  As commercial interest in proximity services increased, the development of
various wireless localization techniques was promoted. In line with this trend,
Ultra-wideband (UWB) is emerging as a promising solution that can realize
proximity services thanks to centimeter-level localization accuracy. In
addition, since the actual location of the mobile device (MD) on the human
body, called pose, affects the localization accuracy, poses are also important
to provide accurate proximity services, especially for the UWB tagless gate
(UTG). In this paper, a real-time pose detector, termed D3, is proposed to
estimate the pose of MD when users pass through UTG. D3 is based on
line-of-sight (LOS) and non-LOS (NLOS) classification using UWB channel impulse
response and utilizes the inertial measurement unit embedded in the smartphone
to estimate the pose. D3 is implemented on Samsung Galaxy Note20 Ultra (i.e.,
SMN986B) and Qorvo UWB board to show the feasibility and applicability. D3
achieved an LOS/NLOS classification accuracy of 0.984, and ultimately detected
four different poses of MD with an accuracy of 0.961 in real-time.
