Relative Localization of Asynchronous Agents Based on Hybrid Active-Passive Two-Way Ranging

To position agents equipped with ultrawideband (UWB) devices without requiring continuous clock synchronization, the primary measurement currently used is the time of flight between agents, estimated through active two-way ranging (TWR). However, the cumbersome signal exchange mechanism in active TWR imposes a trade-off between the number of agents and the positioning frequency. To address this issue, this paper proposes a relative localization scheme using hybrid active-passive TWR to accommodate more agents without compromising the positioning refresh rate. Additionally, this scheme not only extends passive TWR into a dynamic form, thereby improving localization accuracy of mobile agents, but also presents a two-step relative positioning method to enhance computational efficiency. The feasibility of the scheme is validated through numerical simulations and real-world tests on a prototype system built with consumer-level UWB chips.