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

Abstract

This invention discloses an anti-interference lidar system and method based on waveform coding and adaptive signal processing, comprising: a control and signal processing unit for coordinating the operation 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 a transmission link and a receiving link; the transmission link includes, in sequence along the optical path, a laser emission module, a programmable waveform coding modulator, and a beam shaping and scanning system; the receiving link includes, in sequence along the optical path, a receiving optical module and a photodetector. Compared with the prior art, this invention achieves extremely high processing gain and anti-interference capability by combining waveform coding with matched filtering; by assigning coding characteristics to the effective signal, the effective signal is made unique, thus suppressing co-frequency crosstalk caused by other lidars, while effectively filtering out distributed backscattering noise.

Description

Technical Field

[0001] This invention relates to the field of laser ranging, and specifically to an anti-interference laser radar system and method based on waveform encoding and adaptive signal processing. Background Technology

[0002] LiDAR is a core sensor for L3 and above autonomous vehicles to achieve high-precision 3D environmental perception within a range of hundreds of meters. When a laser beam propagates through rain, snow, or fog, it interacts with precipitation particles (raindrops, snowflakes) or aerosols (fog droplets, dust) in the air, producing severe backscattering. These backscattered signals return to the receiver before or along with the echoes from the real targets, forming strong background noise that drowns out the weak effective signals. Traditional LiDAR (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" from the signal waveform, resulting in a significant decrease in signal-to-noise ratio, a shortened effective detection range, and sparse or even ineffective point clouds. In addition, with the increase in vehicles equipped with LiDAR, multiple LiDARs may operate simultaneously in the same area. When laser pulses emitted by other radars enter the receiving field of view of this radar, crosstalk occurs. These interfering pulses overlap with their own echoes in time, causing the system to generate "ghost" targets or misjudge the distance of real targets, seriously threatening driving safety. Summary of the Invention

[0003] The purpose of this invention is to address the problems of severe signal-to-noise ratio degradation in adverse weather conditions and susceptibility to crosstalk from co-frequency radars in existing lidar technologies. To overcome these shortcomings, an anti-interference lidar system and method based on waveform coding and adaptive signal processing is proposed.

[0004] To achieve the above objectives, the present invention adopts the following technical solution: An anti-jamming lidar system based on waveform encoding and adaptive signal processing includes: The control and signal processing unit is used to coordinate the operation of the entire system, generate coded sequences, and dynamically adjust the coding strategy and filtering parameters according to environmental feedback; the control and signal processing unit is electrically connected to the transmit link and the receive link; The transmission link comprises the following components arranged sequentially along the optical path: A laser emitting module is used to generate laser pulses; the laser emitting module includes a laser emitter. A programmable waveform encoder modulator has an optical input terminal coupled to the output terminal of a laser and an electrical input terminal coupled to the output terminal of a control and signal processing unit for encoding drive signals. It is used to modulate the laser according to the received encoding drive signals and output laser pulses carrying encoded information. The beam shaping and scanning system has an optical input end coupled to the optical output end of a programmable waveform encoder modulator. It is used to adjust the angle of the laser pulse according to the scanning command issued by the control and signal processing unit and project it into the space to be measured. The beam shaping and scanning system includes a beam expander and a deflection device. The receiving link comprises the following components arranged sequentially along the optical path: Receiver optical module: Used to receive the returned light signal and focus it onto the detector; the receiver optical module adopts a telescope system, consisting of an objective lens and an eyepiece group; A photodetector is used to convert optical signals into electrical signals. The optical input end of the photodetector is coupled to the output end of the receiving optical module and is coupled to the optical path before the programmable waveform encoder modulator through an optical splitter to obtain local reference light for coherent detection. The photodetector adopts an avalanche photodiode or a balanced detector.

[0005] As a further preferred embodiment of the present invention, the programmable waveform encoding modulator is an electro-optic phase modulator or an acousto-optic modulator.

[0006] The encoded drive signal enables the programmable waveform encoder to perform linear frequency modulation encoding or binary phase encoding on the laser.

[0007] As a further preferred embodiment of the present invention, the transmission link further includes: an optical amplifier for amplifying the power of the laser pulse carrying encoded information; the optical input terminal of the optical amplifier is coupled to the optical output terminal of the programmable waveform encoding modulator, and the optical output terminal is coupled to the optical input terminal of the beam scanning system; the optical amplifier is an erbium-doped fiber amplifier.

[0008] As a further preferred embodiment of the present invention, the receiving link further includes: An optical bandpass filter is used to suppress background light noise; the optical bandpass filter is disposed in the optical path between the receiving optical antenna and the photodetector, and the optical bandpass filter is an interference filter; A transimpedance amplifier is used to convert a current signal into a voltage signal and amplify the voltage signal; the input terminal of the transimpedance amplifier is coupled to the electrical output terminal of the photodetector. An analog-to-digital converter (ADC) is used for digital-to-analog conversion; the input of the ADC is coupled to the output of the transimpedance amplifier, and the output is coupled to the input of the adaptive matched filter module.

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

[0010] As a further preferred embodiment of the present invention, the control and signal processing unit further includes an encoding management module for storing and managing an encoding library containing multiple orthogonal waveform encodings, and controlling the encoding driving signal to dynamically switch at different detection cycles or different scanning angles.

[0011] As a further preferred embodiment of the present invention, the control and signal processing unit includes an adaptive matched filtering module. The input terminal of the adaptive matched filtering module is coupled to the electrical output terminal of the photodetector, and is used to receive electrical signals and perform correlation operations on the electrical signals according to the local reference code copy generated by the encoding management module to obtain the correlation operation results, so as to extract the matching target echo signal.

[0012] As a further preferred embodiment of the present invention, the adaptive matched filtering module includes a digital correlator / pulse compressor and a threshold detection and target judgment module; The digital correlator / pulse compressor processes the digital echo signal based on the local reference code copy generated by the encoding management module and outputs a correlation result sequence; the input of the digital correlator / pulse compressor is coupled to the electrical output of the photodetector. The threshold detection and target judgment module is used to dynamically set a target detection threshold based on the noise level of the correlation calculation results output by the adaptive matched filtering module, and to identify valid targets from the correlation calculation results based on this threshold. The input of the threshold detection and target judgment module is coupled to the output of the adaptive matched filtering module. The threshold detection and target judgment module is configured to: calculate the noise statistics of the correlation calculation results in real time, and set the target detection threshold as a function of the noise statistics, so as to realize the dynamic adjustment of the target detection threshold with the ambient noise level.

[0013] A method for an anti-jamming lidar system based on waveform encoding and adaptive signal processing includes the following steps: The laser emitting module emits a laser, and the control and signal processing unit generates coded driving electrical signals. The encoding drive electrical signal corresponds to the selected encoding scheme, such as a linear frequency modulated waveform or a binary pseudo-random sequence; The programmable waveform encoder modulator receives the input laser, and the signal processing unit drives the programmable waveform encoder modulator to modulate the phase or intensity of the input laser, and outputs a laser pulse carrying specific encoded information. The beam shaping and scanning system receives scanning commands from 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 command, and emits the collimated laser pulse pointing in a specific direction into the environment under test. The receiving optical module receives a mixed optical signal returned from the environment under test; the mixed optical signal includes coded echoes reflected from the real target, noise generated by rain / fog particle scattering, and interference light emitted by other lidar. An optical bandpass filter filters out most of the background radiation, such as sunlight, allowing only a narrow band of light near the laser wavelength to pass through, thereby improving the signal-to-noise ratio. After filtering, the photodetector converts the mixed optical signal into an electrical signal. The control and signal processing unit performs correlation operations between the electrical signal and the stored local reference code copy to extract the target echo signal that matches the local reference code copy. Monitor the noise level of the relevant calculation results; The target detection threshold is dynamically calculated and updated based on the noise level. The relevant calculation results are compared with the updated target detection threshold to determine the final valid target point cloud data.

[0014] The anti-interference lidar system and method based on waveform encoding and adaptive signal processing proposed in this invention have the following advantages compared with the prior art: 1. This invention achieves extremely high processing gain and anti-interference capability by combining waveform encoding with matched filtering; linear frequency modulation and phase encoding have a large time-bandwidth product, and matched filtering can compress the wide pulse energy of the transmitted signal into a narrow pulse, generating processing gain; enabling the system to extract effective echoes from signals below the noise floor, thereby significantly improving the signal-to-noise ratio; 2. By assigning coding features to the effective signal, the present invention makes the effective signal unique, thus suppressing co-frequency crosstalk caused by other lidars (reducing the number of "ghost" targets from 5-10 per frame to close to 0), while effectively filtering out most of the distributed backscattering noise generated by rain, snow, and fog particles; 3. This invention 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; it maintains a low false alarm rate under severe weather (high noise) conditions; and improves the detection sensitivity of weak targets under good weather (low noise) conditions, thus achieving optimal performance under all operating conditions. 4. The present invention adds a programmable code modulator (such as an acousto-optic modulator AOM or an electro-optic modulator EOM), which does not require excessively high laser power. Therefore, the system involved in the present invention does not need to violate human eye safety regulations to pursue high power, nor does it need to rely on extremely expensive hardware to improve resolution. That is, it solves the core pain point of the industry at a relatively low cost and has extremely high commercial value. Detailed Implementation

[0015] The following specific embodiments will provide a detailed description of the present invention.

[0016] This invention assigns a unique "identity code" to each emitted laser pulse and passes it through a "smart filter" at the receiving end that precisely matches the emission code, allowing only the target echo signal carrying the correct "identity code" to pass through, while suppressing interference signals (including weather backscatter and co-channel crosstalk) that do not carry or carry the wrong code to the greatest extent.

[0017] Example 1: An anti-interference lidar system based on waveform coding and adaptive signal processing includes: a control and signal processing unit for coordinating the operation 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 transmit link and the receive link.

[0018] The control and signal processing unit includes an encoding management module, a scanning module, and an adaptive matched filtering module. The encoding management module and the scanning module ensure that the emitted encoded laser pulses and the received processing are synchronized in time and space. They are responsible for generating codes, controlling scanning, and interacting closely with the signal processing module to achieve dynamic switching of codes and adaptive adjustment of the system's operating mode.

[0019] The encoding management module is used to store and manage an encoding library containing multiple orthogonal waveform encodings, and to control the encoding drive signal to dynamically switch at different detection cycles or different scanning angles.

[0020] The control and signal processing unit includes an adaptive matched filtering module. The input of the adaptive matched filtering module is coupled to the electrical output of the photodetector. It receives electrical signals and performs correlation operations on the electrical signals based on a local reference code copy generated by the encoding management module, obtaining the correlation result to extract the matching target echo signal. The adaptive matched filtering module includes a digital correlator / pulse compressor and a threshold detection and target judgment module. The digital correlator / pulse compressor processes the digital echo signal based on the local reference code copy generated by the encoding management module, outputting a correlation result sequence. If the echo contains a signal matching the local code, a sharp correlation peak will appear at the time delay position of that signal; mismatched noise and interference are suppressed to a low-level background. The input of the digital correlator / pulse compressor is coupled to the electrical output of the photodetector. The threshold detection and target judgment module is used to dynamically set a target detection threshold (e.g., threshold = noise mean + K × noise standard deviation, where K is an adjustable constant) based on the noise level of the correlation calculation results output by the adaptive matched filtering module, and to identify valid targets from the correlation calculation results based on this threshold. The input of the threshold detection and target judgment module is coupled to the output of the adaptive matched filtering module. The threshold detection and target judgment module is configured to: calculate the noise statistics of the correlation calculation results in real time, and set the target detection threshold as a function of the noise statistics, so as to realize the dynamic adjustment of the target detection threshold with the ambient noise level.

[0021] The transmission link comprises the following components arranged sequentially along the optical path: A laser emitting module is used to generate laser pulses; the laser emitting module includes a laser emitter.

[0022] A programmable waveform encoder modulator (CDM) has its optical input coupled to the laser's output and its electrical input coupled to the encoding drive signal output of a control and signal processing unit. It modulates the laser beam according to the received encoding drive signal, outputting laser pulses carrying encoded information. The CDM employs an electro-optic phase modulator or an acousto-optic modulator, such as a lithium niobate Mach-Zehnder intensity modulator or phase modulator. The encoding drive signal enables the CDM to perform linear frequency modulation encoding or binary phase encoding on the laser beam.

[0023] An optical amplifier is used to amplify the power of laser pulses carrying encoded information; the optical input of the optical amplifier is coupled to the optical output of a programmable waveform encoding modulator, and the optical output is coupled to the optical input of the beam scanning system; the optical amplifier is an erbium-doped fiber amplifier.

[0024] The beam shaping and scanning system has an optical input end coupled to the optical output end of a programmable waveform encoder modulator. It is used to adjust the angle of the laser pulse according to the scanning command issued by the control and signal processing unit and project it into the space to be measured. The beam shaping and scanning system includes a beam expander and a deflection device. The deflection device is, for example, a MEMS micromirror, a rotating polygon mirror, or an optical phased array.

[0025] The receiving link comprises the following components arranged sequentially along the optical path: Receiving optical module: used to receive the returned light signal and focus it onto the detector; the receiving optical module adopts a telescope system, consisting of an objective lens and an eyepiece group, and its aperture is larger than the transmitting antenna to collect more echo light.

[0026] An optical bandpass filter is used to suppress background light noise. The optical bandpass filter is disposed in the optical path between the receiving optical antenna and the photodetector. The optical bandpass filter is an interference filter. The center wavelength of the interference filter matches the laser wavelength and has an extremely narrow bandwidth.

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

[0028] A transimpedance amplifier is used to convert a current signal into a voltage signal and amplify the voltage signal; the input terminal of the transimpedance amplifier is coupled to the electrical output terminal of the photodetector.

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

[0030] Example 2: A method for an anti-interference lidar system based on waveform coding and adaptive signal processing, comprising the following steps: The laser emitting module emits a laser, and the control and signal processing unit generates coded driving electrical signals. The encoding drive electrical signal corresponds to the selected encoding scheme, such as a linear frequency modulated waveform or a binary pseudo-random sequence; The programmable waveform encoder modulator receives the input laser, and the signal processing unit drives the programmable waveform encoder modulator to modulate the phase or intensity of the input laser, and outputs a laser pulse carrying specific encoded information. The beam shaping and scanning system receives scanning commands from 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 command, and emits the collimated laser pulse pointing in a specific direction into the environment under test. The receiving optical module receives a mixed optical signal returned from the environment under test; the mixed optical signal includes coded echoes reflected from the real target, noise generated by rain / fog particle scattering, and interference light emitted by other lidar. An optical bandpass filter filters out most of the background radiation, such as sunlight, allowing only a narrow band of light near the laser wavelength to pass through, thereby improving the signal-to-noise ratio. After filtering, the photodetector converts the mixed optical signal into an electrical signal. The control and signal processing unit performs correlation operations between the electrical signal and the stored local reference code copy to extract the target echo signal that matches the local reference code copy.

[0031] Monitor the noise level of the relevant calculation results; The target detection threshold is dynamically calculated and updated based on the noise level. The relevant calculation results are compared with the updated target detection threshold to determine the final valid target point cloud data.

[0032] Example 3: Tests were conducted in a laboratory fog simulation environment to compare the performance of traditional pulsed lidar with that of the present invention.

[0033] Example 1 uses the system and method involved in this 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 human eye standard; Comparative Example 1 uses a traditional pulsed lidar.

[0034] The tests were conducted in a laboratory fog simulation environment, and the results of each performance test are shown in Table 1 below.

[0035] Table 1. Performance test results of Example 1 and Comparative Example 1

[0036] Based on the above data analysis, it can be concluded that the present invention effectively improves the signal-to-noise ratio, extends the detection range, reduces the target loss rate, effectively suppresses interference signals, reduces the false alarm rate, and improves the overall detection sensitivity.

[0037] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments do not limit the present invention in any way, and all technical solutions obtained by equivalent substitution or equivalent transformation fall within the protection scope of the present invention.

Claims

1. An anti-interference lidar system based on waveform encoding and adaptive signal processing, characterized in that, include: The control and signal processing unit is used to coordinate the operation of the entire system, generate coded sequences, and dynamically adjust the coding strategy and filtering parameters according to environmental feedback; the control and signal processing unit is electrically connected to the transmit link and the receive link; The transmission link comprises the following components arranged sequentially along the optical path: A laser emitting module is used to generate laser pulses; the laser emitting module includes a laser emitter. The programmable waveform encoder modulator has an optical input terminal coupled to the output terminal of the laser and an electrical input terminal coupled to the output terminal of the encoder drive signal of the control and signal processing unit. It is used to modulate the laser according to the received coded drive signal and output laser pulses carrying coded information; The beam shaping and scanning system has an optical input end coupled to the optical output end of a programmable waveform encoder modulator. It is used to adjust the angle of the laser pulse according to the scanning command issued by the control and signal processing unit and project it into the space to be measured. The beam shaping and scanning system includes a beam expander and a deflection device. The receiving link comprises the following components arranged sequentially along the optical path: Receiver optical module: Used to receive the returned light signal and focus it onto the detector; the receiver optical module adopts a telescope system, consisting of an objective lens and an eyepiece group; A photodetector is used to convert optical signals into electrical signals. The optical input end of the photodetector is coupled to the output end of the receiving optical module and is coupled to the optical path before the programmable waveform encoder modulator through an optical splitter to obtain local reference light for coherent detection. The photodetector uses an avalanche photodiode or a balanced detector.

2. The anti-interference lidar system based on waveform encoding and adaptive signal processing according to claim 1, characterized in that, The programmable waveform encoder modulator is an electro-optic phase modulator or an acousto-optic modulator. The encoded drive signal enables the programmable waveform encoder to 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 transmission link further includes: an optical amplifier for amplifying the power of the laser pulse carrying encoded information; the optical input of the optical amplifier is coupled to the optical output of the programmable waveform encoding modulator, and the optical output is coupled to the optical input of the beam scanning system; the optical amplifier is 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 also includes: An optical bandpass filter is used to suppress background light noise; the optical bandpass filter is disposed in the optical path between the receiving optical antenna and the photodetector, and the optical bandpass filter is an interference filter; A transimpedance amplifier is used to convert a current signal into a voltage signal and amplify the voltage signal; the input terminal of the transimpedance amplifier is coupled to the electrical output terminal of the photodetector. An analog-to-digital converter (ADC) is used for digital-to-analog conversion; the input of the ADC is coupled to the output of the transimpedance amplifier, and the output is coupled to the input 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 laser wavelength, and its 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 also includes an encoding management module, which stores and manages an encoding library containing multiple orthogonal waveform encodings, and controls the encoding drive signal to dynamically switch at different detection cycles or different scanning angles.

7. The anti-interference lidar system based on waveform encoding and adaptive signal processing according to claim 6, characterized in that, The control and signal processing unit includes an adaptive matched filtering module. The input of the adaptive matched filtering module is coupled to the electrical output of the photodetector. It is used to receive electrical signals and perform correlation operations on the electrical signals according to the local reference code copy generated by the encoding management module to obtain the correlation operation results, so as to extract the matching 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 filtering module includes a digital correlator / pulse compressor and a threshold detection and target judgment module; The digital correlator / pulse compressor processes the digital echo signal based on the local reference code copy generated by the encoding management module and outputs a sequence of correlation results. The input of the digital correlator / pulse compressor is coupled to the electrical output of the photodetector; The threshold detection and target judgment module is used to dynamically set the target detection threshold based on the noise level of the correlation calculation results output by the adaptive matched filtering module, and to identify valid targets from the correlation calculation results based on this threshold; the input of the threshold detection and target judgment module is coupled to the output of the adaptive matched filtering module. The threshold detection and target judgment module is configured to: calculate the noise statistics of the relevant calculation results in real time, and set the target detection threshold as a function of the noise statistics, so as to realize the dynamic adjustment of the target detection threshold with the ambient noise level.

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, Includes the following steps: The laser emitting module emits a laser, and the control and signal processing unit generates coded drive electrical signals. The encoding drive electrical signal corresponds to the selected encoding scheme, such as a linear frequency modulated waveform or a binary pseudo-random sequence; The programmable waveform encoder modulator receives the input laser, and the signal processing unit drives the programmable waveform encoder modulator to modulate the phase or intensity of the input laser, and outputs a laser pulse carrying specific encoded information. The beam shaping and scanning system receives scanning commands from 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 command, and emits the collimated laser pulse pointing in a specific direction into the environment under test. The receiving optical module receives a mixed optical signal returned from the environment under test; the mixed optical signal includes coded echoes reflected from the real target, noise generated by rain / fog particle scattering, and interference light emitted by other lidar. An optical bandpass filter filters out most of the background radiation, such as sunlight, allowing only a narrow band of light near the laser wavelength to pass through, thereby improving the signal-to-noise ratio. After filtering, the photodetector converts the mixed optical signal into an electrical signal. The control and signal processing unit performs correlation operations between the electrical signal and the stored local reference code copy to extract the target echo signal that matches the local reference code copy. Monitor the noise level of the relevant calculation results; The target detection threshold is dynamically calculated and updated based on the noise level. The relevant calculation results are compared with the updated target detection threshold to determine the final valid target point cloud data.

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