共查询到20条相似文献,搜索用时 15 毫秒
1.
The discrete rotational Fourier transform 总被引:10,自引:0,他引:10
We define a discrete version of the angular Fourier transform and present the properties of the transform that show it to be a rotation in time-frequency space, this new transform is a generalization of the DFT. Efficient algorithms for its computation can then be based on the FFT and the eigenstructure of the DFT 相似文献
2.
The discrete fractional Fourier transform 总被引:3,自引:0,他引:3
We propose and consolidate a definition of the discrete fractional Fourier transform that generalizes the discrete Fourier transform (DFT) in the same sense that the continuous fractional Fourier transform generalizes the continuous ordinary Fourier transform. This definition is based on a particular set of eigenvectors of the DFT matrix, which constitutes the discrete counterpart of the set of Hermite-Gaussian functions. The definition is exactly unitary, index additive, and reduces to the DFT for unit order. The fact that this definition satisfies all the desirable properties expected of the discrete fractional Fourier transform supports our confidence that it will be accepted as the definitive definition of this transform 相似文献
3.
The discrete Fourier transform method is a numerical technique designed to take advantage of the convolution structure that often appears in the differential-integral equations arising from electromagnetic scattering. It used the fast Fourier transform (FFT) to compute both the derivatives and the convolution integrals. As a consequence, this method is easy to program, uses less computer memory than comparable methods, yields accurate predictions, and in general, offers a better rate of convergence. This technique, which is particularly suited for solving problems where the scatterer is made of a dielectric material and has a shape which can be approximated accurately by a rectangular grid, is applied to thin dielectric slabs with both electric and magnetic properties. It is shown that by choosing the conductivity sufficiently large, a thin dielectric slab behaves like a metallic plate. On the other hand, with a suitable choice of conductivity, a particular thin dielectric slab will act like a resistive plate 相似文献
4.
The discrete Fourier transform method (DFTM) is used to calculate the radar cross section (RCS) or orthogonal or nonorthogonal dihedral reflectors. In order to accurately model the mutual interactions between the two plates, a four-point bivariate Lagrange interpolation is incorporated into the DFTM. The resulting algorithm is simple and efficient. Results obtained with it compare favorably with measurements and predictions computed using the method of moments 相似文献
5.
《IEEE transactions on information theory / Professional Technical Group on Information Theory》1978,24(6):683-692
Distortion-rate theory is used to derive absolute performance bounds and encoding guidelines for direct fixed-rate minimum mean-square error data compression of the discrete Fourier transform (DFT) of a stationary real or circularly complex sequence. Both real-part-imaginary-part and magnitude-phase-angle encoding are treated. General source coding theorems are proved in order to justify using the optimal test channel transition probability distribution for allocating the information rate among the DFT coefficients and for calculating arbitrary performance measures on actual optimal codes. This technique has yielded a theoretical measure of the relative importance of phase angle over the magnitude in magnitude-phase-angle data compression. The result is that the phase angle must be encoded with 0.954 nats, or 1.37 bits, more rate than the magnitude for rates exceeding 3.0 nats per complex element. This result and the optimal error bounds are compared to empirical results for efficient quantization schemes. 相似文献
6.
《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1987,75(9):1283-1292
A number of previous attempts at the vectorization of the fast Fourier transform (FFT) algorithm have fallen somewhat short of achieving the full potential speed of vector processors. The algorithm formulation and implementation described here not only achieves full vector utilization but successfully copes with the problems of hierarchical storage. In the present paper, these techniques are described and extended to the general mixed radix algorithms, prime factor algorithm (PFA), the multidimensional discrete Fourier transform (DFT), the rectangular transform convolution algorithms, and the Winograd fast Fourier transform algorithm. Some of the methods were used in the Engineering Scientific Subroutine Library for the IBM 3090 Vector Facility. Using this approach, very good and consistent performance was obtained over a very wide range of transform lengths. 相似文献
7.
《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1975,63(9):1370-1371
An efficient structure is suggested for the frequency-domain windowing of discrete Fourier transforms. In this scheme, multiplications are replaced by shifts in the position of the binary point. Three new window functions are described which can be realized by the suggested structure. 相似文献
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We introduce a new discrete fractional Fourier transform (DFrFT) based on only the DFT matrix and its powers. Eigenvectors of the DFT matrix are obtained in a simple-yet-elegant and straightforward manner. We show that this DFrFT definition based on the eigentransforms of the DFT matrix mimics the properties of continuous fractional Fourier transform (FrFT) by approximating the samples of the continuous FrFT. By appropriately combining existing commuting matrices we obtain a new commuting matrix which performs better. We show the validity of the proposed algorithms by computer simulations comparing DFrFT points and continuous FrFT samples for various signals. 相似文献
10.
受数字系统有限字长的影响,滑动离散傅里叶变换(滑动DFT)算法的频率单元存在输出不稳定的缺点。利用改进Goertzel算法的递归单元对滑动DFT算法的频率单元改造后,不仅可以直接计算起始频谱值,而且滑动DFT算法可以每隔N个输出值就对频率单元清零,并能提供准确的新谱值,保证了滑动DFT算法的频率单元可以长时间连续不断的处理输入数据,而不会出现输出不稳定现象。这种方法在连续地、实时地进行时频谱分析中具有重要的意义。 相似文献
11.
Quisquater M. Preneel B. Vandewalle J. 《IEEE transactions on information theory / Professional Technical Group on Information Theory》2003,49(8):2038-2040
Discrete Fourier theory has been applied successfully in digital communication theory. In this correspondence, we prove a new inequality linking the number of nonzero components of a complex valued function defined on a finite Abelian group to the number of nonzero components of its Fourier transform. We characterize the functions achieving equality. Finally, we compare this inequality applied to Boolean functions to the inequality arising from the minimal distance property of Reed-Muller codes. 相似文献
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The relationship between z-transform and Fourier transform of a discrete series is presented. The Fourier transform of a discrete series whose z-transform has poles on the unit circle can be derived using these results.<> 相似文献
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利用描述光波傍轴传输的光学分数傅里叶变换基本关系式,对单透镜系统进行分析,结果表明,单透镜系统可实现任意阶分数傅里叶变换,Lohmann第一类光学分数傅里叶变换装置是其特例,单透镜成像过程是进行阶次为π的分数傅里叶变换,进一步表明光学分数傅里叶变换的物理实质是光波的菲涅耳衍射。 相似文献
16.
由于CCD采集的变形条纹图是空域有限的,在对其作窗口傅立叶变换处理时,高斯窗在图像边缘的不完整会产生测量误差。针对这种情况,提出了采用Gerchberg迭代法对条纹进行外插延拓,扩展窗口傅立叶变换处理的有效区域范围,进而改善窗口傅立叶变换的测量精度。 相似文献
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18.
《Proceedings of the IEEE. Institute of Electrical and Electronics Engineers》1974,62(10):1395-1396
A previous technique for deriving Chebyshev shading coefficients using a cosine series is rewritten in the form of an inverse discrete Fourier transform (DFT) thus allowing one to take advantage of standard DFT algorithms. The reduced accuracy required for intermediate calculations is retained. Additionally, the fast Fourier transform can be used giving computational savings. 相似文献
19.
Sundararajan D. Ahmad M.O. Swamy M.N.S. 《Signal Processing, IEEE Transactions on》1997,45(8):2010-2022
Fast algorithms for the computation of the discrete Fourier transform (DFT) of real signals are important since the signals in practical situations are mostly real. The more efficient algorithms for real data are those that are derived from the algorithms for complex data. So far, all such algorithms use a real array to store the data. However, as the data values are real and their transform values are mostly complex, two possible data structures can be used for these algorithms: real or complex. DFT algorithms for real data that use a complex array for storing both the real data and their transform values are derived from the Cooley-Tukey radix-2 algorithm for complex data. This approach reduces the number of bit-reversal and array-index updating operations, eliminates independent data-swapping operations, and yields a computational structure that is almost as regular as that of the algorithms for complex data. Detailed derivations of the proposed algorithms for the computation of both the DFT of real data and the inverse DFT of the transform of real data, as well as their computational complexities, are presented. A C-language program of one of the proposed algorithms is given, illustrating the use of all the features of the new approach in software implementation. Comparison results are included to show that the proposed algorithms are faster and simpler than the real-valued split-radix and other algorithms 相似文献
20.
本文提出一种FFT新算法,其计算量不大于现有的各种基2DFT算法.然后,与Winograd小DFT(4,8,16点)结合使用,得出一种计算DFT的最快速算法. 相似文献