FMCW LiDAR AM-FM Signal Paths for Fast Range and Velocity
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Solution Overview
Problem
Frequency modulated continuous wave (FMCW) LIDAR systems face limitations in quickly obtaining target information due to the need to wait for upchirp and downchirp signals, and they can alias short-range targets, leading to disambiguation issues.
Innovation Solution
The implementation of a LIDAR system that applies amplitude modulation (AM) or time of flight (TOF) signaling to frequency modulation (FM) signals, enabling simultaneous range and velocity measurement by processing reflection signals with active or passive modulation, and using time-frequency diagrams to extract range and Doppler information.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If FMCW LIDAR systems use upchirp and downchirp signals to capture target information, then measurement precision can be achieved, but the system cannot quickly obtain target information due to waiting for signal transmission and reception
Solution Approach 1:
The patent segments the signal processing into separate AM and FM paths. The AM path processes amplitude modulation for rapid range information, while the FM path processes frequency modulation for velocity and precise range. This segmentation allows the system to obtain quick range data from AM signals without waiting for the complete FMCW cycle, thereby improving data acquisition speed while maintaining measurement precision through the complementary FM path.
Solution Approach 2:
The system performs preliminary action by extracting range information from the AM path before completing the full FMCW measurement cycle. The AM modulation provides immediate range data that can be used preliminarily while the more precise FM measurements are still being acquired, reducing the overall waiting time for target information.
2Loss of information
If FMCW LIDAR systems use traditional upchirp and downchirp signaling, then comprehensive target information can be obtained, but short-range targets are aliased leading to disambiguation issues
Solution Approach 1:
The patent segments the measurement function into two independent paths: AM path for unambiguous range measurement and FM path for velocity and refined range measurement. This segmentation eliminates the aliasing problem for short-range targets in the AM path, as AM modulation provides direct range information without the folding issues inherent in traditional FMCW, while the FM path continues to provide comprehensive target information including velocity.
Solution Approach 2:
The AM modulation acts as an intermediary that provides unambiguous range information for short-range targets. By introducing this intermediate measurement method, the system can disambiguate short-range targets that would otherwise be aliased in traditional FMCW, while the FM path serves as the mediator for obtaining complete target information including velocity.
3Reliability
If the system waits for complete FMCW signal cycles to process target information, then measurement reliability is improved, but the speed of obtaining target information decreases
Solution Approach 1:
The patent segments the information extraction process to occur in parallel across AM and FM paths. The AM path can be processed independently and quickly to provide reliable range information without waiting for the complete FMCW cycle, while the FM path processes in parallel for velocity and refined range. This segmented parallel processing maintains measurement reliability through cross-validation while reducing the time loss associated with waiting for complete signal cycles.
Solution Approach 2:
The system maintains continuity of useful action by processing AM and FM signals simultaneously in parallel paths rather than sequentially waiting for complete FMCW cycles. This continuous parallel processing extracts useful information from both modulation types ongoing throughout the measurement period, improving the speed of obtaining target information while maintaining reliability through the corroborating measurements from both paths.
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 allows for efficient and accurate simultaneous measurement of range and velocity, reducing aliasing issues and improving the speed of data acquisition in LIDAR systems.
Implementation Method 1
frequency modulated continuous wave (FMCW) LIDAR systems utilize 'upchirp' (or 'up sweep') and downchirp (or 'down sweep') signals
Implementation Method 2
simultaneous determination of range and velocity in an FMCW LIDAR system
Implementation Method 3
The implementation of a LIDAR system that applies amplitude modulation (AM) or time of flight (TOF) signaling to frequency modulation (FM) signals
Implementation Method 4
amplitude modulation (AM) or time of flight (TOF) signaling to frequency modulation (FM) signals, enabling simultaneous range and velocity measurement
Data Source
AI summary
A light detection and ranging (LIDAR) system has a modulator to modulate a light signal from an optical source with a low-power mode at a section of a sweep signal to generate a pulsed light signal transmitted towards a target. The LIDAR system has a photodetector to receive a return beam from the target with an amplitude modulated (AM) signal portion and a frequency modulated (FM) signal portion. The LIDAR system processes the return beam with in-phase/quadrature (I/Q) detection to extract the AM signal portion and the FM signal portion. The system determines a range value and a velocity value for the target based on the extracted AM signal portion and the extracted FM signal portion.