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406 results about "Fractional Fourier transform" patented technology

In mathematics, in the area of harmonic analysis, the fractional Fourier transform (FRFT) is a family of linear transformations generalizing the Fourier transform. It can be thought of as the Fourier transform to the n-th power, where n need not be an integer — thus, it can transform a function to any intermediate domain between time and frequency. Its applications range from filter design and signal analysis to phase retrieval and pattern recognition.

Radar moving target radon-fractional Fourier transform long-time phase-coherent accumulation detection method

ActiveCN103176178AEffective accumulationImprove complex (noise) ratioWave based measurement systemsRadar signal processingConstant false alarm rate
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.
Owner:NAVAL AVIATION UNIV

System and methods for fast implementation of equally-sloped tomography

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.
Owner:RGT UNIV OF CALIFORNIA

Sea surface micromotion target detection and feature extraction method based on short-time fractional Fourier transform

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.
Owner:NAVAL AVIATION UNIV

Multi-target detection method based on short-time Fourier transform and fractional Fourier transform

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.
Owner:ZHONGBEI UNIV

Multi-fractal detection method of targets in FRFT (Fractional Fourier Transformation) domain sea clutter

ActiveCN102967854AReduce the demand for signal-to-clutter ratio in target detectionThe need to reduce the signal-to-clutter ratioWave based measurement systemsTime domainTarget signal
The invention discloses a multi-fractal detection method of targets in FRFT (Fractional Fourier Transformation) domain sea clutter and belongs to the radar signal processing field. According to the conventional multi-fractal detection methods of targets in sea clutter, echo sequences in the radar time domain are processed directly, and therefore detection performance of weak moving targets in strong sea clutter background is poor. The multi-fractal detection method of targets in FRFT domain sea clutter is characterized in that fractional Fourier transformation is organically combined with the multi-fractal processing method, and the generalized Hurst index number of the sea-clutter fractional Fourier transformation spectrum is extracted to form detection statistics by comprehensively utilizing the advantage that the fractional Fourier transformation is capable of effectively improving the signal to clutter ratio of the moving target on the sea surface and the feature that the multi-fractal characteristic is capable of breaking the tether of the signal to clutter ratio to a certain extent. The detection method comprehensively utilizes the advantages of phase-coherent accumulation and multi-fractal theory and has excellent separating capability on the weak moving targets in sea clutter; and simultaneously, the method is also suitable for tracking target signals in nonuniform fractal clutter and has popularization and application values.
Owner:NAVAL AERONAUTICAL & ASTRONAUTICAL UNIV PLA

Compressed sensing synthetic aperture radar (SAR) imaging method based on fractional order fourier transformation

InactiveCN102879782AReduce the amount of measurement dataRelieve the pressure of signal storage and transmissionRadio wave reradiation/reflectionSynthetic aperture sonarDimension measurement
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.
Owner:BEIJING INSTITUTE OF TECHNOLOGYGY

Radar moving target detection method based on short-time sparse fractional Fourier transform (ST-SFRFT)

ActiveCN106526568AImplement time-frequency representationGuaranteed energy concentrationRadio wave reradiation/reflectionDecompositionTarget signal
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.
Owner:NAVAL AVIATION UNIV

Double-random-phase optical color image encryption device and method

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.
Owner:ZHEJIANG NORMAL UNIVERSITY

Method for sea clutter suppression and moving target detection based on FRFT (Fractional Fourier Transform) domain non-coherent accumulation

ActiveCN102169175AReduce computational complexityOvercome the disadvantage of easily weakening the energy of slow-moving targetsWave based measurement systemsTime domainPrior information
The present invention discloses a method for sea clutter suppression and moving target detection based on FRFT domain non-coherent accumulation, and belongs to the field of radar signal processing and detecting technology. A conventional time domain clutter map cancellation technology is difficult to detect a target moving at a low speed, and under the background of strong sea clutter, signal-to-clutter ratio in a target unit is quite low and sea clutter peak is easy to cause false alarm, thus detecting performance is decreased. Therefore, a moving target detecting technology based on the FRFT provided in the invention respectively employs an FRFT domain mean value accumulation method and an FRFT domain simple pole feedback accumulation method to finish the non-coherent accumulation via iterative smoothing of FRFT domain delay data, and the technology carries out cancellation of FRFT domain signal and accumulated data to suppress the sea clutter and improve the signal-to-clutter ratio, with the amplitude of output signal being taken as detection statistics. A detector provided in the invention has an ability to detect a weakly moving target, with no need of the prior information of an optimum transformation angle, and can estimate the motion parameter of the target, being suitable for the condition of low signal-to-clutter ratio, being simple in realization and having popularization and application values.
Owner:NAVAL AVIATION UNIV

Holographic projection method

ActiveCN102749793ABreak through the limitation of imaging distanceProjectorsGrismSpatial light modulator
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.
Owner:SOUTHEAST UNIV

Method for separating monaural overlapping speeches based on fractional Fourier transform (FrFT)

The invention relates to a method for separating monaural overlapping speeches based on fractional Fourier transform (FrFT), which belongs to the technical field of audio signal processing. The method comprises the following steps: firstly, preprocessing overlapping speech signals so as to remove mute-section signals of the overlapping speech signals and find out sonant frames; then, carrying out pitch detection on sonant-frame signals based on FrFT so as to separate the fundamental frequencies of the overlapping speeches; and finally, integrating the fundamental frequencies with a sinusoidal model of speech signals so as to synthesize speeches, thereby obtaining each speech signal subjected to separation. The method provided by the invention has the advantages that the fundamental frequencies of a plurality of overlapping speeches can be separated and extracted effectively, and finally, the effective separation of the overlapping speeches can be realized; and the pitch frequencies are extracted based on FrFT instead of traditional fast Fourier transform (FFT), thereby reducing the extension of a harmonic frequency spectrum and then obtaining more accurate fundamental frequencies of original signals. The method provided by the invention is especially suitable for the separation of monaural overlapping speeches containing speeches of two persons.
Owner:BEIJING INSTITUTE OF TECHNOLOGYGY

Single-channel color image encryption method based on chaos and phase retrieval process

A single-channel color image encryption method based on chaos and phase retrieval process comprises a color image chaos scrambling and decomposition step, a pure phase extraction and modulation step and a chaos diffusion step. Combining fractional Fourier transform and paired Logistic chaotic mapping, an encrypted image has nonlinearity and randomness, security and convergence speed of an encryption system are raised, and the problem of slow convergence speed existing in a present encryption method is solved. Meanwhile, complexity of the color image encryption system is reduced, the system is simple, and operation is convenient.
Owner:XIAN UNIV OF TECH

Digital demodulation signal identification method under non-gaussian noise

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.
Owner:XIDIAN UNIV

Detection and parameter estimation method for linear frequency modulation signals

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.
Owner:ELECTRONICS ENG COLLEGE PLA

Seismic signal time-frequency decomposition method based on short-time fractional Fourier transform

InactiveCN102798891AOvercoming the unsatisfactory decomposition effectAccurate and reliable spectrumSeismic signal processingFrequency spectrumWigner ville
The invention discloses a seismic signal time-frequency decomposition method based on short-time fractional Fourier transform. A Gaussian window function is selected; high frequency resolution is obtained by adjusting the window width in a self-adapting way; through the characteristic of fractional kernel function angle rotation, the best energy accumulation of the seismic signal is obtained at the optimal rotation angle and the cross term is eliminated; the higher frequency resolution and more accurate frequency location are more conductive to recognizing specific geologic structure, so that the method solves the defects of the existing seismic signal time-frequency decomposition method. The method has the positive effects of overcoming the defects of traditional algorithm such as short-time Fourier and Wigner-Ville distribution and the like and having great significance on seismic signal spectral analysis.
Owner:UNIV OF ELECTRONICS SCI & TECH OF CHINA

Multipath time delay and Doppler frequency shift estimation method in signal channel based on fractional Fourier transform and system for implementing method

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.
Owner:HARBIN INST OF TECH

Artificial circuit fault diagnosis pattern sorting algorithm

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.
Owner:NAVAL AERONAUTICAL & ASTRONAUTICAL UNIV PLA

Methods and Apparatus for Compressed Imaging Using Modulation in Pupil Plane

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
Owner:LUCENT TECH INC

Modified FRFT (fractional Fourier transform) maneuvering weak target detection method

ActiveCN103675759AThere is no cross term interference problemCumulative gain is idealRadio wave reradiation/reflectionTime domainFast Fourier transform
The invention discloses a modified FRFT (fractional Fourier transform) maneuvering weak target detection method. The method includes: establishing a high-speed maneuvering weak target uniformly accelerated motion signal model; performing FT on echo original data in a fast time-domain, performing Keystone transform on the transformed data, correcting the problem of movements of distance units, caused by primary phase, performing IFFT (inverse fast Fourier transform) in the fast time-domain, solving all-order FRFT in p[0, 2] for all distance units in the obtained final echo data to generate signal energy which is in two-dimensional distribution in a two-dimensional parameter plane (p, u) composed of fractional order p and fractional order transform domain u, and performing peak point two-dimensional search on the plane so as to detect accelerated targets. Through the application of the method, maneuvering weak targets can be detected in the low signal-noise ratio background environment and reliability, feasibility and timeliness are good.
Owner:盐城市凤凰园科技发展有限公司

Broadband linear frequency-modulated (LFM) signal multi-decoy interference method based on fractional Fourier domain channelization

InactiveCN103532656AIntegrity guaranteedReduce instantaneous bandwidth requirementsCommunication jammingBroadbandEngineering
The invention relates to a broadband linear frequency-modulated (LFM) signal multi-decoy interference method based on fractional Fourier domain channelization, in particular to an interference method for performing multi-decoy deception on a broadband LFM signal in a pulse on the basis of fractional Fourier domain channelization, and belongs to the technical field of electronic interference. According to the broadband LFM signal multi-decoy interference method based on fractional Fourier domain channelization, all broadband LFM signals can be focused into one channel for outputting by using the energy focusing property of fractional Fourier transform on instable signals, so that the completeness of the signals is ensured, and the problems of reduction of signal energy and distortion of waveforms since the energy of the broadband LFM signals overflow into two or more channels in the conventional Fourier domain channelization are solved; meanwhile, the requirement on the instant bandwidth of a DRFM (Digital Radio Frequency Memory) system is lowered.
Owner:BEIJING INSTITUTE OF TECHNOLOGYGY

Encrypted kinoform based digital image watermarking embedding and extracting methods and systems

ActiveCN102142131AReduce data volumeGood clipping resistanceImage data processing detailsHuman visual system modelKinoform
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.
Owner:PEKING UNIV

Image registration method and device

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.
Owner:SHENZHEN THUNDER NETWORK TECH

Image encryption method based on quantum chaotic mapping and fractional domain transformation

InactiveCN107239708AAchieve scramblingNon-cyclical goodDigital data protectionSpatial domainSingle use
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.
Owner:GUANGDONG UNIV OF TECH

Fractional-Fourier-transform-based random noise suppression method

The invention provides a fractional-Fourier-transform-based random noise suppression method, which comprises the following steps of: calculating related coefficients of the tendency of an in-phase axis in seismic data for the acquired seismic data by utilizing an orthogonal polynomial approximation method and adopting maximum similarity coefficient criterion; performing pseudo-linear spatial transformation on the seismic data by utilizing the calculated related coefficients; calculating an optimal order of a fractional domain with the most centralized signals in the seismic data according to a fractional-Fourier-transform-based optimal order calculation method; transforming the seismic data from a time-space domain to the fractional domain by utilizing fractional Fourier transform under the optimal order; resolving a prediction operator of a seismic channel, and predicting the seismic data of the seismic channel by utilizing the prediction operator to eliminate irregularly distributedrandom noises; transforming the denoised seismic data from the fractional domain to the time-space domain by utilizing the inverse fractional Fourier transform; and performing inverse linear transformation on the seismic data by utilizing the calculated related coefficients to finish the random noise suppression of the seismic data.
Owner:BC P INC CHINA NAT PETROLEUM CORP +1

Method and device for estimating parameters of chirp signal of underwater acoustic channel

The invention belongs to the technical field of underwater acoustic communications, and particularly relates to a method and device for estimating parameters of a chirp signal of an underwater acoustic channel. The method includes the following steps: constructing an underwater acoustic channel signal model; receiving an N-component Chirp signal processed by the underwater acoustic channel model,performing order search by the fractional Fourier transform to obtain a modulation frequency of the N-component Chirp signal; performing frequency modulation compensation on the N-component Chirp signal, and estimating and outputting the initial frequency by the fast Fourier transform. The method rotates the FRFT domain starting frequency estimation to the FFT domain after the frequency modulationcomponent processing to obtain an initial frequency estimation value with a smaller mean signal error under a low SNR, and obtains multi-component Chirp signal parameter estimation in the backgroundof underwater acoustic multipath channel by modeling the underwater acoustic channel, thereby improving the initial frequency estimation performance, ensuring the signal reconstruction accuracy, improving the underwater acoustic communication quality, ensuring the stable communication, and having stable performance and high efficiency, which has strong practical application value and development prospects.
Owner:PLA STRATEGIC SUPPORT FORCE INFORMATION ENG UNIV PLA SSF IEU

Nonlinear signal time-frequency analysis method based on short-time fractional order Fourier transform

ActiveCN107290589AImprove accuracyImprove the accuracy of time-frequency separationSpectral/fourier analysisTarget signalImage resolution
The invention discloses a nonlinear signal time-frequency analysis method based on short-time fractional order Fourier transform, and the nonlinear signal time-frequency analysis method belongs to the technical field of target signal analysis. The nonlinear signal time-frequency analysis method utilizes short-time fractional order Fourier transform, subjects a signal to segmentation processing and combined processing of different orders of fractional order Fourier transform through short-time fractional order Fourier transform, adopts an angle constraint method for fractional-order order searching, improves the time-frequency resolution of the target signal and the precision of time-frequency analysis, completes the time-frequency analysis of single-component and multi-component nonlinear signals, solves the problems of low time-frequency resolution and difficult separation of the target nonlinear echo signal, is conductive to parameter estimation of the weak target signal, improve the precision of signal parameter estimation, has the advantages of high time-frequency resolution and precise separation of different signals in the time-frequency domain, significantly reduces the amount of computing, provides reliable data support for a follow-up system to complete tasks, and is worthy of adoption and popularization.
Owner:ZHONGBEI UNIV

Sea clutter zone target detection and adaptive clutter inhibition method based on fractional transform

The invention provides a sea clutter zone target detection and adaptive clutter inhibition method based on fractional transform, in order to deal with the serious disturbance of high frequency ground wave radar first-order sea clutter to ship target detection. The method detects a maneuvering target in a fractional fourier transform treatment mode, restrains sea clutter, transforms to a domain through extending a regular feature decomposition method, and removes sea clutter in an echo spectrum under the condition of not influencing target signals. Based on a full consideration of target signal modulation features, the method adaptively restrains sea clutter through fractional domain feature decomposition, simultaneously completely restrains clutter components under the condition of not damaging target signals, and fills the technical blanks of high frequency radar first-order spectral region target detection under the condition of not increasing system complexity.
Owner:WUHAN UNIV

Asymmetric double-image encryption method based on fractional Fourier domain phase recovery procedure

An asymmetric double-image encryption method based on a fractional Fourier domain phase recovery procedure comprises the steps of pure phase extraction, phase modulation and fractional Fourier transform. The asymmetric double-image encryption method based on the fractional Fourier domain phase recovery procedure is applied to double-image encryption, the encryption process is different from the decryption process, an encryption key is different from a decryption key, and the defects that a traditional symmetric encryption algorithm is easy to attack and an encryption key is the same as a decryption key are overcome. Through attack tests, it is proved that the method is high in resistance to violent attacks, noise attacks and other specific attacks. Meanwhile, key space is large, the problem that a traditional encryption algorithm is insufficient in key space is solved, the decryption process can be realized through an optical method, and a system is simple and convenient to operate.
Owner:XIAN UNIV OF TECH

Combined cooperative multi-satellite weak echo signal time delay and doppler frequency shift estimation 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.
Owner:XIDIAN UNIV +1

Laser radar weak signal extraction and decomposition method based on fractional order Fourier transformation

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.
Owner:NANJING UNIV OF AERONAUTICS & ASTRONAUTICS
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