coupling method. The suitable conditions for achieving synchronization of the fractional order differential system are derived by using the Laplace transform theory. It is noticed that the time required for achieving synchronization of the drive system and the response system and the synchronization effect sensitively depend on the coupling strength. Numerical simulations are performed to verify the theoretical analysis. 相似文献
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以静止图像为研究对象,文章提出了一种离散分数傅立叶变换（DFRFT）域的图像数字水印算法,该算法通过对载体图像进行某个级次的分数傅立叶变换,将加密水印嵌入到载体图像的分数傅立叶谱中,从而得到含水印的图像。实验结果表明,该算法实现了水印图像的不可见性,同时对常见的图像攻击具有较好的鲁棒性。 相似文献
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建立了非增函数的加权Ｆｏｕｒｉｅｒ变换范数不等式。还给出了一类具有单调性条件函数的Ｋ－变换加权范数不等式的相应结果。 相似文献
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初始孔压均布的饱和土一维热固结解析解 总被引：1，自引：0，他引：1
基于热弹性力学和饱和土固结理论,通过热固结方程的建立和求解,研究了饱和土的一维热固结问题.利用有限Fourier变换及其逆变换,得到土层内部超静孔压、温度增量的解析解,并依此求出地基沉降、平均固结度的表达式.根据所得解编制了计算程序,分析了饱和土的一维热固结性状,并与Terzaghi解进行了比较.结果表明,超静孔压随时间延长最终消散为零,但在热同结过程中可能会产生负孔压;地基沉降受温度影响而减小;平均固结度按变形定义和按孔压定义是不同的:热扩散系数与同结系数的比值的大小对热同结性状有重要影响. 相似文献
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对阶跃函数在二维广义傅氏变换的四分屏蔽效应进行了探讨,并给出了相关定理的证明和应用。 相似文献
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基于目标宽度特征的脉间跳频雷达距离精确成像 总被引：2，自引：0，他引：2
根据雷达目标的宽度特征 ,提出了目标检测窗口内雷达信号的逆Chirp z变换局部成像处理方法 .利用有限的输入数据长度 ,有效提高目标局部距离像的采样分辨率 ,获得更精确的距离像 .与传统的数据长度补零逆傅里叶变换方法相比 ,在相同的采样分辨率条件下 ,该方法能有效减小计算量 .仿真实验结果与理论分析相符合 ,证明了该方法的有效性 . 相似文献
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利用入射激光经过转台散射所得信号光与参考光进行混频的方法得出转台的转速。使激光器出射光通过分束器后分成两束同频光,一束作为参考光,另一束经转台散射后即为信号光。参考光和信号光在探测器光敏面上进行混频,随后通过傅里叶变换(FFT)处理数据,计算出转台转动速度并与实际速度进行比较,结果表明该系统用于转台的转速测量是切实可行的,精度可达0.4%。 相似文献
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In wireless communications, the channel is typically modeled as a random, linear, time-varying system that spreads the transmitted signal in both time and frequency due to multi-path propagation and Doppler effects. Estimated channel parameters allow system designers to develop coherent receivers that increase the system performance. In this paper, we show how time-frequency analysis can be used to model and estimate the time-varying channel of a multi-carrier spread spectrum (MCSS) system using a complex quadratic sequence as the spreading code. We will show that for this spreading code, the effects of time delays and Doppler frequency shifts, caused by the mobility of environment objects, can be combined and represented effectively as time shifts. The discrete evolutionary transform (DET), as a time-frequency analysis method, enables us to estimate the effective time shifts via a spreading function and to use them to equalize the channel. Using the effective time shifts, the time-varying channel can be represented simply as linear-time invariant system by embedding the Doppler shifts that characterize the time-varying channel into effective time shifts. The channel parameters are used to estimate the data bit sent. To illustrate the performance of the proposed method we perform several simulations with different levels of channel noise, jammer interference, and Doppler frequency shifts. 相似文献
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小波变换突破了传统傅里叶变换等信号处理方法的限制,在时域和频域上可同时对信号实现局部化处理,这更符合信号非平稳的变频带结构特征,因而在信号检测奇异性等方面具有广泛的应用价值。本文简要地介绍了小波应用在信号奇异性检测方面变换的基本原理,并通过仿真实验进行了验证。 相似文献
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利用IPIX雷达回波数据分析了海杂波的统计特性.并利用LFM信号在分数阶Fourier域良好的能量聚集性,提出基于分数阶Fourier变换的海面动目标检测方法.此方法能较好的聚集动目标回波能量,而对海杂波回波的能量聚集不明显,可以较好的检测出动目标.最后采用实测海杂波数据做了仿真分析,证实了此方法的有效性. 相似文献
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《Journal of The Franklin Institute》2022,359(16):9313-9333
This paper studies the fault monitoring problem of a spacecraft control moment gyro (CMG) in complex environments based on the data-driven method. First, the wavelet denoising method and short-time Fourier transform (STFT) are utilized to preprocess the signal measured by an industrial personal computer (IPC) to obtain the frequency spectrum of each failure mode. Then, a slice residual attention network (SRAN) based on the ResNeXt model, attention mechanism, and random slice idea is proposed, which can fully capture the edge features of images while satisfying the learning efficiency. Furthermore, a set of comparative experiments are carried out to validate the ability of the proposed method, and the performance of SRAN is further verified under different datasets. Finally, based on the confusion matrix and t-SNE dimension reduction technique, the monitoring ability of SRAN for various faults is analyzed. Experimental results show that SRAN processes good fault monitoring capability and ideal robustness and can identify different fault degrees under the real-time fault monitoring scenario. 相似文献
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G.F. Nalesso 《Journal of The Franklin Institute》1982,313(5):247-266
The problem of the magnetic field diffusion through cylindrical structures is considered. An analytic solution is given for the problem of diffusion, through any number of resistive coaxial layers, of the three components of a quite general input vector magnetic field assigned on a boundary cylindrical surface. The limitations on the class of input functions (or more generally distributions) are the existence of the double space Fourier transform and the time Laplace transform; this makes the solution suitable for studying the transient-state behaviour in cylindrical structures of finite or infinite length. 相似文献