Resolving ToF Distance Ambiguities Using Coded-Modulation Phase Images
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Solution Overview
Problem
Indirect time-of-flight (ToF) measurements, such as continuous-wave (CW) ToF and coded-modulation ToF, suffer from distance ambiguities due to phase wrapping, which complicates depth detection and requires additional measurements to resolve, increasing data storage and processing demands.
Innovation Solution
The use of two or more coded-modulation measurements with specifically selected modulation codes and reference signals to resolve distance ambiguities without additional CW phase measurements, by obtaining correlation values that overlap and determine the actual distance range through mask values.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional CW ToF measurements are used, then depth detection can be performed, but distance ambiguities occur due to phase wrapping
Solution Approach 1:
The patent combines multiple coded-modulation measurements with different modulation codes into a single integrated measurement process. By merging the information from multiple codes and using joint correlation analysis, the system resolves distance ambiguities without requiring separate additional measurement sets, thus improving reliability while maintaining measurement precision.
Solution Approach 2:
The patent changes the modulation code parameters used in coded-modulation ToF measurements. By using multiple different modulation codes with distinct autocorrelation properties, the system creates multiple measurement perspectives that, when combined, resolve the phase wrapping ambiguity and improve distance measurement reliability.
2Reliability
If additional phase sets of measurements are performed with different reference signal frequencies, then distance ambiguities can be resolved, but data storage and processing power requirements increase
Solution Approach 1:
The patent segments the measurement process into multiple coded-modulation measurements using different modulation codes within a single phase set. Instead of performing complete additional phase sets with different frequencies, the system divides the resolution task across multiple codes, reducing the overall data volume and processing complexity while maintaining ambiguity resolution capability.
Solution Approach 2:
The patent makes a single phase set of measurements serve multiple functions by using different modulation codes. The same measurement framework processes multiple codes simultaneously, extracting both depth information and ambiguity resolution information without requiring separate dedicated measurement sets, thus reducing device complexity.
3Length of stationary object
If coded-modulation measurements are used to extend ambiguity distance, then measurement range increases, but phase wrapping problems persist
Solution Approach 1:
The patent creates a composite measurement approach by combining multiple coded-modulation measurements with different modulation codes. This composite measurement strategy leverages the extended ambiguity distance of coded modulation while using the diversity of multiple codes to resolve remaining phase wrapping issues, achieving both extended range and high reliability.
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 efficiently eliminates distance ambiguities in ToF measurements, enabling accurate depth mapping without the need for extra data collection, thereby reducing processing power and storage requirements while improving depth resolution.
Implementation Method 1
determine the distance to an imaged object or scene by determining a phase difference between modulated light illuminating the object or scene and reflected light received at the imaging sensor
Implementation Method 2
depth measurements, i.e., measurements of the distance to various features of an object or objects in view of an image sensor may be performed as indirect time-of-flight (ToF) measurements
Implementation Method 3
the correlation function for the modulating waveform and the corresponding reference signal is itself a periodic waveform
Data Source
AI summary
Distance ambiguities arising from indirect time-of-flight (ToF) measurements are resolved by using additional information from two or more coded-modulation measurements. An indirect ToF measurement is performed for a pixel of an image processor, to obtain a value indicative of an apparent distance to an imaged object or scene. First and second coded-modulation measurements are also performed, using respective combination of modulation code and reference signals, such that correlation peaks corresponding to these measurements overlap and cover respective first and second adjoining ranges of distances to imaged objects. First and second mask values are determined from the correlation values obtained from the coded-modulation measurements and are used to determine whether the value indicating the apparent distance indicates an actual distance within the first range of distances or within the second range of distances.