Hierarchical De-aliasing Time-of-Flight Depth Measurement
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Solution Overview
Problem
Time-of-flight (TOF) systems face challenges in disambiguating depth distance measurements due to phase shift ambiguity, especially in the presence of noise, and existing methods to increase the aliasing interval range by decreasing modulation frequency result in lower resolution and increased power consumption.
Innovation Solution
The implementation of a hierarchical dealiasing method using multiple modulation frequencies, where intermediate frequencies are generated and phases are computed to achieve a larger aliasing interval range while maintaining high resolution, effectively dealing with noise and ambiguity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If modulation frequency is decreased to increase aliasing interval range, then unambiguous range is improved, but resolution and power consumption performance deteriorate
Solution Approach 1:
The patent segments the dealiasing process into multiple hierarchical steps, using different modulation frequencies at different levels. The first level uses a lower modulation frequency to establish a coarse unambiguous range, while subsequent levels use higher modulation frequencies to refine the measurement with higher resolution. This segmentation allows the system to achieve both large unambiguous range and high resolution without the performance penalties of continuously operating at low frequency.
Solution Approach 2:
The system dynamically switches between different modulation frequencies based on the measurement requirements and current operating conditions. The modulation frequency is not fixed but adapts across hierarchical levels, allowing the system to optimize between unambiguous range and resolution dynamically. This dynamic frequency adjustment resolves the contradiction by using low frequency only when necessary for extended range and switching to high frequency for precise measurements.
2Length of stationary object
If modulation frequency is decreased to increase aliasing interval range, then unambiguous range is improved, but power consumption increases
Solution Approach 1:
The patent segments the measurement process into hierarchical levels where lower modulation frequencies are used only for coarse range determination and higher frequencies are used for precise measurements. This segmentation reduces the overall time the system operates at low frequencies, thereby reducing the power consumption penalty associated with extended unambiguous range while maintaining measurement accuracy.
Solution Approach 2:
The system uses partial action by applying low modulation frequency only partially - specifically only for the initial coarse range estimation and only when necessary. Once the coarse range is established, the system transitions to higher frequencies for the remaining precise measurements. This partial use of low frequency operation achieves extended unambiguous range capability without the full power consumption penalty that would result from continuous low frequency operation.
3Length of stationary object
If multiple modulation frequencies are used to achieve larger aliasing interval range, then unambiguous range is improved, but device complexity increases
Solution Approach 1:
The patent segments the multiple frequency operation into a structured hierarchical framework with clear levels and progression rules. Each level has a specific purpose and the transition between levels follows defined criteria. This segmentation organizes the complexity into a manageable hierarchy rather than a chaotic multi-frequency system, making the increased device complexity acceptable and systematic.
Solution Approach 2:
The patent introduces intermediate frequencies that serve as mediators between the base frequency and the final measurement frequency. These intermediate levels facilitate smooth transitions and provide stepping stones for the hierarchical dealiasing process, reducing the abrupt complexity jump that would result from directly using multiple high frequencies simultaneously. The intermediaries break down the complexity into manageable stages.
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 allows for an increased unambiguous range with low noise amplification, providing high resolution and efficiency, even at high modulation frequencies or large unambiguous ranges, without the performance penalties associated with lowering modulation frequency.
Implementation Method 1
comparing phase shift (θ) between emitted optical energy and reflected detected optical energy
Implementation Method 2
time-of-flight (TOF) systems that acquires depth images at distances (Z) by comparing phase shift
Implementation Method 3
examining phase-shift in the optical signal reflected from the target object back to the TOF system
Data Source
AI summary
A TOF system acquires depth data using n≧3 modulation frequencies f1, f2, . . . , fm separately, associated with separate aliasing interval ranges Z1, Z2, . . . , Zm. Next, n intermediate frequencies fDE1, fDE2, . . . , fDEn are generated sorted by order of fDE1<fDE2< . . . <fDEn and corresponding phases are computed from the data acquired separately using f1, f2, . . . , fm. Hierarchically dealiasing of the thus-acquired data is carried out using the generated intermediate frequencies. Hierarchical dealiasing may be carried out one step at a time, if desired. Thus operated, the TOF system provides an effective aliasing interval range ZD>Zk for k=1 . . . n as if said TOF system operated at a very low modulation frequency fD, while simultaneously providing depth resolution certainty as if said TOF system operated at a high modulation frequency fE. Preferably high modulation frequency fE is a function of all modulation frequencies f1, f2, . . . , fm, which function may be an arithmetic mean or a weighted average of f1, f2, . . . , fm.