CN108801398B - A kind of 120GHz frequency modulated continuous wave radar level meter and distance measuring method - Google Patents
A kind of 120GHz frequency modulated continuous wave radar level meter and distance measuring method Download PDFInfo
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Abstract
The invention discloses a kind of 120GHz frequency modulated continuous wave radar level meter and distance measuring method, radar levelmeter includes FM module, intermediate-freuqncy signal conditioning and sampling module, echo signal processing module, threshold curve generation module and Power estimation module；Wherein, FM module is configurable for generating the difference frequency orthogonal signalling IF_Q for the difference frequency in-phase signal IF_I and TX and RX for sending frequency TX and reception frequency RX；Intermediate-freuqncy signal conditioning and sampling module are configurable for respectively successively handling to generate intermediate frequency quadrature signal IF_I', IF_Q' after digitlization difference frequency in-phase signal IF_I and difference frequency orthogonal signalling IF_Q；Echo signal processing module is configurable for intermediate frequency quadrature signal IF_I', IF_Q' being converted into spectrum curve from time-domain signal；Threshold curve generation module is configurable for being dynamically generated threshold curve according to the spectrum curve of above-mentioned generation, to obtain multiple echoes.The present invention has many advantages, such as that measurement blind area is small, precision is high.
Description
Technical Field
The invention relates to a level meter, in particular to a 120GHz frequency modulation continuous wave radar level meter.
Background
In the implementation processes of industrial process control and factory automation, whether the height of the material level can be stably and reliably measured is very critical. Radar level gauges have rapidly become popular because of their non-contact, accurate measurement, and simple and convenient maintenance.
The radar level meter is divided into a pulse radar level meter and a frequency modulation radar level meter:
a pulse radar level meter calculates a target distance by measuring a time difference between a transmitted microwave pulse and a reflected microwave pulse, and when the target distance is only a few meters, the time difference between the transmitted microwave pulse and the reflected microwave pulse is only a few nanoseconds, and the target distance can be measured after the nanosecond-level time difference is expanded to a millimeter level by a time expansion technique, wherein the time expansion technique requires a slightly different transmission clock frequency and a sampling clock frequency, the two clock frequencies require very high resolution, precision and linearity, and very stable time base control, but temperature drift can change device parameters of a frequency generation unit of the pulse radar, so that the measurement accuracy of the pulse radar is reduced.
The other is an FMCW radar level meter, and compared with a pulse radar, the FMCW radar has the characteristics of quick and stable measurement and high accuracy. Frequency Modulated Continuous Wave (FMCW) radar continuously transmits microwaves with linearly changing frequencies during a frequency modulation period, and simultaneously receives reflected microwaves, the spatial distance between the radar and the target resulting in a frequency difference (intermediate frequency signal, IF) between the currently transmitted microwave frequency and the reflected microwave frequency, which intermediate frequency signal can be obtained by mixing. And then, carrying out filtering sampling and FFT operation on the intermediate frequency signal to obtain the frequency of the intermediate frequency signal, and converting to obtain the corresponding target distance.
The higher the frequency of radar, the shorter the wavelength, the smaller the required antenna size, and the smaller the beam angle, more is applicable to the measurement of the small tank body and the fine powder, and also has the characteristics of small blind area and high precision. According to the calculation formula of the distance resolution of the FMCW radar: C/2B, the larger the bandwidth B is, the higher the resolution of the distance is.
Frequency modulation radar on the current market, the frequency generally is 24GHz ~ 26GHz or 78GHz ~ 80GHz, and the frequency modulation bandwidth is the highest 1GHz, is unfavorable for the measurement of little jar of body, can not reach little blind area, high accuracy measurement's requirement.
Disclosure of Invention
In view of the above, the first objective of the present invention is to provide a 120GHz fm continuous wave radar level gauge, which has the advantages of small measurement blind area, high accuracy, etc.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a120 GHz frequency modulation continuous wave radar level meter comprises a frequency modulation module, an intermediate frequency signal conditioning and sampling module, an echo signal processing module, a threshold curve generating module and a spectrum estimating module; wherein,
the frequency modulation module is configured to generate a difference frequency in-phase signal IF _ I of a transmission frequency TX and a reception frequency RX and a difference frequency quadrature signal IF _ Q of the TX and the RX, wherein the values of the transmission frequency TX and the reception frequency RX are 120GHz ~ 130 GHz.
The intermediate frequency signal conditioning and sampling module is configured to amplify, low-pass filter and analog-to-digital conversion the difference frequency in-phase signal IF _ I and the difference frequency quadrature signal IF _ Q in sequence, and then generate digitized intermediate frequency quadrature signals IF _ I 'and IF _ Q';
the echo signal processing module is configured to convert the intermediate frequency orthogonal signals IF _ I ', IF _ Q' from time domain signals into frequency spectrum curves by complex fast Fourier transform, dynamically generate threshold curves according to the generated frequency spectrum curves to obtain a plurality of echoes, and then evaluate the echoes according to the energy of the echoes; and determining the highest point position of the target echo as a target frequency point corresponding to the target distance.
Preferably, the frequency modulation module comprises a phase-locked loop, a loop filter, a voltage-controlled oscillator, a 32-fold frequency divider, a 90 ° phase shifter, a 2-frequency multiplier, a first power amplifier, a second power amplifier, a low noise amplifier, a first mixer, a second mixer, a transmitting antenna and a receiving antenna; the phase-locked loop, the loop filter, the voltage-controlled oscillator, the frequency multiplier 2 and the first power amplifier are electrically connected in sequence; the input end of the 32-time frequency divider is connected with the other output end of the voltage-controlled oscillator, and the output end of the 32-time frequency divider is connected with the input end of the phase-locked loop; the other output end of the 2 frequency multiplier is connected with the input end of a second power amplifier, and the output end of the second power amplifier is respectively connected with the input ends of the first frequency mixer and the 90-degree phase shifter; the other input end of the first mixer is connected with the output end of a low noise amplifier, and the input end of the low noise amplifier is connected with a receiving antenna; and two input ends of the second frequency mixer are respectively connected with the 90-degree phase shifter and the output end of the low-noise amplifier.
Preferably, the echo signal processing module is further configured to perform curve fitting on the peak of the target echo to obtain a fitted curve, and determine that the highest point of the fitted curve is a target frequency point corresponding to the target distance.
Preferably, the echo signal processing module is implemented by a high-speed digital signal processor and is configured with an extended external static memory.
Preferably, the intermediate frequency signal conditioning and sampling module includes:
the first processing branch circuit consists of a third power amplifier, a first low-pass filter and a first analog-to-digital converter which are connected in sequence; and
the second processing branch circuit consists of a fourth power amplifier, a second low-pass filter and a second analog-to-digital converter which are connected in sequence;
the first processing branch and the second processing branch respectively process the difference frequency in-phase signal IF _ I and the difference frequency quadrature signal IF _ Q.
The second purpose of the invention is to provide a distance measuring method based on a radar level gauge, which has the advantages of small measuring blind area, high precision and the like.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a method of radar level gauge based ranging, comprising:
s01, generating a difference frequency in-phase signal IF _ I of a transmitting frequency TX and a receiving frequency RX and a difference frequency quadrature signal IF _ Q of the TX and the RX, wherein the values of the transmitting frequency TX and the receiving frequency RX are 120GHz ~ 130 GHz;
s02, amplifying, low-pass filtering and analog-to-digital converting the difference frequency in-phase signal IF _ I and the difference frequency orthogonal signal IF _ Q in sequence respectively to generate digitized intermediate frequency orthogonal signals IF _ I 'and IF _ Q';
s03, converting the intermediate frequency orthogonal signals IF _ I 'and IF _ Q' from time domain signals into frequency spectrum curves through complex fast Fourier transform;
s04, dynamically generating a threshold curve according to the generated spectrum curve to obtain a plurality of echoes;
s05, evaluating the echoes according to the energy of the echoes, wherein the echo with the largest energy is used as a target echo, and the highest point position of the target echo is determined as a target frequency point corresponding to the target distance;
s06, calculating the distance between the target and the radar level gauge by using the target frequency points; wherein, the distance value is equal to the index value of the target frequency point multiplied by the measurement precision Sacc.
Preferably, the calculation formula of the measurement accuracy Sacc isWherein, Sacc: measuring precision; fs is sampling frequency; t: frequency modulation time; c, the speed of light; nfft is the number of FFT operation points; b: the frequency modulation bandwidth is wide.
Preferably, the method further comprises the following steps: and refining the frequency spectrum curve by adopting a zero filling mode.
Preferably, the method further comprises the following steps:
and performing curve fitting on the wave crest of the target echo by using a wave crest fitting method to obtain a fitting curve, and determining the highest point of the fitting curve as a target frequency point corresponding to the target distance.
Preferably, the specific generation method of the threshold curve includes:
s041, firstly, performing moving average filtering on the frequency spectrum curve by using a first filtering width to obtain a smoothed curve;
s042, performing sliding average filtering on the frequency spectrum curve by using the second filtering width to obtain another smooth curve, and combining the smooth curve with the smooth curve generated in the step S041 to obtain a required threshold curve;
wherein the first filter width is greater than the second filter width.
The technical effects of the invention are mainly reflected in the following aspects: by using the 120GHz terahertz frequency band and the frequency modulation bandwidth up to 10GHz and combining the echo signal processing algorithm realized by using the high-speed DSP, the problems that the frequency modulation radar level meter in the existing market has large blind area and low precision, and is not suitable for measuring small tank bodies and the like are solved.
Drawings
FIG. 1 is a diagram of a frequency modulation module according to an embodiment;
FIG. 2 is a block diagram of an intermediate frequency signal conditioning and sampling module according to an embodiment;
FIG. 3 is a block diagram of an echo signal processing module according to an embodiment;
FIG. 4 is a diagram illustrating a threshold curve generated in an embodiment;
FIG. 5 is a schematic diagram of a peak fitting curve in the example.
Detailed Description
The following detailed description of the embodiments of the present invention is provided in order to make the technical solution of the present invention easier to understand and understand.
The first embodiment,
The embodiment provides a 120GHz frequency modulation continuous wave radar level gauge which comprises a frequency modulation module, an intermediate frequency signal conditioning and sampling module, an echo signal processing module, a threshold curve generating module and a spectrum estimating module.
Referring to fig. 1, the frequency modulation module includes a phase locked loop 1, a Loop Filter (LF) 2, a Voltage Controlled Oscillator (VCO) 4, a 32-fold frequency divider 6, a 90 ° phase shifter 15, a 2-frequency multiplier 8, a first power amplifier 10a, a second power amplifier 10b, a Low Noise Amplifier (LNA) 13, a first mixer 14a, a second mixer 14b, a transmitting antenna 11, and a receiving antenna 12; the phase-locked loop 1, the Loop Filter (LF) 2, the Voltage Controlled Oscillator (VCO) 4, the frequency multiplier 28 and the first power amplifier 10a are electrically connected in sequence; the input end of the 32-time frequency divider 6 is connected with the other output end of the Voltage Controlled Oscillator (VCO) 4, and the output end is connected with the input end of the phase-locked loop 1; the other output end of the frequency multiplier 28 is connected with the input end of a second power amplifier 10b, and the output end of the second power amplifier 10b is respectively connected with the input ends of a first mixer 14a and a 90-degree phase shifter 15; the other input end of the first mixer 14a is connected with the output end of a Low Noise Amplifier (LNA) 13, and the input end of the Low Noise Amplifier (LNA) 13 is connected with the receiving antenna 12; two input ends of the second mixer are respectively connected with the 90-degree phase shifter 15 and the output end of the Low Noise Amplifier (LNA) 13.
The working principle of the frequency modulation module is that a phase-locked loop (PLL) 1 is set to linearly output a frequency of 1.875GHz ~ 2.03125.03125 GHz in a frequency modulation period, during frequency modulation, pulse current output by the PLL passes through a Loop Filter (LF) 2 to generate linearly increased voltage 3, the linear voltage controls a Voltage Controlled Oscillator (VCO) 4 to generate linearly changed oscillation frequency 5, the oscillation frequency 5 is divided into two paths from 60GHz to 65GHz, one path generates a frequency 7 of 1.875GHz ~ 2.03125.03125 GHz after passing through a 32-time frequency divider 6 and is fed back to the PLL 1, the other path generates an output frequency 9 of 120GHz ~ 130GHz through a 2-time multiplier 8, and the output frequency 9 is passed through a first power amplifier 10a to obtain a final transmission signal TX which is transmitted through a transmission antenna 11.
The receiving antenna 12 receives a frequency signal RX of 120GHz ~ 130GHz, amplifies the signal by a Low Noise Amplifier (LNA) 13, and inputs the amplified signal to a first mixer 14a, the other input of the first mixer 14a is a transmission frequency TX. obtained by amplifying a frequency 9 by a second power amplifier 10b, the mixed signal is mixed, the first mixer 14a outputs a difference frequency in-phase signal IF _ i of the transmission frequency TX and the reception frequency RX, the other output of the second power amplifier 10b is phase-shifted by a 90 ° phase shifter 15 to generate a signal orthogonal to the transmission frequency TX, the signal is input to the second mixer 14b, mixed with the reception signal RX, and a difference frequency orthogonal signal IF _ Q of the TX and the RX is output.
It can be seen that the frequency of transmission and reception is changed from 120GHz to 130GHz linearly, the bandwidth B is as high as 10GHz, and the distance resolution can reach 1.5 cm calculated by the formula C/2B.
Referring to fig. 2, the intermediate frequency signal conditioning and sampling module includes a first processing branch composed of a third power amplifier 17a, a first low pass filter 18a, and a first analog-to-digital converter 19a, which are connected in sequence; and a second processing branch consisting of a fourth power amplifier 17b, a second low-pass filter 18b and a second analog-to-digital converter 19b which are connected in sequence.
The working principle of the intermediate frequency signal conditioning and sampling module is as follows: the intermediate frequency quadrature signal IF _ I, IF _ Q is amplified by the third power amplifier 17a and the fourth power amplifier 17b, then input to the first low pass filter 18a and the second low pass filter 18b for filtering, and then sampled by the first analog-to-digital converter 19a and the second analog-to-digital converter 19b to obtain digitized intermediate frequency quadrature signals IF _ I 'and IF _ Q'.
Referring to fig. 3, the echo signal processing module 20 is implemented by a high-speed digital signal processor. The echo signal processing module 20 processes the intermediate frequency sampling signal. The digitized intermediate frequency quadrature signals IF _ I ', IF _ Q' are subjected to a complex Fast Fourier Transform (FFT) 21 and then converted from time domain signals to spectral curves 22.
The frequency resolution of the spectrum curve 22 is the sampling frequency Fs divided by the number N of FFT points, and the higher the frequency resolution is, the higher the corresponding distance measurement accuracy is. The measurement accuracy of the frequency modulation radar is calculated by the formula(Sacc: precision; Fs: sampling frequency; T: frequency modulation time; C: light velocity; Nfft: FFT number of points; B: bandwidth). In a frequency modulation period, the number of sampling points is limited, and in order to improve the frequency resolution, the frequency spectrum can be refined by using a zero padding mode, but the larger the number of zero padding points is, the larger the execution time of the FFT and the larger the required storage space are consumed. Therefore, a high-speed digital signal processor is adopted and an extended external static memory is used as an auxiliary, so that the defect is avoided, the number of FFT points after zero padding can reach 6 ten thousand points at most, the measurement precision is greatly improved, and when the measurement range is 50 meters, the measurement precision can reach +/-0.76 mm.
The noise suppression module 23 averages the spectrum curve 22 for multiple times, suppresses random noise, and improves the signal-to-noise ratio to obtain a spectrum curve 25, as shown in fig. 4.
The threshold curve generation module 24 dynamically generates a threshold curve from the spectral curve 25, as shown in fig. 4. In fig. 4, the spectral curve 25 has an echo 26 very close to the transmitted wave. The spectrum curve 25 is firstly filtered by the first filter width W2 in a sliding average manner to obtain a smoothed curve 27, and it can be seen that the curve 27 cannot effectively distinguish between the transmitted wave and the echo, so the spectrum curve 25 is filtered by the smaller second filter width W1 in the sliding average manner to obtain a smoothed curve 28, and the smoothed curve 28 is combined with the smoothed curve 27 to obtain a final threshold value curve 29. The threshold curve 29 can effectively segment the echoes close to the transmitted waves, and reduce the blind zone of measurement. The threshold curve 29 will cut the spectrum curve 25 into multiple echoes, with echoes of ranging targets and echoes of fixed obstacles.
The spectrum estimation module 30 estimates the echo according to the energy of the echo, and the echo with the largest energy is used as the target echo 31. Generally, the highest point position of the target echo is a frequency point corresponding to the target distance, if the ranging target is a particulate matter, or the surface is uneven, a pile angle exists, and the like, the peak of the target echo can become wide, have sawteeth, and does not have an obvious highest point, and then curve fitting is performed by using a peak fitting function 32 to find the highest point of the peak.
Fig. 5 is a schematic diagram of the peak fitting function 32. And performing curve fitting on the irregular peak 33 to obtain a fitted curve 34, wherein the highest point 35 of the fitted curve 34 is used as a frequency point corresponding to the target distance, and the index value of the frequency point is W3. The peak obtained after the peak fitting can reflect the average condition of the target material level, and the accuracy is improved. The index value W3 of the target frequency point is processed by the distance calculation module 36 to obtain the distance between the target and the radar level gauge, and the distance value is equal to the index value W3 of the target frequency point multiplied by the measurement accuracy Sacc.
Example II,
In this embodiment, on the basis of the first embodiment, a distance measuring method based on a radar level gauge is provided, and the method includes:
s01, generating a difference frequency in-phase signal IF _ I of a transmitting frequency TX and a receiving frequency RX and a difference frequency quadrature signal IF _ Q of the TX and the RX, wherein the values of the transmitting frequency TX and the receiving frequency RX are 120GHz ~ 130 GHz;
s02, amplifying, low-pass filtering and analog-to-digital converting the difference frequency in-phase signal IF _ I and the difference frequency orthogonal signal IF _ Q in sequence respectively to generate digitized intermediate frequency orthogonal signals IF _ I 'and IF _ Q';
s03, converting the intermediate frequency orthogonal signals IF _ I 'and IF _ Q' from time domain signals into frequency spectrum curves through complex fast Fourier transform;
s04, dynamically generating a threshold curve according to the generated spectrum curve to obtain a plurality of echoes;
s05, evaluating the echoes according to the energy of the echoes, wherein the echo with the largest energy is used as a target echo, and the highest point position of the target echo is determined as a target frequency point corresponding to the target distance;
s06, calculating the distance between the target and the radar level gauge by using the target frequency points; wherein, the distance value is equal to the index value of the target frequency point multiplied by the measurement precision Sacc.
In the above steps, the calculation formula of the measurement accuracy Sacc is as followsWherein, Sacc: measuring precision; fs is sampling frequency; t: frequency modulation time; c, the speed of light; nfft is the number of FFT operation points; b: the frequency modulation bandwidth is wide.
In step S03, the spectrum curve is further refined by zero padding.
As a further improvement of this embodiment, in the above step, a peak fitting method is further used to perform curve fitting on the peak of the target echo to obtain a fitting curve, and the highest point of the fitting curve is determined as the target frequency point corresponding to the target distance.
In addition, a specific method for generating the threshold curve includes:
s041, firstly, performing moving average filtering on the frequency spectrum curve by using a first filtering width to obtain a smoothed curve;
s042, performing sliding average filtering on the frequency spectrum curve by using the second filtering width to obtain another smooth curve, and combining the smooth curve with the smooth curve obtained in the step S041 to obtain a required threshold curve;
wherein the first filter width is greater than the second filter width.
The above are only typical examples of the present invention, and besides, the present invention may have other embodiments, and all the technical solutions formed by equivalent substitutions or equivalent changes are within the scope of the present invention as claimed.
Claims (9)
1. A120 GHz frequency modulation continuous wave radar level meter is characterized by comprising a frequency modulation module, an intermediate frequency signal conditioning and sampling module and an echo signal processing module; wherein,
the frequency modulation module is configured to generate a difference frequency in-phase signal IF _ I of a transmission frequency TX and a reception frequency RX and a difference frequency quadrature signal IF _ Q of the TX and the RX, wherein the values of the transmission frequency TX and the reception frequency RX are 120GHz ~ 130 GHz.
The intermediate frequency signal conditioning and sampling module is configured to amplify, low-pass filter and analog-to-digital conversion the difference frequency in-phase signal IF _ I and the difference frequency quadrature signal IF _ Q in sequence, and then generate digitized intermediate frequency quadrature signals IF _ I 'and IF _ Q';
the echo signal processing module is configured to convert the intermediate frequency orthogonal signals IF _ I ', IF _ Q' from time domain signals into frequency spectrum curves by complex fast Fourier transform, dynamically generate threshold curves according to the generated frequency spectrum curves to obtain a plurality of echoes, and then evaluate the echoes according to the energy of the echoes; and determining the highest point position of the target echo as a target frequency point corresponding to the target distance.
2. The 120GHz frequency modulated continuous wave radar level gauge according to claim 1, wherein said frequency modulation module comprises a phase locked loop, a loop filter, a voltage controlled oscillator, a 32-fold frequency divider, a 90 ° phase shifter, a 2-frequency multiplier, a first power amplifier, a second power amplifier, a low noise amplifier, a first mixer, a second mixer, a transmitting antenna and a receiving antenna; the phase-locked loop, the loop filter, the voltage-controlled oscillator, the frequency multiplier 2 and the first power amplifier are electrically connected in sequence; the input end of the 32-time frequency divider is connected with the other output end of the voltage-controlled oscillator, and the output end of the 32-time frequency divider is connected with the input end of the phase-locked loop; the other output end of the 2 frequency multiplier is connected with the input end of a second power amplifier, and the output end of the second power amplifier is respectively connected with the input ends of the first frequency mixer and the 90-degree phase shifter; the other input end of the first mixer is connected with the output end of a low noise amplifier, and the input end of the low noise amplifier is connected with a receiving antenna; and two input ends of the second frequency mixer are respectively connected with the 90-degree phase shifter and the output end of the low-noise amplifier.
3. The 120GHz FM continuous wave radar level gauge according to claim 1, wherein said echo signal processing module is further configured to perform curve fitting on the peak of said target echo to obtain a fitted curve, and determine the highest point of said fitted curve as the target frequency point corresponding to the target distance.
4. A 120GHz fm continuous wave radar level gauge according to claim 1 or 3, wherein said echo signal processing module is implemented using a high speed digital signal processor and is provided with extended external static memory.
5. The 120GHz frequency modulated continuous wave radar level gauge according to claim 1, wherein said intermediate frequency signal conditioning and sampling module comprises:
the first processing branch circuit consists of a third power amplifier, a first low-pass filter and a first analog-to-digital converter which are connected in sequence; and
the second processing branch circuit consists of a fourth power amplifier, a second low-pass filter and a second analog-to-digital converter which are connected in sequence;
the first processing branch and the second processing branch respectively process the difference frequency in-phase signal IF _ I and the difference frequency quadrature signal IF _ Q.
6. A distance measuring method based on a radar level gauge is characterized by comprising the following steps:
s01, generating a difference frequency in-phase signal IF _ I of a transmitting frequency TX and a receiving frequency RX and a difference frequency quadrature signal IF _ Q of the TX and the RX, wherein the values of the transmitting frequency TX and the receiving frequency RX are 120GHz ~ 130 GHz;
s02, amplifying, low-pass filtering and analog-to-digital converting the difference frequency in-phase signal IF _ I and the difference frequency orthogonal signal IF _ Q in sequence respectively to generate digitized intermediate frequency orthogonal signals IF _ I 'and IF _ Q';
s03, converting the intermediate frequency orthogonal signals IF _ I 'and IF _ Q' from time domain signals into frequency spectrum curves through complex fast Fourier transform;
s04, dynamically generating a threshold curve according to the generated spectrum curve to obtain a plurality of echoes;
s05, evaluating the echoes according to the energy of the echoes, wherein the echo with the largest energy is used as a target echo, and the highest point position of the target echo is determined as a target frequency point corresponding to the target distance;
s06, calculating the distance between the target and the radar level gauge by using the target frequency points; wherein, the distance value is equal to the index value of the target frequency point multiplied by the measurement precision Sacc; the calculation formula of the measurement precision Sacc isWherein, Sacc: measuring precision; fs is sampling frequency; t: frequency modulation time; c, the speed of light; nfft is the number of FFT operation points; b: the frequency modulation bandwidth is wide.
7. The ranging method of claim 6, further comprising: and refining the frequency spectrum curve by adopting a zero filling mode.
8. The ranging method of claim 6, further comprising:
and performing curve fitting on the wave crest of the target echo by using a wave crest fitting method to obtain a fitting curve, and determining the highest point of the fitting curve as a target frequency point corresponding to the target distance.
9. The ranging method according to claim 6, wherein the threshold curve is generated by a specific method comprising:
s041, firstly, performing moving average filtering on the frequency spectrum curve by using a first filtering width to obtain a smoothed curve;
s042, performing sliding average filtering on the frequency spectrum curve by using the second filtering width to obtain another smooth curve, and combining the smooth curve with the smooth curve generated in the step S041 to obtain a required threshold curve;
wherein the first filter width is greater than the second filter width.
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| CN109529171B (en) * | 2018-12-26 | 2021-07-13 | 速眠创新科技（深圳）有限公司 | Method and device for determining sleep-aid area, computer equipment and storage medium |
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