MIMO Differential Radar Using Null Point Beams for Vital Sign Detection in the Presence of Body Motions

Abstract

A multiple-input and multiple-output (MIMO) differential radar using null point beams is proposed to detect vital signs of multiple people in the presence of random body movements. Multiple beams are employed by digital beamforming of virtual receiver arrays obtained through a MIMO operation. A differential method using null points of array beam patterns is proposed to reduce motion artifacts. It effectively magnifies magnitude differences of received signals from adjacent two beams which have smaller angle separation than the main lobe beam width. Common body motion artifacts can be reduced by demodulating the phase difference signal from the differential beams. This is again expanded to four beams in azimuth and elevation angles, of which six phase differences are combined by a weighted-summing method. Vital signs of multiple subjects can be measured simultaneously by utilizing multiple differential-beams. The proposed method is experimentally verified by a 60 GHz frequency-modulated continuous-wave (FMCW) MIMO radar with three transmitters and four receivers. Experimental results show that the differential MIMO radar can simultaneously extract vital signs of two people in the presence of body movements.