CASINOR: Combination of adaptive filters using single noise reference signal for heart rate estimation from PPG signals
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ORIGINAL PAPER
CASINOR: Combination of adaptive filters using single noise reference signal for heart rate estimation from PPG signals K. R. Arunkumar1 · M. Bhaskar1 Received: 7 November 2019 / Revised: 20 February 2020 / Accepted: 3 April 2020 © Springer-Verlag London Ltd., part of Springer Nature 2020
Abstract The accuracy of the heart rate (HR) estimated from the photoplethysmography (PPG) signal is always skeptical due to the ubiquity of the motion artifact (MA) in the signal. To ensure the HR estimated from the PPG signal is accurate, a new algorithm is proposed for the removal of MA component from the PPG signal using accelerometer signals. In this paper, the combination of adaptive filters using single noise reference signal referred to as CASINOR is proposed. The recursive least square (RLS) and normalized least mean square (NLMS) adaptive filters are used for denoising the PPG signals. The selection of single noise reference signal is based on the power value of the accelerometer signals. The MA-reduced PPG signals obtained from these RLS and NLMS filters are combined to a single PPG signal using sigmoid function, and the HR is estimated. The estimated HR is refined by using phase vocoder. The proposed method resulted in less HR estimation error of 1.92 beat per minute (BPM) on 23 PPG datasets (IEEE SP CUP 2015). Reduced error value, less computational time and improved accuracy augment this technique to be implemented in wearable devices. Keywords Photoplethysmography · MA removal · Combination of RLS and NLMS adaptive filters · Phase vocoder · HR estimation
1 Introduction Cardiovascular parameters are monitored by processing the electrocardiography (ECG) signals. Despite being accurate, ECG is not preferred for wearable devices because it is not comfortable due to sensor placements. PPG sensors are promising alternative to ECG sensors as they are simple, low cost and easily embedded on a wearable device like smart watch [1]. The PPG sensors emit the light to the skin and measure the changes in the intensity of the light collected at the photodetector (PD). The intensity of the light collected at the PD correlates with the cardiac rhythm. Thus, the PPG signal helps in estimating the HR. HR is estimated from the PPG signal by placing the PPG sensors at various peripheral positions such as ear [2], finger [3], forehead [4] and wrist [5]. The placement of PPG sensors in the wrist
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K. R. Arunkumar [email protected] M. Bhaskar [email protected]
1
Department of Electronics and Communication Engineering, National Institute of Technology Tiruchirappalli, Tiruchirappalli, Tamil Nadu, India
is cozy but the wrist movement is frequent; due to this, the PPG signal data collected from the wrist are susceptible to MA. To reduce the effect of MA components from PPG signal, many signal processing techniques have been proposed and their performance is evaluated using PPG dataset. Kim et al. used independent component analysis technique for removing the MA component from the PPG signal [6]. Zhang et al. [7]
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