Multi-frequency Unwrapping for Time-of-Flight Range Ambiguity
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Solution Overview
Problem
Time-of-flight systems face challenges with phase wrapping at higher modulation frequencies, leading to ambiguity in range measurements, which existing methods address with computationally expensive solutions.
Innovation Solution
A frequency-unwrapping method that uses a transformation matrix to reduce dimensionality and generate a one-dimensional lookup table, allowing for accurate and precise range determination with simple integer arithmetic, suitable for multiple modulation frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If higher modulation frequencies are used to improve depth noise and resolution, then measurement precision is improved, but phase wrapping occurs leading to ambiguity in range measurements
Solution Approach 1:
The patent employs multiple modulation frequencies (first, second, and third frequencies) to perform periodic measurements at different phase wrapping intervals. By combining results from these periodic measurements at different frequencies, the system resolves phase wrapping ambiguity while maintaining the high measurement precision provided by higher modulation frequencies.
2Reliability
If existing methods are used to address phase wrapping, then range measurement reliability is improved, but computational complexity increases significantly
Solution Approach 1:
The patent segments the range measurement problem into multiple independent frequency-based measurements. Each frequency measurement is processed separately to determine its phase wrapping state, and these segmented results are then combined to achieve the final unambiguous range measurement, reducing overall computational complexity.
Solution Approach 2:
The patent introduces an additional dimension by using multiple modulation frequencies beyond the traditional single-frequency approach. This dimensional expansion allows the system to resolve phase wrapping ambiguity through frequency diversity rather than through computationally intensive processing of single-frequency data.
3Reliability
If multiple modulation frequencies are used to resolve phase wrapping, then range measurement reliability is improved, but device complexity increases
Solution Approach 1:
The patent implements a multi-frequency modulation system where the same hardware infrastructure handles multiple frequencies simultaneously. The imaging array and signal processing components serve universal functions across all frequency channels, reducing device complexity compared to having separate systems for each frequency.
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 provides high accuracy and precision in range measurement while reducing computational complexity, enabling handling of multiple frequencies and improving noise robustness, thus enhancing depth noise and resolution.
Implementation Method 1
Time-of-flight (ToF) systems produce a depth image of an object, each pixel of such image encoding the distance to the corresponding point in the object
Data Source
AI summary
The time-of-flight system disclosed herein includes a frequency unwrapping module configured to generate an input phase vector with M phases corresponding to M sampled signals from an object, determine an M−1 dimensional vector of transformed phase values by applying a transformation matrix (T) to the input phase vector, determine an M−1 dimensional vector of rounded transformed phase values by rounding the transformed phase values to a nearest integer, and determine a one dimensional lookup table (LUT) index value by transforming the M−1 dimensional rounded transformed phase values. The index value is input into the one dimensional LUT to determine a range of the object.