Ing. Josef Krška

This paper proposes an approach of TDoA positioning in UWB networks, where user tags localize themselves by means of exploitation of the broadcasted synchronization messages of the anchor network. Such approach promises unlimited number of localized devices, moreover, the position is available directly at the user terminal. The key challenge of this method is to eliminate errors caused by tag clock drifts, which render the TDoA measurements useless when left uncorrected. Our method employs extended Kalman filtering (EKF) for the estimation of position and elimination of the drift-induced errors. It is shown that the system performance is similar to 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 position of those tags, since the synchronization messages are exploited. Therefore, it is possible to use both directions of the 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 RMS horizontal accuracy of 25.9 cm and 33.6 cm, respectively.

The Time Difference of Arrival is a popular method for UWB-based positioning, since it allows high position update rate even for multiple users. However, it requires the network infrastructure (anchors) to be synchronized, preferably with sub-nanosecond accuracy. Herein, an approach for synchronizing multiple anchors in a wireless, line-of-sight manner is described. This method is able to deal with UWB modules equipped with inexpensive drift-prone oscillators, as such impairments are estimated and compensated. By applying the proposed approach the influence of generally variable environment (e.g. temperature) on timing and positioning performance is reduced. Moreover, the presented algorithm is suitable for straightforward chaining of the line-of sight-segments in order to allow synchronization of distant anchors that cannot be synchronized with the master anchor directly.

In the ultra-wide band (UWB) localization networks the time difference of arrival (TDoA) is often used. The TDoA method is advantageous in comparison with two-way ranging approach, however, requires the UWB infrastructure of the network to be synchronized to a sub-nanosecond level. The wireless synchronization is in favor due to practical reason, nonetheless its application is constrained by the need of line-of-sight between the synchronized nodes. This paper focuses on an experimental evaluation of a Kalman-filter-based chained synchronization algorithm, which allows synchronization of a distant, directly unreachable UWB nodes through multiple nodes and the respective line-of-sight path segments.