An overnight vital signs monitoring system for elderly people using dual microwave radars

There were two key problems in applying Doppler radar to night-time heartbeats and respiration measurement systems. The first is noise associated with body movement and the second is the presence of undesired harmonics and intermodulation. We propose a background subtraction processing and three different methods of combining the radar output spectra. In particular, a method involving real-time selection of the best radar-output channel by comparing the numbers of large peaks in the FFT spectrum, is found to be effective in improving the measurement accuracy. A prototype of the system was set up at a nursing home and field tests were carried out with elderly subjects. Despite the subjects engaging in frequent body movements while sleeping, the system was quite effective in monitoring vital signs (r=0.625-0.812).