FMCW LiDAR Chirp-Rate Fusion for Doppler Ambiguity Removal
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Solution Overview
Problem
Existing FMCW LiDAR systems face Doppler ambiguity issues that hinder achieving high pixel rates due to the need for multiple measurements and FFT computations, which are not feasible for meeting the requirements of autonomous vehicles in terms of angular resolution, field of view, and frame rate.
Innovation Solution
An FMCW LiDAR system utilizing two or three light sources with different chirp rates, combined through an optical combiner, and employing a decision tree analysis to resolve Doppler ambiguity, reducing the number of measurements and FFT computations to two or one, respectively.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple measurements with different FTR are performed to resolve Doppler ambiguity, then measurement precision is improved, but measurement time increases and pixel rate decreases
Solution Approach 1:
The patent combines multiple FMCW measurements with different chirp rates into a single measurement interval by using multiple light sources simultaneously. This allows Doppler ambiguity resolution without requiring sequential measurements, thereby maintaining high pixel rate while achieving accurate range and velocity measurement.
Solution Approach 2:
The patent introduces an additional dimension by using multiple light sources with different chirp rates simultaneously. This transforms the problem from temporal sequencing (multiple measurements over time) to spatial/multidimensional measurement (multiple measurements concurrent in frequency domain), enabling parallel processing and maintaining high frame rates.
2Measurement precision
If multiple sequential FFT computations are performed to eliminate Doppler ambiguity, then measurement precision is improved, but computational overhead increases
Solution Approach 1:
The patent merges multiple FFT computations into a single FFT by simultaneously acquiring multiple FMCW signals with different chirp rates. This reduces computational complexity while maintaining the ability to resolve Doppler ambiguity through multi-frequency analysis in the frequency domain.
Solution Approach 2:
The patent performs preliminary frequency separation and signal organization before the FFT computation. By pre-organizing the multiple FMCW signals with different chirp rates into structured data formats, the subsequent FFT computation becomes more efficient and requires less processing overhead.
3Manufacturing precision
If measurement time is extended to achieve better distance resolution, then manufacturing precision is improved, but productivity decreases
Solution Approach 1:
The patent achieves better distance resolution without extending measurement time by utilizing the frequency domain dimension. Multiple light sources with different chirp rates provide parallel measurement paths, allowing high-resolution distance measurement through frequency analysis while maintaining short measurement intervals for high frame rates.
Solution Approach 2:
The patent changes the measurement parameter from temporal duration to frequency diversity. By using multiple chirp rates simultaneously, the system achieves improved distance resolution through frequency-domain analysis rather than extending the time-domain measurement window, thereby maintaining high productivity.
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 enhances pixel rate, improves signal-to-noise ratio, and achieves better distance resolution and repeatability by minimizing computational overhead and measurement time.
Implementation Method 1
a detector (32) detects a superposition of the reference light and the input light
Implementation Method 2
An optical combiner combines the first light and the second light, thereby obtaining measuring light having at least two different frequency components during a measurement interval
Implementation Method 3
a scanning unit directs the output light towards an object along different directions and receives input light that is obtained by reflection of the output light at the object
Implementation Method 4
The frequency difference between the two signals, which is usually referred to as beat frequency, is measured and used to compute the range R of the object and the relative velocity v in beam direction
Data Source
AI summary
The invention relates to a system and a method for simultaneous range and velocity measurement in an FMCW LiDAR system. A first light source produces first light having a first frequency that varies according to a first chirp rate. A second light source produces second light having a second frequency that is constant or that varies according to a second chirp rate. A splitter separates the measuring light into reference light and output light, and a scanning unit directs the output light towards an object and receives input light that is obtained by reflection of the output light at the object. A detector detects a superposition of the reference light and the input light. A computing unit computes unambiguously the range and relative velocity by analyzing beat frequencies resulting from the superposition. Ambiguities due to Doppler frequency shifts are removed by performing a decision tree analysis.