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

In this paper, we propose FlexTDOA, an indoor localization method and a system using ultra-wideband (UWB) radios. 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 our system. The anchors communicate using a custom-designed, flexible time-division multiple-access (TDMA) scheme in which time is divided in slots, and in each slot one anchor interrogates one or more anchors which respond in the same slot. Clock synchronization between the anchors is not needed. We implemented FlexTDOA on in-house designed hardware using a commercial UWB module. We 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. We also evaluate the localization accuracy under multiple conditions by varying parameters such as the number of responses, their order, 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.