CN113114160B - Linear frequency modulation signal noise reduction method based on time-varying filter - Google Patents
Linear frequency modulation signal noise reduction method based on time-varying filter Download PDFInfo
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- CN113114160B CN113114160B CN202110571578.2A CN202110571578A CN113114160B CN 113114160 B CN113114160 B CN 113114160B CN 202110571578 A CN202110571578 A CN 202110571578A CN 113114160 B CN113114160 B CN 113114160B
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- H—ELECTRICITY
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- H03H—IMPEDANCE NETWORKS, e.g. RESONANT CIRCUITS; RESONATORS
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Abstract
The invention discloses a linear frequency modulation signal noise reduction method based on a time-varying filter, which comprises the following steps: (1) Determining a frequency point where a signal at the current moment is located according to prior information of the linear frequency modulation signal and signal duration; (2) Calculating a zero pole of the band-pass filter according to the frequency point of the signal at the current moment, wherein the current frequency point is set as a pole; (3) Calculating a transfer function of the band-pass filter according to the zero pole parameter, and filtering a signal at the current moment; (4) And combining the filtered signals at all moments according to the arrival time to obtain the final noise-reduced linear frequency modulation signal. The invention carries out noise reduction treatment on the linear frequency modulation signal and has good application effect.
Description
Technical Field
The invention relates to the field of signal processing, in particular to a linear frequency modulation signal noise reduction method based on a time-varying filter.
Background
In military applications, higher and higher requirements are put forward on performance indexes such as the acting distance, the resolving power, the measurement accuracy and the like of the radar. In order to improve the resolving power and the ranging accuracy, the signal is required to have a large bandwidth; in order to improve the speed resolution and the speed measurement accuracy, the signals are required to have a large time width. Chirp (linear frequency modulation signal) is a modulation technique widely used in the radar field, and the frequency bandwidth occupied by the signal is far greater than the information bandwidth, so that a great system processing gain can be obtained. The higher signal band bandwidth increases the required passband bandwidth of the filter and reduces the noise reduction when the linear fm signal is noise reduced.
In actual signal processing, the spectral characteristics of the signal are not constant. When the frequency characteristics of a signal change over time, such a signal cannot be processed well if a fixed tap filter is used. Time-varying filter frequency characteristics as a function of recording time, the time-varying filter can be better adapted to signal characteristics by changing the taps of the filter. A chirp signal is a signal whose spectral characteristics change with time, and a better filtering effect can be obtained by processing the signal with a time-varying filter.
Aiming at the problem of noise reduction of the linear frequency modulation signal, a linear frequency modulation signal noise reduction method based on a time-varying filter is provided. The frequency value of the chirp signal is linear with the time of arrival and the frequency bin signal at the current time can be determined if the duration of the signal is known. Once the frequency signal is determined for each instant, the zero and pole of the band pass filter can be determined and the coefficients of the filter calculated from the pole-zero. When the frequency point signal of the signal changes with time, the coefficient of the filter also changes with time. And after the signals at all moments are filtered, merging according to the arrival time to obtain the final noise-reduced linear frequency modulation signal.
Disclosure of Invention
The invention aims to: aiming at the problem of noise reduction of the linear frequency modulation signal, the invention provides a linear frequency modulation signal noise reduction method based on a time-varying filter. According to the change rule of the original linear frequency modulation signal frequency point information along with time, the coefficient of the filter at each moment is dynamically adjusted to carry out filtering noise reduction.
The technical scheme is as follows: the invention relates to a linear frequency modulation signal noise reduction method based on a time-varying filter, which comprises the following steps:
(1) Determining a frequency point where a signal at the current moment is located according to prior information of the linear frequency modulation signal and signal duration;
(2) Calculating a zero pole of the band-pass filter according to the frequency point of the signal at the current moment, wherein the current frequency point is set as a pole;
(3) Calculating a transfer function of the band-pass filter according to the zero pole parameter, and filtering a signal at the current moment;
(4) And combining the filtered signals at all moments according to the arrival time to obtain the final noise-reduced linear frequency modulation signal.
The beneficial effects are that: compared with the prior art, the invention has the remarkable advantages that: the method can design the corresponding time-varying filter tap according to the frequency distribution characteristics of different arrival times of the linear frequency modulation signals, and filter the linear frequency modulation signals by using the time-varying filter. Experiments show that compared with the method of filtering and denoising by using a fixed tap filter, the method can further reduce noise in the linear frequency modulation signal.
Drawings
FIG. 1 is a schematic flow chart of a time-varying filter-based method for noise reduction of a chirp signal according to the present invention;
FIG. 2 is a time domain waveform of an original signal, an original signal with high white noise, a fixed filter for filtering, and a time-varying filter for filtering signals under the condition of-10 dB signal ratio;
FIG. 3 is a waveform of the frequency domain of the original signal, the original signal with high white noise, the fixed filter, the time-varying filter under the condition of-10 dB signal ratio;
Detailed Description
The present invention will be further described in detail below with reference to specific embodiments and with reference to the accompanying drawings, in order to make the objects, technical solutions and advantages of the present invention more apparent.
In this example the start frequency fs of the linear FM signal 0 At 100Hz, end frequency fs end 130Hz, duration PW of 120s, frequency modulation factor of the signalSampling frequency fs of digital signal sample Is 400Hz. The overall steps of filtering using a time-varying filter can be seen in fig. 1, which includes the steps of:
(1) Determining a frequency point where a signal at the current moment is located according to prior information of the linear frequency modulation signal and signal duration;
in this embodiment, assuming that the current processing time is the t second of the chirp signal, the frequency point fs at the current time can be obtained according to a priori knowledge t ＝fs 0 +k*t。
(2) Calculating a zero pole of the band-pass filter according to the frequency point of the signal at the current moment, wherein the current frequency point is set as a pole;
in this embodiment, in step (1), the frequency point of the current radar signal is first converted into a digital frequencyThe bandpass filter is designed here so that the filter does not require a zero. At the same time (I)>Is one pole of the filterAccording to symmetry->And should also be a pole of the filter.
(3) Calculating a transfer function of the band-pass filter according to the zero pole parameter, and filtering a signal at the current moment;
after both the zero and pole of the filter are determined, the transfer function H (z) of the filter can be calculated.
After H (z) is determined, the radar signal at the current time may be filtered.
(4) And combining the filtered signals at all moments according to the arrival time to obtain the final noise-reduced linear frequency modulation signal.
And after all the sub-signals are processed, combining the radar signals at all the moments according to the arrival time sequence. Fig. 2 and fig. 3 show waveforms of a time domain and a frequency domain of an original signal, an original signal with a signal ratio of-10 dB, a white gaussian noise, a fixed filter for filtering, and a time-varying filter for filtering signals, wherein the fixed filter refers to that a linear frequency modulation signal is filtered by a band-pass filter with a passband range of 100-130 MHz in the whole course. The time-varying filter may filter the linear frequency modulated signal better than a fixed tap filter.
The method can adjust the tap of the time-varying filter according to the arrival time of the linear frequency modulation signal, and can effectively reduce the noise in the linear frequency modulation signal by using the time-varying filter to filter the linear frequency modulation signal.
The foregoing disclosure is only illustrative of the preferred embodiments of the present invention and is not to be construed as limiting the scope of the invention, which is defined by the appended claims.
Claims (2)
1. A linear frequency modulation signal noise reduction method based on a time-varying filter is characterized by comprising the following steps of:
(1) Determining a frequency point where a signal at the current moment is located according to prior information of the linear frequency modulation signal and signal duration;
(2) Calculating a zero pole of the band-pass filter according to the frequency point of the signal at the current moment, wherein the current frequency point is set as a pole;
(3) Calculating a transfer function of the band-pass filter according to the zero pole parameter, and filtering a signal at the current moment;
(4) Filtering the signals at all moments, and combining the filtered signals according to the arrival time to obtain a final noise-reduced linear frequency modulation signal;
the method comprises the steps of (1) determining the initial frequency and the frequency modulation coefficient of a signal according to phenomenon prior information by linearly changing the frequency parameter of a linear frequency modulation signal along with the arrival time, and calculating the frequency point information of the radar signal at the current moment;
assuming the current processing time is the t second of the linear frequency modulation signal, obtaining a frequency point fs at the current time according to priori knowledge t ＝fs 0 +k×t, where fs 0 For the initial frequency fs end In order to end the frequency of the signal,k is the frequency modulation coefficient of the signal, PW is the duration of the signal;
the step (2) is to convert the current frequency point into a digital frequencyfs sample For the sampling frequency of the digital signal, the band-pass filter does not need zero, a +.>Is a pole of the filter, according to symmetry +.>Also a pole of the filter;
and (3) calculating the transmission parameters of the filter according to the pole-zero information of the filter calculated in the step (2).
2. The time-varying filter-based chirp signal noise reduction method as defined in claim 1, characterized in that: and (4) processing and denoising the signals at all the moments after the filtering processing.
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6288414A (en) * | 1985-10-11 | 1987-04-22 | インタ−ナショナル ビジネス マシ−ンズ コ−ポレ−ション | Filter for suppressing energy in frequency varied along withthe rogress of time |
| US6219637B1 (en) * | 1996-07-30 | 2001-04-17 | Bristish Telecommunications Public Limited Company | Speech coding/decoding using phase spectrum corresponding to a transfer function having at least one pole outside the unit circle |
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| US6868346B2 (en) * | 2002-11-27 | 2005-03-15 | Cardiac Pacemakers, Inc. | Minute ventilation sensor with automatic high pass filter adjustment |
| TWI246056B (en) * | 2003-10-27 | 2005-12-21 | Ali Corp | Method of setting a transfer function of an adaptive filter |
| US10514883B2 (en) * | 2017-02-23 | 2019-12-24 | Rossum Electro-Music, LLC | Multi-channel morphing digital audio filter |
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Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS6288414A (en) * | 1985-10-11 | 1987-04-22 | インタ−ナショナル ビジネス マシ−ンズ コ−ポレ−ション | Filter for suppressing energy in frequency varied along withthe rogress of time |
| US6219637B1 (en) * | 1996-07-30 | 2001-04-17 | Bristish Telecommunications Public Limited Company | Speech coding/decoding using phase spectrum corresponding to a transfer function having at least one pole outside the unit circle |
Non-Patent Citations (1)
| Title |
|---|
| 基于时频变换的时变滤波器性能仿真与优化;马忠超;信息科技辑;第2018卷(第02期);第I136-1134页 * |
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