Ranging method based on frequency modulation nonlinear correction and related device

文档序号：789307 发布日期：2021-04-09 浏览：18次中文

阅读说明：本技术 基于调频非线性校正的测距方法及相关装置 (Ranging method based on frequency modulation nonlinear correction and related device ) 是由巫红英李强于 2020-02-07 设计创作，主要内容包括：一种基于调频非线性校正的测距方法,包括：获取参考路拍频信号和测量路拍频信号(S501)；根据参考路拍频信号计算得到调频非线性度；并根据测量路拍频信号计算得到初始飞行时间τ(S502)；当调频非线性度不小于第一预设阈值时,根据参考路拍频信号计算得到激光器发射信号的调频非线性项ε(t),根据初始飞行时间τ和激光器发射信号的调频非线性项ε(t)对测量路拍频信号进行非线性迭代校正,以得到目标飞行时间(S503)；根据目标飞行时间计算得到目标距离(S504)。可以提高激光雷达的测距精度与测距范围。(A distance measurement method based on frequency modulation nonlinear correction comprises the following steps: acquiring a reference-path beat signal and a measurement-path beat signal (S501); calculating according to the beat frequency signal of the reference path to obtain the frequency modulation nonlinearity; calculating to obtain initial flight time tau according to the beat frequency signal of the measuring path (S502); when the frequency modulation nonlinearity is not less than a first preset threshold value, calculating a frequency modulation nonlinearity term epsilon (t) of a laser emission signal according to a reference-path beat signal, and performing nonlinear iterative correction on a measurement-path beat signal according to the initial flight time tau and the frequency modulation nonlinearity term epsilon (t) of the laser emission signal to obtain a target flight time (S503); the target distance is calculated from the target flight time (S504). The range finding precision and range finding range of the laser radar can be improved.)

1. A distance measurement method based on frequency modulation nonlinear correction is characterized by comprising the following steps:

acquiring a reference road beat frequency signal and a measurement road beat frequency signal; the reference road beat frequency signal and the measurement road beat frequency signal are obtained respectively based on a laser emission signal;

calculating according to the reference-path beat frequency signal to obtain frequency modulation nonlinearity; calculating to obtain initial flight time tau according to the beat frequency signal of the measuring path;

determining that the frequency modulation nonlinearity is not less than a first preset threshold value, calculating a frequency modulation nonlinearity term epsilon (t) of the laser emission signal according to the reference-path beat signal, and performing nonlinear iterative correction on the measurement-path beat signal according to the initial flight time tau and the frequency modulation nonlinearity term epsilon (t) of the laser emission signal to obtain target flight time;

and calculating to obtain the target distance according to the target flight time.

2. The method of claim 1, wherein the non-linear iterative correction of the measured-path beat signal as a function of an initial time-of-flight τ and a frequency-modulated non-linearity term, ε (t), of the laser emission signal to obtain a target time-of-flight comprises:

s1: according to the time delay flight time tau'_i-1Frequency modulation nonlinear term epsilon of laser emission signal(t) delaying to obtain a frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Time-of-flight τ'_i-1Is based on said time of flight τ_i-1Obtaining;

s2: according to the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Performing frequency modulation nonlinear correction on the beat frequency signal of the measuring path to obtain a corrected beat frequency signal;

and S3, determining the target flight time according to the corrected beat frequency signal.

3. The method of claim 2, wherein said determining the target time of flight from the corrected beat signal comprises:

obtaining a time of flight τ from the corrected beat signal_i；

When the peak of the frequency spectrum peak is_iWhen a preset condition is met, the flight time tau is measured_iDetermining the target time of flight; when the peak of the frequency spectrum peak is_iIf the preset condition is not met, making i ═ i +1, and repeatedly executing steps S1-S3; the peak value peak of the frequency spectrum_iThe peak value of the frequency domain signal corresponding to the corrected beat frequency signal is obtained;

when the i is 1, the peak_i-1For the initial spectral peak, the time of flight τ_i-1Is the initial time of flight τ.

4. A method according to claim 3, characterized in that the preset condition is (peak)_i-peak_i-1)/peak_i-1<Thr_rateThr is as defined above_rateIs a third preset threshold.

5. The method of claim 1, wherein the non-linear iterative correction of the measured-path beat signal as a function of an initial time-of-flight τ and a frequency-modulated non-linearity term, ε (t), of the laser emission signal to obtain a target time-of-flight comprises:

performing nonlinear iterative computation on the beat frequency signal of the measuring circuit for M times according to the initial flight time tau and a frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser to obtain the target flight time, wherein M is an integer greater than 1,

wherein, when the ith nonlinear iterative computation is carried out, the flight time tau 'is delayed'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) (ii) a Time delay flight time tau'_i-1Is based on said time of flight τ_i-1Obtaining;

according to the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Performing frequency modulation nonlinear correction on the beat frequency signal of the measuring path to obtain a corrected beat frequency signal; obtaining a time of flight τ from the corrected beat signal_i；

Wherein, when i ═ 1, the time of flight τ_i-1Is the initial time of flight τ; when the i is M, the target flight time is the flight time tau_i。

6. A method according to any one of claims 3 to 5, wherein said time of flight τ is obtained from said corrected beat signal_iThe method comprises the following steps:

performing Fast Fourier Transform (FFT) on the corrected beat frequency signal to obtain a frequency domain signal corresponding to the corrected beat frequency signal;

acquiring the flight time tau according to the frequency domain signal corresponding to the corrected beat frequency signal_i。

7. The method of any one of claims 2-6, wherein the corrected beat signal comprises a first corrected beat signal or a second corrected beat signal; the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Performing frequency modulation nonlinear correction on the beat frequency signal of the measurement circuit to obtain a corrected beat frequency signal, including:

when the signal-to-noise ratio of the beat frequency signal of the measuring line is lower than the second preset threshold value, according to the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Carrying out receiving end frequency modulation nonlinear term correction on the compensated beat frequency signal to obtain a second corrected beat frequency signal;

the beat frequency signal after compensation is obtained by compensating the frequency modulation nonlinear term of the transmitting end of the beat frequency signal of the measuring circuit according to the frequency modulation nonlinear term epsilon (t) of the signal transmitted by the laser.

8. The method of claim 7, wherein calculating an initial time of flight τ from the measured beat signal comprises:

determining the frequency of the measurement circuit beat signal according to the frequency domain signal corresponding to the measurement circuit beat signal, and calculating the initial flight time tau according to the frequency of the measurement circuit beat signal;

the frequency of the measurement-path beat signal is a frequency corresponding to a peak point position of a frequency-domain signal corresponding to the measurement-path beat signal, or a frequency corresponding to a middle point position of a half-height width of the frequency-domain signal.

9. The method of claim 7, wherein calculating an initial time of flight τ from the measured beat signal comprises:

when the signal-to-noise ratio of the beat frequency signal of the measuring circuit is lower than a second preset threshold value; performing frequency modulation nonlinear term compensation on the beat frequency signal of the measuring circuit at a transmitting end according to the frequency modulation nonlinear term epsilon (t) of the signal transmitted by the laser to obtain a compensated beat frequency signal; the frequency modulation nonlinear term of the laser emission signal is obtained by calculation based on the reference-path beat frequency signal;

performing FFT on the compensated beat frequency signal to obtain a frequency domain signal corresponding to the compensated beat frequency signal;

determining the frequency of the compensated beat frequency signal according to the frequency domain signal corresponding to the compensated beat frequency signal, and calculating the initial flight time tau according to the frequency of the compensated beat frequency signal;

the frequency of the compensated beat frequency signal is a frequency corresponding to a peak point position of a frequency domain signal corresponding to the compensated beat frequency signal, or a frequency corresponding to a middle point position of a half-height width of the frequency domain signal.

10. The method according to any one of claims 1-9, wherein said calculating a frequency modulation nonlinear term e (t) of the laser emission signal from said reference-path beat signal comprises:

performing Hilbert transform on the reference-path beat frequency signal to obtain a transformed beat frequency signal;

calculating the frequency modulation frequency of the laser emission signal according to the converted beat frequency signal;

and calculating the frequency modulation nonlinear term epsilon (t) of the laser emission signal according to the frequency modulation frequency and the ideal linear frequency modulation frequency of the laser emission signal.

11. A distance measuring device based on frequency modulation nonlinear correction is characterized by comprising:

the acquisition unit is used for acquiring a reference circuit beat frequency signal and a measurement circuit beat frequency signal;

the calculation unit is used for calculating frequency modulation nonlinearity according to the reference path beat frequency signal; calculating to obtain initial flight time tau according to the beat frequency signal of the measuring path;

the determining unit is used for determining that the frequency modulation nonlinearity is not less than a first preset threshold value, the calculating unit is also used for calculating a frequency modulation nonlinearity term epsilon (t) of a laser emission signal according to the reference-path beat signal,

the correction unit is used for carrying out nonlinear iterative correction on the beat frequency signal of the measuring circuit according to the initial flight time tau and a frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser device so as to obtain target flight time;

and the calculating unit is also used for calculating the target distance according to the target flight time.

12. The apparatus according to claim 11, wherein the correction unit is specifically configured to:

s1: according to the time delay flight time tau'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the measuring channel echo signal'_i-1) Time-of-flight τ'_i-1Is based on said time of flight τ_i-1Obtaining;

and S3, determining the target flight time according to the corrected beat frequency signal.

13. The apparatus of claim 12, wherein in said determining the target time of flight from the corrected beat signal, the correction unit is specifically configured to:

obtaining a time of flight τ from the corrected beat signal_i；

When the peak of the frequency spectrum peak is_iWhen a preset condition is met, the flight time tau is measured_iDetermining the target time of flight; when the peak of the frequency spectrum peak is_iNot meet the requirements ofWhen the preset condition is met, i is made to be i +1, and steps S1-S3 are repeatedly executed; the peak value peak of the frequency spectrum_iThe peak value of the frequency domain signal corresponding to the corrected beat frequency signal is obtained;

when the i is 1, the peak_i-1For the initial spectral peak, the time of flight τ_i-1Is the initial time of flight τ.

14. The apparatus of claim 13, wherein the preset condition is (peak)_i-peak_i-1)/peak_i-1<Thr_rateThr is as defined above_rateIs a third preset threshold.

15. The apparatus according to claim 11, wherein the correction unit is specifically configured to:

Wherein, when i ═ 1, the time of flight τ_i-1Is the initial time of flight τ; when the i is M, the target flight time is the flight time tau_i。

16. The method according to any one of claims 13-15Means for obtaining a time of flight τ from said corrected beat signal_iIn an aspect, the correction unit is specifically configured to:

performing Fast Fourier Transform (FFT) on the corrected beat frequency signal to obtain a frequency domain signal corresponding to the corrected beat frequency signal;

acquiring the flight time tau according to the frequency domain signal corresponding to the corrected beat frequency signal_i。

17. The apparatus of any one of claims 12-16, wherein the corrected beat signal comprises a first corrected beat signal or a second corrected beat signal; the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Performing frequency modulation nonlinear correction on the measurement beat frequency signal to obtain an aspect of a corrected beat frequency signal, where the correction unit is specifically configured to:

18. The apparatus according to claim 17, wherein, in said calculating an initial time of flight τ from the measured beat signal, the calculating unit is specifically configured to:

19. The apparatus according to claim 17, wherein, in said calculating an initial time of flight τ from the measured beat signal, the calculating unit is specifically configured to:

performing FFT on the compensated beat frequency signal to obtain a frequency domain signal corresponding to the compensated beat frequency signal;

20. The apparatus according to any of claims 11-19, wherein the computing unit is specifically configured to, in calculating the frequency modulation non-linearity term e (t) of the laser emission signal from the reference beat signal:

performing Hilbert transform on the reference-path beat frequency signal to obtain a transformed beat frequency signal;

calculating the frequency modulation frequency of the laser emission signal according to the converted beat frequency signal;

21. A distance measuring device based on frequency modulation nonlinear correction is characterized by comprising:

a memory to store instructions; and

at least one processor coupled to the memory;

wherein the instructions, when executed by the at least one processor, cause the processor to perform the method of any of claims 1-10.

22. A computer storage medium, characterized in that the computer storage medium stores a computer program comprising program instructions that, when executed by a processor, cause the processor to perform the method according to any one of claims 1-10.

23. A radar, comprising:

a laser, and a processor coupled with the laser;

the processor is configured to perform the method of any one of claims 1 to 10.

Technical Field

The application relates to the field of laser radars, in particular to a ranging method based on frequency modulation nonlinear correction and a related device.

Background

Frequency Modulated Continuous Wave (FMCW) LiDAR (Light Detection and Ranging, LiDAR) is an optical remote sensing technology, can complete functions such as Ranging, speed measurement, target Detection, tracking and imaging identification, and can be applied to the fields of intelligent transportation, automatic driving, atmospheric environment monitoring, geographical mapping, unmanned aerial vehicle and the like.

FMCW LiDAR is a method of obtaining positional information of an object under test by measuring the frequency domain response of a beat signal that is obtained by the coherence of the emitted light signal and the return signal. The basic process is shown in figure 1. Estimating the frequency difference f between the transmitted signal and the echo signal by performing a frequency domain analysis on the beat signal_bAnd further according to the frequency difference f_bAnd calculating the flight time tau, and finally calculating the distance of the detected target according to the flight time.

FIG. 2 is a block diagram of a typical FMCW LiDAR system architecture. The laser signal is emitted by injecting proper driving current into the tunable laser, the light beam is divided into two laser beams by the coupler after passing through the isolator, one of the two laser beams is used as reference light, and the other laser beam is emitted to a measured target object through the circulator and the lens in sequence and is called measuring light. The measuring light is collected by a lens after being reflected by the surface of a target, passes through a circulator and a coupler together with the reference light, is coherent on a photosensitive surface of a balanced detector, and generates a beat frequency signal with the frequency in direct proportion to the flight time tau; obtaining a frequency value f of the beat frequency signal by carrying out frequency domain analysis on the beat frequency signal_bI.e. the frequency difference between the transmitted signal and the echo signal; and then according to known parameters such as frequency modulation period, frequency modulation bandwidth and the like, the flight time tau can be calculated, and further the target distance can be estimated.

In the ideal chirp case, the chirp curves of the transmitted signal and the return signal should be consistent and vary linearly in frequency with time, and there is only flight delay between the two, so the chirp linearity of the transmitted signal can greatly affect the ranging accuracy of FMCW LiDAR. In practice, the output frequency of the laser is controlled by varying the drive current of the laser, which exhibits a significant non-linearity with the modulation current due to the frequency modulation effect inherent in the semiconductor laser itself, as shown in fig. 3. Compared with linear frequency modulation, when frequency modulation nonlinearity exists, the beat frequency signal is no longer a single-frequency signal, the beat frequency can change along with time, the frequency spectrum can be broadened, the signal-to-noise ratio of the beat frequency signal is reduced, and the ranging precision and the ranging range are seriously influenced.

Disclosure of Invention

The embodiment of the application provides a ranging method and a related device based on frequency modulation nonlinear correction so as to improve the ranging precision and the ranging range of a laser radar.

In a first aspect, an embodiment of the present application provides a ranging method based on frequency modulation nonlinear correction, including:

acquiring a reference circuit beat frequency signal and a measurement circuit beat frequency signal, wherein the reference circuit beat frequency signal and the measurement circuit beat frequency signal are respectively obtained based on signals emitted by a laser; calculating according to the beat frequency signal of the reference path to obtain the frequency modulation nonlinearity; calculating according to the beat frequency signal of the measuring path to obtain initial flight time tau; determining that the frequency modulation nonlinearity is not less than a first preset threshold, calculating a frequency modulation nonlinearity term epsilon (t) of a laser emission signal according to a reference-path beat signal, and performing nonlinear iterative correction on a measurement-path beat signal according to the initial flight time tau and the frequency modulation nonlinearity term epsilon (t) of the laser emission signal to obtain a target flight time; and calculating the target distance according to the target flight time.

The beat frequency signal of the measuring path is subjected to nonlinear iterative correction based on the flight time tau and the frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser, so that the influence of frequency modulation nonlinearity on the beat frequency signal of the measuring path is eliminated, the deviation between the finally estimated target flight time and the actual target flight time is minimized, the target distance can be determined according to the target flight time, and the ranging precision of the laser radar is improved.

In one possible embodiment, the nonlinear iterative correction of the beat frequency signal of the measurement circuit according to the initial flight time τ and the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the target flight time comprises:

s1: according to time delay flight time tau'_i-1To laserDelaying the frequency modulation nonlinear term epsilon (t) of the optical device emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Time of flight τ'_i-1Is based on time of flight τ_i-1Obtaining;

s2: according to the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Carrying out frequency modulation nonlinear correction on the beat frequency signal of the measuring path to obtain a corrected beat frequency signal;

and S3, determining the flight time of the target according to the corrected beat frequency signal.

The beat frequency signal of the measuring circuit is subjected to frequency modulation nonlinear correction according to the frequency modulation nonlinear term of the signal emitted by the laser, so that the influence of the frequency modulation nonlinearity on the beat frequency signal of the measuring circuit is eliminated, the accuracy of the flight time obtained based on the corrected beat frequency signal is improved, and the ranging precision is further improved.

In one possible embodiment, determining the target time of flight from the corrected beat signal includes:

obtaining time of flight tau from corrected beat signal_i(ii) a When the peak of the spectrum peak_iWhen the preset condition is met, the flight time tau is measured_iDetermining the target flight time; when the peak of the spectrum peak_iIf the preset condition is not satisfied, making i equal to i +1, and repeatedly executing the steps S1-S3; peak of the spectrum peak_iCorrecting the peak value of the frequency domain signal corresponding to the beat frequency signal;

peak when i is 1_i-1For the initial spectral peak, time of flight τ_i-1Is the initial time of flight τ.

By carrying out iterative correction on the beat frequency signal of the measuring circuit, the influence of frequency modulation nonlinearity on the beat frequency signal of the measuring circuit can be eliminated to a great extent, the accuracy of the flight time obtained based on the corrected beat frequency signal is improved, and the ranging precision is further improved.

In one possible embodiment, the preset condition is (peak)_i-peak_i-1)/peak_i-1＜Thr_rateThe Thr_rateIs a third preset threshold.

carrying out nonlinear iterative computation on the beat frequency signal of the measuring circuit for M times according to the initial flight time tau and the frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser to obtain the target flight time, wherein M is an integer larger than 1,

wherein, when the ith nonlinear iterative computation is carried out, the flight time tau 'is delayed'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) (ii) a Time-of-flight τ'_i-1Is based on time of flight τ_i-1Obtaining;

according to the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Carrying out frequency modulation nonlinear correction on the beat frequency signal of the measuring path to obtain a corrected beat frequency signal; obtaining time of flight tau from corrected beat signal_i；

Wherein, when i is 1, the flight time τ_i-1Is the initial time of flight τ; when i is equal to M, the target time of flight is time of flight τ_i。

By carrying out frequency modulation nonlinear correction on the beat frequency signal of the measuring circuit for multiple times, the influence of frequency modulation nonlinearity on the beat frequency signal of the measuring circuit can be eliminated to a great extent, the accuracy of the flight time obtained based on the corrected beat frequency signal is improved, and the ranging precision is further improved.

In one possible embodiment, the time of flight τ is obtained from the corrected beat signal_iThe method comprises the following steps:

performing FFT (fast Fourier transform) on the corrected beat frequency signal to obtain a frequency domain signal corresponding to the corrected beat frequency signal; acquiring the flight time tau according to the frequency domain signal corresponding to the corrected beat frequency signal_i。

In one possible embodiment, the corrected beat signal includes a first corrected beat signal or a second corrected beat signal; according to the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Frequency modulation nonlinear correction is carried out on the beat frequency signal of the measuring circuit to obtain a corrected beat frequency signal, and the method comprises the following steps:

when the signal-to-noise ratio of the beat signal of the measuring line is not lower than a second preset threshold, according to the frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser and the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Carrying out frequency modulation nonlinear term correction on the beat frequency signal of the measuring path to obtain a first corrected beat frequency signal; when the signal-to-noise ratio of the beat signal of the measuring line is lower than a second preset threshold value, according to the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Carrying out receiving end frequency modulation nonlinear term correction on the compensated beat frequency signal to obtain a second corrected beat frequency signal;

When the signal-to-noise ratio of the beat frequency signal of the measuring path is low, the initial flight time calculated based on the beat frequency signal of the measuring path has a large estimation error, so that in order to reduce the calculation error of the initial flight time and reduce the iteration times, the beat frequency signal of the measuring path is compensated according to the frequency modulation nonlinear term epsilon (t) of the laser emission signal, and the compensated beat frequency signal is obtained, so that when the beat frequency signal of the measuring path is corrected, the frequency modulation nonlinear correction is only needed to be performed on the compensated beat frequency signal according to the frequency modulation nonlinear term of the echo signal of the measuring path, and the influence of the frequency modulation nonlinear on the beat frequency signal of the measuring path is also eliminated.

In one possible embodiment, calculating the initial time of flight τ from the measured beat signal includes:

when the signal-to-noise ratio of the measurement circuit beat frequency signal is not lower than a second preset threshold, performing FFT (fast Fourier transform) on the measurement circuit beat frequency signal to obtain a frequency domain signal corresponding to the measurement circuit beat frequency signal; determining the frequency of the beat frequency signal of the measuring circuit according to the frequency domain signal corresponding to the beat frequency signal of the measuring circuit, and calculating to obtain the initial flight time tau according to the frequency of the beat frequency signal of the measuring circuit;

In one possible embodiment, calculating the initial time of flight τ from the measured beat signal includes:

when the signal-to-noise ratio of the beat frequency signal of the measuring circuit is lower than a second preset threshold value; frequency modulation nonlinear term compensation of a transmitting end is carried out on the beat frequency signal of the measuring circuit according to the frequency modulation nonlinear term epsilon (t) of the signal transmitted by the laser device, so as to obtain a compensated beat frequency signal; the frequency modulation nonlinear term of the laser emission signal is obtained by calculation based on the reference path beat frequency signal;

performing FFT (fast Fourier transform) on the compensated beat frequency signal to obtain a frequency domain signal corresponding to the compensated beat frequency signal; determining the frequency of the compensated beat frequency signal according to the frequency domain signal corresponding to the compensated beat frequency signal, and calculating to obtain the initial flight time tau according to the frequency of the compensated beat frequency signal;

When the signal-to-noise ratio of the beat frequency signal of the measurement path is low, the initial flight time calculated based on the beat frequency signal of the measurement path has a large estimation error, so in order to reduce the calculation error of the initial flight time and reduce the iteration times, the frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser is used for carrying out frequency modulation nonlinear term compensation on the beat frequency signal of the measurement path at the emitting end to obtain the beat frequency signal compensated by the frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser, only the frequency modulation nonlinear term corresponding to the echo signal is left in the beat frequency signal, and the initial flight time tau with a small estimation error is calculated based on the beat frequency signal.

In one possible embodiment, the frequency modulation nonlinear term epsilon (t) of the laser emission signal is calculated according to the reference-path beat frequency signal, and comprises the following steps:

performing Hilbert transform on the reference-path beat frequency signal to obtain a transformed beat frequency signal; calculating the frequency modulation frequency of the laser emission signal according to the converted beat frequency signal; and calculating the frequency modulation nonlinear term epsilon (t) of the laser emission signal according to the frequency modulation frequency and the ideal linear frequency modulation frequency of the laser emission signal.

In a second aspect, an embodiment of the present application provides a ranging apparatus based on frequency modulation nonlinear correction, including:

the device comprises an acquisition unit, a processing unit and a control unit, wherein the acquisition unit is used for acquiring a reference circuit beat frequency signal and a measurement circuit beat frequency signal which are respectively obtained based on signals emitted by a laser;

the calculation unit is used for calculating frequency modulation nonlinearity according to the reference-path beat signal; calculating according to the beat frequency signal of the measuring path to obtain initial flight time tau;

the calculating unit is also used for calculating a frequency modulation nonlinear term epsilon (t) of the laser emission signal according to the reference path beat frequency signal when the determining unit determines that the frequency modulation nonlinearity is not less than a first preset threshold value,

the correction unit is used for carrying out nonlinear iterative correction on the beat frequency signal of the measuring circuit according to the initial flight time tau and the frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser device to obtain the target flight time;

and the calculating unit is used for calculating the target distance according to the target flight time.

The beat frequency signal of the measuring path is subjected to nonlinear iterative correction based on the flight time tau and the frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser, so that the influence of frequency modulation nonlinearity on the beat frequency signal of the measuring path can be eliminated to a great extent, the deviation between the finally estimated target flight time and the actual target flight time is minimum, the target distance can be determined according to the target flight time, and the ranging precision of the laser radar is improved.

In a possible embodiment, the correction unit is specifically configured to:

s1: according to time delay flight time tau'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Delay timeTime of flight τ'_i-1Is based on time of flight τ_i-1Obtaining;

and S3, determining the flight time of the target according to the corrected beat frequency signal.

In a possible embodiment, the correction unit is specifically configured to, in determining the target time of flight from the corrected beat signal:

peak when i is 1_i-1For the initial spectral peak, time of flight τ_i-1Is the initial time of flight τ.

In one possible embodiment, the preset condition is (peak)_i-peak_i-1)/peak_i-1＜Thr_rateThe Thr_rateIs a third preset threshold.

In a possible embodiment, the correction unit is specifically configured to include:

wherein, when the ith nonlinear iterative computation is carried out, the flight time tau 'is delayed'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) (ii) a Time-of-flight τ'_i-1Is based on time of flight τ_i-1Obtaining;

based on measurement path echo informationFrequency modulation nonlinear term epsilon (t-tau ') corresponding to sign'_i-1) Carrying out frequency modulation nonlinear correction on the beat frequency signal of the measuring path to obtain a corrected beat frequency signal; obtaining time of flight tau from corrected beat signal_i；

Wherein, when i is 1, the flight time τ_i-1Is the initial time of flight τ; when i is equal to M, the target time of flight is time of flight τ_i。

In one possible embodiment, the time of flight τ is obtained from the corrected beat signal_iThe computing unit is specifically configured to:

In one possible embodiment, the corrected beat signal includes a first corrected beat signal or a second corrected beat signal; the frequency modulation nonlinear term epsilon (t-tau ') corresponding to echo signals according to a measuring line'_i-1) The frequency modulation nonlinear correction is performed on the beat frequency signal of the measurement path to obtain an aspect of corrected beat frequency signal, and the correction unit is specifically configured to:

In a possible embodiment, the calculation unit is specifically configured to, in calculating the initial time of flight τ from the measured beat signals:

In a possible embodiment, in terms of calculating the frequency modulation nonlinearity term ∈ (t) of the laser emission signal from the reference-path beat signal, the calculation unit is specifically configured to:

In a third aspect, an embodiment of the present application provides a ranging apparatus based on frequency modulation nonlinear correction, including:

a memory to store instructions; and

at least one processor coupled to the memory;

wherein the instructions, when executed by the at least one processor, cause the processor to perform all or part of the method of the first aspect.

In a fourth aspect, the present application provides a computer storage medium storing a computer program, the computer program comprising program instructions that, when executed by a processor, cause the processor to perform all or part of the method as set forth in the first aspect.

In a fifth aspect, embodiments of the present application provide a lidar comprising a laser and a processor coupled to the laser, the processor performing all or part of the method as shown in the first aspect.

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.

FIG. 1 is a schematic diagram of FMCW lidar ranging principles;

FIG. 2 is a block diagram of a system architecture of an FMCW lidar;

FIG. 3 is a beat signal under non-linear frequency modulation;

FIG. 4 is a schematic diagram of a prior art method for pre-distortion based on modulated laser drive current;

fig. 5 is a schematic flowchart of a ranging method based on frequency modulation nonlinear correction according to an embodiment of the present disclosure;

fig. 6 is a schematic flowchart of a nonlinear iterative correction of a beat signal of a measured circuit according to an embodiment of the present application;

fig. 7 is a schematic flowchart of another non-linear iterative correction for a beat signal of a measured circuit according to an embodiment of the present application;

fig. 8 is a schematic flowchart of another distance measuring method based on frequency modulation nonlinear correction according to an embodiment of the present disclosure;

FIG. 9a is a graph showing a comparison of range errors before and after non-linear correction;

FIG. 9b is a frequency spectrum of the beat signal after iterative correction of the non-linear term;

fig. 10 is a schematic structural diagram of a ranging apparatus based on frequency modulation nonlinear correction according to an embodiment of the present disclosure;

fig. 11 is a schematic structural diagram of another distance measuring device based on frequency modulation nonlinear correction according to an embodiment of the present application.

Detailed Description

In order to make the technical solutions better understood by those skilled in the art, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application.

In order to improve the ranging accuracy and increase the ranging range, methods for correcting frequency modulation nonlinearity have been proposed. Among the existing methods for correcting frequency modulation nonlinearity, one of the more common methods is a processing method based on predistortion of the driving current of a modulated laser. As shown in fig. 4, by estimating the current measured laser actual output frequency v_k(t) and the ideal linear frequency v_dFrequency difference e between (t)_k(t) to adjust the next measurement of the laser drive current u_k+1(t) to change the output frequency of the laser at the next measurement. After a plurality of times of iterative correction, the laser output frequency is finally made to tend to be linear.

The main problem with this solution is that the non-linearity can only be reduced to a relatively small range by controlling the output frequency of the laser by adjusting the drive current, and cannot be completely eliminated in principle. Furthermore, the result of the current non-linearity correction can only be used for the next measurement. If the interference of external factors such as temperature, vibration and the like is caused, the output frequency of the laser at the next measurement is controlled by the driving current estimated by the predistortion at the last measurement, and the frequency value of the driving current is not matched with the expected value, so that the result of the predistortion estimation at the last time is invalid, and the aim of iterative correction is not achieved.

The resampling algorithm is a method for frequency modulation nonlinear correction at a receiving end. The core idea is that the beat frequency signal is resampled by the estimated sampling time sequence, so that the signal is changed into a single frequency signal again. The specific principle is as follows:

(1) transmitting a signal:

(2) echo signals: s_r(t)＝s_t(t-τ)

(3) Beat frequency signal:(ignoring higher order terms of τ)

(4) Order toThen s'_b(t)＝exp{j2π[f₀+αt′]τ}

Considering t 'as a new sampling time sequence, for the beat signal s'_b(t) resampling is performed so that the resampled beat signal is converted back to a single frequency signal.Is a frequency modulated non-linear term.

The resampling algorithm assumes that the delay τ of the beat signal is a small value, so that the high-order term of τ can be ignored, and for a distant target, the corresponding range error of the resampled beat signal is still large because the delay τ does not satisfy the premise assumption. Therefore, the resampling performance is related to the distance to be measured, and has great practical limitation.

Based on the above reasons, the present application provides a schematic flow chart of a ranging method based on frequency modulation nonlinear correction. As shown in fig. 5, the method includes:

s501, obtaining a reference circuit beat frequency signal and a measurement circuit beat frequency signal.

Specifically, a laser signal emitted by the laser is divided into two paths, one path is an optical signal of the reference path, and the other path is an optical signal of the measurement path. The reference path optical signal and the measurement path optical signal have the same frequency and phase.

The optical signal of the reference path is divided into two paths, and the fixed arm length difference can be preset to be tau_DThe Mach-Zehnder interferometer (MZI) obtains a reference beat signal s_ref(t) of (d). Specifically, one path of optical signal passes through the short arm of the MZI, the other path of optical signal passes through the long arm of the MZI, and because the optical paths of the two paths of optical signals are different, the two paths of optical signals are coherent on the photosensitive surface of the balanced detector, and a reference path beat frequency signal s is obtained_ref(t)。

The optical signal of the measuring path is divided into two paths, wherein one path is a local oscillation signal, the other path is transmitted to a measured target object, and an echo signal is obtained by the surface reflection of the target object. The echo signal and the local oscillator signal are coherent on the photosensitive surface of the balanced detector to obtain a beat signal s of the measurement path_b(t)。

S502, calculating according to the beat frequency signal of the reference path to obtain frequency modulation nonlinearity; and calculating to obtain the initial flight time tau according to the beat frequency signal of the measuring circuit.

Specifically, the calculating of the frequency modulation nonlinearity according to the reference-path beat signal includes:

beat frequency signal s to reference path_ref(t) performing a Hilbert transform to obtain a transformed signal H_b(t) obtaining an instantaneous phase of the reference beat signal from the transformed signal

Wherein the content of the first and second substances,H_b，real＝real(H_b(t))，H_b，imag＝imag(H_b(t))，H_b(t)＝hilbert(s_ref(t))，real(H_b(t)) is the transformed signal H_bReal part of (t), imag (H)_b(t)) is the transformed signal H_bThe imaginary part of (t).

According to the frequency f (t) of the laser emission signal and the instantaneous phase of the reference-path beat frequency signalCalculating the frequency modulation frequency f (t) of the laser emission signal, wherein,

calculating a frequency modulation nonlinearity from the frequency modulation frequency, the frequency modulation nonlinearityf_ideal(t) is the ideal chirp frequency, f_ideal(t)＝f₀t+0.5αt²，f₀The carrier frequency is alpha, the corresponding frequency modulation slope when the ideal linear frequency modulation is carried out, and B is the frequency modulation bandwidth.

Alternatively, the frequency modulation nonlinearity can be determined according to the frequency modulation nonlinearity term of the laser emission signal (i.e. the frequency modulation frequency f (t) and the ideal chirp frequency f of the laser emission signal)_idealDifference of (t) and the bandwidth of the modulation (B) are calculated, and the nonlinearity of the modulation can be expressed as:

optionally, the frequency f (t) of the laser emission signal and the ideal chirp frequency f can be used_ideal(t) deviation to measure the frequency modulation nonlinearity of the laser, i.e. f (t) and f_idealThe Root Mean Square Error (RMSE) between (t), i.e. the Root Mean Square Error (RMSE)

It should be noted here that the frequency modulation frequency f (t) and the ideal chirp frequency f_ideal(t) can be seen as discrete signals, so f_kFor a frequency corresponding to the kth discrete point at frequency f (t), f_ideal，kIs an ideal linear frequency modulation frequency f_ideal(t) the frequency corresponding to the kth discrete point.

S503, when the frequency modulation nonlinearity is not smaller than a first preset threshold value, calculating to obtain a frequency modulation nonlinearity term epsilon (t) of a laser emission signal according to the reference-path beat signal, and carrying out nonlinear iterative correction on the measurement-path beat signal according to the initial flight time tau and the frequency modulation nonlinearity term epsilon (t) of the laser emission signal to obtain the target flight time.

Wherein, the first preset threshold Thr_nonRateThe maximum non-linearity of the laser that can be received by the FMCW ranging system.

Specifically, the frequency modulation nonlinear term ∈ (t) of the laser emission signal is obtained based on the following formula:

in a possible embodiment, the beat signal s is based on a measured path_b(t) calculating an initial time of flight τ comprising:

when measuring the beat frequency signal s_b(t) when the signal-to-noise ratio is not less than a second preset threshold, the beat frequency signal s of the measuring path is measured_b(t) performing fast FFT to obtain a frequency domain signal corresponding to the beat frequency signal sb (t) of the measurement circuit, and determining the beat frequency of the measurement circuit based on the frequency domain signalSignal s_bFrequency f of (t)_b(ii) a When measuring the beat frequency signal s_bWhen the signal-to-noise ratio of (t) is less than a second preset threshold value, measuring circuit beat frequency signal s is subjected to frequency modulation nonlinear term epsilon (t) of laser emission signal_b(t) compensating the frequency modulation nonlinear term of the transmitting end to obtain a compensated beat frequency signal s'_b(t); to the compensated beat signal s'_b(t) performing FFT to obtain a frequency domain signal corresponding to the compensated beat frequency signal; determining a compensated beat signal s 'according to a frequency domain signal corresponding to the compensated beat signal'_bFrequency f of (t)'_b(ii) a According to the frequency f of the beat signal_bOr compensated beat signal s'_bFrequency f of (t)'_bCalculating to obtain initial flight time tau; initial time of flight τ of f_bAlpha or f'_bThe alpha is the corresponding frequency modulation slope when the ideal linear frequency modulation is carried out;

wherein the beat frequency signal s of the measuring circuit_bFrequency f of (t)_bFor measuring the beat frequency s of the road_b(t) a frequency corresponding to a peak point position of the corresponding frequency domain signal, or a frequency corresponding to a center position of a half-height width of the frequency domain signal; compensated beat signal s'_bFrequency f of (t)'_bIs a compensated beat signal s'_b(t) a frequency corresponding to a peak point position of the corresponding frequency domain signal, or a frequency corresponding to a center position of a full width at half maximum of the frequency domain signal.

In one possible embodiment, the nonlinear iterative correction is performed according to the initial flight time τ and the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the target flight time, and comprises:

s1: according to time delay flight time tau'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') of the echo signal of the measuring line'_i-1) Wherein the delayed time of flight τ'_i-1Is based on time of flight τ_i-1Obtaining;

s2, carrying out frequency modulation nonlinear term correction on the beat frequency signal of the measuring path according to the frequency modulation nonlinear term corresponding to the echo signal of the measuring path to obtain a corrected beat frequency signal;

and S3, determining the flight time of the target according to the corrected beat frequency signal.

Further, determining a target time of flight from the corrected beat signal includes:

obtaining time of flight tau from corrected beat signal_i(ii) a When the peak of the spectrum peak_iWhen the preset condition is met, the flight time tau is measured_iDetermining the target flight time; when the spectrum peak value peaki does not meet the preset condition, making i equal to i +1, and repeatedly executing steps S1-S3; peak of the spectrum peak_iCorrecting the peak value of the frequency domain signal corresponding to the beat frequency signal;

peak when i is 1_i-1Time of flight τ for the initial spectral peak_i-1Is the initial time of flight τ.

Wherein the preset condition is (peak)_i-peak_i-1)/peak_i-1＜Thr_rate，Thr_rateIs a third preset threshold.

wherein, when the ith nonlinear iterative computation is carried out, the flight time tau 'is delayed'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) (ii) a Time-of-flight τ'_i-1Is based on time of flight τ_i-1Obtaining;

Wherein, when i is 1, the flight time τ_i-1Is the initial time of flight τ; when i is equal to M, the target time of flight is time of flight τ_i。

In one possible embodiment, the time of flight τ is obtained from the corrected beat signal_iThe method comprises the following steps:

FFT is carried out on the corrected beat frequency signal to obtain a frequency domain signal corresponding to the corrected beat frequency signal, and the flight time tau is obtained according to the frequency domain signal corresponding to the corrected beat frequency signal_i。

the compensated beat frequency signal is obtained by compensating the frequency modulation nonlinear term of the transmitting end of the beat frequency signal of the measuring circuit according to the frequency modulation nonlinear term epsilon (t) of the signal transmitted by the laser, so that the compensated beat frequency signal can be called as the beat frequency signal which is subjected to frequency modulation nonlinear compensation of the transmitting end.

In particular, when measuring the beat signal s_bWhen the signal-to-noise ratio of (t) is not lower than a second preset threshold, according to the frequency modulation nonlinear term epsilon (t) of the laser emission signal and the frequency modulation nonlinear term epsilon (t-tau) of the echo signal_i) For measurement path beat frequency signal s_b(t) frequency modulation nonlinear term correction to obtain the secondA corrected beat signalWhen measuring the beat frequency signal s_bWhen the signal-to-noise ratio of (t) is lower than a second preset threshold value, according to the frequency modulation nonlinear term epsilon (t-tau) of the echo signal of the measuring channel_i) The beat frequency signal s 'subjected to frequency modulation and nonlinear compensation of the transmitting end is subjected to frequency modulation and nonlinear compensation'_b(t) performing frequency modulation nonlinear term correction on the receiving end to obtain a second corrected beat frequency signal

Specifically, as shown in fig. 6:

S10A, according to flight time tau_i-1Obtaining delayed flight time tau'_i-1。

Optionally, time of flight τ 'is delayed'_i-1＝τ_i-1And + p, p is a preset step length. Of course, the delayed flight time tau 'can be obtained based on other modes'_i-1。

S20A according to delayed flight time tau'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') of the echo signal of the measuring line'_i-1)。

In other words, the frequency-modulated nonlinear term ε (t) of the laser emission signal is subjected to one τ'_i-1Obtaining a frequency modulation nonlinear term epsilon (t-tau ') of the echo signal of the measuring line'_i-1)。

S30A, when measuring the beat frequency signal S_bWhen the signal-to-noise ratio of (t) is not lower than a second preset threshold value, according to the frequency modulation nonlinear term epsilon (t) of the laser emission signal and the frequency modulation nonlinear term epsilon (t-tau ') of the measuring line echo signal'_i-1) For measurement path beat frequency signal s_b(t) performing frequency modulation nonlinear term correction to obtain a first corrected beat signalWherein the first corrected beat signal is:s_b(t) is the initial beat signal of the measurement path, in other words, s_bAnd (t) is a corresponding beat signal before the nonlinear term of the measuring path is iteratively corrected. When measuring the beat frequency signal s_bWhen the signal-to-noise ratio of (t) is lower than a second preset threshold value, according to the frequency modulation nonlinear term epsilon (t-tau ') of the echo signal of the measuring line'_i-1) Beat frequency signal s 'compensated by non-linear term of frequency modulation of transmitter side'_b(t) performing frequency modulation nonlinear term correction on the receiving end to obtain a second corrected beat frequency signalWherein the second corrected beat signal is:for the first corrected beat signalOr second correcting beat signalPerforming FFT to obtain the first corrected beat frequency signalOr second correcting beat signalCorresponding frequency domain signal based on which the time of flight τ is obtained_iAnd spectral peak_i。

Specifically, the frequency of the first corrected beat signal is determined according to the frequency domain signal corresponding to the first corrected beat signal, and the time of flight τ is determined according to the frequency of the first corrected beat signal_i(ii) a Or determining the frequency of the second correction beat signal according to the frequency domain signal corresponding to the second correction beat signal, and determining the flight time tau according to the frequency of the second correction beat signal_i。

WhereinThe frequency of the first corrected beat signal is the peak value peak of the frequency domain signal corresponding to the first corrected beat signal_iThe frequency corresponding to the position or the frequency corresponding to the half-height width center position of the frequency domain signal; the frequency of the second correction beat frequency signal is the peak value peak of the frequency domain signal corresponding to the second correction beat frequency signal_iThe frequency corresponding to the position, or the frequency corresponding to the position of the center of the full width at half maximum of the frequency domain signal.

S40A, peak (peak)_i-peak_i-1)/peak_i-1＞＝Thr_rateWhen the value is 1+1, repeatedly executing steps S10A-S40A; when (peak)_i-peak_i-1)/peak_i-1＜Thr_rateThen, step S50A is executed. Wherein, Thr_rateIs a third preset threshold value, which is a peak growth rate threshold value.

Wherein peak is given when i is 1_i-1Time of flight τ for the initial spectral peak_i-1For initial time of flight τ, when measuring the beat signal s_b(t) when the signal-to-noise ratio is not lower than a second preset threshold, the initial spectrum peak value is a measurement circuit beat signal s_b(t) a peak value of the corresponding frequency domain signal; when measuring the beat frequency signal s_b(t) when the signal-to-noise ratio is lower than a second preset threshold, the initial spectrum peak value is the compensated beat frequency signal s'_b(t) the peak of the corresponding frequency domain signal.

S50A, determining the target flight time as the flight time tau_i。

More specifically, as shown in fig. 7:

S10B, according to flight time tau_i-1Obtaining delayed flight time tau'_i-1. Optionally, time of flight τ 'is delayed'_i-1＝τ_i-1And + p, p is a preset step length. Of course, the delayed flight time tau 'can be obtained based on other modes'_i-1。

S20B according to delayed flight time tau'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') of the echo signal of the measuring line'_i-1). In other words, the frequency-modulated non-linear term ε (t) of the laser emission signalLine of τ'_i-1Obtaining a frequency modulation nonlinear term epsilon (t-tau ') of the echo signal of the measuring line'_i-1)。

S30B, when the signal-to-noise ratio of the beat frequency signal of the measuring line is not lower than a second preset threshold value, according to the frequency modulation nonlinear term epsilon (t) of the laser emission signal and the frequency modulation nonlinear term epsilon (t-tau ') of the echo signal of the measuring line'_i-1) For measurement path beat frequency signal s_b(t) performing frequency modulation nonlinear term correction to obtain a first corrected beat signalAnd according to the first corrected beat signalObtaining time of flight τ_iAnd spectral peak_i. Wherein the first corrected beat signal is:s_band (t) is a beat frequency signal of the measuring circuit. When the signal-to-noise ratio of the beat frequency signal of the measuring line is lower than a second preset threshold value, according to the frequency modulation nonlinear term epsilon (t-tau ') of the echo signal of the measuring line'_i-1) Beat frequency signal s 'compensated by non-linear term of frequency modulation of transmitter side'_b(t) performing frequency modulation nonlinear term correction on the receiving end to obtain a second corrected beat frequency signalAnd according to the second corrected beat signalObtaining time of flight τ_iAnd spectral peak_i. Wherein the second corrected beat signal is:

specifically, the frequency of the first corrected beat signal is determined according to the frequency domain signal corresponding to the first corrected beat signal, and the frequency of the first corrected beat signal is determined according to the first corrected beat signalCorrecting the frequency of the beat signal to determine the time of flight tau_i(ii) a Or determining the frequency of the second correction beat signal according to the frequency domain signal corresponding to the second correction beat signal, and determining the flight time tau according to the frequency of the second correction beat signal_i。

Wherein the frequency of the first corrected beat frequency signal is the peak value peak of the frequency domain signal corresponding to the first corrected beat frequency signal_iThe frequency corresponding to the position or the frequency corresponding to the half-height width center position of the frequency domain signal; the frequency of the second correction beat frequency signal is the peak value peak of the frequency domain signal corresponding to the second correction beat frequency signal_iThe frequency corresponding to the position, or the frequency corresponding to the position of the center of the full width at half maximum of the frequency domain signal.

S40B, when i < M, making i equal to 1+1, and repeatedly executing steps S10B-S40B; when i is equal to M, step S50B is performed.

S50B, time of flight t being the target time of flight_i。

Wherein, when i is 1, the flight time τ_i-1Is the initial time of flight; when i is equal to M, the target time of flight is time of flight τ_i。

It should be noted that, before the method shown in fig. 7 is executed, i is initialized so that i becomes 1.

And S504, calculating to obtain the target distance according to the target flight time.

Wherein, the target distance R is cT/2, c is the speed of light, and T is the target flight time.

In a specific embodiment, as shown in fig. 8, the reference path beat frequency signal is obtained, specifically, the optical signal of the reference path is divided into two paths, which can be set by a preset fixed arm length difference τ_DThe MZI of (1) obtains a reference beat signal s_ref(t) of (d). One path of optical signal passes through the short arm of the MZI, the other path of optical signal passes through the long arm of the MZI, and because the optical paths of the two paths of optical signals are different, the two paths of optical signals are coherent on the photosensitive surface of the balanced detector, and a reference path beat frequency signal s is obtained_ref(t)。

Obtaining a reference beat signal s_ref(t) after, beat frequency signal s according to reference path_ref(t)Calculating the frequency f (t) of the frequency modulation of the laser emission signal. Specifically, the beat signal s is added to the reference path_ref(t) performing a Hilbert transform to obtain a transformed beat signal H_b(t), the beat signal can be represented as H_b(t)＝hilbert(s_ref(t)), and then obtaining an instantaneous phase of the reference-path beat signal from the converted beat signalThe instantaneous phaseCan be expressed as:wherein H_b，imagIs H_bImaginary part of (t), H_b，realIs H_bThe real part of (t).

Calculating according to the frequency modulation frequency f (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t) and the frequency modulation nonlinearity non of the laser emission signal_rate. Specifically, according to the frequency modulation frequency f (t) of the laser emission signal and the instantaneous phase of the reference-path beat frequency signalThe frequency modulation frequency f (t) is calculated, wherein,then, according to the frequency modulation frequency f (t), calculating to obtain the frequency modulation nonlinear term epsilon (t) and the frequency modulation nonlinear degree non of the laser emission signal_rate. Frequency modulation nonlinear term of laser emission signalDegree of frequency modulation nonlinearityWherein f is_ideal(t) is the ideal chirp frequency, f_ideal(t)＝f₀t+0.5αt²，f₀The carrier frequency is alpha, the corresponding frequency modulation slope when the ideal linear frequency modulation is carried out, and B is the frequency modulation bandwidth.

Obtaining beat frequency signals of a measuring path, specifically, dividing optical signals of the measuring path into two paths, wherein one path of signals is used as local oscillation signals, the other path of signals is transmitted to a measured target object, and echo signals are obtained through reflection on the surface of the target object. The echo signal and the local oscillator signal are coherent on the photosensitive surface of the balanced detector to obtain a beat signal s of the measurement path_b(t)。

FFT is carried out on the beat frequency signal of the measuring path, and the frequency f of the beat frequency signal is calculated_bAnd spectral peak_last. Specifically, when the signal-to-noise ratio of the measurement beat signal is not lower than a second preset threshold, the measurement beat signal s is subjected to_b(t) performing FFT to obtain a frequency domain signal corresponding to the beat frequency signal of the measurement circuit, and calculating the frequency f of the beat frequency signal of the measurement circuit based on the frequency domain signal_bAnd spectral peak_lastAnd according to the frequency f of the beat signal of the measuring circuit_bCalculating to obtain the flight time tau; when the signal-to-noise ratio of the beat frequency signal of the measuring line is lower than a second preset threshold value, carrying out frequency modulation nonlinear term compensation on the transmitting end of the beat frequency signal of the measuring line according to the frequency modulation nonlinear term epsilon (t) of the transmitting signal of the laser to obtain a compensated beat frequency signal s'_b(t); to the compensated beat signal s'_b(t) performing FFT to obtain a frequency domain signal corresponding to the compensated beat signal, and calculating to obtain a beat signal s 'after the measurement circuit compensation based on the frequency domain signal'_bFrequency f of (t)'_bAnd spectral peak_lastAt this time the peak of the spectrum_lastIs the peak value of the frequency domain signal corresponding to the compensated beat frequency signal and is compensated according to the frequency f 'of the beat frequency signal after the compensation of the measuring circuit'_bThe time of flight τ is calculated.

When the frequency modulation is not linear_rateIs greater than a first preset threshold Thr_nonRateUpdating the flight time tau according to the step length p, wherein the updated flight time tau is tau + p, and delaying the updated flight time tau for the frequency modulation nonlinear term epsilon (t) of the signal emitted by the laser to obtain the frequency modulation nonlinear term epsilon (t-tau) of the echo signal corresponding to the measuring path; when the signal-to-noise ratio of the beat frequency signal of the measurement circuit is not lower than a second preset threshold value, the beat frequency signal s of the measurement circuit is subjected to frequency modulation nonlinear term epsilon (t) and frequency modulation nonlinear term epsilon (t-tau)_b(t) performing frequency modulation nonlinear term correction to obtain a first corrected beat signalWhen the signal-to-noise ratio of the beat frequency signal of the measuring path is not lower than a second preset threshold, according to the frequency modulation nonlinear term epsilon (t-tau) pair corresponding to the echo signal of the measuring pathBeat frequency signal s 'compensated by transmit-side frequency modulation nonlinear term'_b(t) correcting the frequency modulation nonlinear term of the receiving end to obtain a second corrected beat frequency signal

For the first corrected beat signalOr second correcting beat signalPerforming FFT to obtain a first corrected beat frequency signalOr second correcting beat signalCorresponding frequency domain signal, calculating a first corrected beat signal based on the frequency domain signalOr second correcting beat signalFrequency and spectral peak of_currAccording to the first corrected beat signalOr second correcting beat signalThe time of flight τ is calculated.

When (peak)_curr-peak_last)/peak_last＞＝Thr_rateTime-of-flight, timeOr second correcting beat signalThe flight time tau obtained by the frequency calculation is updated to obtain the updated flight time, and the steps are repeatedly executed until (peak)_curr-peak_last)/peak_last＜Thr_rate；

When (peak)_curr-peak_last)/peak_last＜Thr_rateAnd calculating a target distance R which is c tau/2 based on the flight time tau calculated according to the frequency of the beat frequency signal after correction, wherein c is the speed of light, namely the distance between the measured target object and the radar.

Fig. 9a shows that the frequency modulation nonlinear correction method effectively improves the accuracy of distance estimation under the condition of frequency modulation nonlinearity. As can be seen from fig. 9b, after the nonlinear iterative correction of the present application, the peak value of the frequency spectrum of the beat signal gradually increases and approaches to the ideal value, so that the frequency domain signal-to-noise ratio of the beat signal can be effectively improved by the nonlinear correction method under the condition of frequency modulation nonlinearity, that is, the farthest ranging range can be effectively improved.

It can be seen that, in the embodiment of the application, the beat frequency signal of the measurement path is subjected to frequency modulation nonlinear correction according to the frequency modulation nonlinear term of the laser emission signal and the frequency modulation nonlinear term of the echo signal of the measurement path, so that the influence of the frequency modulation nonlinearity on the beat frequency signal of the measurement path can be eliminated to a great extent, the accuracy of the flight time obtained based on the corrected beat frequency signal is improved, and the ranging accuracy is further improved.

Referring to fig. 10, fig. 10 is a schematic structural diagram of a ranging apparatus based on frequency modulation nonlinear correction according to an embodiment of the present application. As shown in fig. 10, the distance measuring apparatus 1000 includes:

an obtaining unit 1001 configured to obtain a reference-path beat signal and a measurement-path beat signal, where the reference-path beat signal and the measurement-path beat signal are obtained based on signals emitted by a laser, respectively;

the calculating unit 1002 is configured to calculate frequency modulation nonlinearity according to the reference-path beat signal; calculating according to the beat frequency signal of the measuring path to obtain initial flight time tau;

the calculating unit 1002 is further configured to calculate a frequency modulation nonlinearity term epsilon (t) of the laser emission signal according to the reference-path beat signal when the determining unit 1004 determines that the frequency modulation nonlinearity is not less than the first preset threshold,

the correction unit 1003 is configured to perform nonlinear iterative correction on the measurement path beat signal according to the initial flight time τ and a frequency modulation nonlinear term epsilon (t) of a signal emitted by the laser, so as to obtain a target flight time;

the calculating unit 1002 is configured to calculate a target distance according to the target flight time.

In one possible embodiment, the correction unit 1003 is specifically configured to:

s1: according to time delay flight time tau'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) Time of flight τ'_i-1Is based on time of flight τ_i-1Obtaining;

and S3, determining the flight time of the target according to the corrected beat frequency signal.

In one possible embodiment, in determining the target time of flight from the corrected beat signal, the correction unit 1003 is specifically configured to:

peak when i is 1_i-1For said initial spectral peak, time of flightτ_i-1Is the initial time of flight τ.

In one possible embodiment, the preset condition is (peak)_i-peak_i-1)/peak_i-1＜Thr_rateThe Thr_rateIs a third preset threshold.

In a possible embodiment, the correcting unit 1003 is specifically configured to include:

wherein, when the ith nonlinear iterative computation is carried out, the flight time tau 'is delayed'_i-1Delaying the frequency modulation nonlinear term epsilon (t) of the laser emission signal to obtain the frequency modulation nonlinear term epsilon (t-tau ') corresponding to the echo signal of the measuring line'_i-1) (ii) a Time-of-flight τ'_i-1Is based on time of flight τ_i-1Obtaining;

Wherein, when i is 1, the flight time τ_i-1Is the initial time of flight τ; when i is equal to M, the target time of flight is time of flight τ_i。

In one possible embodiment, the time of flight τ is obtained from the corrected beat signal_iIn an aspect of (1), the calculating unit 1002 is specifically configured to:

In one possible embodiment, the corrected beat signal includes a first corrected beat signal or a second corrected beat signal; the frequency modulation nonlinear term epsilon (t-tau ') corresponding to echo signals according to a measuring line'_i-1) Performing frequency modulation nonlinear correction on the beat frequency signal of the measuring path to obtainIn terms of correcting the beat signal, the correction unit 1003 is specifically configured to:

In a possible embodiment, in terms of calculating the initial time of flight τ from the measured beat signals, the calculating unit 1002 is specifically configured to:

In a possible embodiment, in terms of calculating the frequency modulation nonlinear term ∈ (t) of the laser emission signal according to the reference-path beat signal, the calculating unit 1002 is specifically configured to:

It should be noted that the above units (the acquisition unit 1001, the calculation unit 1002, the correction unit 1003, and the determination unit 1004) are used to execute the relevant steps of the above method. Such as an acquisition unit 1001 for executing the relevant content of step S501, a calculation unit 1002 for executing the relevant content of steps S502 and S504, and a correction unit 1003 and a determination unit 1004 for executing the relevant content of step S503.

In the present embodiment, the distance measuring device 1000 based on frequency modulation nonlinear correction is presented in the form of a unit. An "element" may refer to an application-specific integrated circuit (ASIC), a processor and memory that execute one or more software or firmware programs, an integrated logic circuit, and/or other devices that may provide the described functionality. Further, the above acquisition unit 1001, calculation unit 1002, correction unit 1003, and determination unit 1004 may be realized by the processor 1101 of the ranging apparatus based on frequency modulation nonlinear correction shown in fig. 11.

The ranging apparatus 1100 shown in fig. 11 may be implemented in the structure of fig. 11, and the ranging apparatus 1100 includes at least one processor 1101, at least one memory 1102 and at least one communication interface 1103. The processor 1101, the memory 1102 and the communication interface 1103 are connected through the communication bus and perform communication with each other.

The processor 1101 may be a general purpose Central Processing Unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits for controlling the execution of programs according to the above schemes.

Communication interface 1103 is used for communicating with other devices or communication Networks, such as ethernet, Radio Access Network (RAN), Wireless Local Area Networks (WLAN), etc.

The Memory 1102 may be, but is not limited to, a Read-Only Memory (ROM) or other type of static storage device that can store static information and instructions, a Random Access Memory (RAM) or other type of dynamic storage device that can store information and instructions, an Electrically Erasable Programmable Read-Only Memory (EEPROM), a Compact Disc Read-Only Memory (CD-ROM) or other optical Disc storage, optical Disc storage (including Compact Disc, laser Disc, optical Disc, digital versatile Disc, blu-ray Disc, etc.), magnetic disk storage media or other magnetic storage devices, or any other medium that can be used to carry or store desired program code in the form of instructions or data structures and that can be accessed by a computer. The memory may be self-contained and coupled to the processor via a bus. The memory may also be integral to the processor.

The memory 1102 is used for storing application program codes for executing the above schemes, and the execution of the application program codes is controlled by the processor 1101. The processor 1101 is configured to execute the application code stored in the memory 1102.

The memory 1102 may store code that may perform the ranging methods provided above based on frequency modulated non-linearity correction, such as obtaining a reference trace beat signal and a measurement trace beat signal; calculating according to the beat frequency signal of the reference path to obtain the frequency modulation nonlinearity; calculating according to the beat frequency signal of the measuring path to obtain initial flight time tau; when the frequency modulation nonlinearity is not less than a first preset threshold value, calculating a frequency modulation nonlinearity term epsilon (t) of a laser emission signal according to a reference-path beat signal, and performing nonlinear iterative correction on a measurement-path beat signal according to the initial flight time tau and the frequency modulation nonlinearity term epsilon (t) of the laser emission signal to obtain a target flight time; and calculating the target distance according to the target flight time.

The present application further provides a computer storage medium, where the computer storage medium may store a program, and the program includes some or all of the steps of any of the distance measuring methods based on frequency modulation nonlinear correction described in the above method embodiments when executed.

It should be noted that, for simplicity of description, the above-mentioned method embodiments are described as a series of acts or combination of acts, but those skilled in the art will recognize that the present application is not limited by the order of acts described, as some steps may occur in other orders or concurrently depending on the application. Further, those skilled in the art should also appreciate that the embodiments described in the specification are preferred embodiments and that the acts and modules referred to are not necessarily required in this application.

In the foregoing embodiments, the descriptions of the respective embodiments have respective emphasis, and for parts that are not described in detail in a certain embodiment, reference may be made to related descriptions of other embodiments.

In the embodiments provided in the present application, it should be understood that the disclosed apparatus may be implemented in other manners. For example, the above-described embodiments of the apparatus are merely illustrative, and for example, the division of the units is only one type of division of logical functions, and there may be other divisions when actually implementing, for example, a plurality of units or components may be combined or may be integrated into another system, or some features may be omitted, or not implemented. In addition, the shown or discussed mutual coupling or direct coupling or communication connection may be an indirect coupling or communication connection of some interfaces, devices or units, and may be an electric or other form.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, functional units in the embodiments of the present application may be integrated into one processing unit, or each unit may exist alone physically, or two or more units are integrated into one unit. The integrated unit can be realized in a form of hardware, and can also be realized in a form of a software functional unit.

The integrated unit, if implemented in the form of a software functional unit and sold or used as a stand-alone product, may be stored in a computer readable memory. Based on such understanding, the technical solution of the present application may be substantially implemented or a part of or all or part of the technical solution contributing to the prior art may be embodied in the form of a software product stored in a memory, and including several instructions for causing a computer device (which may be a personal computer, a server, or a network device) to execute all or part of the steps of the method described in the embodiments of the present application. And the aforementioned memory comprises: a U-disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a removable hard disk, a magnetic or optical disk, and other various media capable of storing program codes.

Those skilled in the art will appreciate that all or part of the steps in the methods of the above embodiments may be implemented by associated hardware instructed by a program, which may be stored in a computer-readable memory, which may include: flash Memory disks, Read-Only memories (ROMs), Random Access Memories (RAMs), magnetic or optical disks, and the like.

The foregoing detailed description of the embodiments of the present application has been presented to illustrate the principles and implementations of the present application, and the above description of the embodiments is only provided to help understand the method and the core concept of the present application; meanwhile, for a person skilled in the art, according to the idea of the present application, there may be variations in the specific embodiments and the application scope, and in view of the above, the content of the present specification should not be construed as a limitation to the present application.

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Ranging method based on frequency modulation nonlinear correction and related device

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