PPG Heart Rate Monitor Motion Compensation via Single FFT
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Solution Overview
Problem
Existing heart rate measurement technologies using photoplethysmography (PPG) signals face challenges in accurately estimating heart rate due to motion-induced artifacts, which current methods struggle to effectively address, especially when motion occurs in multiple axes.
Innovation Solution
A method that combines motion compensation signals from three-axis accelerometers with PPG signals using normalized least mean squares (NLMS) filters, followed by coherent combining and a single Fourier Transform, to generate a frequency domain signal for improved heart rate estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If motion compensation is performed using traditional multi-FFT methods, then motion artifacts are reduced, but computational complexity increases
Solution Approach 1:
The patent combines multiple motion compensation operations and multiple Fast Fourier Transforms into a single unified FFT operation. By merging the compensation signals from different axes and performing one coherent FFT instead of multiple separate FFTs, the computational load is significantly reduced while maintaining the ability to remove motion artifacts across multiple dimensions
Solution Approach 2:
The patent segments the motion compensation process by handling each accelerometer axis separately through dedicated NLMS filters, then combines these segmented results coherently. This segmentation allows targeted motion artifact removal for each axis while the final combination achieves comprehensive motion compensation with reduced overall complexity
2Reliability
If three-axis accelerometer data is processed separately, then motion artifacts from all directions are compensated, but processing time increases
Solution Approach 1:
The patent maintains continuous motion compensation by processing all three accelerometer axes simultaneously through parallel NLMS filters and combining their outputs in a single coherent FFT operation. This continuous processing approach ensures that motion artifacts from any direction are compensated without interruption or sequential delays
Solution Approach 2:
The patent performs preliminary motion compensation by applying NLMS filters to each accelerometer axis before the final FFT operation. This preliminary processing removes motion artifacts in advance, allowing the subsequent FFT to focus solely on extracting heart rate information from the cleaned PPG signal
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 reduces motion-induced errors in heart rate estimation, achieving a mean error of at least 1.27 beats per minute, with reduced complexity compared to prior methods, and is suitable for embedded applications.
Implementation Method 1
Photoplethysmography (PPG) is a well-known optical method for measuring the change in blood flow. In PPG, a light source at a particular wavelength, typically, red, infra-red or green, is kept at a skin surface and the reflected light is measured and related to blood flow.
Implementation Method 2
receiving an X-axis acceleration signal, a Y-axis acceleration signal, and a Z-axis acceleration signal from an accelerometer of the heart rate monitor device
Data Source
AI summary
A method for heart rate measurement in a photoplethysmograph (PPG) heart rate monitor device is provided that includes performing motion compensation on a PPG signal wherein a motion compensated PPG signal PPGaccX is generated with reference to an X-axis acceleration signal, a motion compensated PPG signal PPGaccY is generated with reference to a Y-axis acceleration signal, and a motion compensated PPG signal PPGaccZ is generated with reference to a Z-axis acceleration signal, combining PPGaccX, PPGaccY, and PPGaccZ to generate a final motion compensated PPG signal, wherein a first weight is applied PPGaccX, a second weight is applied to PPGaccY, and a third weight is applied to PPGaccZ, performing a single Fourier Transform (FT) on the final motion compensated PPG signal to generate a frequency domain PPG signal; and estimating a heart rate based on the frequency domain PPG signal.