RAILS: 3-D Real-Time Angle of Arrival Ultrasonic Indoor Localization System
Andrea Gabbrielli, Joan Bordoy, Wenxin Xiong, Georg Fischer, Thomas Schaechtle, Johannes Wendeberg, Fabian Höflinger, Christian Schindelhauer, Stefan J. Rupitsch
Abstract
The demand for a replacement of global navigation satellite systems in indoor environments has led researchers to investigate the field of indoor localization. In this contribution, we propose RAILS, a 3-D real-time angle of arrival ultrasonic indoor localization system. The proposed system is capable of accurately and precisely locating a source in three-dimensions using angle of arrival (AoA) measurements. Our acoustic AoA technique relies on a constellation of spatially distributed arrays of microphones and on a source emitting inaudible ultrasonic chirp signals. Real-time features are enabled by introducing a localization chirp detector that constantly listens to the medium and triggers the localization algorithms only when signals of interest are approaching. The core of the 3-D localization method are the time delay estimates, aiming to compute the 3-D direction vectors. In order to overcome the challenges introduced by the acoustic indoor channel and to provide accuracy and robustness in the delay estimates, we have designed a time delay estimator. Furthermore, an ad hoc 3-D positioning algorithm based on 3-D vector intersection has been developed to furnish reliable 3-D source positions. The performance of our proposed ultrasonic indoor localization system has been evaluated through static single-source real-world experiments in a warehouse-like scenario, covering an area of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$40~\text {m}^{2}$ </tex-math></inline-formula> with a maximum source-receiver range of 10 m. The system achieved an outstanding average of 10-cm 3-D positioning accuracy, with an average standard deviation of 1 cm over all the measurements. Furthermore, dynamic single-source experiments have been carried out demonstrating that our system is capable not only of locating a source but also to track it.