Concurrent Bidirectional TDoA Positioning in UWB Network With Free-Running Clocks

This article proposes an approach of time-difference-of-arrival (TDoA) positioning in ultrawideband networks, where user tags localize themselves by means of the exploitation of the broadcasted synchronization messages of the anchor network. Such an approach promises an unlimited number of localized devices; moreover, the position is available directly at the user terminal. The key challenge of this method is to eliminate the errors caused by tag clock drifts, which render the TDoA measurements useless when left uncorrected. Our method employs extended Kalman filtering for the estimation of position and the elimination of the drift-induced errors. It is shown that the system performance is similar to that of the more common TDoA method, where the tags transmit blinks received by the anchors. However, the anchors are still able to receive the blink messages and estimate the position of those tags, since the synchronization messages are exploited. Therefore, it is possible to use both the directions of TDoA positioning concurrently; a limited number of tags is tracked by the infrastructure and all tags may compute their positions. The TDoA solutions have achieved a root-mean-square horizontal accuracy of 25.9 and 33.6 cm, respectively.