Sound of Motion: Real-time Wrist Tracking with A Smart Watch-Phone Pair

Proliferation of smart environments entails the need for real-time and ubiquitous human-machine interactions through, mostly likely, hand/arm motions. Though a few recent efforts attempt to track hand/arm motions in real-time with COTS devices, they either obtain a rather low accuracy or have to rely on a carefully designed infrastructure and some heavy signal processing. To this end, we propose SoM (Sound of Motion) as a lightweight system for wrist tracking. Requiring only a smart watch-phone pair, SoM entails very light computations that can operate in resource constrained smartwatches. SoM uses embedded IMU sensors to perform basic motion tracking in the smartwatch, and it depends on the fixed smartphone to act as an "acoustic anchor": regular beacons sent by the phone are received in an irregular manner due to the watch motion, and such variances provide useful hints to adjust the drifting of IMU tracking. Using extensive experiments on our SoM prototype, we demonstrate that the delicately engineered system achieves a satisfactory wrist tracking accuracy and strikes a good balance between complexity and performance.