PPG Motion Artifact Detection Using Wavelet Transform
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Solution Overview
Problem
PPG signals are often distorted by motion artifacts and radio noise, making it difficult to accurately detect heart rate and other physiological parameters, as these artifacts cannot be removed effectively using simple filters and require advanced signal processing techniques.
Innovation Solution
A method using wavelet transform to detect and remove motion artifacts from PPG signals, involving signal synchronization, noise removal, and wavelet decomposition to isolate and correct frequency bands affected by motion artifacts, employing cross-correlation for time synchronization and discrete wavelet transforms with FIR filters to filter out noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PPG signal is measured using a single sensor attached to body terminal part, then ease of operation is improved, but measurement precision deteriorates due to motion artifacts and radio noise
Solution Approach 1:
The patent combines multiple PPG signals from different body terminal parts (finger, earlobe, toe) into a composite signal. By merging multiple measurement channels, the system maintains the ease of using simple PPG sensors while improving measurement precision through signal integration and motion artifact cancellation across channels.
Solution Approach 2:
The patent introduces an intermediary processing system that receives multiple PPG signals, performs time-synchronization, applies wavelet transform for motion artifact detection, and generates a corrected composite PPG signal. This intermediary processing stage acts as a mediator between the simple sensor measurements and the final accurate health parameters.
2Measurement precision
If wavelet transform is applied to detect motion artifacts, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The patent segments the PPG signal processing into distinct frequency bands using wavelet transform. By dividing the signal into approximation coefficients (low frequency) and detail coefficients (high frequency), the system can specifically target motion artifacts in certain frequency ranges while preserving the underlying physiological signal, thereby improving detection accuracy without overwhelming complexity.
Solution Approach 2:
The patent applies wavelet transform selectively to detect and remove motion artifacts rather than processing the entire signal uniformly. By focusing computational resources on identifying and correcting specific artifact portions through thresholding and coefficient modification, the system achieves high measurement precision while controlling overall processing complexity.
Data Source
AI summary
A motion artifact detecting method using wavelet transform which is capable of removing the problem caused by a radio noise and a motion artifact generated during the measurement of a PPG signal which is one of bio-signals, the method including: measuring a PPG signal; generating a signal obtained by removing a radio noise from the measured PPG signal; setting a reference signal from the signal from which the radio noise is removed; selecting a base signal based on the set reference signal; performing wavelet transform using the base signal; and detecting and removing a motion artifact using the wavelet-transformed value.