83 results about "Cyclic frequency" patented technology

The invention provides a broadband tuning terahertz wave generator based on ultrasonic grating frequency shift and cyclic frequency shift. The broadband tuning terahertz wave generator comprises a laser, a circulator, a beam splitter, a cyclic frequency shift link based on the ultrasonic grating frequency shift, a beam combiner, an optoisolator and a photoelectric converter with a terahertz radiating antenna; light output by the laser passes through the circulator and then is split into a first path and a second path by the beam splitter; the first path is reference light and the second path is input to the cyclic frequency shift link to generate cyclic frequency shift light; the reference light and the cyclic frequency shift light are superposed in the beam combiner to generate beat frequency light in the range of the terahertz frequency; and the generated beat frequency light is processed by the optoisolator and then is received by the photoelectric converter with the terahertz radiating antenna, and the photoelectric converter radiates coherent terahertz waves. The generator provided by the invention has small volume, easiness for integration due to fewer optical elements, large tuning scope, high tuning efficiency and high efficiency in generating terahertz.

Disclosed is a method for estimating carrier frequency of a PSK (phase shift keying) signal in Alpha-stable distribution noise. The method includes: valuing a cyclic covariance function of the received PSK signal with the Alpha-stable distribution noise; valuing a cyclic covariance spectrum by subjecting the cyclic covariance function to Fourier transform; extracting a section with cyclic frequency being epsilon=0Hz according to the obtained cyclic covariance spectrum; searching peak values of a positive semi-axis and a negative semi-axis of the section respectively to find a positive frequency value and a negative frequency value corresponding to the peak values, and valuing a mean value as the estimated value of the carrier frequency after absolute values are valued. The method is capable of estimating the carrier frequency of the PSK signal in the Alpha-stable distribution noise and is good in estimating performance in an environment of low signal to noise ratio.

The invention provides a broadband tuning teraHertz wave generator based on modulator frequency shift and cyclic frequency shift, comprising a laser, a circulator, a light beam splitter, a cyclic frequency shift link based on the modulator frequency shift, a light beam synthesizer, a photoisolator and a photoelectric transducer with a teraHertz radiating antenna, wherein light output by the laser passes through the circulator and then is divided into a first path and a second path by the light beam splitter; the light in the first path belongs to reference light; the light in the second path is input into the cyclic frequency shift link to generate cyclic frequency shift light; the reference light and the cyclic frequency shift light are superposed in the light beam synthesizer to generate beat frequency light in the range of teraHertz frequency; and the beat frequency light passes through the photoisolator and then is received by the photoelectric transducer with the teraHertz radiating antenna, and the photoelectric transducer with the teraHertz radiating antenna gives off coherent teraHertz waves. The generator provided by the invention has the advantages that the volume is small, and fewer optical elements are used, thus being easy to integrate, the tuning range is wide, the tuning efficiency is high and the generating efficiency of the teraHertz waves is high.

Systems and methods for cognitive radio spectrum sensing of a signal are disclosed herein. On exemplary method comprises applying a pre-defined cyclostationary feature to detect the presence of the signal; detecting the signal; detecting a spectrum associated with the signal; sampling randomly the detected signal from its cyclic frequency domain; and applying a compressive sensing algorithm to classify the signal based on the cyclostationary feature. The signal can be sparse in time, space, frequency, or code domains. Thereby, the systems and methods described in the present disclosure involve exploiting compressive sensing in a specific sparse domain (i.e., cyclic domain) and also utilize a cyclostationary feature based compressive spectrum sensing scheme to perform spectrum analysis.

The invention discloses a microwave photonic down-conversion apparatus and method based on a bidirectional cyclic frequency shift, and relates to the field of microwave photonics. The microwave photonic down-conversion apparatus and method aim to solve the defects of small bandwidth, large loss and the like confronted by a traditional electrical frequency converter and the defect that high-frequency electrical local oscillation is needed by an optical frequency conversion technology. The apparatus provided by the invention consists of a laser, a cyclic frequency shift module and a photoelectric detector; and the cyclic frequency shift module includes a 2*2 optical coupler, a polarization controller, a dual-drive electro-optical intensity modulator, an electrical local oscillation source, an optical amplifier, an optical band pass filter and an optical adjustable delay line. In the cyclic frequency shift module, first-order optical sidebands of a to-be-converted radio-frequency signal and an electrical local oscillation signal on an optical carrier simultaneously perform opposite optical sideband movement step by step at a same frequency shift, and at last photoelectric detection isperformed on two opposite frequency shift optical sidebands having nearest frequencies to implement down-conversion of the radio-frequency signal; and with the characteristic of opposite frequency shift of the cyclic frequency shift module, by changing a frequency of the electrical local oscillation source, the wide frequency range under low-frequency electrical local oscillation and the down-conversion of a tunable microwave signal are implemented.

The invention discloses a cyclic frequency extraction method for the characteristic components of the transient conditions of a gearbox. The cyclic frequency extraction method comprises the steps of performing interpolation on the frequency curve of the characteristic components at an original sampling interval, performing fitting on the interpolated frequency curve to determine a linear frequency modulation base function within multiple scale intervals, calculating the projection coefficient of a vibration signal within each interval to the base function, searching for the projection coefficients scale by scale to determine a piecewise linear path and adaptively segmenting the vibration signal of which the frequency changes arbitrarily in the form of a curve into a plurality of signal segments which are different in scale and of which the frequencies change linearly according to the path, performing least square fitting on each segment of the frequency curve, determining and calculating the filter order of FRFT and a filter center parameter, orderly performing FRFT single-order filtering on each signal segment according to the parameter, and then orderly connecting the filtered signals, thereby realizing the cyclic frequency extraction of the characteristic components of which the frequencies change in the form of the curve. The method is capable of realizing adaptive cyclic frequency extraction of the characteristic components; other components and the noise interference can be effectively stripped in the extraction process; careful analysis is performed on the extracted characteristic components; as a result, the early-stage weak faults of the gearbox can be diagnosed more accurately.

The invention belongs to the field of mechanical equipment fault diagnosis. The invention discloses a bearing fault diagnosis method using a probabilistic principal component to enhance a cyclic bispectrum. The method includes the steps of firstly, establishing a probabilistic principal component model capable of reflecting a potential relation between an original signal and a principal componentvector; secondly, de-noising the original signal by using the probabilistic principal component model to completely preserve useful components of the signal, greatly increase the signal-to-noise ratioand solve the problem that a fault signal is susceptible to noise interference; and thirdly, subjecting the de-noised signal to cyclic bispectrum analysis, and diagnosing a bearing fault from a contour map of the single cyclic frequency bispectrum. For one thing, by using the probabilistic principal component analysis for de-noising, the method of the invention can effectively increase the signal-to-noise ratio and suppress the noise to highlight a phenomenon of fault frequency modulation near the bearing resonance frequency, thereby increasing the definition of a hexagonal structure formed by the cyclic bispectrum; and for another, can visually detect the type of bearing fault from the contour map of the single cyclic frequency bispectrum.

The invention relates to a rupture disk fatigue tester for 400MPa gas cylinders, which is used for testing the durability of the rupture disks. The tester comprises a control system and a testing system, wherein the control system is used for controlling the testing system to carry out test and the testing system comprises a drive loop, a first high-pressure loop and a second high-pressure loop. The tester realizes regulating the controlled cycling pressure, cyclic frequency, pressure holding time and continuous pressure cycling by utilizing the control system to control the reducing valve, so that the data are accurately processed, thus improving the reliability of the whole system, ensuring stable work and reducing the maintenance work.

The invention discloses a cooperative spectrum sensing method in a cognitive vehicular ad-hoc network. The main process is that each cognitive vehicle receives authorized user signals in a band of interest and the following operation is carried out: (1) a cyclic ambiguity function method is adopted to carry out Doppler frequency shift estimation on the received authorized user signals; (2) a double-threshold cyclic spectrum energy detection method is adopted for spectrum sensing, and when the cyclic spectrum energy value is larger than a large threshold value or smaller than a small threshold value, the local judgment result acquired by the cognitive vehicle and the position information are transmitted to a road side unit on a public control channel; and finally, the road side unit fuses information of cognitive vehicles participating in cooperation through a position relative decision method to judge whether the authorized user band is free. The method considers influences on detection by the Doppler frequency shift, the spectrum information at all cyclic frequencies is used, a cooperative weighting factor is changed dynamically according to the real-time change of the relative position between the cognitive vehicles, and the detection performance is improved.

The invention discloses a blind estimation method of a signal-to-interference-pulse-noise ratio (SINR) in a power line communication system. A proper time delay variable and a proper cyclic frequency variable are selected for effectively separating the signal power from the interference-pulse-noise power through calculating a periodic autocorrelation function of a receiving signal and respectively analyzing energy distribution graphs of the periodic autocorrelation functions of a transmitting signal, background noise, impulse noise and a receiving signal, so as to estimate the estimated value of the SINR. The method has the advantages that pilot frequency information does not need to be transmitted, cyclic stationary characteristics of the transmitting signal itself is used, blind estimation of the SINR is realized through analyzing the periodic autocorrelation function energy distribution of the transmitting signal, the background noise and the impulse interference and through selecting proper time delay value and the proper frequency value, a higher spectrum utilization rate is provided in comparison with a traditional pilot frequency transmitting method, the estimation value of SINR in the pulse interference environment can be estimated accurately and effectively, the estimation complexity is low, and the estimation accuracy is high.

The invention relates to a calculation method of the first-order natural circular frequency of bending vibration of a stepped beam, which belongs to the calculation method of mechanical vibration. (1) Based on the bending free vibration theory of equal straight bars, the bending free vibration equations of each section of the stepped beam are listed; (2) The modal solution of the stepped beam is assumed by the method of separation of variables; (3) The boundary conditions and analysis of the whole beam are listed. (4) Substituting the hypothetical modal solution into the bending free vibration equation of each segment of the stepped beam to obtain the mode shape function of each segment; The state solution is brought into the boundary conditions and continuity conditions, and the corresponding boundary condition equations and continuity equations are obtained; (6) Solving the boundary condition equations and continuity equations, and solving the equations simultaneously, the elimination of elements only contains two undetermined coefficients and (7) Find the frequency equation of the stepped beam according to the condition that the equation system has a non-zero solution; (8) Use Matcad software to solve the frequency equation to obtain the first-order natural circular frequency value.

The invention provides a radar interference identification and suppression method based on cyclostationarity. The method comprises the steps of establishing an echo signal model and an interference signal model; based on the echo signal model and the interference signal model, superposing the echo signal model and the interference signal model with a stationary noise signal to obtain a first reference signal, calculating the cycle frequency of the first reference signal, and recording the cycle frequency as a first cycle frequency; based on the echo signal model and the stationary noise signal, calculating to obtain a second cycle frequency; comparing the number of the second cyclic frequencies with the number of the first cyclic frequencies, and identifying whether interference exists ornot according to a comparison result; acquiring an echo signal to be measured; if it is judged that interference exists currently, inputting the echo signal to be detected into a frequency shift filter to achieve interference suppression; obtaining the cyclic frequency on the basis of a cyclic stability theory to realize accurate interference identification, and carrying out interference suppression by using a designed frequency shift filter. The interference suppression effect is obvious, and the problems of difficulty in interference identification and poor suppression effect in a vehicle-mounted millimeter wave radar are solved.

The invention relates to the field of signal detection and estimation, and discloses a time difference estimation method and device for a linear frequency modulation signal, and the method comprises the steps that a sampling quantification module carries out the sampling quantification of the received linear frequency modulation signal, and then a cross-correlation module carries out the cross-correlation operation of the sampled and quantified linear frequency modulation signal; a peak value detection module performs peak value detection on the cross-correlation operation result, detects themaximum result value, and obtains a corresponding serial number; and finally, a time difference estimation module calculates the arrival time difference of the linear frequency modulation signal according to the serial number. According to the method, the time difference of the arrival signals can be accurately estimated without priori information such as the cyclic frequency of the linear frequency modulation signals, so that the method can also be applied to a non-cooperative signal environment; the method and the device provided by the invention can be used for high-precision measurement oflinear frequency modulation signal time difference in the fields of radar, communication, sonar, electronic warfare and the like, and provide a basis for passive time difference positioning.

The invention discloses a radio frequency hopping signal generation method based on cyclic frequency shift. The method comprises the following steps: dividing an optical signal with the frequency of fc into two paths; performing frequency shift on the first path of optical signal to obtain a reference optical signal; converting the second path of optical signal into a periodic optical pulse signalthrough an optical switch, inputting the optical pulse signal into a cyclic frequency shift module, and outputting an optical frequency hopping signal from the cyclic frequency shift module; and carrying out beat frequency on the optical frequency hopping signal and a reference optical signal to obtain a radio frequency hopping signal, and adjusting the center frequency of the radio frequency hopping signal by changing the frequency shift amount of the first path of optical signal. The invention also discloses a radio frequency hopping signal generation device based on cyclic frequency shift.According to the invention, the bandwidth range of the frequency hopping signal can be expanded, high-speed frequency hopping is realized, and the center frequency and the frequency hopping speed ofthe frequency hopping signal are controllable.

The invention discloses a motor rolling bearing partial pitting fault diagnosis method and a diagnosis system thereof. The motor rolling bearing partial pitting fault diagnosis method comprises the following steps: arranging a measuring point at an end cover of a bearing seat of the motor rolling bearing, wherein a vibration acceleration sensor collects a vibration signal of the measuring point; generating a kurtosis distribution diaphragm based on the vibration signal, determining filter center frequency and frequency band width corresponding to the maximum kurtosis value; performing filtering processing on the vibration signal based on the filter center frequency and frequency band width so as to obtain the filtered characteristic enhancement signal; performing cyclostationary analysis based on the characteristic enhancement signal so as to generate a cyclic spectrum density map; detecting whether the bearing fault characteristic frequency is existent in a cyclic frequency domain ofthe cyclic spectrum density map, and determining the vibration frequency of the fault impact waveform based on the cyclic frequency domain, thereby diagnosing the motor rolling bearing pitting fault.

The invention discloses a method for acquiring a cyclic spectrum alpha section based on frequency domain smoothing. The method comprises the following steps of: setting a certain time length for the received signal to perform discrete Fourier transform (DFT); and fixing a Fourier frequency value k, utilizing the calculating result of the discrete Fourier transform, setting a value of a cyclic frequency variable alpha as m1+m2 and selecting two smoothing windows to perform cross transposition and performing frequency domain smoothing calculation to acquire the cyclic spectrum alpha section corresponding to the cyclic frequency variable alpha, wherein the centers of the two smoothing windows are k+m1 and k-m2 respectively and the lengths of the two smoothing windows are 2M+1. In the method,the cyclic spectrum alpha section is acquired through the cross transposition of the two smoothing windows in the frequency domain, the spectrum information at the odd number position of the section can be effectively recovered, so that the spectrum information of the odd position in the cross section can be effectively restored, alpha section spectrum information loss caused by a DFT barrier effect can be reduced, the spectrum information of the acquired cyclic spectrum alpha section is more complete, and the requirements of subsequent signal processing processes, such as parameter extraction, modulation mode identification and the like, can be met.

A longitudinal folding machine comprises a folding blade and a folding table. The folding blade is driven with a cyclical frequency, in a synchronized manner relative to one or more elements of a web-processing machine, which is located upstream of the longitudinal folding machine, or relative to a flow of incoming products. The entry of a leading edge of products is detected at a first measurement point on the delivery route of the folding table. A relative phase position between the movement of the folding blade and the phase position of the elements mounted upstream and/or the phase position of the flow of products is deliberately modified by the use of one of a control and a regulation device in order to adjust a contact point of the folding blade with the products to be folded. The relative phase position is modified such that, at least in one operating mode or phase of production, the leading edges of the products to be folded, and which were transported on the folding table, are maintained at a distance from the measurement point on the delivery route by varying the relative phase position so that due to the detection of the leading edges of one or of a certain number of successive products at this measurement point, the relative phase position varies either for the first contact of the product and the folding blades and/or for the contact point having a placement nearer to the entry side of the incoming products.

The invention discloses a combined OFDM/OQAM time frequency synchronization method under a multipath channel. According to the method, different weight values are respectively endowed to each sub channel of an OFDM/OQAM system; a multipath channel model is equivalent to multiple flat fading sub channel models; a cyclic cumulant of a reception signal is calculated; time delay is estimated according to ratios of the cyclic cumulant under different cyclic frequencies, frequency offset is estimated according to ratios of the cyclic cumulant under different time delays, and combined OFDM/OQAM time frequency synchronization during non-cooperative communication under the multipath channel is realized. When a signal to noise ratio is in a range of 0-20dB, fluctuation ranges of mean square errors of time delay and frequency offset are not large, the method is not easily influenced by noise, excellent estimation performance is realized under a low signal to noise ratio; when the signal to noise ratio is in the range of 0-20dB, a time delay estimation mean square error can reach 10-4 order of magnitudes, a normalized frequency offset estimation mean square error can reach 10-2 order of magnitudes, and the method is effective and feasible for non-cooperative communication under the multipath channel.

The invention relates to a comb spectrum generation device and a method based on a double spectrum line cyclic frequency shift mode. The device comprises a quadruplicated frequency system and a cyclic frequency shift loop, wherein the quadruplicated frequency system comprises a cascaded dual-electrode Mach-Zehnder modulator, a cosine microwave signal source, a phase shifter and the phase shifter; and the cyclic frequency shift loop comprises a 3dB coupler, a polarization controller (PC), the cascaded dual-electrode Mach-Zehnder modulator, the cosine microwave signal source, the phase shifter, the phase shifter, a semiconductor optical amplifier (SOA), an optical filter, an adjustable delay line, a direct-current bias power supply and an optical fiber which is random in length but short as much as possible. The method comprises the steps as follows: firstly, generating two flat spectrums with an interval of 12.5 GHz through the quadruplicated frequency system; secondly, transmitting the spectrums into the loop for cyclic frequency shift; thirdly, carrying out down-conversion on every two spectrum lines through the loop, circulating in sequence, and compensating power through the SOA; and lastly, filtering out 16 required flat spectrum lines through the optical filter.

Facilitate frequency hopping for a single carrier frequency division multiple access (SC-FDMA) transmission is described herein. By way of example, user data transmitted within a transmission allocation unit can be frequency shifted with respect to time based slots of the allocation unit. As a result, frequency hopping can be accomplished while preserving single carrier constraints and a low peak to average power ratio (PAPR). Furthermore, various frequency shifted mechanisms are disclosed to accomplish preservation of single carrier restraints. For example, a scheduler can select between cyclic frequency shifting, transposed frequency shifting, and multiplexing of frequency selective scheduled and frequency hopped data based on an audit of scheduled data for the transmission allocation unit. As a result, the reduction in interference achieved through frequency hopping can be combined with the low PAPR for various data allocation configurations.