Real-Time Anchor Node Selection for Two-Way-Ranging (TWR) Ultra-Wideband (UWB) Indoor Positioning Systems
Ben Van Herbruggen, Dries Van Leemput, Jaro Van Landschoot, Eli De Poorter
Abstract
The progress in cm-accurate ultra-wideband localization systems encourages the adoption on larger scales. To calculate the distance between a mobile tag and anchor nodes with known locations, a two-way-ranging (TWR) scheme is often used where the time-of-flight (TOF) is determined by exchanging at least two packets. This TWR scheme avoids the need for synchronization between devices to compensate for clock drift. However, in TWR systems, mobile tags continuously need to decide with which anchor nodes to range. Currently, most scientific papers assume the tag ranges sequentially with all anchor nodes, thereby limiting the scalability. In addition, precious time is wasted trying to range with anchors that encounter poor channel characteristics. This letter proposes two novel anchor selection algorithms that tackle both problems. Anchors are selected in real-time based on their link quality, improving accuracy by selecting the best-performing anchor nodes. The algorithms are based on heuristic methods to estimate the link quality and the corresponding ranging error. The algorithm's two variants are evaluated in a realistic dynamic industrial setup, reaching an accuracy up to 15 cm. This represents a 50% improvement compared with ranging with all available anchors.