FlexTDOA: Robust and Scalable Time-Difference of Arrival Localization Using Ultra-Wideband Devices

In this paper, we propose FlexTDOA, an indoor localization method using ultra-wideband (UWB) radios, and we demonstrate its performance in a functional system. Our method uses time-difference of arrival (TDOA) localization so that the user device remains passive and is able to compute its location simply by listening to the communication between the fixed anchors, ensuring the scalability of the system. The anchors communicate using a custom and flexible time-division multiple-access (TDMA) scheme in which time is divided in slots. In each time slot, one anchor interrogates one or more anchors which respond in the same slot. The anchors do not need to have their clocks synchronized. We implemented FlexTDOA on in-house designed hardware using a commercial UWB module. We evaluate the localization accuracy of FlexTDOA with different system parameters such as the number of responses, the order of responses, and the number of anchors. We simulate and evaluate the effect of the physical speed of the tag on the choice of optimum system parameters. We also compare FlexTDOA against the classic TDOA approach and range-based localization in a deployment of ten anchors and one tag, both with and without obstructions. Results show that FlexTDOA achieves the highest localization accuracy in most of the scenarios, with up to 38% reduction in the localization error compared to the classic approach.