Ranging and Positioning with UWB

Abstract

Indoor location is one of the key use cases enabled by UWB for navigation and asset tracking. The 802.15.4a and 802.15.4z standards describe several techniques for determining the distance between a mobile device client and a set of static anchors. Two of them (SS-TWR and DS-TWR) use a bidirectional exchange between the client and the anchor, with the resulting distance being calculated on the initiating side (SS-TWR) or both sides (DS-TWR). OWR does not require an exchange and simply relies on the comparison of arrival times of signals (TDoA). With UL-TDoA, the time of arrival of the client signal is compared on several anchors, drawing distance hyperbolae from which the client location is deduced. With DL-TDoA, the reverse happens: the client compares the time of arrival of signals from several anchors and deduces its position. A third family of techniques is not described in the Standard but is commonly implemented in the field: AoA, where a comparison of the phase of the signal among two or more antennas is used to compute the direction of the sender. From these elements, a location engine computes the mobile device’s position. This chapter examines these techniques in detail.