Three-Level Pseudo Noise Modulation for Time-of-Flight Cameras
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Solution Overview
Problem
Time-of-flight distance measurement systems using continuous wave modulation suffer from high measurement noise and ambiguity issues, particularly in multi-user environments, where interfering signals lead to inaccurate measurements.
Innovation Solution
The use of pseudo noise digital sequences, specifically maximal length sequences combined with a delayed and inverted version of the same sequence, creates a three-level digital modulation signal that suppresses interfering signals and improves measurement precision.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If continuous wave modulation is used, then the system is simple to implement, but measurement precision deteriorates due to high measurement noise
Solution Approach 1:
The patent changes the modulation parameter from continuous wave (sinusoidal) to pseudo-random digital sequences. This parameter change transforms the signal characteristics to achieve better noise performance and measurement precision while maintaining implementation simplicity through digital signal processing
2Device complexity
If continuous wave modulation is used, then hardware components can be optimized to one specific frequency, but measurement precision deteriorates due to signal superposition errors in multi-user environments
Solution Approach 1:
The patent segments the measurement system into independent digital signal processing channels, where each user is assigned a unique pseudo-random code. This segmentation allows multiple users to operate simultaneously without mutual interference, as each user's signal can be distinguished through code differentiation in the digital domain
Solution Approach 2:
The patent uses copied pseudo-random sequences with different codes for multiple users. Each user receives a copy of the base pseudo-random sequence modulated with a unique code, allowing the system to maintain hardware simplicity while achieving multi-user compatibility through digital code differentiation
3Measurement precision
If high-frequency modulation waves are used, then measurement noise is reduced, but non-ambiguous measurement range deteriorates due to 2pi wrapping nature
Solution Approach 1:
The patent uses periodic pseudo-random sequences with programmable period length. The sequence period can be adjusted to match the desired measurement range, allowing the system to achieve both low noise (through high frequency content) and extended unambiguous range (through appropriate period selection) simultaneously
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 enhances measurement precision and reduces ambiguity, allowing for reliable operation of 3D time-of-flight cameras in both single-camera and multi-camera environments, while maintaining comparable maximum measurement range and signal power to sinusoidal modulation.
Implementation Method 1
The kind of signal carrier typically is manifold, ultra sonic, water or electromagnetic waves. Any time-of-flight measurement system, however, works in the same principle independent on the form of the carrier used.
Implementation Method 2
A general set-up scheme for time-of-flight distance measurement systems is shown in FIG. 1. The distance information is calculated as: where R is the distance between the measurement system 100 and the object 10, v is the propagation speed of the signal 114 from the signal source 110 and T is the measured time needed for the signal to travel between the measurement system 100 and the object 10 forth and back and then detected by the sensor 112.
Implementation Method 3
The time-of-flight measurement is usually accomplished by correlating the detected modulation signal d(t) with a reference signal r(t).
Data Source
AI summary
The modulation scheme disclosed in this invention report allows for utilizing multiple 3D time-of-flight cameras at the same time by exploiting the inherent pseudo noise properties of the optical modulation signals. Compared to recent systems based on pure pseudo noise modulation signals, the stochastic measurement error in a single-camera environment is significantly reduced. The basic concept relies on the generation of a three level optical modulation signal that includes two pseudo noise sequences.