Benefits of Coherent Low-IF for Vital Signs Monitoring Using Doppler Radar

Sensing of Life Activities at the Human-Microwave Frontier

“…Measurements on a mechanical target demonstrated effective signal-to-noise ratio improvement. Measurements on a human subject about 3 m away demonstrated low-IF heart rate detection with a root-mean-square error of less than 0.8 beats/min, whereas a reference direct conversion system failed in that case [16].…”

“…To tackle the problem, coherent low-intermediatefrequency (IF) systems were adopted [15]. A comprehensive analysis showed that this architecture has the range correlation benefits of the homodyne system, while minimizing the baseband flicker noise [16]. Measurements on a mechanical target demonstrated effective signal-to-noise ratio improvement.…”

Digitally assisted low IF architecture for noncontact vital sign detection

“…te is the amount of time to introduce a 90° phase shift for SI F (t), that is te = 2IT/ 4 WIF ' One of the advantages of the digitally assisted low IF architecture can be seen in (4)-(6): by demodulating the IF signal with the sampled IF carrier SIF(t), the phase noise ((JIF(t) is depressed. Low IF systems presented in [6] and [7] use separately generated IF carriers…”

“…The system uses a 70 MHz IF carrier and an AID converter for digital demodulation. In [7], a coherent low IF heterodyne architecture is proposed. The architecture explores the advantage of range correlation and digitally demodulates the received radar IF signal to achieve a significant improvement of signal to noise ratio (SNR).…”

Time-Domain Doppler Biomotion Detections Immune to Unavoidable DC Offsets

“…However, the arctangent function mathematically has a native codomain range of (-π/2, π/2), which will cause discontinuities in demodulated signals. It also suffers from the flicker noises and direct current (DC) offsets unavoidable in zero-IF receivers [11].…”