Human Activity Classification Based on Point Clouds Measured by Millimeter Wave MIMO Radar With Deep Recurrent Neural Networks

• Published in: IEEE sensors journal Vol. 21; no. 12; pp. 13522 - 13529
• Main Authors: Kim, Youngwook, Alnujaim, Ibrahim, Oh, Daegun
• Format: Journal Article
• Language: English
• Published: New York IEEE 15.06.2021; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Angular resolution; Azimuth; Classification; deep convolutional neural networks; deep recurrent neural networks; Feature extraction; FMCW radar; Human activity classification; Human performance; Human subjects; Millimeter wave radar; Millimeter waves; MIMO radar; Neural networks; point clouds; Radar; Radar antennas; Radar equipment; Radar measurements; Recurrent neural networks; Shape; Three-dimensional displays
• DOI: 10.1109/JSEN.2021.3068388
• ISSN: 1530-437X

We investigate the feasibility of classifying human activities measured by a MIMO radar in the form of a point cloud. If a human subject is measured by a radar system that has a very high angular azimuth and elevation resolution, scatterers from the body can be localized. When precisely represented, individual points form a point cloud whose shape resembles that of the human subject. As the subject engages in various activities, the shapes of the point clouds change accordingly. We propose to classify human activities through recognition of point cloud variations. To construct a dataset, we used an FMCW MIMO radar to measure 19 human subjects performing 7 activities. The radar had 12 TXs and 16 RXs, producing a <inline-formula> <tex-math notation="LaTeX">33\times 31 </tex-math></inline-formula> virtual array with approximately 3.5 degrees of angular resolution in azimuth and elevation. To classify human activities, we used a deep recurrent neural network (DRNN) with a two-dimensional convolutional network. The convolutional filters captured point clouds' features at time instance for sequential input into the DRNN, which recognized time-varying signatures, producing a classification accuracy exceeding 97%.