Littérature scientifique sur le sujet « IFFT-FD »

In recent years, target detection has drawn increasing attention in the field of radar signal processing. In this paper, we address the problem of coherent integration for detecting high-speed maneuvering targets, involving range migration (RM), quadratic RM (QRM), and Doppler frequency migration (DFM) within the coherent processing interval. We propose a novel coherent integration algorithm based on the frequency-domain second-order phase difference (FD-SoPD) approach. First, we use the FD-SoPD operation to reduce the signal from three to two dimensions and simultaneously eliminate the effects of QRM and DFM, which leads to signal-to-noise ratio improvement in the velocity-acceleration domain. Next, we estimate the target motion parameters from the peak position without the need for a search procedure. We show that this algorithm can be easily implemented by using complex multiplications combined with fast Fourier transform (FFT) and inverse FFT (IFFT) operations. We perform comparisons with several representative algorithms and show that the proposed technique can be used to achieve a good trade-off between computational complexity and detection performance. We present both simulated and experimental data to demonstrate the effectiveness of the proposed method.

A time-domain (TD) double diffraction solution is proposed with the source illumination for one or both sides of non-perfectly conducting wedges. The frequency domain redefined reflection angles as well as modified reflection coefficients are used in the different angular region of wedges for developing TD double diffraction. The accuracy of the proposed model is confirmed with IFFT- FD solution. Finally, the table of computational efficiency has been given for both the methods (TD and IFFT-FD) for hard polarization.

Abstract Savitzky-Golay (SG) filter is an effective and convenient gradient calculation method employed for full-field strain measurement in digital image correlation (DIC). Currently, the strain field can be conveniently obtained by moving smoothing filtering with SG filters. This is a way of spatial filtering, which offers the advantages of easy implementation and high accuracy. This study proposed a strain calculation method based on frequency domain SG (FD-SG) filtering. Prior to performing FD-SG filtering, data extension operations involving outer-boundary padding and zero-padding were performed on the displacement field data. Similarly, the SG filters template was extended with zero-padding and circularly shift operations. Subsequently, FD-SG filters were generated by applying the fast Fourier transform (FFT) to the expanded SG template. Thereafter, FD-SG filtering was implemented through the multiplication of the displacement in the Fourier-domain by an FD-SG filter. Finally, the strain field was obtained via inverse fast Fourier transform (IFFT) and valid data interception operation. The simulation and practical experiments confirmed the equivalent accuracy exhibited by FD-SG and spatial domain SG (SD-SG) filtering. Thus, the proposed FD-SG filtering method has great potential for real-time strain measurement in DIC.

Generally, higher order diffraction coefficient is used for the consideration of multiple diffraction. Due to this, the calculation becomes complex as well as not consider all possible order of diffraction among the wedges. In this paper, frequency and time-domain multiple-order diffraction for double wedge has been proposed. Only, single-order diffraction coefficient is used for higher-order diffraction calculation. So the proposed method is very simple and considers all possible order of diffraction. Both the IFFT-FD solution and proposed TD solution has been compared to confirm the accuracy.

A comparative analysis of time-domain (TD) solution, based on an established UTD diffraction model, are presented for modeling of Ultra-wideband (UWB) signal for lossy dielectric obstacles which gives accurate result to any arbitrary position of transmitter and receiver in a complex channel environment. Obstacles considered in the work include dielectric Wedge with homogenous, isotropic, low-loss dielectric characteristics. Different UTD-TD Diffraction Coefficients are proposed and compared with the IFFT of rigorous (i.e., Maliuzhinets) diffraction coefficient (RDC). The proposed work provides an in-depth analysis of the UTD model and presents an accurate and computationally more efficient TD solution for the available UTD diffraction coefficients for lossy dielectric medium, for both soft and hard polarizations. Moreover the reciprocity and symmetry for the diffraction coefficient in the time-domain have been proven for different position of transmitter and receiver. The time-domain modeling for transmission and reflection of UWB signals for 2-D & 3-D multi-modeled obstacle is also done. The obstacle is called multi-modeled since the obstacle consists of two entirely different structure i.e. dielectric wedge followed by dielectric slab. The comparison between the TD solution and the numerical inverse fast Fourier transform of the FD (IFFT-FD) solution proves the accuracy of the proposed solution. The significant gain in the computational speed achieved through the proposed TD solution is demonstrated by comparing its computation time with that of the exact IFFT-FD solution.