CN109374969B - Down-sampling sinusoidal signal phase difference measurement method based on coherent accumulation DFT - Google Patents
Down-sampling sinusoidal signal phase difference measurement method based on coherent accumulation DFT Download PDFInfo
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Abstract
The invention discloses a phase difference measuring method of a down-sampling sinusoidal signal based on DFT of coherent accumulation in the field of signal processing, which comprises the following steps: respectively sampling two groups of sinusoidal signals with the same frequency by using a down-sampling mode to obtain two groups of sampling signals; respectively carrying out coherent accumulation on the two groups of sampling signals to obtain two groups of accumulated signals; respectively carrying out discrete Fourier transform on the two groups of accumulated signals to obtain initial phases of two groups of sinusoidal signals with the same frequency; and calculating the phase difference between the two groups of sinusoidal signals according to the initial phase between the two groups of sinusoidal signals with the same frequency.
Description
Technical Field
The invention relates to the field of signal processing, and particularly discloses a phase difference measuring method for a down-sampling sinusoidal signal based on DFT (discrete Fourier transform) of coherent accumulation.
Background
Phase difference measurement of sinusoidal signals is an important research topic in many applications such as power system monitoring, radio frequency communication, radar positioning, laser ranging, and the like. Furthermore, it can also be applied to phase calibration, especially useful in phase calibration on single-pass on-board/on-board InSAR systems.
Many different phase difference measurement methods have been discussed for a long time, such as least squares or Discrete Fourier Transform (DFT) methods, hilbert transform methods, ICA methods, and zero crossing detection methods. However, the DFT-based spectrum analysis method requires one complete sampling period in calculation; the zero-crossing detection method is unreliable in the case where noise is superimposed on the signal; furthermore, when the signal frequency is too high, there is a lack of research on how to select the sampling frequency and what phase difference measurement method to use.
Disclosure of Invention
The invention aims to solve the technical defect that the phase difference of the adopted sinusoidal signals cannot be obtained when the signal frequency is too high in the prior art.
In order to achieve the above object, the present invention provides a down-sampling sinusoidal signal phase difference measurement method based on coherent accumulation DFT, which comprises the following steps:
s1: respectively sampling two groups of sinusoidal signals with the same frequency by using a down-sampling mode to obtain two groups of sampling signals;
s2: respectively carrying out coherent accumulation on the two groups of sampling signals to obtain two groups of accumulated signals;
s3: respectively carrying out discrete Fourier transform on the two groups of accumulated signals to obtain initial phases of two groups of sinusoidal signals with the same frequency;
s4: and calculating the phase difference between the two groups of sinusoidal signals according to the initial phase between the two groups of sinusoidal signals with the same frequency.
Preferably, S1 includes the steps of:
s11: sampling the sinusoidal signal to obtain a sampled signal frequency spectrum;
s12: filtering the signal spectrum to obtain a baseband signal spectrum;
s13: reconstructing a baseband signal by adopting inverse Fourier transform according to the baseband signal frequency spectrum;
s14: and reconstructing the high-frequency signal according to the frequency and the initial phase of the baseband signal.
Preferably, the signal spectrum obtained at S11 is as follows:
wherein the content of the first and second substances,the angular frequency is represented by the angular frequency,in order to be able to sample the frequency,is the frequency of the signal or signals,is a natural constant and is a natural constant,as an initial phase, the phase of the phase,the number of shifts (which is an integer),in the form of an impulse signal, the signal is,in the form of a circumferential ratio,in units of imaginary numbers.
Preferably, the baseband signal of S13 is as follows:
wherein the content of the first and second substances,is the frequency of the baseband signal and is,is the initial phase of the baseband signal.
Preferably, the high frequency signal of S14 is as follows:
wherein the content of the first and second substances,in order to be the sampling period of time,in order to be the length of the sample,is a signal vibration pair.
Preferably, the initial phase of S3 is as follows:
The invention has the following beneficial effects:
1. the measuring method can effectively filter noise in the signal, improve the measuring precision of the phase difference of the sinusoidal signal and greatly reduce the measuring error;
2. the measuring method of the invention has the advantages that when the signal frequency is too high, the selection of the down-sampling frequency under the down-sampling condition is wider.
The present invention will be described in further detail below with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:
fig. 1 is a flow chart of a down-sampling sinusoidal signal phase difference measurement method based on coherent accumulation DFT according to a preferred embodiment of the present invention.
FIG. 2 is a signal spectrum diagram of a preferred embodiment of the present invention;
FIG. 3 is a signal diagram before and after coherent accumulation in accordance with a preferred embodiment of the present invention;
fig. 4 is a schematic phase difference diagram of the preferred embodiment of the present invention.
Detailed Description
The embodiments of the invention will be described in detail below with reference to the drawings, but the invention can be implemented in many different ways as defined and covered by the claims.
The DFT full name Discrete Fourier Transform is Discrete Fourier Transform, which is a form in which the Fourier Transform is Discrete in both time domain and frequency domain.
The invention firstly provides a phase difference measuring method of a down-sampling sinusoidal signal based on DFT of coherent accumulation, referring to figure 1, comprising the following steps:
s1: and respectively sampling two groups of sinusoidal signals with the same frequency by using a down-sampling mode to obtain two groups of sampling signals.
whereinIs the amplitude of the signal that is not known,is the frequency of the signal or signals,is the time of day or the like,is an unknown initial phase. According to the Nyquist sampling theorem,must be 2 or moreThe original signal can be accurately restored. However, when it is desired to measure the phase difference of two sinusoidal signals,must be much greater than 2. However, when the signal frequency itself is very high, the sampling frequency will be higher and higher as the signal frequency increases, and is difficult to achieve even under the existing equipment and technical conditions, so that the implementation is difficult. Therefore, it is necessary to reduce the sampling frequency according to the band-pass sampling theorem, that is, to sample the signal by using the down-sampling method.
The sampling of the sinusoidal signal by means of down-sampling comprises the following steps:
s11: and sampling the sinusoidal signal to obtain a sampled signal frequency spectrum.
SignalSpectrum ofAs shown in fig. 2 (a). WhereinAngular frequency is indicated, arrows represent amplitude spectra, and solid black dots represent phase spectra. The spectral expression of the sampled signal is as follows:
wherein the content of the first and second substances,the angular frequency is represented by the angular frequency,in order to be able to sample the frequency,is the frequency of the signal or signals,is a natural constant and is a natural constant,as an initial phase, the phase of the phase,in order to be the number of shifts,in the form of an impulse signal, the signal is,in the form of a circumferential ratio,in units of imaginary numbers.
Frequency spectrum of sampled signalAs shown in fig. 2(b), obviously, to avoid spectrum aliasing, the following condition must be satisfied between the sampling frequency and the signal frequency:
namely:
s12: and filtering the signal spectrum to obtain a baseband signal spectrum.
The sampled spectrum is gained byThe band pass range isThe rest is the spectrum of the baseband signal. At this time, there may be two cases, as shown in fig. 2(c), (d). Wherein the part marked with "1" is the signal spectrumAs a result of shifting right n times, the portion labeled "2" is the signal spectrumLeft shift n times.
In the case shown in fig. 2(c), the condition is satisfied:
namely:
the spectrum of the baseband signal obtained at this time is:
in the case shown in fig. 2(d), the condition is satisfied:
namely:
the spectrum of the baseband signal obtained at this time is:
s13: and reconstructing the baseband signal by adopting inverse Fourier transform according to the baseband signal frequency spectrum.
Performing inverse fourier transform on equation (7) to obtain a reconstructed baseband signal:
wherein the content of the first and second substances,is the frequency of the baseband signal and is,for the initial phase of the baseband signal, it can be known from equation (8)
Performing inverse fourier transform on equation (11) to obtain a reconstructed baseband signal:
from the formula (13)
S14: and reconstructing the high-frequency signal according to the frequency and the initial phase of the baseband signal.
From low-frequency baseband signalsFrequency of (2)And initial phaseCan reconstruct high frequency signals(ii) a And the phase difference of two sinusoidal signals of the same frequency can be measured by selecting a sampling frequency satisfying the condition (6) or (11).
Assuming that the sampling frequency satisfies the condition of equation (11), the sampling length isA point, and the number of sampling points in one baseband signal period isAnd satisfy the relationship(Positive integer), the sampled signal is:
wherein the content of the first and second substances,is a sampling period,In order to be the length of the sample,is a signal vibration pair.
S2: and respectively carrying out coherent accumulation on the two groups of sampling signals to obtain two groups of accumulated signals.
The sampled signalAndwith baseband signalsPeriod of (2)Coherent accumulation is performed for the period to filter gaussian noise. Namely, it is
The sampling result is shown in fig. 3 (a).
The sampling result is shown in fig. 3 (b).
S3: and respectively carrying out discrete Fourier transform on the two groups of accumulated signals to obtain the initial phases of the two groups of sinusoidal signals with the same frequency.
For the accumulated signalsAndrespectively performing discrete Fourier transform to calculate the initial phases of two sinusoidal signalsAnd:
the sampling result is shown in fig. 3 (c).
The sampling result is shown in fig. 3 (d).
S4: and calculating the phase difference between the two groups of sinusoidal signals according to the initial phase between the two groups of sinusoidal signals with the same frequency.
The phase difference between the two sinusoidal signals can be obtained according to the initial phases of the two sinusoidal signals:
the obtained phase difference results are shown in FIG. 4(c), and the phase difference errors are shown in FIG. 4 (d). While the phase difference measured by the conventional DFT method is shown in fig. 4(a), and the phase difference error is shown in fig. 4 (b). Compared with the traditional DFT method, the method has the advantages that the phase difference is more accurate and the phase difference error is smaller.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. A down-sampling sinusoidal signal phase difference measuring method based on coherent accumulation DFT is characterized by comprising the following steps:
s1: respectively sampling two groups of sinusoidal signals with the same frequency by using a down-sampling mode to obtain two groups of sampling signals;
s2: respectively carrying out coherent accumulation on the two groups of sampling signals to obtain two groups of accumulated signals;
s3: respectively carrying out discrete Fourier transform on the two groups of accumulated signals to obtain initial phases of two groups of sinusoidal signals with the same frequency;
s4: calculating the phase difference between the two groups of sinusoidal signals according to the initial phase between the two groups of sinusoidal signals with the same frequency; the S1 includes the steps of:
s11: sampling the sinusoidal signal to obtain a sampled signal frequency spectrum;
s12: filtering the signal spectrum to obtain a baseband signal spectrum;
s13: reconstructing a baseband signal by adopting inverse Fourier transform according to the baseband signal frequency spectrum;
s14: and reconstructing the high-frequency signal according to the frequency and the initial phase of the baseband signal.
2. The method of claim 1, wherein the signal spectrum obtained at S11 is as follows:
wherein the content of the first and second substances,the angular frequency is represented by the angular frequency,in order to be able to sample the frequency,is the frequency of the signal or signals,is a natural constant and is a natural constant,as an initial phase, the phase of the phase,in order to be the number of shifts,in the form of an impulse signal, the signal is,in the form of a circumferential ratio,in units of imaginary numbers.
5. The method for measuring the phase difference of the down-sampled sinusoidal signals based on the DFT of the coherent accumulation as claimed in claim 1, wherein the high frequency signals of S14 are as follows:
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