An Experimental Characterization of Chain of PLLs for Wired Clock Synchronization of UWB Anchors for Indoor Location

The Internet of Things (IoT) enables services in a variety of domains. However, some of them, such as autonomous vehicles, may require information about the location where the sensed data is obtained. Well-established location technologies (e.g. the Global Navigation Satellite System - GNSS) can be used for outdoor devices, but they may fail indoors. On the contrary, Ultra-Wide Band (UWB) technology is one of the most promising solutions for Indoor Real-Time Location System (IRTLS). In general, these solutions allow for the location of devices (called tags), in relation to nodes placed in known positions in space (called anchors). Several approaches for device localization using UWB technology are known in the literature. Some of them, like the Time Differential of Arrival (TDoA) method, necessitate a time synchronization solution in order to distribute the time accurately among the anchors. The use of a wired method for anchor time synchronization is studied in this research, since the architecture of the clock distribution network may affect the signal accuracy provided to each anchor. The reference method would be to connect each anchor directly to a common clock source, however this solution is the most demanding in terms of wiring. The chain topology, in which the clock is used and then re-distributed by each of the clock network's nodes, is an intriguing option for reducing overall cabling requirements. According to the experimental characterization, the phase error of the clock generated by a chain topology is 9.3% larger than the phase error of the reference topology, but it is still within the usage requirements.