An Extendable Auto-Position for UWB-based Indoor Positioning Systems

Indoor positioning systems with centimeter accuracy have been developed to support services in indoor locations where the Global Navigation Satellite System (GNSS) is unable to operate. The most ubiquitous method involves a tag measuring ranges with at least three static anchors by applying ultra-wideband (UWB) technology that provides centimeter ranging accuracy. However, most existing systems require intensive survey and calculation on anchor placements before deployment of the systems. As a result, installing such a system is complicated and time-consuming as well as restricting the expansion in a dynamic and ad-hoc indoor positioning system. In this paper, we implemented an auto-positioning system where the system will automatically obtain the positions of the anchors once added into the system without human intervention. Therefore, the time needed for the installation process will be reduced. In our system, there is no restriction on the number of anchors involved in the system. In other words, our system was intended to be ad-hoc and dynamic. We employed the Double-sided Two-way ranging (DS-TWR) mechanism as well as a simple trilateration calculation for position computation. In addition, to increase the position accuracy we put more effort on reducing ranging errors by applying the ADS-TWR formula and performing antenna delay calibration of the devices in the system. Even though the calibration process may be considered time consuming, the process is done once and for all. Our experiments showed that antenna delay calibration is crucial to achieve high position accuracy of the auto-positioning RTLS.