Coherent Lidar Phase Modulation Hardwired Correlation Filtering
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Solution Overview
Problem
Current lidar systems, particularly time-of-flight systems, face limitations in accurately measuring distance and relative speed due to ambiguity issues in multiple reflections and high manufacturing costs, while coherent lidar systems with phase modulation struggle with digital evaluation sensitivity and range.
Innovation Solution
A coherent lidar system employing phase modulation with pseudo-random discrete phase values, utilizing a hardwired digital circuit for two-dimensional correlation filtering, and optimizing signal processing through twiddle factors and fast Fourier transforms to enhance detection sensitivity and accuracy, allowing for precise distance and speed measurement of multiple objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If phase modulation with pseudo-random discrete phase values is used in coherent lidar systems, then ambiguity issues in multiple reflections are resolved and detection accuracy is improved, but digital evaluation becomes more elaborate and sensitivity decreases
Solution Approach 1:
The patent divides the correlation filtering process into two separate dimensions: time shift correlation and frequency shift correlation. This segmentation allows each dimension to be processed independently using dedicated hardware circuits, resolving the contradiction by enabling accurate phase modulation evaluation while maintaining sensitivity through specialized hardware optimization for each correlation dimension.
Solution Approach 2:
The patent replaces general-purpose digital signal processing with dedicated hardwired digital circuits that perform correlation filtering. This substitution of mechanical/computational systems with specialized hardware eliminates the elaborateness of digital evaluation while maintaining or improving sensitivity through optimized hardware implementation of the correlation operations.
2Measurement precision
If two-dimensional correlation filtering is performed for accurate distance and speed measurement, then detection sensitivity and range are improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent replaces complex software-based two-dimensional correlation filtering with hardwired digital circuits that perform the filtering in dedicated hardware. This substitution reduces device complexity by eliminating the need for elaborate digital signal processing software while maintaining measurement accuracy through optimized hardware implementation of both time and frequency correlation operations.
Solution Approach 2:
The patent segments the two-dimensional correlation filtering into independent time-shift and frequency-shift processing stages, each handled by dedicated hardware circuits. This segmentation reduces overall system complexity by allowing each dimension to be processed separately with optimized hardware, rather than requiring a monolithic complex processing system.
3Reliability
If coherent lidar systems are used instead of time-of-flight systems, then sensitivity at higher distances and manufacturing cost are improved, but the ability to directly measure relative speed via Doppler effect requires complex signal processing
Solution Approach 1:
The patent replaces complex software-based signal processing for Doppler effect measurement with hardwired digital circuits that perform frequency correlation filtering. This substitution maintains the sensitivity advantages of coherent lidar at higher distances while reducing signal processing complexity through dedicated hardware implementation that directly extracts speed information from frequency shifts.
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 system achieves high sensitivity and range capabilities, effectively addressing ambiguity issues and reducing manufacturing costs by leveraging digital signal processing and efficient hardware implementation.
Implementation Method 1
signals reflected back from objects, which are delayed with respect to the emitted signal by the distance-dependent transit time and are shifted in frequency by the relative speed-dependent Doppler effect
Implementation Method 2
the emitted electromagnetic wave is modulated, i.e., it alters in at least one of the parameters of amplitude, frequency or phase over time
Data Source
AI summary
A coherent lidar system for capturing the surroundings is configured to emit a phase-modulated signal with pseudo-random change over discrete phase values. The system receives the signals reflected back from objects and converts the signals into a low-frequency signal by mixing and digitizing. The system includes a digital signal processing for correlation filtering of the low-frequency received signal. At least a part of the two-dimensional correlation filter is realized by a hardwired digital circuit embodied as a pipeline, wherein multiple or all of the output values are determined per clock frequency of the digital circuit in one of the two dimensions, and over a sequence of clock frequencies in the other dimension.