FMCW LiDAR Doppler Aliasing Resolution via Dual Chirp Segmentation
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Solution Overview
Problem
FMCW LiDAR systems face errors in distance and speed measurements due to Doppler aliasing, where the Doppler beat frequency is greater than the range beat frequency, causing the measured beat frequency to be mirrored to the positive frequency domain, leading to inaccuracies in distance and speed calculations.
Innovation Solution
The method involves generating a first and second detection signal with corresponding local oscillator signals, each comprising multiple segments of continuous wave signals with specific frequency sweep directions and constant frequencies, allowing for the determination of Doppler aliasing and accurate calculation of target object distance and speed using beat frequencies and algorithms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FMCW LiDAR uses coherent mixing of detection light and local oscillator light, then signal-to-noise ratio is improved, but Doppler aliasing occurs when Doppler beat frequency exceeds range beat frequency, causing measurement errors
Solution Approach 1:
The patent segments the measurement process into multiple chirp sequences with different sweep directions (up-chirp and down-chirp). By dividing the measurement into multiple segments with opposite frequency sweep directions, the system can distinguish between range beat frequency and Doppler beat frequency contributions, thereby resolving Doppler aliasing while maintaining high measurement precision
Solution Approach 2:
The patent employs inversion by using opposite frequency sweep directions for different chirp sequences. The up-chirp sequence sweeps frequency from low to high, while the down-chirp sequence sweeps from high to low. This inversion allows the system to create a system of equations where the Doppler and range components can be separated and solved, eliminating measurement errors caused by Doppler aliasing
2Device complexity
If single laser FMCW LiDAR is used, then device complexity is reduced, but inability to resolve Doppler aliasing leads to measurement errors
Solution Approach 1:
The patent makes each laser module multi-functional by enabling it to generate multiple chirp sequences with different sweep directions. The first laser generates both up-chirp and down-chirp sequences, and the second laser does the same. This universality allows the system to achieve Doppler aliasing resolution without requiring four separate laser modules, thus maintaining relatively low device complexity while improving measurement precision
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 improves the accuracy of LiDAR distance and speed measurements by identifying and correcting Doppler aliasing, ensuring precise calculations even in scenarios where Doppler aliasing occurs, enhancing the reliability of FMCW LiDAR systems.
Implementation Method 1
the LiDAR receives the local oscillator light and the echo light formed by the detection light reflected by the target object through the photoelectric detection module for coherent mixing
Implementation Method 2
There may be Doppler aliasing phenomenon, when the Doppler beat frequency is greater than the range beat frequency, the measured beat frequency will be mirrored to the positive frequency domain
Data Source
AI summary
A LiDAR range and speed measurement method and a LiDAR, are disclosed. Through the technical solution provided by the embodiment of the present application, it is possible to determine whether Doppler aliasing occurs based on a first local oscillator signal generated by a first laser and a second local oscillator signal generated by a second laser, the first local oscillator signal including multiple segments of first continuous wave signals, the second local oscillator signal including multiple segments of second continuous wave signals, the second continuous wave signal including a first swept frequency signal and a first constant frequency signal. In the event of Doppler aliasing, a first algorithm is used to calculate the distance and/or speed of the target object relative to the LiDAR, thereby improving the accuracy of the LiDAR ranging and speed measurement.