Opportunities for Activity Recognition using Ultrasound Doppler Sensing on Unmodified Mobile Phones

Nowadays activity recognition on smartphones is ubiqui-tously applied, for example to monitor personal health. The smartphone’s sensors act as a foundation to provide infor-mation on movements, the user’s location or direction. In-corporating ultrasound sensing using the smartphone’s native speaker and microphone provides additional means for per-ceiving the environment and humans. In this paper, we out-line possible usage scenarios for this new and promising sens-ing modality. Based on a custom implementation, we provide results on various experiments to assess the opportunities for activity recognition systems. We discuss various limitations and possibilities when wearing the smartphone on the hu-man body. In stationary deployments, e.g. while placed on a night desk, our implementation is able to detect movements in proximities up to 2 m as well as discern several gestures performed above the phone. Author Keywords ultrasound sensing; activity recognition; acoustic sensin