Anti-interference laser radar system and method based on waveform coding and adaptive signal processing

Abstract

The invention discloses an anti-interference laser radar system and method based on waveform coding and adaptive signal processing, and the system comprises a control and signal processing unit which is used for coordinating the work of the whole system, generating a coding sequence, and dynamically adjusting a coding strategy and filtering parameters according to environment feedback; the control and signal processing unit is electrically connected with the transmitting link and the receiving link; the transmitting link comprises a laser transmitting module, a programmable waveform coding modulator and a light beam shaping and scanning system which are sequentially arranged in the light path direction. The receiving link comprises a receiving optical module and a photoelectric detector which are sequentially arranged in the light path direction, and compared with the prior art, by combining waveform coding with matched filtering, extremely high processing gain and anti-jamming capability are obtained; by endowing the effective signal with the coding feature, the effective signal has uniqueness, so that co-frequency crosstalk caused by other laser radars can be suppressed, and distributed backscattering noise can be effectively filtered out.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of laser ranging, in particular to an anti-interference laser radar system and method based on waveform coding and adaptive signal processing. BACKGROUND

[0002] Laser radar is the core sensor for L3 and above autonomous vehicles to realize high-precision three-dimensional environment perception within hundreds of meters. When the laser beam propagates in rain, snow, and fog, it will interact with the precipitation particles (raindrops, snowflakes) or aerosols (fog droplets, soot) in the air, producing serious backscattering. These backscattering signals will return to the receiver before or together with the real target echo, forming strong background noise and drowning out the weak effective signal. Traditional laser radar (especially direct time-of-flight dToF) uses simple pulse energy detection and cannot distinguish between "useful echoes from obstacles" and "interference echoes from weather particles" in terms of signal waveform, resulting in a significant decrease in signal-to-noise ratio, a reduction in effective detection distance, and a sparse or even ineffective point cloud. In addition, as the number of vehicles equipped with laser radars increases, multiple laser radars may operate simultaneously in the same area. When the laser pulses emitted by other radars enter the receiving field of view of the radar, crosstalk occurs. These interference pulses overlap with their own echoes in time, causing the system to produce "ghost" targets or misjudge the distance of real targets, seriously threatening road safety. SUMMARY

[0003] The present application aims to solve the problems of existing laser radar technology, such as severe signal-to-noise ratio degradation in bad weather and susceptibility to same-frequency radar crosstalk. To address these issues, an anti-interference laser radar system and method based on waveform coding and adaptive signal processing are proposed.

[0004] To achieve the above objectives, the present application adopts the following technical solutions: An anti-interference laser radar system based on waveform coding and adaptive signal processing, comprising: A control and signal processing unit for coordinating the work of the entire system, generating a coding sequence, and dynamically adjusting the coding strategy and filtering parameters according to environmental feedback; the control and signal processing unit is electrically connected to the transmission link and the receiving link; The transmission link includes, in order along the optical path direction: A laser emission module for generating laser pulses; the laser emission module includes a laser emitter; A programmable waveform coding modulator, the optical input end of the programmable waveform coding modulator is coupled to the output end of the laser, and the electrical input end is coupled to the coding driving signal output end of the control and signal processing unit; for modulating the laser according to the received coding driving signal and outputting laser pulses carrying coding information; The light beam shaping and scanning system is coupled with the light output end of the programmable waveform coding modulator, and is used for adjusting the angle of the laser pulse according to the scanning instruction sent by the control and signal processing unit, and projecting the laser pulse to the space to be measured; the light beam shaping and scanning system comprises a beam expander and a deflection device. The receiving link comprises, in sequence along the light path, a receiving optical antenna, a receiving optical module, an optical band-pass filter, a photoelectric detector, a trans-impedance amplifier, an analog-digital converter and an adaptive matched filter module. The receiving optical module is used for receiving the returned optical signal and converging the optical signal onto the detector; the receiving optical module adopts a telescope system, which is composed of an objective lens and an ocular lens group. The photoelectric detector is used for converting the optical signal into an electrical signal; the light input end of the photoelectric detector is coupled with the output end of the receiving optical module, and is coupled to the light path before the programmable waveform coding modulator through an optical splitter to obtain a local reference light, so as to realize coherent detection; the photoelectric detector adopts an avalanche photodiode or a balanced detector.

[0005] As a further preferred embodiment of the present application, the programmable waveform coding modulator adopts an electro-optic phase modulator or an acousto-optic modulator.

[0006] The coding driving signal is used for enabling the programmable waveform coding modulator to perform linear frequency modulation coding or binary phase coding on the laser.

[0007] As a further preferred embodiment of the present application, the transmitting link further comprises an optical amplifier, which is used for power amplifying the laser pulse carrying the coded information; the light input end of the optical amplifier is coupled with the light output end of the programmable waveform coding modulator, and the light output end is coupled with the light input end of the light beam scanning system; the optical amplifier adopts an erbium-doped fiber amplifier.

[0008] As a further preferred embodiment of the present application, the receiving link further comprises: The optical band-pass filter is used for suppressing background light noise; the optical band-pass filter is arranged on the light path between the receiving optical antenna and the photoelectric detector, and the optical band-pass filter adopts an interference filter; The trans-impedance amplifier is used for converting a current signal into a voltage signal and amplifying the voltage signal; the input end of the trans-impedance amplifier is coupled with the electrical output end of the photoelectric detector. The analog-digital converter is used for analog-digital conversion; the input end of the analog-digital converter is coupled with the output end of the trans-impedance amplifier, and the output end is coupled with the input end of the adaptive matched filter module.

[0009] As a further preferred embodiment of the present application, the center wavelength of the interference filter matches the wavelength of the laser, and the bandwidth is extremely narrow.

[0010] As a further preferred embodiment of the present application, the control and signal processing unit further comprises a code management module for storing and managing a code library containing a plurality of orthogonal waveform codes, and for controlling the dynamic switching of the code drive signal in different detection periods or for different scanning angles.

[0011] As a further preferred embodiment of the present application, the control and signal processing unit comprises an adaptive matched filter module, the input end of which is coupled to the electrical output end of the photodetector for receiving the electrical signal, and the adaptive matched filter module is configured to perform correlation operation on the electrical signal according to the local reference code replica generated by the code management module, to obtain a correlation result, and to extract a matched target echo signal.

[0012] As a further preferred embodiment of the present application, the adaptive matched filter module comprises a digital correlator / pulse compressor, a threshold detection and target judgment module; The digital correlator / pulse compressor is configured to perform operation and processing on the digital echo signal according to the local reference code replica generated by the code management module, and to output a correlation result sequence; the input end of the digital correlator / pulse compressor is coupled to the electrical output end of the photodetector. The threshold detection and target judgment module is configured to dynamically set a target detection threshold according to the noise level of the correlation result output by the adaptive matched filter module, and to identify valid targets from the correlation result based on the threshold; the input end of the threshold detection and target judgment module is coupled to the output end of the adaptive matched filter module; the threshold detection and target judgment module is configured to calculate the noise statistics of the correlation result in real time, and to set the target detection threshold as a function of the noise statistics, so as to dynamically adjust the target detection threshold according to the environmental noise level.

[0013] A method of an anti-interference laser radar system based on waveform coding and adaptive signal processing, comprising the following steps: The laser emission module emits laser, and the control and signal processing unit generates a code drive electrical signal; The code drive electrical signal corresponds to a selected coding scheme, such as a linear frequency modulation waveform or a binary pseudo-random sequence; The programmable waveform coding modulator receives input laser, and the control and signal processing unit drives the programmable waveform coding modulator to modulate the phase or intensity of the input laser, to output laser pulses carrying specific coding information; The beam shaping and scanning system receives scanning instructions from the control and signal processing unit, determines the emission direction of the laser pulses, expands the laser pulses to reduce the divergence angle, and then deflects the collimated laser pulses pointing to a specific direction to the environment to be detected according to the scanning instructions; The receiving optical module receives a mixed light signal returned from the environment to be measured; the mixed light signal includes an encoded echo reflected by a real target, noise generated by rain / snow / mist particle scattering, and interference light emitted by other lidars, An optical band-pass filter filters out most of the background radiation such as sunlight, and only allows light in a very narrow band around the laser wavelength to pass through, thereby improving the signal-to-noise ratio; after filtering, the photodetector converts the mixed light signal into an electrical signal; The electrical signal is correlated with the stored local reference copy by the control and signal processing unit to extract the target echo signal matched with the local reference copy; The noise level of the correlation result is monitored; Based on the noise level, the target detection threshold is dynamically calculated and updated; The correlation result is compared with the updated target detection threshold to determine the final effective target point cloud data.

[0014] The anti-interference lidar system and method based on waveform coding and adaptive signal processing proposed by the present application have the following beneficial effects compared with the prior art: 1. The present application obtains very high processing gain and anti-interference ability by waveform coding combined with matched filtering; linear frequency modulation and phase coding have a large time-bandwidth product, and matched filtering can compress the wide pulse energy of the transmitted signal to a narrow pulse, resulting in processing gain; the system can extract effective echoes from signals below the noise floor, thereby significantly improving the signal-to-noise ratio; 2. The present application gives the effective signal coding features, so that the effective signal has uniqueness, thus suppressing the same frequency crosstalk caused by other lidars (the number of "ghost" targets is reduced from 5-10 per frame to nearly 0), and effectively filtering out most of the distributed backscattering noise caused by rain, snow and mist particles; 3. The present application adjusts the detection threshold according to the real-time noise level, which can automatically balance the detection probability and false alarm probability under different interference intensities; in severe weather (high noise), a low false alarm rate is maintained; in good weather (low noise), the detection sensitivity to small targets is improved, achieving optimal performance in all working conditions; 4. The present application adds a programmable coding modulator (such as an acousto-optic modulator AOM or an electro-optic modulator EOM), which does not have a high requirement for laser power; therefore, the system involved in the present application does not need to violate the eye safety regulations to pursue high power, and does not need to rely on extremely expensive hardware to improve resolution, i.e. solves the industry core pain point at relatively low cost, and has very high commercial value. DETAILED DESCRIPTION

[0015] The following specific embodiments will specifically introduce the present application.

[0016] The present application gives each emitted laser pulse a unique "identity code", and at the receiving end, through a "smart filter" that exactly matches the transmission code, only allows the target echo signal carrying the correct "identity code" to pass through, while the interference signals (including weather backscattering and same-frequency crosstalk) that do not carry or carry incorrect codes are maximally suppressed.

[0017] Embodiment one: an anti-interference laser radar system based on waveform coding and adaptive signal processing, comprising: a control and signal processing unit for coordinating the work of the entire system, generating coding sequences, and dynamically adjusting coding strategies and filtering parameters according to environmental feedback; the control and signal processing unit is electrically connected with the transmission link and the receiving link.

[0018] The control and signal processing unit includes an encoding management module, a scanning module, and an adaptive matched filter module; the encoding management module and the scanning module ensure that the transmitted coded laser pulses are synchronized with the receiving and processing in space and time. They are responsible for generating codes, controlling scanning, and closely interacting with the signal processing module to achieve dynamic switching of codes and adaptive adjustment of system operating modes.

[0019] The encoding management module is used to store and manage a coding library containing multiple orthogonal waveform codes, and to control the dynamic switching of the coding driving signals in different detection periods or for different scanning angles.

[0020] The control and signal processing unit includes an adaptive matched filter module, an input end of the adaptive matched filter module is coupled to an electrical output end of the photodetector, used for receiving an electrical signal, and performing correlation operation on the electrical signal according to a local reference code copy generated by the code management module to obtain a correlation operation result, so as to extract a matched target echo signal. The adaptive matched filter module includes a digital correlator / pulse compressor and a threshold detection and target judgment module; the digital correlator / pulse compressor performs operation processing on the digital echo signal according to the local reference code copy generated by the code management module, and outputs a correlation result sequence; if the echo contains a signal matched with the local code, a sharp correlation peak will appear at the time delay position of the signal; and the noise and interference that are not matched are suppressed to a low-level background. An input end of the digital correlator / pulse compressor is coupled to an electrical output end of the photodetector. The threshold detection and target judgment module is used for dynamically setting a target detection threshold (for example, threshold = noise mean + K x noise standard deviation, K is an adjustable constant) according to a noise level of the correlation operation result output by the adaptive matched filter module, and identifying an effective target from the correlation operation result based on the threshold; an input end of the threshold detection and target judgment module is coupled to an output end of the adaptive matched filter module; and the threshold detection and target judgment module is configured to: calculate a noise statistic quantity of the correlation operation result in real time, and set the target detection threshold as a function of the noise statistic quantity, so as to realize dynamic adjustment of the target detection threshold with the environmental noise level.

[0021] The transmitting link includes, which are sequentially arranged along the optical path direction: A laser emitting module, used for generating laser pulses; the laser emitting module includes a laser emitter.

[0022] A programmable waveform coding modulator, an optical input end of the programmable waveform coding modulator is coupled to an output end of the laser, and an electrical input end is coupled to a code driving signal output end of the control and signal processing unit; used for modulating the laser according to the received code driving signal to output laser pulses carrying code information; the programmable waveform coding modulator adopts an electro-optical phase modulator or an acousto-optical modulator, for example, a lithium niobate Mach-Zehnder intensity modulator or a phase modulator. The code driving signal causes the programmable waveform coding modulator to perform linear frequency modulation coding or binary phase coding on the laser.

[0023] An optical amplifier, used for power amplifying the laser pulses carrying code information; an optical input end of the optical amplifier is coupled to an optical output end of the programmable waveform coding modulator, and an optical output end is coupled to an optical input end of the beam scanning system; the optical amplifier adopts an erbium-doped fiber amplifier.

[0024] The light beam shaping and scanning system is coupled to the output end of the programmable waveform coding modulator, and is used for adjusting the angle of the laser pulse according to the scanning instruction sent by the control and signal processing unit, and projecting the laser pulse into the space to be measured; the light beam shaping and scanning system comprises a beam expander and a deflection device; the deflection device is, for example, a MEMS micro mirror, a rotating polygon mirror or an optical phased array.

[0025] The receiving link comprises, in sequence along the light path direction: A receiving optical module is used for receiving the returned optical signal and converging the returned optical signal onto a detector; the receiving optical module adopts a telescope system, which is composed of an objective lens and an eyepiece group, and has a larger aperture than the transmitting antenna to collect more echo light.

[0026] An optical band-pass filter is used for suppressing background light noise; the optical band-pass filter is arranged on the light path between the receiving optical antenna and the photodetector, and adopts an interference filter; the center wavelength of the interference filter matches the wavelength of the laser, and the bandwidth is extremely narrow.

[0027] A photodetector is used for converting the optical signal into an electrical signal; the light input end of the photodetector is coupled to the output end of the receiving optical module, and is coupled to the light path before the programmable waveform coding modulator through an optical splitter to obtain a local reference light, which is used for realizing coherent detection; the photodetector adopts an avalanche photodiode or a balanced detector, and has high sensitivity to the wavelength of 1550 nm.

[0028] A transimpedance amplifier is used for converting a current signal into a voltage signal and amplifying the voltage signal; the input end of the transimpedance amplifier is coupled to the electrical output end of the photodetector.

[0029] An analog-to-digital converter is used for analog-to-digital conversion; the input end of the analog-to-digital converter is coupled to the output end of the transimpedance amplifier, and the output end is coupled to the input end of the adaptive matched filter module.

[0030] Embodiment two: a method of an anti-interference laser radar system based on waveform coding and adaptive signal processing, comprising the following steps: A laser transmitting module transmits laser, and a control and signal processing unit generates a coded driving electrical signal; The coded driving electrical signal corresponds to a selected coding scheme, for example: a linear frequency modulation waveform or a binary pseudo-random sequence; A programmable waveform coding modulator receives input laser, and the control and signal processing unit drives the programmable waveform coding modulator to modulate the phase or intensity of the input laser, and outputs laser pulses carrying specific coding information; The light beam shaping and scanning system receives the scanning instruction sent by the control and signal processing unit, determines the emission direction of the laser pulse, expands the laser pulse to reduce the divergence angle, and then deflects the laser pulse to a specific angle according to the scanning instruction, and emits the collimated laser pulse pointing to a specific direction into the environment to be detected; The receiving optical module receives the mixed light signal returned from the environment to be detected; the mixed light signal includes the coded echo reflected by the real target, the noise generated by the rain / mist particle scattering, and the interference light emitted by other laser radars, The optical band-pass filter filters out most of the background radiation such as sunlight and only allows light in a very narrow waveband near the laser wavelength to pass through, thereby improving the signal-to-noise ratio; after filtering, the photodetector converts the mixed light signal into an electrical signal; The control and signal processing unit correlates the electrical signal with the stored local reference code copy to extract the target echo signal matched with the local reference code copy.

[0031] The noise level of the correlation result is monitored; Based on the noise level, the target detection threshold is dynamically calculated and updated; The correlation result is compared with the updated target detection threshold to determine the final effective target point cloud data.

[0032] Example three: test in a laboratory fog simulation environment, compare the performance of the traditional pulsed laser radar and the present invention.

[0033] Example 1 uses the system and method disclosed in the present invention, wherein the laser wavelength is 1550nm, the pulse width is 10ns, the frequency modulation bandwidth is 2GHz, and the emission energy meets the Class 1 eye safety standard; Comparative example 1 uses a traditional pulsed laser radar.

[0034] Test in a laboratory fog simulation environment, the performance test results are shown in Table 1 below.

[0035] Table 1 Performance test results of example 1 and comparative example 1

[0036] According to the above data analysis, it is concluded that the present invention effectively improves the signal-to-noise ratio, the detection distance is longer, the target loss rate is lower, the interference signal can be effectively suppressed, the false alarm rate is reduced, and the overall detection sensitivity is improved.

[0037] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the above examples do not limit the present invention in any form, and any technical solution obtained by equivalent substitution or equivalent transformation falls within the scope of the present invention.

Claims

1. An anti-jamming lidar system based on waveform coding and adaptive signal processing, characterized in that, The application relates to a laser radar system, which comprises the following parts: a control and signal processing unit for coordinating the whole system, generating an encoding sequence and dynamically adjusting an encoding strategy and filtering parameters according to environmental feedback; the control and signal processing unit is electrically connected with a transmitting link and a receiving link; the transmitting link comprises the following parts arranged in sequence along an optical path direction: a laser transmitting module for generating laser pulses; the laser transmitting module comprises a laser transmitter; a programmable waveform encoding modulator, the light input end of which is coupled with the output end of the laser transmitter, and the electric input end of which is coupled with the encoding driving signal output end of the control and signal processing unit; the programmable waveform encoding modulator is used for modulating the laser according to the received encoding driving signal and outputting laser pulses carrying encoding information; an optical beam shaping and scanning system, the light input end of which is coupled with the light output end of the programmable waveform encoding modulator, and which is used for adjusting the angle of the laser pulses according to the scanning instruction from the control and signal processing unit and projecting the laser pulses into a space to be detected; the optical beam shaping and scanning system comprises a beam expander and a deflection device; the receiving link comprises the following parts arranged in sequence along an optical path direction: a receiving optical module for receiving returned optical signals and converging the optical signals onto a detector; the receiving optical module adopts a telescope system and is composed of an objective lens and an ocular lens group; a photoelectric detector for converting optical signals into electric signals; the light input end of the photoelectric detector is coupled with the output end of the receiving optical module and is coupled with an optical shunt before the programmable waveform encoding modulator through an optical splitter to obtain local reference light, which is used for realizing coherent detection; the photoelectric detector adopts an avalanche photodiode or a balanced detector.

2. The anti-jamming lidar system based on waveform coding and adaptive signal processing according to claim 1, characterized in that, the programmable waveform encoding modulator adopts an electro-optic phase modulator or an acousto-optic modulator; the encoding driving signal makes the programmable waveform encoding modulator perform linear frequency modulation encoding or binary phase encoding on the laser.

3. The anti-jamming lidar system based on waveform coding and adaptive signal processing of claim 1, wherein, the transmitting link further comprises an optical amplifier for power amplifying the laser pulses carrying encoding information; the light input end of the optical amplifier is coupled with the light output end of the programmable waveform encoding modulator, and the light output end is coupled with the light input end of the optical beam scanning system; the optical amplifier adopts an erbium-doped fiber amplifier.

4. The anti-jamming lidar system based on waveform coding and adaptive signal processing of claim 1, wherein, the receiving link further comprises: an optical band-pass filter for suppressing background light noise; the optical band-pass filter is arranged on the optical path between a receiving optical antenna and the photoelectric detector; the optical band-pass filter adopts an interference filter; a transimpedance amplifier for converting a current signal into a voltage signal and amplifying the voltage signal; the input end of the transimpedance amplifier is coupled with the electric output end of the photoelectric detector; an analog-to-digital converter for analog-digital conversion; the input end of the analog-to-digital converter is coupled with the output end of the transimpedance amplifier, and the output end is coupled with the input end of the adaptive matched filter module.

5. The anti-jamming lidar system based on waveform coding and adaptive signal processing of claim 4, wherein, the center wavelength of the interference filter matches the wavelength of the laser, and the bandwidth is extremely narrow.

6. The anti-jamming lidar system based on waveform coding and adaptive signal processing of claim 1, wherein, the control and signal processing unit further comprises an encoding management module for storing and managing an encoding library containing multiple orthogonal waveform encodings and controlling the encoding driving signal to be dynamically switched in different detection periods or for different scanning angles.

7. The anti-jamming lidar system based on waveform coding and adaptive signal processing according to claim 6, characterized in that, The control and signal processing unit comprises an adaptive matched filter module, an input end of the adaptive matched filter module being coupled to an electrical output end of the photodetector, for receiving the electrical signal and performing correlation operation on the electrical signal according to a local reference code replica generated by the code management module, to obtain a correlation result, so as to extract a matched target echo signal.

8. The anti-jamming lidar system based on waveform coding and adaptive signal processing according to claim 7, characterized in that, The adaptive matched filter module comprises a digital correlator / pulse compressor and a threshold detection and target judgment module. The digital correlator / pulse compressor performs operation and processing on the digital echo signal according to the local reference code replica generated by the code management module, and outputs a correlation result sequence. An input end of the digital correlator / pulse compressor is coupled to an electrical output end of the photodetector. The threshold detection and target judgment module is configured to dynamically set a target detection threshold according to a noise level of the correlation result output by the adaptive matched filter module, and to determine an effective target based on the threshold; an input end of the threshold detection and target judgment module is coupled to an output end of the adaptive matched filter module. The threshold detection and target judgment module is configured to calculate a noise statistic of the correlation result in real time, and to set the target detection threshold as a function of the noise statistic, so as to dynamically adjust the target detection threshold according to the noise level of the environment.

9. A method for using an anti-jamming laser radar system based on waveform coding and adaptive signal processing according to any one of claims 1 to 8, characterized in that, The method comprises the following steps: The laser emission module emits laser, and the control and signal processing unit generates a code driving electrical signal; The code driving electrical signal corresponds to a selected code scheme, such as a linear frequency modulation waveform or a binary pseudo-random sequence; The programmable waveform code modulator receives input laser, and the control and signal processing unit drives the programmable waveform code modulator to modulate the phase or intensity of the input laser, and outputs laser pulses carrying specific code information; The beam shaping and scanning system receives a scanning instruction output by the control and signal processing unit, determines the emission direction of the laser pulses, expands the laser pulses to reduce the divergence angle, and then deflects the collimated laser pulses pointing to a specific direction to the environment to be measured according to the scanning instruction; The receiving optical module receives a mixed light signal returned from the environment to be measured; the mixed light signal comprises a code echo reflected by a real target, noise caused by rain / snow particle scattering, and interference light emitted by other laser radars, An optical bandpass filter performs filtering to filter out most of the background radiation such as sunlight, and only allows light in a very narrow waveband near the laser wavelength to pass through, thereby improving the signal-to-noise ratio; after filtering, the photodetector converts the mixed light signal into an electrical signal; The control and signal processing unit performs correlation operation on the electrical signal and the stored local reference code replica, so as to extract a target echo signal matched with the local reference code replica; The noise level of the correlation result is monitored; Based on the noise level, the target detection threshold is dynamically calculated and updated; The correlation result is compared with the updated target detection threshold, and the final effective target point cloud data is determined.

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