N-TWR: An accurate time-of-flight-based N-ary ranging protocol for Ultra-Wide band

In the last decade, wireless positioning systems have drawn a strong interest from a research point of view, especially for indoor environments where Global Positioning Systems (GPS) is not available. As an alternative, emerging applications relying on Ultra-Wide Band (UWB) communication technology have been proposed to offer a ranging accuracy in the order of some dozens of centimeters. Indeed, UWB radios' increased accuracy originates in the high time resolution of UWB signals that can be leveraged to measure precisely travel times of signals (e.g. Time of Flight, ToF). ToF can be easily translated to inter-node distance. In this work we propose N-TWR, a ToF-based N-ary ranging protocol created for localization using UWB. The proposed N-TWR protocol is based on the estimation of the ToF between a target node to be localized (which may be mobile or static) and a set of N anchors. It has been designed to minimize the number of messages exchanged between all nodes compared to a naive solution that exploits the state-of-the-art UWB ranging method. Validation has been made using experiments carried out in our Open Source Framework, DecaDuino, which enables fast prototyping of protocols sitting on top of UWB Physical layer. The N-ary ranging provided by N-TWR achieves the same level of accuracy as the naive protocol exploiting SDS-TWR but using four times less messages. We exhibit as well that N-TWR can be efficiently leveraged to design a simple and elegant trilateration localization algorithm.