Coherent LIDAR True Peak Identification via Doppler Compensation
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Solution Overview
Problem
LIDAR systems face challenges in accurately determining target locations due to ghosting issues caused by Doppler shifts, which result in false peak detection and incorrect target positioning, especially when the system and targets are in motion.
Innovation Solution
The method involves transmitting up-chirp and down-chirp frequencies towards targets, receiving adjusted frequency signals, and using phase non-linearities to differentiate between true peaks and peak images by calculating and comparing frequency bins and peak shape estimates to determine the correct target location.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Doppler shift compensation is not applied, then the system structure remains simple, but false peak detection occurs and target location accuracy deteriorates
Solution Approach 1:
The patent applies preliminary action by performing Doppler shift compensation before peak detection. The system calculates Doppler shifts based on known target velocities, compensates for these shifts in the frequency domain, and then performs peak detection on the compensated signals. This preliminary compensation prevents false peak detection and improves target location accuracy without requiring complex additional hardware.
Solution Approach 2:
The patent employs feedback by using detected peak locations to refine Doppler shift estimates, which are then used to adjust the compensation applied to subsequent signals. This iterative feedback loop continuously improves measurement precision by correcting for Doppler effects based on actual observed data, resolving the contradiction between simple structure and accurate measurement.
2Reliability
If traditional peak detection is used without Doppler compensation, then processing is faster, but ghosting artifacts appear and reliability deteriorates
Solution Approach 1:
The patent extracts and separates the Doppler shift component from the total frequency shift. By identifying and removing the Doppler-induced frequency offset before peak detection, the system eliminates ghosting artifacts that would otherwise cause false detections. This extraction approach improves reliability by ensuring that only true target peaks are detected, while the processing time increase is minimized through efficient frequency domain operations.
3Measurement precision
If up-chirp and down-chirp frequencies are used without Doppler compensation, then the system can detect velocity, but peak association between up and down sweeps becomes unreliable
Solution Approach 1:
The patent exploits the asymmetric effect of Doppler shifts on up-chirp and down-chirp frequencies. By calculating and compensating for the different Doppler shifts that affect each chirp direction, the system can reliably associate peaks between up and down sweeps. The compensation accounts for the fact that a target moving toward the system causes different frequency shifts in up-chirp versus down-chirp, enabling accurate peak pairing and velocity measurement while maintaining manageable processing complexity.
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 mitigates ghosting by accurately identifying true peaks and determining target locations, even in scenarios with significant Doppler shifts, thereby improving the precision of range and velocity measurements in LIDAR systems.
Implementation Method 1
the one or more returned signals includes an adjusted up-chirp frequency shifted from the at least one up-chirp frequency caused by a relative motion of at least one of the target and the LIDAR system, and an adjusted down-chirp frequency shifted from the at least one down-chirp frequency caused by the relative motion
Data Source
AI summary
A light detection and ranging (LIDAR) system to transmit an optical beam toward a target and receive a returned optical beam. The optical beam includes an up-chirp frequency and a down-chirp frequency, and is modulated to have phase non-linearities. The LIDAR system generates a baseband signal from the returned optical beam, which includes a plurality of peaks corresponding with the up-chirp frequency and the down-chirp frequency. The LIDAR system identifies a first true peak in the baseband signal, and identifies a second true peak in the baseband signal based, at least in part, on a spectral shape of the second true peak caused by the phase non-linearities. The LIDAR system is to determine the location of the target using the first true peak and the second true peak.