Sub-sweep Sampling in Chirped LiDAR for Simultaneous Range and Velocity
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Solution Overview
Problem
Traditional LiDAR systems are unable to simultaneously measure range and velocity due to their reliance on direct time-of-flight detection, which leads to crosstalk issues and limitations in applications like autonomous driving, especially at long ranges and fast-measurement systems.
Innovation Solution
A multiple-wavelength chirped LiDAR system that uses independently modulated optical beams with frequency sweeps and sub-sweep sampling to simultaneously measure beat frequencies, allowing for accurate determination of range and velocity through antiphase chirp and chirp-DC modulation schemes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional pulse-based TOF detection is used, then range measurement is achieved, but velocity measurement capability is lost and crosstalk occurs
Solution Approach 1:
The patent changes the fundamental detection parameter from direct time-of-flight pulse detection to frequency-modulated continuous wave detection. By modulating the optical carrier wave at a frequency much higher than the pulse rate and detecting the beat frequency between transmitted and received waves, the system simultaneously achieves range measurement through the beat frequency and velocity measurement through Doppler shift analysis, eliminating the crosstalk problem inherent in traditional pulse-based systems.
Solution Approach 2:
The patent introduces an intermediary detection mechanism using beat frequency detection as a mediator between the transmitted optical waves and the target properties. Instead of directly detecting pulse return times, the system uses the beat frequency generated by mixing transmitted and received modulated waves as an intermediary parameter that encodes both range and velocity information, enabling simultaneous measurement without crosstalk.
2Measurement precision
If FM LiDAR with long sweep time is used, then long-range measurement capability is improved, but measurement speed decreases
Solution Approach 1:
The patent segments the frequency sweep into multiple sub-sweeps, each covering a portion of the total frequency band. By processing multiple sub-sweeps in parallel or sequentially within a single modulation period, the system maintains the long sweep time necessary for long-range measurement capability while effectively increasing the measurement rate through multi-segment processing, thus resolving the contradiction between range capability and measurement speed.
Solution Approach 2:
The patent introduces a frequency domain dimension by using frequency modulation of the optical carrier wave. This frequency domain approach allows the system to encode both range and velocity information in the beat frequency spectrum, enabling simultaneous measurement capabilities that transcend the time-domain limitations of traditional pulse-based systems and allow for both long-range detection and fast measurement rates.
3Device complexity
If single-beam LiDAR is used, then system complexity is reduced, but simultaneous multi-dimensional measurement capability is limited
Solution Approach 1:
The patent makes the optical detection system universal by enabling a single modulated optical beam to perform multiple measurement functions simultaneously. Through frequency modulation and beat frequency detection, the same single-beam system can measure both range and velocity dimensions at the same time, eliminating the need for separate measurement systems and reducing overall device complexity while enhancing multi-dimensional measurement capability.
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
Enables accurate and simultaneous measurement of range and velocity across two dimensions, improving long-range and fast-measurement capabilities without the need for a scanner, suitable for applications in autonomous driving and other sensing environments.
Implementation Method 1
at least the first transmitted optical beam being frequency modulated with sweeps of a frequency band to produce chirps
Implementation Method 2
The phase difference between these two waveforms yields a beat frequency... determining a range and velocity of the target from the multiple simultaneous measurements of the first and second beat frequencies
Implementation Method 3
detect first and second return optical beams into which light incident upon the target is collected
Data Source
AI summary
A light detection and ranging (LIDAR) system includes an optical circuit configured to generate a first transmitted optical beam and a second transmitted optical beam being frequency modulated with sweeps being divisible into multiple sub-sweeps over respective sub-bands of the frequency band, one or more receivers configured to produce a simultaneous measurement of a first beat frequency and a second beat frequency for each sub-sweep of the respective sub-band of the frequency band from return signals, and a signal processor. The signal processor is configured to determine a range and a velocity of a target from the simultaneous measurement and determine a custom sub-band size for a custom sub-sweep within the sweep. The signal processor is further configured to produce an additional simultaneous measurement of the beat frequencies based on the custom sub-sweep and determine an additional value of the range and the velocity from the additional simultaneous measurement.