LiDAR Triangular Wave Modulation Doppler Blind Area
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Solution Overview
Problem
LiDAR systems face errors in calculating the distance and speed of objects within a close range due to the Doppler effect, leading to a measurement blind area when the frequency shift caused by the Doppler effect exceeds the frequency offset from the flight time of the reflected light beam.
Innovation Solution
The LiDAR method involves generating a frequency-sweeping beam, splitting it into signal and local-oscillation light beams, and performing time delay or frequency-shift on these beams, along with in-phase quadrature coherent demodulation to obtain scalar values of the beat frequency, thereby expanding the ranging spectrum and avoiding measurement blind areas.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If continuous wave LiDAR measures fast-moving target objects, then the measurement speed capability is improved, but the Doppler frequency shift exceeds the frequency offset causing measurement errors and blind areas
Solution Approach 1:
The patent applies dynamics by implementing a triangular wave frequency modulation pattern that dynamically adjusts the frequency sweeping direction. The system switches between frequency-increasing phase and frequency-decreasing phase, allowing the beat frequency to remain within the detectable spectrum range even for fast-moving targets, thus resolving the measurement blind area problem while maintaining high speed capability
Solution Approach 2:
The patent changes the frequency modulation parameters by using triangular wave modulation instead of linear frequency modulation. This parameter change allows the system to generate both positive and negative frequency sweeps, creating beat frequencies that can be detected even when Doppler shifts are large, thereby expanding the measurable velocity range and eliminating blind areas
2Adaptability or versatility
If the frequency shift caused by Doppler effect is greater than the frequency offset from flight time, then fast moving objects can be detected, but errors are generated in calculation of information within close range creating measurement blind area
Solution Approach 1:
The system dynamically switches between frequency-increasing and frequency-decreasing phases using triangular wave modulation. This dynamic approach ensures that for any target velocity, the beat frequency during one of the phases will fall within the detectable spectrum range, eliminating measurement blind areas and improving reliability for both close-range and fast-moving object detection
Solution Approach 2:
The patent converts the harmful effect of large Doppler frequency shifts into a beneficial measurement mechanism. By using triangular wave modulation, the system intentionally creates large frequency variations that, when combined with the Doppler shift, produce detectable beat frequencies. The frequency-decreasing phase specifically compensates for large positive Doppler shifts, turning what would be a measurement error into an accurate measurement opportunity
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively determines the speed and distance of objects by accurately obtaining the scalar values of the beat frequency, expanding the measurement range, and eliminating the measurement blind area caused by the Doppler effect.
Implementation Method 1
the reflected light beam used to calculate the distance and the speed includes the optical Doppler frequency shift introduced by the movement of the target object
Implementation Method 2
the frequency offset caused by the flight time of the reflected light beam
Data Source
AI summary
A LiDAR method and system and an autonomous vehicle are provided. The method includes: generating a frequency-sweeping beam which is split into a signal light beam and a local-oscillation light beam; transmitting the signal light beam; receiving a reflected light beam; performing time delay or frequency-shift on at least one of the signal light beam, the reflected light beam or the local-oscillation light beam, and/or performing in-phase quadrature coherent demodulation on the local-oscillation light beam and the reflected light beam, so as to obtain scalar values of beat frequencies between the local-oscillation light beam and the reflected light beam; determining a speed of an object and/or a distance between the object and the LiDAR system.