Modulated Wave Time of Flight Sensor Noise Rejection
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Solution Overview
Problem
Continuous wave (CW) time of flight (ToF) LIDAR sensors face challenges in accurately measuring distance due to interference from ambient light and electronic noise, which degrades measurement quality and accuracy, especially in high-noise environments like daylight conditions.
Innovation Solution
The modulated wave time of flight (mwToF) sensor uses a carrier wave modulation technique to filter out ambient light and electronic noise by employing bandpass filters centered at the carrier frequency, allowing for higher precision time of flight measurements by demodulating the signal and reducing noise content.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If quadrature sampling is used to perform signal analysis on returned optical signal, then mutual interference and noise performance is improved, but distance ambiguities occur that are dependent on frequency and contrast decay limits sensitivity and accuracy under high ambient noise conditions
Solution Approach 1:
The patent modulates the optical carrier signal with a pseudorandom binary sequence (PRBS) code, changing the temporal pattern of the optical signal. This modulation allows the returned signal to be correlated with the known transmitted code pattern, enabling precise distance measurement through cross-correlation peak detection while maintaining frequency selectivity to reject ambient light noise.
Solution Approach 2:
The patent uses periodic modulation of the optical carrier with a pseudorandom binary sequence, creating a time-varying signal pattern that can be distinguished from ambient light. The periodic nature of the modulation allows for coherent integration over multiple cycles, improving signal-to-noise ratio while the known pattern enables unambiguous distance measurement through correlation processing.
2Object-affected harmful factors
If hardware solutions such as using multiple capacitors at the detectors are used to reduce the effects of sunlight, then ambient light interference is reduced, but the approach is not very effective and device complexity increases
Solution Approach 1:
The patent replaces hardware-based noise reduction approaches (multiple capacitors) with signal processing-based solutions. By modulating the optical carrier with a pseudorandom binary sequence and using correlation detection, the system achieves ambient light rejection through temporal signal characteristics rather than physical filtering components, improving effectiveness while reducing device complexity.
Solution Approach 2:
The patent changes the temporal parameter of the optical signal by modulating it with a pseudorandom binary sequence. This allows the system to distinguish the modulated signal from unmodulated ambient light through correlation processing, achieving effective ambient light rejection without relying on hardware filtering that proves ineffective against broad-spectrum sunlight.
3Device complexity
If pulsed LIDAR is used for distance measurement, then the approach is relatively simple, but performance degrades significantly in the presence of other LIDARs or in noisy environments and pulse amplitude varies wildly
Solution Approach 1:
The patent uses periodic modulation of the optical carrier with a pseudorandom binary sequence instead of simple pulsed illumination. This periodic modulation creates a time-varying signal pattern that can be distinguished from ambient light and other LIDAR signals through correlation detection, improving performance in noisy environments while maintaining reasonable system complexity.
Solution Approach 2:
The patent applies preliminary modulation to the optical carrier using a known pseudorandom binary sequence before transmission. This preliminary action embeds identifying characteristics in the transmitted signal that enable the receiver to distinguish the desired signal from interference through correlation processing, improving reliability in multi-LIDAR or noisy environments.
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 the accuracy and sensitivity of distance measurements by effectively rejecting ambient light and electronic noise, enabling higher precision and robustness in LIDAR applications even in noisy conditions.
Implementation Method 1
The light scattered by the object is detected by a photodetector
Implementation Method 2
The modulated carrier signal is sent to illuminate the object. The object returns a delayed version of the modulated carrier signal to the detector. The detector demodulates the returned signal to recover the (delayed) light signal of interest
Data Source
AI summary
A modulated wave time of flight (mwToF) sensor combines modern digital signal processing techniques with CW quadrature sampling methods to produce a sensor that is better at rejecting environmental noise such as ambient light as well as electronic noise that comes from sources such as signal amplification.