Motion-Induced Bias in UWB Asynchronous TWR: Modeling, Analysis, and Implications

Abstract

Motion-induced uncertainties fundamentally limit the performance of asynchronous two-way ranging (TWR) localization systems, yet existing literature lacks a unified definition and characterization of these uncertainties for TWR methods. This work introduces a comprehensive characterization of motion-induced errors in TWR, establishing explicit analytical relationships between target velocity, message timing asymmetries, and the resulting ranging error. Using this formulation, four widely adopted TWR methods, single-sided TWR (SS-TWR) and symmetric double-sided TWR (SDS-TWR), each evaluated under sequential and parallel reply schemes, are assessed and compared within an optimized deployment framework derived from the spatial Cramér–Rao bound. The analysis reveals that sequential methods, commonly implemented in commercial ultra-wideband devices, offer the best performance under static conditions but degrade rapidly with motion due to accumulated timing asymmetries. In contrast, parallel configurations remain largely unaffected by velocity but are constrained by longer cumulative reply times in larger networks. Furthermore, SDS-TWR is found to be consistently more sensitive to motion than SS-TWR despite its superior correction of clock drift. The proposed framework provides the first systematic basis for quantifying motion effects in asynchronous TWR and offers practical guidelines for selecting and deploying ranging strategies in dynamic environments.