Joint Angle and Respiration Estimation for Passive and Device-Free Respiration Monitoring

In the field of wireless sensing, several systems built around off-the-shelf wireless communication hardware have been described in the literature that can sense the respiration of subjects nearby. Although these systems can capture the respiration of multiple persons, they do not allow a reliable separation of the breathing activity of different subjects. Moreover, prior studies used a phase calibration technique that restricts to Orthogonal Frequency Division Multiplex (OFDM) systems like e.g. WiFi. In this contribution, we propose a completely new approach for such kind of applications: As it is supported e.g. by recent versions of the Bluetooth standard, we propose the use of an antenna array at the receiver for sensing purposes. Therefore, a new phase calibration technique is introduced that can be implemented even with non-OFDM systems. Together with a novel Matching Pursuit based Joint Angle and Respiration Estimation (JARE) algorithm, this enables the reliable separation of the breathing activity of multiple subjects under different angles in a room. An application example could hence be the respiration monitoring of persons in different bedsides for medical use. Using a Bluetooth implementation of the recommended approach, the respiration rate of two subjects in a room could be measured with a median uncertainty of just 0.2 bpm (breaths per minute, 3.3 mHz).