406 results about "Fractional Fourier transform" patented technology

The invention relates to a radar moving target Radon-fractional Fourier transform (RFRFT) long-time phase-coherent accumulation detection method, and belongs to the technical field of radar signal processing and detection. The radar moving target Radon-fractional Fourier transform long-time phase-coherent accumulation detection method includes steps of 1), performing range demodulation and pulse pressure for radar echo to complete intra-pulse accumulation; 2), initializing parameters; 3), completing long-time inter-pulse phase-coherent accumulation by RFRFT compensation distance and Doppler frequency migration; 4), traversing all search parameters and creating a distance-RFRFT domain detection unit graph; 5), performing constant false alarm rate detection for the detection unit graph; and 6), estimating movement parameters of a target and outputting movement point traces. The radar moving target Radon-fractional Fourier transform long-time phase-coherent accumulation detection method has the advantages that amplitude information and phase information of the echo of the moving target are simultaneously utilized for long-time phase-coherent accumulation, the distance and the Doppler frequency migration in a long-time accumulation procedure are compensated, background clutter and noise are effectively suppressed, an accumulation gain is increased, dim moving targets in the heavy cluster can be detected, the movement point traces of the target can be acquired, and the method has popularization and application value.

A system and method for projection number and radiation dose reduction in tomographic imaging that creates a three dimensional cross sectional image of an object by the reconstruction of its projections. Images of a superior quality can be obtained with a fewer number projections than seen with conventional methods by reconstruction of projections that have been pre-processed and preferably placed in the Fourier domain with a Fractional Fourier Transform (FrFT) or forward Pseudo-polar Fast Fourier transform (PPFFT). The projections are iteratively refined through formulation of a constrained optimization problem with constraints in object space and Fourier space preferably solved with a gradient descent algorithm incorporating a Bregman iterative regularization or a continuative regularization. By using an exact Fourier-based iterative algorithm as well as physical and mathematical constraints, convergence to a lowest-possible noise state that is also strictly consistent with the measured data can be obtained.

The invention relates to a sea surface micromotion target detection and feature extraction method based on short-time fractional Fourier transform (STFRFT) and belongs to the technical field of radar signal processing and detection. The method comprises the following steps: 1) sea peak identification: dividing sea clutters into sea peak sequences and sea clutter background sequences free of sea peaks; 2) sea clutter data screening: selecting the sea clutter background sequences corresponding to the minimal mean power as data to be detected; 3) FRFT domain micromotion target detection: taking the FRFT domain signal amplitude values as detection statistical quantities and comparing the detection statistical quantities with the thresholds; 4) optimal FRFT domain filtering: extracting multi-component micromotion signals by using a narrow bandpass filter; and 5) setting an optimal time window length and estimating micromotion features in the STFRFT domain. The method can automatically adapt to suppress sea clutters to improve the signal-to-clutter ratio, can effectively isolate and extract the multi-component micromotion signals, provides a new approach to sea surface weak target detection and feature extraction, and is significant in promotion and application.

The invention discloses a multi-target detection method based on short-time Fourier transform and fractional Fourier transform, which belongs to the technical field of the radar target detection. The method comprises the following steps that the short-time Fourier transform is firstly used for conducting the primary detection on a signal, then a binaryzation method is used for processing a primary detection result, phase position of the signal is kept in the processing, the fractional Fourier transform is used for detecting a signal after being restored by the short-time Fourier transform, by adopting multiple methods for combined processing, advantages of overcoming phenomenon that a strong signal side lobe presses a weak signal main lobe, improving the signal-to-noise ratio of the signal to be detected, and solving the problem of the large false alarm possibility which is caused by adopting traditional method to detect the signal at the low signal-to-noise ratio can be realized; and meanwhile, an image contrast method and a gradual elimination method are adopted, multiple strong signals and weak signals with different or identical frequency modulation rates can be detected by utilizing the space and power strength information of the signal, so that the detection probability and the calculation efficiency can be further improved, easiness in project realization is realized, and the method is worth of being adopted and popularized.

The invention provides a compressed sensing synthetic aperture radar (SAR) imaging method based on fractional order fourier transformation, and belongs to the technical field of microwave imaging. For a sparse target scene, a system emits a linear frequency modulation pulse signal; by adopting a method for projecting an echo signal to a low-dimension measurement matrix, measurement data which are much smaller than those required by a Nyquist sampling principle are acquired; due to the echo signal, after a reconstruction matrix is constructed by a simplified fractional order fourier transformation domain sparse mode and a data acquisition mode, a calculated distance pulse pressure result is optimized by a compressed sensing signal reconstruction method and is subjected to distance migration correction and direction pulse pressure to obtain a target scene imaging result. By the imaging method, the measurement data amount of a target scene with a sparse characteristic can be greatly reduced; and pressure on data storage and data transmission can be effectively relieved.

The invention relates to a radar moving target detection method based on short-time sparse fractional Fourier transform (ST-SFRFT), and belongs to the technical field of radar signal processing and detection. The method comprises the steps of: performing radar echo demodulation and pulse compression to realize high range resolution, and selecting a range unit to be detected; performing spare time-frequency analysis parameter initialization, comprising selection of a short-time window function and a window length and design of a sparse decomposition dictionary; performing ST-SFRFT operation for spare optimization solution, thus completing high-resolution spare time-frequency representation of moving target echo; traversing all range search units, performing moving target signal spare domain detection and estimating a target moving parameter. By adopting a high-resolution spare representation method, high-resolution and low-complexity time-frequency representation of time-varying signals is realized at the time frequency-spare domain; and the method is suitable for analyzing the time varying non-stability of signals, suppresses background clutter while improving energy concentration of moving target signals, and significantly improves the radar moving target detection and parameter estimation capability.

The invention relates to a double-random-phase optical color image encryption device and method, which belong to the field of optical image processing technique. The double-random-phase optical color image encryption device comprises an optical image encryption device and an optical image decryption device. The double-random-phase optical color image encryption device has high flexibility by adopting a joint fractional Fourier transform correlator, and the encryption technique based on the joint fractional Fourier transform correlator structure has high safety even if a correct phase mask cannot decrypt the original image information if the position has a slight change due to the translation variability of the fractional Fourier transform. The decryption device can be achieved only by arranging an electronic shutter of the encryption device and using the original illumination parallel light as the light source, and does not generate the optical field distribution conjugated to the encryption process. Based on the parallel processing characteristics of an optical information processing system, the double-random-phase optical color image encryption device can achieve color image encryption and decryption by use of single wavelength. Therefore, the double-random-phase optical color image encryption device has the advantages of simple structure, simplified system, lowered cost, high safe performance, and wide application range, and is convenient in operation.

The invention discloses a holographic projection method which comprises the following steps of: (10) laying projection devices: successively laying a phase spatial light modulator, a beam splitting prism, a lens and a screen, laying a mono-color laser and a polarizing film on the same side of the beam splitting prism, and connecting the phase spatial light modulator with a computer; (20) measuring the distance of an imaging face; (30) measuring and calculating the relationship between the focal length of the lens and the distance of the imaging face; (40) after determining the order of fractional Fourier transformation in the system, and carrying out iteration by using the fractional Fourier transformation formula and the inverse transformation formula to obtain the phase of a two-dimensional image; and (50) transmitting the phase hologram to the phase spatial light modulator via the computer, and projecting the phase hologram onto the screen in the specific location by using the phase spatial light modulator. With the holographic projection method, the holographic reconstructed two-dimensional image can be projected onto any plane behind the lens, and the focal length of the lens does not need to be changed to control the distance of imaging.

The invention discloses a novel digital demodulation identification method based on generalized fractional fourier transform (GFRFT) and fractional lower Wigner-Ville distribution (FLOWVD). The novel digital demodulation identification method comprises the steps as follows: received signals are sampled firstly, and then complex envelopes of the signals are restored through Hilbert transform; the maximum value of zero center normalization instantaneous amplitude spectrum density for the signals based on the GFRFT is calculated; the maximum value of the FLOWVD amplitude for the signals is calculated and is taken as characteristic quantity; and in addition, a sorter based on a decision tree is adopted, and the signals adopting different demodulation manners can be identified through data processing, threshold setting and comparison decision. Under the non-gaussian Alpha stable distribution noise, the novel digital demodulation identification method achieves the performance that remarkably surpasses the traditional method, and also achieves higher identification rate and favorable robustness.

The invention relates to a detection and parameter estimation method for linear frequency modulation signals. The method comprises the following steps: (1) carrying dimension normalization for signals received; (2) carrying out discrete fractional Fourier transform self-adaptive calculation for signals after dimension normalization; and (3) extracting parameters based on interpolative calculation to obtain a central frequency calculation frequency of the linear frequency modulation signals. According to the invention, when the signals are received, the DFRET of the model is calculated by using an adaptive algorithm, so that the time delay generated by the calculation of DFRET after completely collecting data. In addition, the signal estimation precision is improved by difference processing in a parameter searching stage in a two-dimensional plane of the DFRFT.

The invention discloses a multipath time delay and Doppler frequency shift estimation method in a signal channel based on fractional Fourier transform and a system for implementing the method, and relates to a signal channel estimation method and the system. The method and the system can solve the problem that the existing Doppler frequency shift and multipath time delay estimation in the signal channel adopts the statistical assumption method, thereby resulting in low estimation accuracy. The method is as follows: a chirp signal produced by a transmitting node produces a signal channel estimation signal after modulating a training sequence and transmits to the signal channel; a target node receives the signal, then filtration and sampling are carried out, sampling values are divided intoN parallel paths, the fractional Fourier transform with the different order is respectively carried out on each path, then the correlation calculation is carried out with a local reference signal, theposition of a peak value of each path is detected, and the multipath time delay and the Doppler frequency shift are estimated according to the positions of the peak values. The device uses N fractional domain modules for calculating the sampling values and adopts a multipath time delay and Doppler frequency shift combined estimation module for estimating the multipath time delay and the Doppler frequency shift. The method and the system are applicable to the performance improvement process of a wireless communication system.

The invention discloses an artificial circuit fault diagnosis pattern sorting algorithm based on signal characteristic space modeling. According to the method, signals collected by test nodes are utilized, optimal fractional Fourier transform (FrFT) and R type cluster analysis are performed on the signals on the basis of the maximum entropy principle (MEP) to describe the characteristics of fault samples, and different spatial distribution modeling of faults are conducted; according to the sort separability criterion of the characteristic evaluation of minimum-in-cluster-distance and maximum-between-cluster-distance, objective optimization functions of nuclear parameters are constructed, and on the basis of a self-adaption genetic algorithm, the objective functions are optimally solved, and the nuclear parameters are adjusted; in combination with Q type cluster analysis, a hierarchical support vector machine classifier (SVC) is constructed to find and separate the faults; and through the algorithm, sensitivity reflecting fault characteristics can be extracted from measurement signals, and higher fault diagnosis speed and higher fault diagnosis accuracy are achieved. The fault diagnosis examples of a Continuous-Time State-Variable Filter circuit and an ML-8 radar prove the speediness and effectiveness of the algorithm.

Methods and apparatus are provided for compressed imaging by performing modulation in a pupil plane. Image information is acquired by modulating an incident light field using a waveplate having a pattern that modifies a phase or amplitude of the incident light field, wherein the waveplate is positioned substantially in a pupil plane of an optical system; optically computing a transform between the modulated incident light field at a plane of the waveplate and an image plane; and collecting image data at the image plane. The transform can be, for example, a Fourier transform or a fractional Fourier transform

The invention discloses encrypted kinoform based digital image watermarking embedding and extracting methods and systems. The digital image watermarking embedding method comprises the following steps of: transforming an original watermarking image through non-cascaded phase recovery and random fractional fourier transform (RFrFT) to acquire an encrypted kinoform of the original watermarking image; and adaptively embedding the encrypted kinoform into a carrier image based on a human visual system (MVS) model. In the invention, the safety of the watermarking of the kinoform is enhanced by using a non-cascaded iterative encryption method; meanwhile, blink watermarking is realized by adopting an adaptive embedding algorithm; and experiments verify that extremely high robustness against various attacks is achieved, and the safety performance is extremely high.

The invention discloses an image registration method, which is used for improving the accuracy of image registration. The method is as follows: carrying out linear Fourier transformation of each image according to preset parameters, and picking up the low frequency domain of each image frequency domain; determining the amount of relative deviation between two images according to the low frequency domain and fraction phase related algorithm; carrying out image mosaic of the two images according to the amount of relative deviation. The invention also discloses a device for realizing the method.

The invention discloses an image encryption method based on quantum chaotic mapping and fractional domain transformation. The method comprises the steps of firstly carrying out iterative scrambling on pixel points by use of Henon mapping; then multiplying a scrambled matrix and a row scrambling matrix to carry out x-direction and alpha-order DFRFT ((Discrete Fractional Fourier Transform); multiplying the transformed matrix and a column scrambling matrix to carry out y-direction and beta-order DFRFT; and finally carrying out a diffusion encryption operation on the transformed matrix by use of quantum Logistic chaotic mapping. According to the method, the defects of few parametric variables, simple system structure, pseudorandom and poor aperiodicity caused by the single use of a certain scheme such as spatial domain, transform domain and chaotic system in conventional methods are overcome, and experiment and simulation results show that the method has the safety higher than that of the conventional encryption method.

The invention discloses a combined cooperative multi-satellite weak echo signal time delay and doppler frequency shift estimation method. According to the method, multiple nonstop wave signals in a reference channel are separated; adaptive inhibition for nonstop wave signals and multi-path signals in an echo channel is carried out; fourth-order cyclic cumulant mutual fuzzy function processing based on four weighted fractional Fourier transform for the signals in the echo channel and the different nonstop wave signals is respectively carried out to acquire multiple characteristic vectors; after spectral peak extraction for fuzzy function peak values is carried out, corresponding coordinates are time delay and doppler frequency shift estimates; the multiple sets of time delay and doppler frequency shift estimates are converted into distances from targets to receivers and speeds, data fusion is further carried out, the distances and the speed values are converted into multiple sets of time delay and doppler frequency shift estimates after data fusion, and thereby time delay and doppler frequency shift of cooperative multi-satellite weak echo signals can be estimated; when a signal to noise ratio is greater than 10dB, a normalization mean square error of signal to noise ratio estimation is smaller than 1.

The invention discloses a laser radar weak signal extraction and decomposition method based on fractional order Fourier transformation, and belongs to the laser radar signal processing technical field; the method comprises the following steps: 1, carrying out fractional order Fourier transformation for noise-containing laser radar echo signals, obtaining a FRFT spectrum, and converting one dimension signals into a 2D image; 2, using a mean filtering, wavelet filtering and Butterworth filtering compound filtering method to make image enhancement for the FRFT spectrum; 3, clustering enhanced FRFT spectrum image data, and determining a clustering quantity and separating each piece of cluster data; 4, recording position and intensity of separated each piece of cluster data, screening valid data points, carrying out least square fitting for reserved data so as to obtain a flight time, a pulse width and an amplitude, thus finishing laser radar echo signal extraction and component decomposition. The 2D time-frequency analysis method for the laser radar signal processing has a stronger anti-noise ability and a more accurate decomposition result.