Indoor localization using time difference of arrival with UWB signals and unsynchronized devices

Abstract

Indoor location using radio frequency (RF) signals has been traditionally focused mainly on RSSI and fingerprint techniques, because methods based on time of arrival (ToA) or time difference of arrival (TDoA) were not suitable for measuring short distances. However, the release of the IEEE 802.15.4a standard, the emergence of commercial ultra wide band (UWB) transceivers that are compliant to this norm and the integration of high frequency oscillators have permitted the design of more accurate indoor localization systems using the RF signal transmission time. In this paper, we propose an indoor localization system based on TDoA for UWB. The method implements an only one way transmission ranging algorithm to measure the time differences of arrival. This feature reduces the complexity of the tags to be localized, since tags only have to transmit but not to receive packets, and allows the implementation of low power applications that are controlled by the tag activity and the system requirements. On the other hand, the proposed localization algorithm does not require a permanent time synchronization of anchors’ clocks and the estimation of the time offsets is performed jointly with the position computation. For the estimation of the time offsets, the algorithm considers the different clock skews of the anchors’ oscillators and compensates the measured offsets accordingly. The proposed algorithm has been evaluated in two different scenarios with real devices. Results show an improvement in terms of localization accuracy that the algorithm allows compared to fingerprinting methods.