Blockwise PPG Enhancement Based on Time-Variant Zero-Phase Harmonic Notch Filtering

Figure 1. Principle of PPG measurement.

Figure 2. ACF with harmonic IIR notch filter.

Figure 3. Direct form 2 implementation of j-th IIR notch filter of harmonic IIR notch filter. a1j = (1 + rj)cos(jθ(n)), a2j = −rj, b1j = −2cos(jθ(n)), and kj = (1 + rj)/2.

Figure 4. Bode plot for ACF. The shape of the frequency response of ACF is determined by δ in Equation (2). The annotation δ↑ indicates the increment of the value of δ.

Figure 5. Block diagram representation of Zero-phase Line Enhancer (ZLE).

Figure 6. Real-time implementation scheme for ZLE algorithm.

Figure 7. Simulation results. Dotted line, dashed line, asterisks, and solid line represent the results of wavelet de-noising method, CFSA, ACF and ZLE, respectively. (a) Correlation coefficient; (b) F1; (c) MAE.

Figure 8. Reference, raw, and reconstructed PPG. Dashed line, dotted line, and solid line represent reference, raw, and reconstructed PPG, respectively. (a) Wavelet de-noising method; (b) CFSA; (c) ACF; (d) ZLE.

Figure 9. Periodogram power spectral density for PPG. Dashed line, dotted line, and solid line represent spectrums of reference, raw, and reconstructed PPG, respectively.

Figure 10. Distribution of correlation coefficient between reference and filtered PPG reconstructed by each MA reduction method. Upper and lower boxes represent the distribution of correlation coefficients from 25th to 75th percentiles. Top and bottom line indicate the 90th and 10th percentiles. (a) Wavelet de-noising method; (b) CFSA; (c) ACF; (d) ZLE.

Figure 11. Distribution of F1 scores for filtered PPG reconstructed by each MA reduction method. Upper and lower boxes represent the distribution of correlation coefficients from 25th to 75th percentiles. Top and bottom line indicate the 90th and 10th percentiles. (a) Wavelet de-noising method; (b) CFSA; (c) ACF; (d) ZLE.

Figure 12. Distribution of MAE for filtered PPG reconstructed by each MA reduction method. Upper and lower boxes represent the distribution of correlation coefficients from 25th to 75th percentiles. Top and bottom line indicate the 90th and 10th percentiles. (a) Wavelet de-noising method; (b) CFSA; (c) ACF; (d) ZLE.