Coherent Lidar Binary Phase Modulation Signal Processing
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Solution Overview
Problem
Existing coherent lidar systems face challenges with complex modulation techniques, such as linear frequency modulation, which result in ambiguity issues and high production costs, as well as less sensitivity and shorter ranges due to elaborate signal evaluation methods.
Innovation Solution
A power-modulated coherent lidar system using a switch or changeover switch for cost-effective signal modulation, combined with a low-outlay signal evaluation method involving a relatively low number of fast Fourier transforms (FFTs) for determining object distance and relative speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If linear frequency modulation is used in coherent lidar systems, then distance measurement is enabled, but ambiguity problems occur in case of multiple reflections and production complexity increases
Solution Approach 1:
The patent changes the modulation parameter from linear frequency modulation to binary phase modulation. The phase modulation uses discrete phase values (0 and 180 degrees) instead of continuous frequency sweeping, which simplifies the modulation generation while maintaining distance measurement capability through phase shift detection.
Solution Approach 2:
Instead of modulating the frequency linearly as in conventional approaches, the patent inverts the approach by using binary phase switching. The phase modulation sequence is generated by switching the laser carrier phase between two discrete values, which simplifies the modulation mechanism and eliminates the ambiguity problems associated with frequency modulation in multi-reflection scenarios.
2Reliability
If phase modulation with pseudo-random change is used, then ambiguity problems are reduced, but digital evaluation complexity increases and sensitivity decreases
Solution Approach 1:
The patent simplifies the phase modulation from pseudo-random phase changes to binary phase switching between fixed values (0 and 180 degrees). This parameter change reduces the complexity of generating the modulation sequence while maintaining the ability to resolve ambiguities through correlation analysis of the binary phase pattern.
Solution Approach 2:
The patent uses a simplified binary phase code that can be easily stored and reproduced, rather than requiring complex pseudo-random phase sequences. The binary phase modulation pattern is copied into a lookup table or memory structure, allowing for simple generation and easy correlation processing during signal evaluation.
3Measurement precision
If elaborate signal evaluation methods are used, then measurement accuracy is improved, but processing outlay increases and range is reduced
Solution Approach 1:
The patent replaces complex digital signal processing operations with simpler correlation-based methods. Instead of using elaborate Fourier transforms and complex algorithms, the system uses correlation analysis between the received signal and the known binary phase modulation sequence, which is computationally more efficient and maintains measurement accuracy.
Solution Approach 2:
The patent applies correlation processing only to the essential features of the signal (the binary phase transitions) rather than processing every detail of the complex signal waveform. This selective processing approach reduces the computational outlay while maintaining sufficient accuracy for object detection and ranging.
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
The proposed solution enables the realization of a high-performance lidar system with low manufacturing costs, achieving improved sensitivity and longer ranges without the disadvantages associated with previous modulation techniques.
Implementation Method 1
shifted in frequency by the relative speed-dependent Doppler effect
Implementation Method 2
delayed with respect to the emitted signal by the distance-dependent transit time
Data Source
AI summary
A coherent lidar system for capturing surroundings emits a power-modulated signal which is realized by irregular switching on and off. The signals reflected back are received and digitized in a receive sequence, wherein the variable dimensions time shift and frequency shift of signals reflected by objects are determined from the receive sequence by digital signal processing. A two-dimensional correlation filtering is used for the dimensions time shift and frequency shift, or a discrete Fourier transform is calculated to reduce the required computing outlay, wherein the respective frequencies are determined from values of said Fourier transform, wherein the receive sequence is turned back in each case in frequency regarding the respective frequencies. The object distance is determined from values of this respective correlation and the radial relative speed of the respective object is determined from the respective frequency.