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| Citation: | LIU Changyu, ZHANG Hao, GENG Fanglin, et al. Dynamic demodulation algorithm for bio-radar sensors based on range tapper[J]. Journal of Radars, in press. doi: 10.12000/JR24151
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Dynamic Demodulation Algorithm for Bio-radar Sensors Based on Range Tapper
DOI: 10.12000/JR24151
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Abstract
In non-inductive radar vital sign monitoring, frequency-modulated radars (such as frequency modulated continuous wave and ultra wideband) are more effective than continuous wave radars at distinguishing targets from clutter in terms of distance. Using range Fourier transform, the heartbeat and breathing signals can be extracted from quasi-static targets across various distance intervals, thereby improving monitoring accuracy. However, the commonly used range fast Fourier transform presents certain limitations: The breathing amplitude of the subject may cross the range bin boundary, compromising signal integrity, while breathing movements can cause amplitude modulation of physiological signals, hindering waveform recovery. To address these reasons, we propose an algorithm architecture featuring range tap reconstruction and dynamic demodulation. We tested the algorithm performance in simulations and experiments for the cross range bin cases. Simulation results indicate that processing signals crossing range bins with our algorithm improves the signal-to-noise ratio by 17 ± 5 dB. In addition, experiments recorded Doppler heartbeat diagram (DHD) signals from eight subjects, comparing the consistency between the DHD signals and the ballistocardiogram. The root means square error of the C–C interval in the DHD signal relative to the J–J interval in the BCG signal was 21.58 ± 13.26 ms (3.40% ± 2.08%). -
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References
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- Figure 1. Range tapper refactoring and dynamic demodulation algorithms
- Figure 2. Amplitude modulation of the signal caused by range FFT and the problem of spanning range bins (a) Amplitude response of range bin 10 and range bin 11 (b) Phase response of range bin 10 and range bin 11(c) Relationship between the amplitude modulation coefficient and the motion amplitude when the center point of the target motion is located in the range bin 10.5 and the range bin 10 respectively. (d) Constellation diagram when the center point of the target motion is located in the range bin 10.5 and the displacement reaches the width of one range bin. (e) Constellation diagram when the center point of the target motion is located in the range bin 10 and the displacement reaches the width of one range bin.
- Figure 3. The conditions of crossing range bin
- Figure 4. DCD extracted from amplitude modulated signals using different demodulation algorithms: a) Amplitude modulated physiological complex signal; b) DCD signal and reference signal after arctan demodulation and the reference; c) DCD signal and reference signal after DACM demodulation and the reference.
- Figure 5. Power spectral density of amplitude modulated physiological complex signal after arctan demodulation
- Figure 6. Power spectral density of DCD signal after processed by the proposed algorithm
- Figure 7. Data processing chain
- Figure 8. Block diagram of the experimental setup and the experimental setup (a) Block diagram of the experimental setup, (b) Photo of the experimental setup, (c) The radar sensor is connected to the PC through the data acquisition board and obtains timestamps through the wireless network; (d) The data collector synchronously collects ECG and BCG through ADC and obtains timestamps through the wireless network.
- Figure 9. Simulation results a) Spectrum diagram of the signal obtained by range FFT and arctan demodulation in 9 different cases; b) Spectrum diagram of the signal obtained after the corresponding data is processed by the algorithm in this paper; c) 8～16 Hz spectrum details of the signal obtained by range FFT; d) 8-16Hz spectrum details of the signal obtained by the proposed algorithm.
- Figure 10. (a)(d) Range-time heatmap, (b)IQ plot of signal from range bin 31, (c) phase of signal from range bin 31, (e) IQ plot of signal via Range tapper refactoring, (f) phase of signal via Range tapper refactoring.
- Figure 11. Cross range bin results (a) DHD signal and synchronized ECG signal, (b) DHD signal IBI and synchronized ECG signal IBI.
- Figure 12. DHD signal extraction procedure (a) Physiological complex signal before and after algorithm processing. (b) Demodulated DCD signal before and after the proposed algorithm processing. (c) DRD and DHD signals extracted from the DCD signal. (d) Detail comparison between the DHD signal and the synchronously acquired BCG signal after filtering with a passband of 7–16 Hz.
- Figure 13. Detected DHD signals for each eight subjects, and details of the DHD signals between 3 and 5 seconds, where the filter passband is 8～20 Hz .
- Figure 14. Relationship between C-C interval in DHD signal and J-J interval in BCG signal