Noncontact Measurement of Human Vital Signs during Sleep Using Low-power Millimeter-wave Ultrawideband MIMO Array Radar

Radar-based noncontact measurements of human bodies have increasingly been attracting attention in healthcare applications because such measurements allow for the unobtrusive sensing of vital signs without sensors being attached to the body. In particular, measurement of the heart rate is considered to be important because it provides various types of information on the physical and mental health of the person under test. In such applications, it is preferable to use low-gain omni-directional antennas so that the person under test does not have to be located at a specific spot. In addition, the use of high-power microwaves is not allowed in many countries owing to public health regulations. Because of such factors, the signal-to-noise ratio is relatively low in these applications although the target person might be within a few meters of the antennas. To overcome this difficulty, we adopt the maximum ratio combining technique with a multiple-input multiple-output antenna array for improving the signal-to-noise ratio and accuracy in measuring the instantaneous heart rate.