Topic
Discrete-time Fourier transform
About: Discrete-time Fourier transform is a research topic. Over the lifetime, 5072 publications have been published within this topic receiving 144643 citations. The topic is also known as: DTFT.
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TL;DR: It is demonstrated that the AFT-MC system effectively minimizes interference in time-varying multipath channels with line-of-sight component and narrow beamwidth of scattered components that often occurs in aeronautical and satellite communications.
Abstract: Multicarrier techniques based on affine Fourier transform (AFT) have been recently proposed for transmission in the wireless channels. The AFT represents a generalization of the Fourier and fractional Fourier transform. We derive the exact and approximated interference power, upper bound and measure of applicability for the AFT based multicarrier (AFT-MC) system. It is demonstrated that the AFT-MC system effectively minimizes interference in time-varying multipath channels with line-of-sight component and narrow beamwidth of scattered components that often occurs in aeronautical and satellite communications.
23 citations
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TL;DR: A sampling theorem without band-limiting constraints for the fractional Fourier transform in the function spaces is established, which can provide a suitable and realistic model of sampling and reconstruction for real applications.
23 citations
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14 Jun 2009
TL;DR: In this paper, the authors compare three algorithms (non-equispaced DFT, interpolated FFT and non-Equispaced FFT) for OCT imaging in terms of speed and accuracy.
Abstract: In OCT imaging the spectra that are used for Fourier transformation are in general not acquired linearly in k-space. Therefore one needs to apply an algorithm to re-sample the data and finally do the Fourier Transformation to gain depth information. We compare three algorithms (Non-Equispaced DFT, interpolated FFT and Non-Equispaced FFT) for this purpose in terms of speed and accuracy. The optimal algorithm depends on the OCT device (speed, SNR) and the object.
23 citations
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TL;DR: The implicitly restarted generalized minimum residual method (IRGMRES) combined with the fast Fourier transform (FFT) technique is developed for solving three-dimensional weak-form volume electric field integral equation of electromagnetic scattering problems.
Abstract: The implicitly restarted generalized minimum residual method (IRGMRES) combined with the fast Fourier transform (FFT) technique is developed for solving three-dimensional (3-D) weak-form volume electric field integral equation of electromagnetic scattering problems. On several electromagnetic scattering problems, the resulted IRGMRES-FFT method converges two-three times faster than the conventional biconjugate gradient (BCG)-FFT method. Comparison with other Krylov-subspace iterative fast Fourier transforms methods also demonstrates the efficiency of the IRGMRES-FFT method.
23 citations
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TL;DR: The following procedures are based on the Cooley-Tukey algor i thm for comput ing the finite Fourier t r ans fo rm of a complex da ta vector; the dimension of the da t a vector is assumed here to be a power of two.
Abstract: The following procedures are based on the Cooley-Tukey algor i thm [1] for comput ing the finite Fourier t r ans fo rm of a complex da ta vector; the dimension of the da t a vector is assumed here to be a power of two. Procedure COMPLEXTRANSFORM computes ei ther the complex Fourier t ransform or its inverse. Procedure REALTRANSFORM computes ei ther the Fourier coefficients of a sequence of real da ta points or eva lua tes a Fourier series wi th given cosine and sine coefficients. The number of ar i thmet ic operat ions for ei ther procedure is proport ional to n logs n, where n is the number of da ta points. Procedures FFT2, REVFFT2, REORDER, and REAL TRAN are building blocks, and are used in the two complete procedures ment ioned above. The fas t t r ans fo rm can be computed in a number of different ways, and these bui lding block procedures were wri t ten so as to make practical the comput ing of large t rans forms on a system wi th vir tual memory. Using a method proposed by Singleton [2], d a t a is accessed in sub-sequences of consecutive a r ray elements , and as m u ch comput ing as possible is done in one section of the d a t a before moving on to another. Procedure FFT2 computes the Fourier t r ans fo rm of da ta in normal order, giving a resu l t in reverse b ina ry order. Procedure REVFFT2 computes the Fourier t r ans fo rm of da ta in reverse b ina ry order and leaves the resul t in normal b inary order. Procedure REORDER permutes a complex vector f rom b inary to reverse b ina ry order or f rom reverse b inary to b inary order; this procedure also permutes real da ta in prepara t ion for efficient use of the complex Fourier t ransform. Procedures FFT2, REVFFT2, and REORDER m a y also be used to compute mul t iva r i a te Fourier t ransforms. The procedure R E A L T R A N is used to unscramble and combine the complex t rans forms of the even and odd numbered e lements of a sequence of real d a t a points . This procedure is not restr ic ted to powers of two and can be used whenever the number of da t a points is even.
23 citations