Distributed MIMO CW Radar for Locating Multiple People and Detecting Their Vital Signs

• Published in: IEEE transactions on microwave theory and techniques Vol. 71; no. 3; pp. 1312 - 1325
• Main Authors: Juan, Pin-Hsun, Chueh, Chi-Yuan, Wang, Fu-Kang
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.03.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithms; Angular resolution; Antenna arrays; Antennas; Beamforming; Continuous radiation; Digital beamforming (DBF); Direction of arrival; direction of arrival (DOA); Direction-of-arrival estimation; distributed multiple-input multiple-output (MIMO) radar; Finite element method; Frequency estimation; frequency estimation algorithm (FEA); Heart rate; Intermediate frequencies; Linear arrays; low intermediate frequency (low-IF); Metal plates; MIMO communication; Position errors; Radar; Radar antennas; vital sign
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2022.3216577

The distributed-multiple-input multiple-output (MIMO) continuous-wave (CW) radar with low-intermediate frequency (low-IF) receiver that is proposed in this work uses uniform linear array (ULA) antennas to estimate the direction of arrival (DOA) of subjects and recover Doppler signals by the digital beamforming (DBF) technique. Without using any modulation bandwidth, the location of multiple subjects can be determined from the known antenna positions and the estimated DOAs. This work proves that the Doppler-weighted method improves the extraction of the initial phase of the baseband signal. With respect to the recovery of each subject's vital signs, the modified-DBF is utilized to separate individual Doppler signals while nullifying interference. The frequency estimation algorithm (FEA) is used to improve the Doppler frequency and angular resolution by 50% and 44%, respectively, in the detection of two closely spaced moving metal plates. Finally, the presented system is experimentally validated by determining the locations and vital signs of people sitting side-by-side. The estimated DOA and position errors were less than 3.3° and 10 cm, respectively. With a 25 s sensing period, the errors in the measured respiration rates (RRs) and heart rates (HRs) were less than 1.2 breath/min and 3 beats/min, respectively.