R3: Reflection Resilient Concurrent Ranging with Ultra-Wideband Radios

Concurrent ranging exploits features of the channel impulse response (CIR) of received packets to allow an ultra-wideband (UWB) initiator node to concurrently measure the distance from multiple UWB responder nodes. Concurrent ranging enables indoor localization systems to reduce the required number of ranging packet exchanges, leading to less air utilization and energy consumption, and faster location update rate. Despite the research in this area, it is still challenging to build a practical UWB concurrent ranging system for real-world environments. Existing concurrent ranging solutions are not scalable because (1) they require strong assumptions about either the responders or the environment and (2) they fail to maintain the ranging accuracy in longer distances due to errors caused by clock drift. In this work, we present R3, a Reflection Resilient Ranging solution, to address these critical scalability issues in UWB concurrent ranging. R3 makes use of the difference in the time deviation of ranging signals to detect concurrent responders and it is equipped with a clock skew correction method that enables accurate concurrent ranging in long distances. We evaluate R3 using Decawave DW1000 UWB chip by deploying the radio nodes in an office environment. Our results show that R3 effectively detects concurrent ranging peaks in the presence of strong multipath. When we equip R3 with a clock skew correction method, it reduces the concurrent ranging error induced by clock drift by at least 54 cm in long distances (>50 m) and by more than 97% in average when the ranging response delay is arbitrarily large.