Heart Rate Estimation Using Frequency Domain Motion Compensation
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Solution Overview
Problem
Conventional photoplethysmography (PPG) techniques for heart-rate estimation face challenges with low Signal-to-Noise Ratio (SNR) and Signal-to-Interference Ratio (SIR) due to motion artifacts, especially in wearable devices, leading to poor performance during motion conditions.
Innovation Solution
A method that involves obtaining frequency domain data blocks for both heart rate and acceleration signals, performing motion compensation by subtracting frequency domain data blocks using a scalar weight, and using a non-linear predictor to correct heart rate estimates, thereby improving heart rate estimation accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If PPG techniques are used for heart rate estimation, then the method is simple and easy to implement, but the Signal-to-Noise Ratio and Signal-to-Interference Ratio become very low in motion conditions
Solution Approach 1:
The patent combines PPG signal processing with accelerometer data fusion to compensate for motion artifacts. The system merges optical heart rate detection with motion sensing data, processing both signals together through a unified algorithm that corrects PPG measurements based on accelerometer-derived motion characteristics, thereby maintaining measurement precision during motion while keeping the overall system relatively simple
Solution Approach 2:
The patent introduces an intermediary processing layer that acts as a mediator between the raw PPG signal and the final heart rate estimate. This intermediary layer uses accelerometer data as a mediator to identify and remove motion-induced artifacts from the PPG signal, allowing the system to maintain high measurement precision without significantly increasing operational complexity
2Measurement precision
If motion compensation techniques are applied to improve signal quality, then SNR and SIR increase, but processing complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-processing the accelerometer data to extract motion characteristics before they contaminate the PPG signal. The system performs preliminary motion characterization and prepares compensation parameters in advance, which are then applied to correct the PPG signal. This approach improves signal quality while managing processing complexity by organizing computations in a structured, multi-stage manner
Solution Approach 2:
The patent segments the processing into distinct stages: accelerometer data acquisition, motion artifact identification, PPG signal correction, and heart rate estimation. Each segment handles a specific aspect of the problem independently, which improves overall signal quality while making the processing complexity more manageable through modular organization of computational tasks
3Measurement precision
If frequency domain techniques are used for motion compensation, then motion artifacts are reduced, but computational requirements increase
Solution Approach 1:
The patent applies partial action by implementing frequency domain compensation only for the specific frequency ranges where motion artifacts are most prominent, rather than processing the entire frequency spectrum. This selective approach effectively reduces motion artifacts in the critical heart rate frequency band while minimizing unnecessary computational power consumption in other frequency ranges
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 effectively enhances heart rate estimation accuracy by overcoming noise and motion-induced interference, providing a high processing gain and a secondary estimator to supplement primary optical estimations.
Implementation Method 1
photoplethysmography (PPG). Photoplethysmography involves obtaining optically a volumetric measurement of an organ (plethysmogram). A photoplethysmogram is often obtained by using a pulse oximeter which illuminates the skin and measures changes in light absorption.
Implementation Method 2
acquire an acceleration signal from an acceleration sensor configured for acquiring an acceleration signal representative of the acceleration of said body organ
Data Source
Figure 1A
Figure 1B
Figure 2
AI summary
Method for the estimation of the heart-rate using photoplethysmography on a body organ, in particular a wrist of a user, comprising acquiring optically (13a, 13b, 17) from said body organ a heart beat signal (o), acquiring (21) an acceleration signal (ax, ay, az) representative of the acceleration of said body organ, selecting data blocks (Bo, Bx, By, Bz) of said acquired heart beat signal (o) and acceleration signal (ax, ay, az), compensating said heart beat signal (o) by the acceleration signal (ax, ay, az), calculating the heart rate value (r) on the basis of said compensated heart beat signal (O') . The method provides obtaining (130) from said selected data blocks (Bo, Bx, By, Bz) corresponding frequency domain data blocks for the heart beat signal (O) and for the acceleration signal (AX, AY, AZ), said compensating operation includes performing a motion compensation (210) in the frequency domain, compensating the frequency domain data blocks for the heart beat (O) with the corresponding frequency domain data blocks for the acceleration signal (AX, AY, AZ).