Method, device and storage medium for simultaneous distance and speed measurement based on pulse sequence

Abstract

The present invention provides a distance and speed simultaneous measurement method and device and storage medium based on a pulse sequence. The measurement method includes the following steps: emitting continuous laser and splitting it into two paths, one path is input into a modulator, and the other path is input into an optical attenuator; performing amplitude modulation on the laser signal input into the modulator to modulate it into a pulse sequence with random positions; amplifying the modulated laser signal, and then transmitting it as a transmission signal to a scanning device of a laser radar after collimation to project it onto a target to be measured, generating an echo signal; performing optical attenuation on the laser signal input into the optical attenuator, and using the attenuated signal as a reference signal; receiving and coupling the echo signal, and sending it together with the reference signal into a combiner for mixing; performing photoelectric conversion on the mixed signal to output an electrical signal; performing data accumulation calculation on the output electrical signal, and analyzing to obtain the distance of the target to be measured; performing non-equally spaced sampling signal spectrum calculation on the output electrical signal, and analyzing to obtain the movement speed of the target to be measured.

Description

Technical Field

[0001] The present invention relates to the field of speed and distance measurement of laser radar, and in particular to a method and device for simultaneous distance and speed measurement based on a pulse sequence and a storage medium. Background Art

[0002] Road environment perception is the core technology for realizing intelligent driving, including the distance, speed and direction of the target. Millimeter-wave radar uses triangular chirp frequency modulation continuous wave to achieve simultaneous measurement of the distance and speed of the target. However, the spatial resolution of millimeter-wave radar is low, and only a few hundred spatial positions are measured per unit time. The length of its measurement signal is several milliseconds. The main purpose of developing lidar is to improve the resolution of spatial imaging. Therefore, the number of spatial points measured per unit time is much larger than that of millimeter-wave radar. The FMCW waveform is too long and cannot meet the technical requirements for improving the spatial resolution of lidar. Since a pulse width cannot cover a cycle of the Doppler signal, the traditional single-pulse method cannot achieve Doppler speed measurement. It can only provide the terminal with a speed estimate by calculating the target distance change rate. The error is large and the time consumed is long. Summary of the invention

[0003] In view of the problem that the existing laser radar cannot use Doppler to measure speed while measuring distance, the present invention proposes a method and device for simultaneous measurement of distance and speed based on a pulse sequence and a storage medium. The purpose of the present invention is to solve the current problem so as to achieve simultaneous measurement of target distance and speed in a road environment and ensure that the length of the measurement signal meets the requirements of intelligent driving for spatial resolution.

[0004] The objective of the present invention is achieved through the following technical solutions:

[0005] The present invention provides a method for simultaneously measuring distance and speed based on a pulse sequence, which is characterized by comprising the following steps: step 1, emitting a continuous laser, splitting the continuous laser into two paths through a beam splitter, wherein one path of the laser is input into a modulator, and the other path of the laser is input into an optical attenuator; step 2, using a modulator to perform amplitude modulation on the input laser signal, so that it is modulated from a continuous light form into a pulse sequence with random positions; step 3, amplifying the modulated laser signal output by the modulator, and then emitting it as a transmission signal to a scanning device of a laser radar after collimation, and the scanning device projects the transmission signal onto a light source to be measured. target, generating an echo signal; step 4, using an optical attenuator to perform optical attenuation on the input laser signal, and using the attenuated signal as a reference signal; step 5, coupling the echo signal from the target to be measured, and sending it to the combiner together with the reference signal for mixing; step 6, inputting the mixed signal into the photoelectric converter, performing photoelectric conversion to output an electrical signal; step 7, performing data accumulation calculation on the electrical signal output by the photoelectric converter, and analyzing to obtain the distance of the target to be measured; step 8, performing non-uniformly spaced sampling signal spectrum calculation on the electrical signal output by the photoelectric converter, and analyzing to obtain the movement speed of the target to be measured.

[0006] Furthermore, in the method for simultaneous distance and speed measurement based on a pulse sequence provided by the present invention, there may also be such a feature: wherein the specific method of amplitude modulation in step 2 is as follows:

[0007] Step 2-1, determine the time length allocated to complete a single measurement based on the number of spatial points that the laser radar is required to measure in a unit time: suppose the number of spatial points required to be measured in a unit time is M, then the maximum time required to complete a single measurement is 1 / M seconds; suppose the maximum distance that the laser radar is required to measure is d meters, the maximum laser flight time is τ = 2d / c seconds, c represents the speed of light, then the maximum value of the pulse sequence length to complete a single measurement is T = 1 / M-τ seconds;

[0008] Step 2-2, modulate according to a predetermined format to obtain a pulse sequence: first, divide the last time of length τ in the time sequence of length M as the waiting time, then divide the remaining time in the time sequence into N time slots of equal length ΔT according to the number of pulses N, then place a pulse at a random position in each time slot and save the interval between adjacent pulses in the array Δτ.

[0009] Furthermore, in the pulse sequence-based distance and velocity simultaneous measurement method provided by the present invention, it may also have the following feature: amplifying the modulated laser signal in step 3 is to amplify the peak power of the pulse sequence.

[0010] Furthermore, in the pulse sequence-based distance and velocity simultaneous measurement method provided by the present invention, there may also be such a feature: wherein the light attenuation in step 4 is specifically: attenuating the input laser signal to half the light intensity of the weakest echo signal to be detected.

[0011] Furthermore, in the pulse sequence-based distance and velocity simultaneous measurement method provided by the present invention, the following features may be provided: wherein the relationship among the reference signal, the echo signal, and the electrical signal is as follows:

[0012] Assume the reference signal is Where E1 represents the intensity of light; f is the frequency of light; is the random initial phase; t is the time;

[0013] Assume the echo signal is Where E2(t) is the light intensity of the echo signal, expressed as a function of time t; f D The Doppler frequency generated by the motion of the target to be measured; Indicates the phase change caused by the change in distance of the target to be measured;

[0014] The optical signal power irradiated to the photosensitive surface of the photoelectric converter is The output signal of the photoelectric converter is filtered out of high frequency and DC to obtain the output formula:

[0015]

[0016] Furthermore, in the method for simultaneous distance and speed measurement based on a pulse sequence provided by the present invention, it can also have the following characteristics: wherein, the specific method for data accumulation calculation in step 7 is as follows: from the start time of the pulse sequence of the transmitted signal, the electrical signal is sampled, the sampling period of the electrical signal is the pulse width, the sampling length is 1 / M seconds, and the adopted data is saved 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 new sequence obtained by shifting the array s(n) to the left by Δτ1 is placed in the second row, and then the new sequence obtained by shifting the second row array to the left by Δτ2 is placed in the third row, and the shifts are made several times in sequence (the shifting and placing process is repeated N-1 times in total according to the above method, where N is the number of pulses in the pulse sequence), and finally all the arrays are added; after the arrays are added, the noise phases at each time point will cancel each other, and at the position corresponding to the laser flight time ΔL, the in-phase addition of each pulse sequence will obtain the maximum peak value, and the distance of the target to be measured can be calculated based on the laser flight time ΔL of this maximum peak.

[0017] Furthermore, in the pulse sequence-based distance and velocity simultaneous measurement method provided by the present invention, the following features can also be provided: wherein, the specific method for calculating the spectrum of the non-uniformly spaced sampling signal in step 8 is as follows: non-uniformly spaced sampling is performed on the electrical signal, and the discrete time data f(t i ) Define Fourier transform, and get the spectrum calculation formula of non-equally spaced signals as:

[0018]

[0019] Where ΔT i is the sampling interval; i corresponds to the i-th pulse, i=1,…,N; t i is the sampling moment of the electrical signal; ω is the frequency of the signal; j is the imaginary unit; e is the exponential function. The spectrum F(ω) of the non-uniformly spaced sampling signal calculated by the above formula is the Doppler frequency of the target to be measured. The speed of the target to be measured can be calculated based on the Doppler frequency.

[0020] The present invention also provides a distance and speed simultaneous measurement device based on a pulse sequence, which is applied to the above-mentioned distance and speed simultaneous measurement method based on a pulse sequence, and is characterized in that it includes: a laser, a beam splitter, an amplifier, a modulator, a collimating lens, an optical attenuator, a combiner, a coupling lens, a photoelectric converter, and a signal processor, wherein the laser is used to generate a continuous laser; the continuous laser enters the beam splitter, and the beam splitter divides the laser beam into two paths, one of which is input into the modulator, and the other is input into the optical attenuator; the modulator is used to modulate the input laser signal, and the modulated laser signal is input into the amplifier for The laser beam is amplified and then transmitted to the collimating lens for collimation. After collimation, it is sent to the scanning device of the laser radar as a transmitting signal, and is projected to the target to be measured by the scanning device; the optical attenuator is used to attenuate the light intensity of the input laser signal, and the attenuated signal is sent to the combiner as a reference signal; the coupling lens is used to receive the echo signal from the target to be measured, and the echo signal is coupled to the optical fiber through the coupling lens and sent to the combiner together with the reference signal for mixing; the signal mixed by the combiner is output to the photoelectric converter, and the photoelectric converter is used to convert the optical signal into an electrical signal; the signal processor is used to analyze and process the electrical signal output by the photoelectric converter.

[0021] The present invention also provides a computer-readable storage medium, characterized in that: a program for simultaneous distance and speed measurement is stored in the computer-readable storage medium, and when the program for simultaneous distance and speed measurement is executed by a processor, the steps of the above-mentioned method for simultaneous distance and speed measurement based on a pulse sequence are implemented.

[0022] Beneficial effects of the present invention:

[0023] The method for simultaneous distance and speed measurement based on a pulse sequence provided by the present invention simplifies the traditional dual detector into a single detector by introducing an optical attenuator, and proposes the use of a pulse position modulation method, a data accumulation method, and a non-uniformly spaced Fourier transform method. The method of the present invention can achieve simultaneous measurement of target distance and speed in a road environment, ensuring that the length of the measurement signal meets the requirements of intelligent driving for spatial resolution. After testing and evaluating the anti-noise performance and measurement error performance of the present invention, it is confirmed that the method and device can be used for road target information perception and are reliable. The present invention ensures that the length of the measurement signal meets the requirements of intelligent driving for spatial resolution, and has a wide range of promotion value. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic structural diagram of a pulse sequence-based distance and speed simultaneous measurement device of the present invention;

[0025] Figure 2 It is a schematic diagram of a pulse sequence position modulation method in a pulse sequence-based distance and velocity simultaneous measurement method of the present invention;

[0026] Figure 3 It is a schematic diagram of a data accumulation method in a pulse sequence-based distance and speed simultaneous measurement method of the present invention;

[0027] Figure 4 It is a schematic diagram of the signal strength output by the photoelectric converter in a noise-free condition in the method for simultaneously measuring distance and speed based on a pulse sequence according to an embodiment of the present invention;

[0028] Figure 5 The peak value corresponding to the laser flight time is obtained by accumulating data in the method for simultaneously measuring distance and speed based on a pulse sequence in an embodiment of the present invention;

[0029] Figure 6 It is a frequency spectrum obtained by sampling data at unequal intervals in a method for simultaneously measuring distance and speed based on a pulse sequence in an embodiment of the present invention;

[0030] Figure 7 This is a diagram analyzing the anti-noise performance of speed measurement of the method for simultaneously measuring distance and speed based on a pulse sequence according to an embodiment of the present invention;

[0031] Figure 8 This is a diagram analyzing the anti-noise performance of distance measurement of the method for simultaneously measuring distance and speed based on a pulse sequence according to an embodiment of the present invention;

[0032] Fig. 9 This is an error analysis diagram of frequency calculation using non-equally spaced data in the pulse sequence-based distance and velocity simultaneous measurement method according to an embodiment of the present invention.

[0033] Figure 1Markings in Chinese: 1-laser; 2-optical fiber; 3-splitter; 4-optical fiber; 5-modulator; 6-amplifier; 7-collimating lens; 8-optical attenuator; 9-combiner; 10-photoelectric converter and signal processor; 11-coupling lens. DETAILED DESCRIPTION

[0034] In order to make the technical means, creative features, objectives and effects of the present invention easy to understand, the following embodiments and the accompanying drawings specifically illustrate the method and device for simultaneous distance and speed measurement based on a pulse sequence and the storage medium of the present invention.

[0035] like Figure 1 As shown, a distance and speed simultaneous measurement device based on a pulse sequence includes: 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.

[0036] The laser 1 is used to generate continuous laser light. The beam splitter 3 is connected to the laser 1. The continuous laser light enters the beam splitter 3, which splits the laser light into two paths, one of which (more than 99%) is input to the modulator 5, and the other (less than 1%) is input to the optical attenuator 8.

[0037] The modulator 5 is used to modulate the input laser signal. The modulated laser signal is input to the amplifier 6 for amplification, and then input to the collimating lens 7 for collimation. After collimation, it is sent to the scanning device of the laser radar (not shown in the figure) as a transmission signal, and is projected to the target to be measured by the scanning device. The optical attenuator 8 is used to attenuate the light intensity of the input laser signal, and the attenuated signal is used as a reference signal.

[0038] The coupling lens 11 is used to receive the echo signal from the target to be measured. After the echo signal is coupled to the optical fiber through the coupling lens 11, it is sent to the combiner 9 together with the reference signal for mixing. The signal mixed by the combiner 9 is output to the photoelectric converter, which is used to convert the optical signal into an electrical signal. The signal processor is connected to the output end of the photoelectric converter and is used to analyze and process the electrical signal output by the photoelectric converter.

[0039] This embodiment also provides a method for simultaneous distance and speed measurement based on a pulse sequence, which is performed using the above-mentioned distance and speed simultaneous measurement device based on a pulse sequence. The method comprises the following steps:

[0040] Step 1, a continuous laser is emitted by laser 1, and the continuous laser is split into two paths by a beam splitter 3, one of which is input to a modulator 5, and the other is input to an optical attenuator 8.

[0041] Step 2, use the modulator 5 to perform amplitude modulation on the input laser signal, so that it is modulated from continuous light to a pulse sequence with random positions.

[0042] The specific method of amplitude modulation of the laser signal is as follows:

[0043] Step 2-1, determine the time length allocated to complete a single measurement based on the number of spatial points that the laser radar requires to measure per unit time:

[0044] Assuming the number of spatial points to be measured per unit time is M, the maximum time required to complete a single measurement is 1 / M seconds;

[0045] Assume that the maximum distance that the laser radar can measure is d meters, the maximum laser flight time is τ = 2d / c seconds, c represents the speed of light, then the maximum length of the pulse sequence to complete a single measurement is T = 1 / M – τ seconds;

[0046] Step 2-2, such as Figure 2 As shown, the pulse sequence is modulated according to the predetermined format:

[0047] First, the last time of length τ in the time series of length M is divided as the waiting time. Then, the remaining time in the time series is divided into N time slots of equal length ΔT according to the number of pulses N. After that, a pulse is placed at a random position in each time slot and the intervals between adjacent pulses are saved in the array Δτ. Figure 2 Where P1 represents the random position in the first time slot in the time series; P i represents the random position in the i-th time slot in the time series; P i+1 represents the random position in the i+1th time slot in the time series; Δτ i Represents the pulse interval determined by the random position in the i-th time slot and the random position in the i+1-th time slot.

[0048] Step 3, first, the modulated laser signal output by the modulator 5 is amplified by the amplifier 6: the peak power of the pulse sequence is amplified within the range allowed by the laser safety standard.

[0049] Then, the amplified pulse sequence is collimated by the collimating lens 7 and transmitted as a transmission signal to the scanning device of the laser radar, and the scanning device projects the transmission signal to the target to be measured to generate an echo signal.

[0050] Step 4, use the optical attenuator 8 to perform optical attenuation on the input laser signal, and attenuate the input laser signal to half the light intensity of the weakest echo signal expected to be detected, and use the attenuated signal output by the optical attenuator 8 as a reference signal.

[0051] Step 5: The coupling lens 11 receives the echo signal from the target to be measured, couples the echo signal to the optical fiber, and sends the echo signal and the reference signal to the combiner 9 for mixing.

[0052] Step 6: Convert the mixed signal into an electrical signal through a photoelectric converter.

[0053] The relationship between the reference signal, echo signal, and electrical signal is as follows:

[0054] Assume the reference signal is Where E1 represents the light intensity of the reference signal; f is the frequency of the reference signal; is the random initial phase; t is the time;

[0055] Assume the echo signal is Where E2 is the light intensity of the echo signal, expressed as a function of time t; f D The Doppler frequency generated by the motion of the target to be measured; Indicates the phase change caused by the change in distance of the target to be measured;

[0056] The optical signal power irradiated to the photosensitive surface of the photoelectric converter is

[0057] Ignoring the constant factor of photoelectric conversion efficiency, the output signal of the photoelectric converter is filtered out with high frequency and DC, and the output formula is:

[0058] Compared with directly detecting the output of the photoelectric converter, there is an additional Doppler frequency fluctuation term in the above formula. In the case of coherent detection, if E1 is too large, the output voltage of some pulses will be lower than DC, and the pulses will have random positive and negative values ​​like noise, which is not conducive to using data accumulation to calculate the flight time of the laser. For this reason, unlike traditional coherent detection that amplifies the signal light by appropriately increasing the reference signal power, this device uses an optical attenuator to attenuate the reference light to half the weakest echo intensity value.

[0059] Step 7, using the signal processor to perform data accumulation calculation on the electrical signal output by the photoelectric converter, and analyzing to obtain the distance of the target to be measured.

[0060] The specific method of data accumulation calculation is as follows:

[0061] From the moment when the pulse sequence of the transmitted signal starts, the electrical signal is sampled and the sampled data is stored in the array s(n);

[0062] like Figure 3 As shown, according to the predetermined data accumulation rule: the array s(n) is placed in the first row, and then the new sequence obtained by shifting the array s(n) to the left by Δτ1 is placed in the second row, and then the new sequence obtained by shifting the second row array to the left by Δτ2 is placed in the third row, and the shifts are repeated several times in sequence (the shifting and placement process is repeated N-1 times in total according to the above method, where N is the number of pulses in the pulse sequence), and finally all the arrays are added. Figure 3 The array waveform at the bottom represents the array obtained by adding all the arrays together.

[0063] After the arrays are added together, the noise phases at each time point will cancel each other out, and at the position corresponding to the laser flight time ΔL, the in-phase addition of each pulse sequence will result in the maximum peak value. The probability of pulses existing at other positions is very low, and there will be small fluctuations, which will be covered by noise. Therefore, according to the laser flight time ΔL of the maximum peak, and according to c represents the speed of light, and the distance d of the target to be measured can be calculated.

[0064] Step 8: Sample the output signal of the photoelectric converter. The sampler can only obtain the Doppler signal sample data at the time corresponding to the pulse position. Since the pulse intervals are not equal, the obtained Doppler signal sampling data intervals are not equal. The fast Fourier transform hardware module performs Fourier transform on the unequally spaced sampling data and calculates the frequency of the Doppler signal. f d is the Doppler frequency, v is the target speed, and λ is the wavelength of the signal. The moving speed of the target can be analyzed.

[0065] The specific method for calculating the spectrum of non-equally spaced sampling signals is as follows:

[0066] The electrical signal is sampled at non-uniform intervals, and the discrete time data f(t i ) Define Fourier transform, and get the spectrum calculation formula of non-equally spaced signals as:

[0067]

[0068] Where ΔT i is the sampling interval; i corresponds to the i-th pulse, i=1,…,N; t i is the sampling time of the electrical signal; ω is the angular frequency of the signal; j is the imaginary unit; e is the exponential function;

[0069] The spectrum F(ω) of the non-uniformly spaced sampling signal calculated by the above formula is the Doppler frequency of the target motion. d is the Doppler frequency, v is the target speed, and λ is the wavelength of the signal, and the moving speed of the target can be calculated.

[0070] The above formula calculates the Doppler frequency corresponding to the target motion speed based on the non-equally spaced sampling data, and does not care about the size of the spectrum amplitude (light intensity). Therefore, the non-equally spaced sampling spectrum calculation formula can be used to calculate the size of the Doppler frequency. Considering the pulse sequence as the sampling pulse of the Doppler signal, the Doppler sampling obtains under-sampled data. The non-equally spaced Fourier transform method in the present invention is effective for the frequency calculation of the under-sampled signal.

[0071] This embodiment also provides a computer-readable storage medium, which stores a program for simultaneous distance and speed measurement. When the program for simultaneous distance and speed measurement is executed by a computer processor, the steps of the above-mentioned method for simultaneous distance and speed measurement based on a pulse sequence are implemented.

[0072] <Verification of principle using examples>

[0073] Reference Figure 2 The rule is to distribute 100 pulses within a duration of 4 μs, and take the pulse amplitude of the echo signal as 1, that is:

[0074]

[0075] The optical amplitude E1 of the reference signal is 0.02. When the receiver noise is ignored, the waveform of the photoelectric converter output signal after filtering out high frequency and DC is as follows: Figure 4 The Doppler frequency modulates the amplitude of the pulse, and the amplitude of the pulse changes according to the cosine law, and the Doppler signal is sampled at the pulse position.

[0076] Will Figure 4 The 100 unequally spaced pulse sequences shown are inserted with a 100 ns delay. Figure 3 The method shown in the figure is used to accumulate data, and the result is as follows Figure 5 shown.

[0077] Depend on Figure 5 It can be seen that at the position corresponding to the delay of 100ns, the accumulated result obtains an obvious peak, while there are slight fluctuations at other time positions, which is consistent with Figure 3 The delay is the laser flight time corresponding to the target distance in the lidar measurement, which is the target value to be determined during the measurement process. Although the Doppler frequency has a modulation effect on the amplitude of the pulse sequence, since the amplitude increases and decreases, on average, it has no effect on the peak value of the data accumulation.

[0078] After determining the position of the pulse sequence by data accumulation, the amplitude of each pulse is corrected according to the spectrum calculation formula of the non-uniformly spaced sampling signal using the pulse interval data from the modulator. The Doppler signal frequency of the modulated pulse peak can be obtained by Fourier transforming the corrected data. Figure 6The signal spectrum diagram obtained by calculating the Doppler signal with a frequency of 12.9MHz in the absence of noise according to the non-equally spaced sampling spectrum calculation formula and Fourier transform is given. 100,000 sets of modulated pulse data are randomly generated, and the pulse peak is modulated with different Doppler frequencies. The frequency is calculated according to this method, and the error between the actual frequency is statistically analyzed to obtain a maximum error of 66.67kHz. The wavelength of the light source of the commonly used laser radar is 1550nm, so 66.67kHz corresponds to a speed error of 0.052m / s, which is far lower than the speed error range allowed by the vehicle motion planning.

[0079] <Reliability verification of the simultaneous distance and speed measurement method>

[0080] The percentage of speed and distance correctly measured at different signal-to-noise ratios is an important indicator for lidar design. The output of the photoelectric converter is obtained by removing high frequency and DC. The first term on the right side is the DC term of the optical power, which represents the average optical power of the pulses in the pulse sequence. Its size 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, and its amplitude E2(t)E1 determines the signal-to-noise ratio used to calculate the Doppler frequency signal.

[0081] Strength is E 2 The current generated by the light on the photoelectric converter is:

[0082] I=ηE 2

[0083] Where η is the photoelectric conversion efficiency.

[0084] The signal power generated by this current in the receiver's transimpedance amplifier is:

[0085] P=I 2 R

[0086] Where R is the gain factor of the transimpedance amplifier.

[0087] Substituting the current calculation formula into the power calculation formula, we get:

[0088] P=η 2 RE 4

[0089] That is, the power of the electrical signal and E 4 There is a linear relationship between them.

[0090] The noise power of the receiver is a certain value Without considering the constant coefficient, the signal-to-noise ratio of the distance measurement signal can be defined as:

[0091]

[0092] E2 represents the peak value of the output of the photoelectric converter, where E2(t). Similarly, the signal-to-noise ratio of the Doppler signal is defined as:

[0093]

[0094] <Reliability verification of speed measurement>

[0095] Take the Doppler signals of 20MHz, 40MHz, 80MHz and 129MHz, and analyze the anti-noise performance of the Fourier frequency calculation of the non-equally spaced data. The results are as follows: Figure 7 See Figure 7 The detection error probability on the vertical axis in the figure refers to the probability of the error between the calculated frequency and the actual Doppler frequency being greater than 70kHz (the error of correct measurement given in the previous section does not exceed 66.67kHz). The curves in the figure are obtained by counting the number of errors that occur in 100,000 frequency calculations at each signal-to-noise ratio sample point. Obviously, the change in frequency has no effect on the anti-noise performance of the frequency calculation.

[0096] The average pulse time interval in the specific embodiment is 40ns. According to the Nyquist theorem, under the condition of equal-interval sampling, the sampling frequency of the 129MHz signal should be greater than 258MHz, that is, the sampling interval should be less than 3.88ns to avoid frequency overlap. Therefore, the sampling of the Doppler signal in the embodiment is under-sampling, and no frequency overlap occurs under the condition of non-equal-interval Fourier calculation, indicating that the method for simultaneous distance and velocity measurement based on a pulse sequence of the present invention can be used to analyze and calculate the frequency of under-sampled signals.

[0097] <Reliability verification of distance measurement>

[0098] In the distance measurement method based on pulse sequence of the present invention, the probability of error detection is calculated by accumulating statistics of data under different signal-to-noise ratios. Figure 8 As shown in the figure. In the calculation, the pulse delay is set to a certain value. If the pulse peak value obtained by data accumulation is inconsistent with the set delay value, it is counted as a detection error. Like the detection error probability curve of frequency, the detection error probability curve of distance measurement is also obtained by calculating 100,000 data accumulations at each signal-to-noise ratio sample point and counting the number of detection errors.

[0099] To ensure that the receiver output s o (t) is greater than zero, and the local reference signal amplitude E1 in the output formula of the photoelectric converter is obtained by removing high frequency and DC. If there are some moments s o(t) is less than zero, then the amplitude and phase relationship between the signal and the noise at different time points is in phase or anti-phase, and data accumulation will not be able to determine the delay of the pulse sequence under low signal-to-noise ratio. According to the output formula of the photoelectric converter obtained by removing the high frequency and DC, the amplitude E1 of the reference signal is not greater than half of the minimum received light intensity, so the Doppler signal intensity used for Fourier calculation can be taken as That is, in the worst case, the signal-to-noise ratio of the signals used to calculate distance and speed is the same. Figure 8 It can be seen that in order to ensure that there are no errors in the detection, the signal-to-noise ratio required for speed measurement is lower than that required for distance measurement. Therefore, when designing the system, the strength of the local reference signal is selected to be the minimum strength that ensures that the speed can be reliably measured.

[0100] <Distance measurement error analysis>

[0101] The error of distance measurement is related to the width of the pulse in the pulse sequence. In the embodiment of the present invention, the pulse width is selected to be 1ns and the sampling rate is 1GHz, so the maximum error of distance measurement is 30cm. The accuracy of 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 present invention.

[0102] <Speed ​​measurement error verification>

[0103] The error performance of the pulse sequence-based distance and velocity simultaneous measurement method of the present invention is compared with the Fourier algorithm of equally spaced data. Through a large number of simulations, it is verified that the error ranges of the two are completely consistent. Fig. 9 , Fig. 9 Given the frequency error data obtained by the non-equally spaced spectrum calculation method for signals between 20MHz and 50MHz with an initial phase of 0, it can be seen that the error varies periodically within a certain range. For a certain frequency, the initial phase is changed in the range of 0 to 2π, and it is also found that the error varies periodically within this range. The maximum error given in the figure is 66.67kHz, and the corresponding speed error is 0.052m / s, which meets the requirements of intelligent driving environment perception.

[0104] The above embodiments are only preferred examples of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention are included in the protection scope of the present invention.

Claims

1. A method for simultaneous distance and velocity measurement based on a pulse sequence, characterized in that: The following steps are involved: Step 1, emitting a continuous laser, and splitting the continuous laser into two paths through a beam splitter, wherein one path of the laser is input into a modulator, and the other path of the laser is input into an optical attenuator; Step 2, using the modulator to perform amplitude modulation on the input laser signal, so that it is modulated from a continuous light form into a pulse sequence with random positions; Step 3, amplifying the modulated laser signal output by the modulator, and then transmitting it as a transmission signal to a scanning device of the laser radar after collimation, and the scanning device projects the transmission signal to the target to be measured to generate an echo signal; Step 4, using the optical attenuator to perform optical attenuation on the input laser signal, and using the attenuated signal as a reference signal; the optical attenuation specifically includes: attenuating the input laser signal to half the light intensity of the weakest echo signal to be detected; Step 5, coupling the echo signal from the target to be measured, and sending it together with the reference signal to a combiner for mixing; Step 6, inputting the mixed signal into the photoelectric converter to perform photoelectric conversion and output an electrical signal; Step 7, performing data accumulation calculation on the electrical signal output by the photoelectric converter, and analyzing and obtaining the distance of the target to be measured; Step 8, performing non-uniform sampling signal spectrum calculation on the electrical signal output by the photoelectric converter, and analyzing to obtain the movement speed of the target to be measured.

2. The method for simultaneous distance and velocity measurement based on a pulse sequence as claimed in claim 1, characterized in that: in, The specific method of amplitude modulating the laser signal in step 2 is as follows: Step 2-1, determine the time length allocated to complete a single measurement based on the number of spatial points that the laser radar requires to measure per unit time: Assuming the number of spatial points to be measured per unit time is M, the maximum time required to complete a single measurement is 1 / M seconds; Assume that the maximum distance that the laser radar can measure is d meters, the maximum laser flight time is τ = 2d / c seconds, c represents the speed of light, then the maximum length of the pulse sequence to complete a single measurement is T = 1 / M – τ seconds; Step 2-2, modulate the pulse sequence according to the predetermined format: First, the last time of length τ in the time series of length M is divided as the waiting time. Then, the remaining time in the time series is divided into N time slots of equal length ΔT according to the number of pulses N. After that, a pulse is placed at a random position in each time slot and the intervals between adjacent pulses are saved in the array Δτ.

3. The method for simultaneous distance and velocity measurement based on a pulse sequence as claimed in claim 2, characterized in that: in, In step 3, amplifying the modulated laser signal includes: amplifying the peak power of the pulse sequence.

4. The method for simultaneous distance and velocity measurement based on a pulse sequence as claimed in claim 1, characterized in that: in, The relationship between the reference signal, the echo signal, and the electrical signal is as follows: Assume the reference signal is Where E1 represents the intensity of light; f is the frequency of light; φ1 is the random initial phase; t is the time; Assume the echo signal is Where E2(t) is the light intensity of the echo signal, expressed as a function of time t; f D The Doppler frequency generated by the motion of the target to be measured; Indicates the phase change caused by the change in distance of the target to be measured; The optical signal power irradiated to the photosensitive surface of the photoelectric converter is The electrical signal output by the photoelectric converter is filtered out of high frequency and direct current to obtain the output formula:

5. The method for simultaneous distance and velocity measurement based on a pulse sequence as claimed in claim 1, characterized in that: in, The specific method of data accumulation calculation in step 7 is as follows: From the start time of the pulse sequence of the transmitting signal, the electrical signal is sampled, the sampling period is the pulse width, the sampling length is 1 / M seconds, and the sampled data is stored in an array s(n); According to the predetermined data accumulation rule, the array s(n) is placed in the first row, and then the new sequence obtained by shifting the array s(n) to the left by Δτ1 is placed in the second row, and then the new sequence obtained by shifting the second row array to the left by Δτ2 is placed in the third row, and the shifts are repeated several times in sequence, and finally all the arrays are added; After the arrays are added together, the noise phases at each time point will cancel each other out, and at the position corresponding to the laser flight time ΔL, the in-phase addition of each pulse sequence will obtain the maximum peak value. The distance of the target to be measured can be calculated based on the laser flight time ΔL of this maximum peak value.

6. The method for simultaneous distance and velocity measurement based on pulse sequence according to claim 1, characterized in that: in, The specific method for calculating the spectrum of the non-equally spaced sampling signal in step 8 is as follows: The electrical signal is sampled at non-uniform intervals, and the discrete time data f(t i ) Define Fourier transform, and get the spectrum calculation formula of non-equally spaced signals as: Where ΔT i is the sampling interval; i corresponds to the i-th pulse, i = 1,…,N; t i is the sampling time of the electrical signal; ω is the frequency of the signal; j is the imaginary unit; e is the exponential function; The frequency spectrum F(ω) of the non-uniformly spaced sampling signal calculated by the above formula is the Doppler frequency of the motion of the target to be measured. The motion speed of the target to be measured can be calculated based on the Doppler frequency.

7. A distance and speed simultaneous measurement device based on a pulse sequence, applied to the distance and speed simultaneous measurement method based on a pulse sequence as claimed in any one of claims 1 to 6, characterized in that: include: Laser, beam splitter, amplifier, modulator, collimating lens, optical attenuator, combiner, coupling lens, photoelectric converter, signal processor, Wherein, the laser is used to generate continuous laser; The continuous laser beam enters the beam splitter, and the beam splitter splits the laser beam into two paths, one of which is input into the modulator, and the other is input into the optical attenuator; The modulator is used to modulate the input laser signal. The modulated laser signal is input to the amplifier for amplification, and then transmitted to the collimating lens for collimation. After collimation, it is sent to the scanning device of the laser radar as a transmission signal, and is projected to the target to be measured by the scanning device. The optical attenuator is used to attenuate the light intensity of the input laser signal, and the attenuated signal is sent to the combiner as a reference signal; The coupling lens is used to receive the echo signal from the target to be measured. After the echo signal is coupled to the optical fiber by the coupling lens, it is sent to the combiner together with the reference signal for mixing; The signal mixed by the combiner is output to the photoelectric converter, and the photoelectric converter is used to convert the optical signal into an electrical signal; The signal processor is used to analyze and process the electrical signal output by the photoelectric converter.

8. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a program for simultaneous distance and speed measurement, and when the program for simultaneous distance and speed measurement is executed by a processor, the steps of the method for simultaneous distance and speed measurement based on a pulse sequence as claimed in any one of claims 1 to 6 are implemented.

Images