Lidar Phase Sequencing for Doppler Compensation and Ranging
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Solution Overview
Problem
Existing lidar sensor systems face challenges in reliably compensating for large frequency shifts due to the Doppler effect, which complicates the correlation between emitted and received signals, making it difficult to accurately determine distance and velocity of detected objects.
Innovation Solution
A lidar system that employs phase-modulated light signals with a transmission unit and reception unit, utilizing phase modulators to divide transmission sequences into unmodulated and phase-modulated portions, enabling reliable Doppler compensation through separate evaluation of these portions to ascertain Doppler frequency and distance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase-modulated light signals are used for lidar measurement, then distance and velocity detection capabilities are improved, but reliable Doppler compensation becomes difficult due to large frequency shifts
Solution Approach 1:
The transmission sequence is divided into two distinct portions: a first portion with constant phase (unmodulated) and a second portion with phase modulation. The unmodulated first portion serves as a reference signal that is not affected by phase coding, enabling reliable Doppler frequency estimation. This segmentation allows the system to separate the Doppler estimation function from the distance measurement function, resolving the contradiction between maintaining measurement precision and achieving reliable Doppler compensation.
2Measurement precision
If FFT analysis is performed on the received signal with phase code spectrum, then distance information can be processed, but Doppler frequency becomes difficult or impossible to detect
Solution Approach 1:
By segmenting the transmission sequence into unmodulated and phase-modulated portions, the system enables separate processing paths. The unmodulated first portion can be analyzed using FFT to extract Doppler frequency without the interfering phase code spectrum, while the phase-modulated second portion provides distance information. This segmentation resolves the difficulty of detecting Doppler frequency when phase codes are present.
Solution Approach 2:
The unmodulated first portion acts as an intermediary reference signal that mediates between the phase-modulated measurement signal and the Doppler estimation process. This reference signal provides a clean spectral baseline that enables Doppler frequency detection without being contaminated by the phase code modulation, thereby facilitating both distance and velocity measurements.
3Measurement precision
If complex hardware is used for Doppler compensation and velocity estimation, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The system uses the transmitted signal itself as a reference signal for Doppler estimation by incorporating an unmodulated portion in the transmission sequence. This self-service approach eliminates the need for separate reference signal generators or complex external calibration equipment, achieving accurate velocity estimation while minimizing hardware complexity and cost.
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 distance estimation and velocity determination with minimal hardware, allowing for improved parallelizability and reliable detection of multiple targets while minimizing costs.
Implementation Method 1
The phase modulator serves to modulate a phase of the light of the laser source
Implementation Method 2
The transmission optic serves to emit the light, modulated by the phase modulator, into an environment of the lidar sensor system
Implementation Method 3
In particular, it is thereby possible to receive reflected light that has been emitted from the transmission unit and reflected at an object in the environment
Implementation Method 4
enables reliable Doppler compensation for phase-modulated light signals. It thus makes possible, in particular, compensation for the large frequency shifts that are possible in the context of the lidar measurement principle due to the Doppler effect
Data Source
AI summary
A lidar sensor system. The lidar sensor system includes a transmission unit having a laser source, a phase modulator for modulating a phase of the light of the laser source, and a transmission optic for emitting the modulated light; a reception unit having a reception optic for receiving light reflected from an object and having an evaluation unit for evaluating the light received by the reception optic; the transmission unit being embodied to emit several transmission sequences of the light; each transmission sequence having a first portion and a second portion; the first portion being an unmodulated constant-phase signal; the second portion being a signal phase-modulated by the phase modulator; and the evaluation unit being embodied to determine at least an absolute value of a Doppler frequency based on the first portion, and to determine a distance to the object based on the Doppler frequency and the second portion.