RAILS: 3-D Real-Time Angle of Arrival Ultrasonic Indoor Localization System

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 40~\text {m}^{2} 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.