Vital-Signs Detector Based on Frequency-Shift Keying Radar

Figures

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  Figure 1. Block diagram of the proposed frequency-shift keying (FSK) radar.

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  Figure 2. Cross-correlation method: (a) In the time domain; (b) in the frequency domain.

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  Figure 3. Proposed envelope detection method for discriminating the baseband signals at each operating frequency of the FSK radar. The frequency-control signal of the signal generator, which is indicated by red and blue shaders in the waveform, is used for synchronous data acquisition: (a) In-phase channel signals; (b) quadrature channel signals.

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  Figure 4. In-phase/quadrature (I/Q) imbalance calibration on the complex plane using the reference distance and the known periodic movement: (a) At the frequency of 2.45 GHz; (b) at the frequency of 2.5 GHz.

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  Figure 5. Direct-current (DC) offset calibration on the complex plane: (a) Uncalibrated signals of each frequency in the baseband; (b) Calibrated signals of each frequency based on the Pratt method.

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  Figure 6. Signal processing procedure in the proposed vital-signs detector.

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  Figure 7. Implemented radar module with two patch antennas on an FR4 printed circuit board (PCB).

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  Figure 8. Measurement setup for detecting the distance and vital signs using the proposed FSK radar.

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  Figure 9. Raw and filtered waveforms measured at a distance of 1 m using the proposed radar.

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  Figure 10. Measured distance and the root-mean-square error (RMSE) in the measurement using the proposed FSK radar with a frequency spacing of 50 MHz and switching time of 0.1 s: (a) Subject A; (b) Subject B; (c) Subject C; (d) averaged data.

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  Figure 11. Spectra of the vital signals measured at a distance of 1 m using the proposed FSK radar.

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  Figure 12. Spectra of the heartbeat signals measured by the proposed FSK radar at each operating frequency and with cross-correlation. The frequency peak of the cross-correlated signals is almost identical to that of the reference electrocardiogram (ECG) signals.