Non-invasive detection of cardiac and respiratory rates from stepped frequency continuous wave radar measurements using the state space method

In this paper, we discuss the design of a stepped frequency continuous wave (SFCW) radar, which transmits long duration pulses with higher average power and much narrower instantaneous bandwidth than UWB waveforms, to facilitate comparable signal resolution. FFT spectrograms, typically used in the extraction of vital signs from radar measurements, produce several spurious peaks at harmonics and intermodulation frequencies of respiration and heart rates, thereby increasing the uncertainty of these estimates, especially the heart rate. We apply a signal processing algorithm based on the state-space method for the extraction of cardiac and respiration rates from the data measured on a human subject using SFCW radar. Results show that accurate estimates of vital signs (heart rate < 1.2% in static mode and < 5.7% in motion) can be obtained without producing inter-modulation products that plague signal resolution in FFT spectrograms.