Kalman Filter based Range Estimation and Clock Synchronization for Ultra Wide Band Networks

This paper presents the development of a Kalman filter-based range estimation technique to precisely calculate the inter-node ranges of Ultra Wide Band (UWB) modules. Relative clock tracking filters running between every anchor pair tracks relative clock dynamics while estimating the time of flight as a filter state. Both inbound and outbound message timestamps are used to update the filter to make the time of flight observable in the chosen state space design. A faster relative clock filter convergence has been achieved with the inclusion of the clock offset ratio as a measurement additional to the timestamps. Furthermore, a modified gradient clock synchronization algorithm is used to achieve global clock synchronization throughout the network. A correction term is used in the gradient clock synchronization algorithm to enforce the global clock rate to converge at the average of individual clock rates while achieving asymptotic stability in clock rate error state. Experiments are conducted to evaluate synchronization and ranging accuracy of the proposed range estimation approach.