CN113238246A - Method and device for simultaneously measuring distance and speed based on pulse sequence and storage medium - Google Patents
Method and device for simultaneously measuring distance and speed based on pulse sequence and storage medium Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
- G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
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- G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
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- G01S17/06—Systems determining position data of a target
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Abstract
The invention provides a method and a device for simultaneously measuring distance and speed based on a pulse sequence and a storage medium. The measuring method comprises the following steps: emitting continuous laser and splitting into two paths, wherein one path is input into a modulator, and the other path is input into an optical attenuator; carrying out amplitude modulation on a laser signal input into a modulator to obtain a pulse sequence with random positions; amplifying the modulated laser signal, collimating the amplified laser signal, and transmitting the collimated laser signal to a scanning device of a laser radar as a transmitting signal to project the transmitting signal to a target to be detected so as to generate an echo signal; performing optical attenuation on a laser signal input into an optical attenuator, and taking the attenuated signal as a reference signal; receiving and coupling echo signals, and sending the echo signals and reference signals to a combiner for frequency mixing; performing photoelectric conversion on the mixed signal to output an electric signal; performing data accumulation calculation on the output electric signals, and analyzing to obtain the distance of the target to be detected; and carrying out non-equal-interval sampling signal frequency spectrum calculation on the output electric signal, and analyzing to obtain the movement speed of the target to be detected.
Description
Technical Field
The invention relates to the field of speed and distance measurement of laser radars, in particular to a method and a device for simultaneously measuring distance and speed based on a pulse sequence and a storage medium.
Background
Road environment perception is a core technology for realizing intelligent driving, and comprises the distance, the speed and the direction of a target. The millimeter wave radar realizes simultaneous measurement of the distance and the speed of a target by using a mode of modulating continuous waves by using triangular chirp frequency, however, the millimeter wave radar has low spatial resolution, only measures hundreds of spatial positions in unit time, and the length of a measurement signal is several milliseconds. The main purpose of developing the laser radar is to improve the resolution of space imaging, so that the spatial point measured in unit time is much larger than that of the millimeter wave radar, the FMCW waveform is too long, and the technical requirement of improving the spatial resolution of the laser radar cannot be met. Because one pulse width cannot cover one period of a Doppler signal, the traditional single pulse mode cannot realize Doppler velocity measurement, and only provides velocity estimation for a terminal in a mode of calculating the change rate of a target distance, so that the error is large and the consumed time is long.
Disclosure of Invention
The invention provides a method and a device for simultaneously measuring distance and speed based on a pulse sequence and a storage medium, aiming at solving the current problems that the existing laser radar cannot measure distance and speed by using Doppler at the same time.
The purpose of the invention is realized by the following technical scheme:
the invention provides a distance and speed simultaneous measurement method based on a pulse sequence, which is characterized by comprising the following steps of: step 1, emitting continuous laser, splitting the continuous laser into two paths through a splitter, wherein one path of laser is input into a modulator, and the other path of laser is input into an optical attenuator; step 2, amplitude modulation is carried out on the input laser signal by using a modulator, so that the laser signal is modulated into a pulse sequence with random positions in a continuous light mode; step 3, amplifying the modulated laser signal output by the modulator, collimating the amplified laser signal and transmitting the collimated laser signal to a scanning device of the laser radar as a transmitting signal, and projecting the transmitting signal to a target to be detected by the scanning device to generate an echo signal; step 4, performing optical attenuation on the input laser signal by using an optical attenuator, and taking the obtained attenuated signal as a reference signal; step 5, coupling echo signals from the target to be detected, and sending the echo signals and the reference signals to a combiner for frequency mixing; step 6, inputting the mixed signal into a photoelectric converter, performing photoelectric conversion and outputting an electric signal; step 7, performing data accumulation calculation on the electric signals output by the photoelectric converter, and analyzing to obtain the distance of the target to be measured; and 8, carrying out non-equal-interval sampling signal frequency spectrum calculation on the electric signal output by the photoelectric converter, and analyzing to obtain the movement speed of the target to be detected.
Further, in the method for simultaneously measuring distance and speed based on pulse sequences provided by the present invention, the method may further have the following characteristics: the specific method of amplitude modulation in step 2 is as follows:
step 2-1, according to the number of space points required to be measured by the laser radar in unit time, determining the time length allocated for completing single measurement: setting the number of space points required to be measured in unit time as M, and setting the maximum time required for completing single measurement as 1/M second; the maximum distance which can be measured by the laser radar is d meters, the maximum flight time of laser is tau is 2d/c seconds, and c represents the speed of light, so that the maximum value of the length of a pulse sequence which completes single measurement is T1/M-tau seconds;
step 2-2, modulating according to a preset format to obtain a pulse sequence: firstly, dividing the time with the length tau in the time sequence with the length M as waiting time, then dividing the rest time in the time sequence into N time slots delta T with equal duration according to the number N of pulses, then placing a pulse at a random position in each time slot and storing the interval between adjacent pulses into an array delta tau.
Further, in the method for simultaneously measuring distance and speed based on pulse sequences provided by the present invention, the method may further have the following characteristics: amplifying the modulated laser signal in the step 3 as follows: the peak power of the pulse train is amplified.
Further, in the method for simultaneously measuring distance and speed based on pulse sequences provided by the present invention, the method may further have the following characteristics: in step 4, the light attenuation is specifically as follows: the input laser signal is attenuated to half the light intensity of the weakest echo signal desired to be detected.
Further, in the method for simultaneously measuring distance and speed based on pulse sequences provided by the present invention, the method may further have the following characteristics: the relationship among the reference signal, the echo signal and the electric signal is as follows:
let the reference signal be
Wherein E1Represents the intensity of light; f is the frequency of the light;
is a random initial phase; t is time;
setting the echo signal as
Wherein E2(t) is the light intensity of the echo signal, expressed as a function of time t; f. ofDDoppler frequency generated for the movement of the target to be measured;
indicating a change phase caused by a distance change of the target to be measured;
the power of the optical signal irradiated to the photosensitive surface of the photoelectric converter is
The electric signal output by the photoelectric converter is filtered to remove high frequency and direct current to obtain an output formula as follows:
further, the distance velocity based on the pulse sequence provided in the inventionThe simultaneous measurement method may further have the following features: the specific method for data accumulation calculation in step 7 is as follows: sampling the electric signal from the start moment of a pulse sequence of the transmitted signal, sampling the electric signal, wherein the sampling period is the pulse width, the sampling length is 1/M second, and storing the adopted data in an array s (n); according to a predetermined data accumulation rule, the array s (n) is placed in the first row, and then the array s (n) is shifted to the left by delta tau1The resulting new sequence is placed in the second row, and the second row group is shifted to the left by Δ τ2Placing the obtained new sequence in a third row, sequentially shifting for a plurality of times (repeating the shift placement process for N-1 times according to the method, wherein N is the number of pulses in the pulse sequence), and finally adding all the arrays; after the arrays are added, the noise phases of all time points can be mutually offset, the maximum peak value can be obtained by in-phase addition of all pulse sequences at the position corresponding to the laser flight time delta L, and the distance of the target to be measured can be calculated according to the laser flight time delta L of the maximum peak value.
Further, in the method for simultaneously measuring distance and speed based on pulse sequences provided by the present invention, the method may further have the following characteristics: the specific method for calculating the spectrum of the non-equidistant sampling signal in the step 8 is as follows: sampling the electrical signal at unequal intervals, and obtaining discrete time data f (t) by samplingi) Defining Fourier transform, and obtaining a non-equidistant signal spectrum calculation formula as follows:
wherein Δ TiIs the sampling interval; i corresponds to the ith pulse, i is 1, …, N; t is tiIs the sampling instant of the electrical signal; omega is the frequency of the signal; j is an imaginary unit; e is an exponential function, the frequency spectrum F (omega) of the non-equidistant sampling signal calculated by the above formula is the Doppler frequency of the movement of the target to be measured, and the movement speed of the target to be measured can be calculated according to the Doppler frequency.
The invention also provides a device for simultaneously measuring the distance and the speed based on the pulse sequence, which is applied to the method for simultaneously measuring the distance and the speed based on the pulse sequence and is characterized by comprising the following steps: the device comprises a laser, a beam splitter, an amplifier, a modulator, a collimating lens, an optical attenuator, a wave combiner, a coupling lens, a photoelectric converter and a signal processor, wherein the laser is used for generating continuous laser; the continuous laser enters a light splitter, and the light splitter splits a laser beam into two paths, wherein one path of laser is input into a modulator, and the other path of laser is input into an optical attenuator; the modulator is used for modulating an input laser signal, the modulated laser signal is input into the amplifier for amplification, then is transmitted to the collimating lens for collimation, and is sent to a scanning device of the laser radar as a transmitting signal after being collimated, and the transmitting signal is projected to a target to be detected by the scanning device; the optical attenuator is used for attenuating the light intensity of the input laser signal, and the attenuated signal is used as a reference signal and is sent to the wave combiner; the coupling lens is used for receiving an echo signal from a target to be detected, and the echo signal is coupled to the optical fiber through the coupling lens and then is sent to the combiner together with the reference signal for frequency mixing; the signals mixed by the wave combiner are output to a photoelectric converter, and the photoelectric converter is used for converting optical signals into electric signals; the signal processor is used for analyzing and processing the electric signal output by the photoelectric converter.
The present invention also provides a computer-readable storage medium characterized in that: the computer-readable storage medium has stored therein a program for simultaneous distance and velocity measurement, which when executed by a processor implements the steps of the above-described pulse sequence-based simultaneous distance and velocity measurement method.
The invention has the beneficial effects that:
according to the distance and speed simultaneous measurement method based on the pulse sequence, the traditional double detectors are simplified into the single detector by introducing the optical attenuator, and a pulse position modulation method, a data accumulation method and a non-equal interval Fourier transform method are provided. Tests prove that the method and the device can be used for sensing the road target information and have reliability. The invention ensures that the length of the measurement signal meets the requirement of intelligent driving on the spatial resolution, and has wider popularization value.
Drawings
FIG. 1 is a schematic structural diagram of a pulse sequence-based simultaneous distance and velocity measuring apparatus according to the present invention;
FIG. 2 is a schematic diagram of a pulse sequence position modulation method in the pulse sequence-based range-velocity simultaneous measurement method of the present invention;
FIG. 3 is a schematic diagram of a data accumulation method in the simultaneous range and velocity measurement method based on pulse sequences according to the present invention;
FIG. 4 is a schematic diagram of signal strength output by the photoelectric converter under the condition of no noise in the method for simultaneously measuring distance and speed based on the pulse sequence according to the embodiment of the invention;
FIG. 5 shows a peak value corresponding to the laser flight time obtained by data accumulation in a pulse sequence-based range-velocity simultaneous measurement method according to an embodiment of the present invention;
FIG. 6 is a frequency spectrum obtained by sampling data at unequal intervals in a method for simultaneously measuring range and velocity based on a pulse sequence according to an embodiment of the present invention;
FIG. 7 is a graph of anti-noise performance analysis of velocity measurements for a pulse sequence based range velocity simultaneous measurement method of an embodiment of the present invention;
FIG. 8 is an analysis graph of the anti-noise performance of distance measurement for a pulse sequence based simultaneous distance and velocity measurement method according to an embodiment of the present invention;
fig. 9 is an error analysis diagram for calculating a frequency using non-equally spaced data in a range-velocity simultaneous measurement method based on a pulse sequence according to an embodiment of the present invention.
In FIG. 1, the labels: 1-a laser; 2-an optical fiber; 3-a beam splitter; 4-an optical fiber; 5-a modulator; 6-an amplifier; 7-a collimating lens; 8-an optical attenuator; 9-a combiner; 10-photoelectric converter and signal processor; 11-coupling lens.
Detailed Description
In order to make the technical means, the creation features, the achievement objects and the functions of the present invention easy to understand, the following embodiments are provided to describe the pulse sequence based distance and velocity simultaneous measurement method and apparatus and the storage medium of the present invention in detail with reference to the accompanying drawings.
As shown in fig. 1, a simultaneous distance and velocity measuring apparatus based on a pulse sequence includes: the optical system comprises a laser 1, a beam splitter 3, a modulator 5, an amplifier 6, a collimating lens 7, an optical attenuator 8, a combiner 9, a photoelectric converter and signal processor 10 and a coupling lens 11.
The laser 1 is used for generating continuous laser light. The beam splitter 3 is connected to the laser 1. The continuous laser enters the optical splitter 3, the optical splitter 3 splits the laser beam into two paths, wherein one path of laser (more than 99%) is input into the modulator 5, and the other path of laser (less than 1%) is input into the optical attenuator 8.
The modulator 5 is used for modulating the input laser signal, the modulated laser signal is input into the amplifier 6 for amplification, then is input into the collimating lens for collimation 7, and is sent into a scanning device (not shown) of the laser radar after being collimated to be used as an emission signal, and the emission signal is projected to a target to be measured by the scanning device. The optical attenuator 8 is used to attenuate the optical intensity of the input laser signal, and the attenuated signal is used as a reference signal.
The coupling lens 11 is used for receiving an echo signal from a target to be measured, and the echo signal is coupled to the optical fiber through the coupling lens 11 and then sent to the combiner 9 together with the reference signal for frequency mixing. The signal mixed by the combiner 9 is output to a photoelectric converter for converting an optical signal into an electrical signal. The signal processor is connected with the output end of the photoelectric converter and is used for analyzing and processing the electric signals output by the photoelectric converter.
The embodiment also provides a distance and speed simultaneous measurement method based on the pulse sequence, which is carried out by adopting the measurement device for simultaneously measuring the distance and speed based on the pulse sequence. The method comprises the following steps:
And 2, modulating the amplitude of the input laser signal by using a modulator 5 to enable the laser signal to be modulated into a pulse sequence with random positions by continuous light.
The specific method for amplitude modulation of the laser signal is as follows:
step 2-1, according to the number of space points required to be measured by the laser radar in unit time, determining the time length allocated for completing single measurement:
setting the number of space points required to be measured in unit time as M, and setting the maximum time required for completing single measurement as 1/M second;
the maximum distance which can be measured by the laser radar is d meters, the maximum flight time of laser is tau is 2d/c seconds, and c represents the speed of light, so that the maximum value of the length of a pulse sequence which completes single measurement is T1/M-tau seconds;
step 2-2, as shown in fig. 2, obtaining a pulse sequence by modulating according to a predetermined format:
firstly, dividing the time with the length tau in the time sequence with the length M as waiting time, then dividing the rest time in the time sequence into N time slots delta T with equal duration according to the number N of pulses, then placing a pulse at a random position in each time slot and storing the interval between adjacent pulses into an array delta tau. P in FIG. 21Represents a random position within the 1 st time slot in the time sequence; piRepresenting a random position in the ith time slot in the time sequence; pi+1Representing the random position in the (i + 1) th time slot in the time sequence; delta tauiIndicating the pulse interval determined by the random position in the ith slot and the random position in the (i + 1) th slot.
Then, the amplified pulse sequence is collimated by the collimating lens 7 and then transmitted to a scanning device of the laser radar as a transmission signal, and the transmission signal is projected to a target to be detected by the scanning device to generate an echo signal.
And step 4, attenuating the input laser signal by using the optical attenuator 8, attenuating the input laser signal to half of the light intensity of the weakest echo signal expected to be detected, and using the attenuated signal output by the optical attenuator 8 as a reference signal.
And step 5, the coupling lens 11 receives the echo signal from the target to be detected, couples the echo signal to the optical fiber, and sends the echo signal and the reference signal to the combiner 9 for frequency mixing.
And 6, performing photoelectric conversion on the mixed signal through a photoelectric converter to obtain an electric signal.
The relationship between the reference signal, the echo signal, and the electrical signal is as follows:
let the reference signal be
Wherein E1Representing the light intensity of the reference signal; f is the frequency of the reference signal;
is a random initial phase; t is time;
setting the echo signal as
Wherein E2Is the light intensity of the echo signal, expressed as a function of time t; f. ofDDoppler frequency generated for the movement of the target to be measured;
indicating a change phase caused by a distance change of the target to be measured;
the power of the optical signal irradiated to the photosensitive surface of the photoelectric converter is
Neglecting the constant factor of photoelectric conversion efficiency, the electric signal output by the photoelectric converter is filtered to remove high frequency and direct current to obtain the output formula
Compared with the direct detection of the output of the photoelectric converter, the Doppler frequency fluctuation term is added in the above formula. Under the condition of coherent detection, if E1 is too large, the output voltage of part of pulses is lower than direct current, and the pulses have random positive and negative values as noise, so that the calculation of the flight time of the laser by data accumulation is not facilitated. For this reason, unlike conventional coherent detection, which amplifies the signal light by appropriately increasing the reference signal power, an optical attenuator is used in the present apparatus to attenuate the reference light to half the intensity value of the weakest echo.
And 7, performing data accumulation calculation on the electric signals output by the photoelectric converter through the signal processor, and analyzing to obtain the distance of the target to be detected.
The specific method of data accumulation calculation is as follows:
sampling the electric signal from the starting moment of the pulse sequence of the transmitted signal, and storing the adopted data in an array s (n);
as shown in fig. 3, according to a predetermined data accumulation rule: place array s (n) in the first row, then shift array s (n) to the left by Δ τ1The resulting new sequence is placed in the second row, and the second row group is shifted to the left by Δ τ2The obtained new sequence is placed in the third row, and is sequentially shifted for a plurality of times (the shifting and placing process is repeated for N-1 times according to the method, wherein N is the number of pulses in the pulse sequence), and finally all the arrays are added. The waveform diagram of the lowest array in fig. 3 represents the array obtained by adding all the arrays.
After the data groups are added, the noise phases of all time points can be mutually offset, the maximum peak value can be obtained by in-phase addition of all pulse sequences at the position corresponding to the laser flight time delta L, the probability of pulse existence at other positions is very low, small fluctuation exists, and the pulse is covered by noise. Therefore, the laser flight time Δ L of the maximum peak is based on
c represents the light speed, namely the distance d of the target to be measured can be calculated.
The specific method for calculating the frequency spectrum of the non-equidistant sampling signal is as follows:
sampling the electrical signal at unequal intervals, and obtaining discrete time data f (t) by samplingi) Defining Fourier transform, and obtaining a non-equidistant signal spectrum calculation formula as follows:
wherein Δ TiIs the sampling interval; i corresponds to the ith pulse, i is 1, …, N; t is tiIs the sampling instant of the electrical signal; omega is the angular frequency of the signal; j is an imaginary unit; e is an exponential function;
the frequency spectrum F (omega) of the non-equidistant sampling signal calculated by the formula is the Doppler frequency of the movement of the target to be measured according to FdAnd calculating the movement speed of the target to be measured by using the Doppler frequency, v as the target speed and lambda as the wavelength of the signal.
The above equation calculates the doppler frequency corresponding to the moving speed of the target from the non-equally spaced sampling data, and does not care about the magnitude of the spectral amplitude (light intensity), so the non-equally spaced sampling spectral calculation equation can be used to find the magnitude of the doppler frequency. The pulse sequence is regarded as the sampling pulse of the Doppler signal, the Doppler sampling is carried out to obtain undersampled data, and the non-equidistant Fourier transform method in the invention is effective to the frequency calculation of the undersampled signal.
The present embodiment further provides a computer-readable storage medium, in which a program for simultaneously measuring distance and speed is stored, and when the program for simultaneously measuring distance and speed is executed by a processor of a computer, the steps of the method for simultaneously measuring distance and speed based on pulse sequences are implemented.
< principle verification Using examples >
With reference to the rule of fig. 2, 100 pulses are allocated within a time duration of 4 μ s, and the pulse amplitude of the retrieved wave signal is 1, that is:
optical amplitude E of reference signal10.02, and the waveform of the output signal of the photoelectric converter after high frequency and direct current are filtered out is shown in fig. 4 under the condition of neglecting the noise of the receiver. The Doppler frequency produces a modulation effect on the amplitude of the pulse, the amplitude of the pulse changes according to the cosine law, and the Doppler signal is sampled at the pulse position.
The 100 unequally spaced pulse sequences shown in fig. 4 are inserted into a 100ns delay, and data accumulation is performed according to the method shown in fig. 3, and the obtained result is shown in fig. 5.
As can be seen from fig. 5, at the position corresponding to the time delay of 100ns, the accumulated result obtains a distinct peak, while at other time positions there is a slight fluctuation, consistent with the schematic result of fig. 3. The time delay is the laser flight time corresponding to the target distance in the laser radar measurement, and is an undetermined target value in the measurement process. Although the doppler frequency has a modulating effect on the amplitude of the pulse sequence, the peak value of the data accumulation is not affected on average because of the increase and decrease of the amplitude.
After the position of a pulse sequence is determined through data accumulation, the amplitude of each pulse is corrected according to a non-equal-interval sampling signal spectrum calculation formula by using pulse interval data from a modulator, and the Doppler signal frequency of a modulation pulse peak value can be obtained by using Fourier transform on the corrected data. Fig. 6 shows a signal spectrum diagram of a doppler signal with a frequency of 12.9MHz in a noise-free case, which is calculated according to a non-equidistant sampling spectrum calculation formula and fourier transform. 10 ten thousand groups of modulation pulse data are randomly generated, pulse peak values are modulated by different Doppler frequencies, the frequency is calculated according to the method, and the error between the frequency and the actual frequency is statistically analyzed to obtain the maximum error of 66.67 kHz. The wavelength of the light source of the common laser radar is 1550nm, and 66.67kHz corresponds to the speed error of 0.052m/s, which is far lower than the speed error range allowed by vehicle motion planning.
< verification of reliability of method for measuring distance and velocity simultaneously >
The percentage of speed and distance that are measured correctly at different signal-to-noise ratios is an important indicator of lidar design. The first term on the right side in the output formula of the photoelectric converter obtained by removing the high frequency and the direct current is a direct current term of the optical power, which represents the average optical power of the pulses in the pulse sequence, and the magnitude of the direct current term determines the signal-to-noise ratio of the distance measurement signal output by the receiving end. The second term is the cosine term of the Doppler signal, the amplitude E of which2(t)E1The signal-to-noise ratio for calculating the doppler frequency signal is determined.
Strength of E2The current generated by the light on the photoelectric converter is:
I＝ηE2
where η is the photoelectric conversion efficiency.
The signal power generated by this current on the trans-impedance amplifier of the receiver is:
P＝I2R
wherein R is the amplification factor of the trans-impedance amplifier.
Substituting the current calculation formula into the power calculation formula to obtain:
P＝η2RE4
i.e. the power of the electrical signal and E4There is a linear relationship between them.
Noise power of the receiver being a constant value
Regardless of the constant coefficients, the signal-to-noise ratio of the distance measurement signal can be defined as:
e2 represents the peak value of E2(t) in the output formula of the photoelectric converter. Also, the signal-to-noise ratio of the doppler signal is defined as:
< verification of reliability of speed measurement >
Doppler signals with four frequencies of 20MHz, 40MHz, 80MHz and 129MHz are taken, the anti-noise performance calculated by the Fourier frequency of non-equidistant data of the Doppler signals is analyzed, and the result is shown in figure 7. Referring to fig. 7, the detection error probability of the ordinate in the graph indicates the occurrence probability that the error between the calculated frequency and the actual doppler frequency is larger than 70kHz (the error of the correct measurement given in the previous section does not exceed 66.67kHz), and curves in the graph are obtained by counting the number of times of errors occurring in 10 ten thousand frequency calculations under each signal-to-noise ratio sampling point, and obviously, the change of the frequency does not affect the anti-noise performance of the frequency calculation.
The average time interval of the pulses in the specific embodiment is 40ns, and according to the nyquist theorem, under the condition of sampling at equal intervals, the sampling frequency of the 129MHz signal should be more than 258MHz, namely, the sampling interval should be less than 3.88ns so as to avoid frequency overlapping. Therefore, in the embodiment, the sampling of the doppler signal is under-sampling, and no frequency overlap occurs in the case of non-equally spaced fourier calculation, which shows that the pulse sequence-based range-velocity simultaneous measurement method of the present invention can be used for analyzing and calculating the frequency of the under-sampled signal.
< verification of reliability of distance measurement >
The method for simultaneously measuring the range and velocity based on the pulse sequence is shown in fig. 8, in terms of distance measurement, by calculating the probability of data accumulation statistical error detection under different signal-to-noise ratios. In the calculation, the pulse delay is set to a certain value, and the pulse peak value obtained by data accumulation is inconsistent with the set delay value, so that the detection error is counted. Like the detection error probability curve of the frequency, the detection error probability curve of the distance measurement is obtained by calculating 10 ten thousand times of data accumulation at each signal-to-noise ratio sampling point and counting the occurrence times of the detection error.
To ensure the output s of the receivero(t) is greater than zero, and the high frequency and the direct current are removed to obtain the local reference signal amplitude E in the output mode of the photoelectric converter1It should not be too large. If there is s at some timeoAnd (t) is less than zero, the amplitude phase relation between the signal and the noise at different time points is in-phase or in opposite phase, and the data accumulation cannot determine the delay of the pulse sequence under low signal-to-noise ratio. The amplitude E of the reference signal is obtained by removing the high frequency and the direct current to obtain the output mode of the photoelectric converter1Not more than half the minimum received light intensity, so the doppler signal intensity for fourier calculation may be taken as
I.e. the signal-to-noise ratio of the signals used for calculating distance and velocity is the same in the worst case. As can be seen from fig. 8, in order to ensure that no error occurs in detection, the signal-to-noise ratio required for speed measurement is lower than that required for distance measurement, and therefore, in system design, the strength of the local reference signal is selected as the lowest strength that ensures that the speed is reliably measured.
< analysis of distance measurement error >
The error of the distance measurement is related to the width of the pulse in the pulse sequence, and the pulse width is selected to be 1ns in the embodiment of the invention, and the sampling rate is 1GHz, so that the maximum error of the distance measurement is 30 cm. The accuracy of the distance measurement can be improved by increasing the sampling rate or using a data delay line, and the measurement principle is consistent with the simulation of the invention.
< speed measurement error verification >
Compared with the Fourier algorithm of the equally-spaced data, the method for simultaneously measuring the distance and the speed based on the pulse sequence has the advantages that the error performance is completely consistent with the error range of the distance and the speed based on the pulse sequence through a large amount of simulation verification. Referring to fig. 9, in the case that the initial phase is 0, fig. 9 shows frequency error data obtained by using a non-equidistant spectrum calculation method for signals with frequencies between 20MHz and 50MHz, and it can be seen that the error varies periodically within a certain range. Varying the initial phase within the range of 0 to 2 pi for a certain frequency also results in an error varying periodically within this range. The maximum error shown in the figure is 66.67kHz, and the corresponding speed error is 0.052m/s, so that the intelligent driving environment perception requirement is met.
The above embodiments are merely preferred examples of the present invention, and are not intended to limit the scope of the present invention. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention shall fall within the protection scope of the present invention.
Claims (9)
1. A distance and speed simultaneous measurement method based on a pulse sequence is characterized by comprising the following steps:
step 1, emitting continuous laser, splitting the continuous laser into two paths through a splitter, wherein one path of laser is input into a modulator, and the other path of laser is input into an optical attenuator;
step 2, the modulator is used for carrying out amplitude modulation on the input laser signal, so that the laser signal is modulated into a pulse sequence with random positions in a continuous light mode;
step 3, amplifying the modulated laser signal output by the modulator, collimating the amplified laser signal to serve as a transmitting signal, transmitting the transmitting signal to a scanning device of the laser radar, and projecting the transmitting signal to a target to be detected by the scanning device to generate an echo signal;
step 4, performing optical attenuation on the input laser signal by using the optical attenuator, and taking the obtained attenuated signal as a reference signal;
step 5, coupling the echo signal from the target to be detected, and sending the echo signal and the reference signal to a combiner for frequency mixing;
step 6, inputting the mixed signal into a photoelectric converter, performing photoelectric conversion and outputting an electric signal;
step 7, performing data accumulation calculation on the electric signals output by the photoelectric converter, and analyzing to obtain the distance of the target to be detected;
and 8, carrying out non-equal-interval sampling signal frequency spectrum calculation on the electric signal output by the photoelectric converter, and analyzing to obtain the movement speed of the target to be detected.
2. The pulse sequence-based simultaneous distance and velocity measuring method according to claim 1, characterized in that:
the specific method for amplitude modulation of the laser signal in step 2 is as follows:
step 2-1, according to the number of space points required to be measured by the laser radar in unit time, determining the time length allocated for completing single measurement:
setting the number of space points required to be measured in unit time as M, and setting the maximum time required for completing single measurement as 1/M second;
the maximum distance which can be measured by the laser radar is d meters, the maximum flight time of laser is tau is 2d/c seconds, and c represents the speed of light, so that the maximum value of the length of a pulse sequence which completes single measurement is T1/M-tau seconds;
step 2-2, modulating according to a preset format to obtain a pulse sequence:
firstly, dividing the time with the length tau in the time sequence with the length M as waiting time, then dividing the rest time in the time sequence into N time slots delta T with equal duration according to the number N of pulses, then placing a pulse at a random position in each time slot and storing the interval between adjacent pulses into an array delta tau.
3. The pulse sequence-based simultaneous distance and velocity measuring method according to claim 2, characterized in that:
amplifying the modulated laser signal in the step 3 as follows: the peak power of the pulse train is amplified.
4. The pulse sequence-based simultaneous distance and velocity measuring method according to claim 1, characterized in that:
wherein, the light attenuation in step 4 specifically is: the input laser signal is attenuated to half the light intensity of the weakest echo signal desired to be detected.
5. The pulse sequence-based simultaneous distance and velocity measuring method according to claim 1, characterized in that:
wherein the relationship among the reference signal, the echo signal and the electric signal is as follows:
let the reference signal be
Wherein E1Represents the intensity of light; f is the frequency of the light; phi is a1Is a random initial phase; t is time;
setting the echo signal as
Wherein E2(t) is the light intensity of the echo signal, expressed as a function of time t; f. ofDDoppler frequency generated for the movement of the target to be measured;
indicating a change phase caused by a distance change of the target to be measured;
the power of the optical signal irradiated to the photosensitive surface of the photoelectric converter is
The electric signal output by the photoelectric converter is filtered to remove high frequency and direct current to obtain an output formula as follows:
6. the pulse sequence-based simultaneous distance and velocity measuring method according to claim 1, characterized in that:
the specific method for the data accumulation calculation in the step 7 is as follows:
sampling the electric signal from the starting moment of the pulse sequence of the emission signal, wherein the sampling period is the pulse width, the sampling length is 1/M second, and the adopted data is stored in an array s (n);
according to a predetermined data accumulation rule, the array s (n) is placed in the first row, and then the array s (n) is shifted to the left by delta tau1The resulting new sequence is placed in the second row, and the second row group is shifted to the left by Δ τ2Placing the obtained new sequence in a third row, sequentially shifting for a plurality of times, and finally adding all the arrays;
after the arrays are added, the noise phases of all time points can be mutually offset, the maximum peak value can be obtained by in-phase addition of all pulse sequences at the position corresponding to the laser flight time delta L, and the distance of the target to be measured can be calculated according to the laser flight time delta L of the maximum peak value.
7. The pulse sequence-based simultaneous distance and velocity measuring method according to claim 1, characterized in that:
the specific method for calculating the spectrum of the non-equidistant sampling signal in the step 8 is as follows:
sampling the electric signal at unequal intervals, and obtaining discrete time data f (t) by samplingi) Defining Fourier transform, and obtaining a non-equidistant signal spectrum calculation formula as follows:
wherein Δ TiIs the sampling interval; i corresponds to the ith pulse, i is 1, …, N; t is tiIs the sampling instant of the electrical signal; omega is the frequency of the signal; j is an imaginary unit; e is an exponential function;
the frequency spectrum F (ω) of the non-equidistant sampling signal calculated by the above formula is the doppler frequency of the movement of the target to be measured, and the movement speed of the target to be measured can be calculated according to the doppler frequency.
8. A simultaneous distance and velocity measuring apparatus based on a pulse sequence, applied to the simultaneous distance and velocity measuring method based on a pulse sequence according to any one of claims 1 to 7, comprising: a laser, a beam splitter, an amplifier, a modulator, a collimating lens, an optical attenuator, a wave combiner, a coupling lens, a photoelectric converter and a signal processor,
wherein the laser is used for generating continuous laser light;
the continuous laser enters the optical splitter, and the optical splitter splits a laser beam into two paths, wherein one path of laser is input into the modulator, and the other path of laser is input into the optical attenuator;
the modulator is used for modulating an input laser signal, the modulated laser signal is input into the amplifier for amplification, then is transmitted to the collimating lens for collimation, and is sent to a scanning device of a laser radar as an emission signal after being collimated, and the emission signal is projected to a target to be detected by the scanning device;
the optical attenuator is used for attenuating the light intensity of the input laser signal, and the attenuated signal is used as a reference signal and is sent to the wave combiner;
the coupling lens is used for receiving an echo signal from the target to be detected, and the echo signal is coupled to an optical fiber through the coupling lens and then is sent to the wave combiner together with the reference signal for frequency mixing;
the signal mixed by the wave combiner is output to the photoelectric converter, and the photoelectric converter is used for converting an optical signal into an electric signal;
the signal processor is used for analyzing and processing the electric signals output by the photoelectric converter.
9. A computer-readable storage medium characterized by: the computer-readable storage medium has stored therein a program for simultaneous distance and velocity measurement, which when executed by a processor implements the steps of the pulse sequence-based simultaneous distance and velocity measurement method according to any one of claims 1 to 8.
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