Estimating the Position of a Wearable Device Using Pulse Wave Peak Time Differences with a Smartwatch
Ryuta Kotera, Kazuya Murao · 2025
Wearable devices come in various forms. In addition to those designed for specific body parts, such as wristwatch, eyeglass, and ring devices, there are also wearable devices that can be attached to arbitrary body positions, such as instant tattoo-type and bandage-type devices. When a wearable device is attached to an arbitrary position on the body, it is necessary for the device to recognize its attachment site in order to adjust its function and processing accordingly. In this paper, we propose a method for estimating the attachment position of a wearable device with an unknown position by using pulse wave sensors mounted on both a device with a known position and a device with an unknown position. Because the arrival time of pulse waves varies depending on the distance from the heart, the time difference between pulse wave peaks at the wrist and another body part can be used to infer the attachment site. The proposed method estimates the device's attachment position based on the difference in pulse wave peak detection times between the wrist and the unknown body part. For evaluation, data were collected from 15 body positions: forehead, nose, mouth, left ear, right ear, neck, left upper arm, right upper arm, left wrist, right wrist, left finger, right finger, waist, left toe, and right toe. The method was evaluated under two conditions: using data collected on the same day and on different days. When estimating two positions, the F1 score was 0.94 for same-day data and 0.64 for different-day data. With fifteen positions, the scores were 0.64 and 0.14, respectively.