  Accurate wireless timing synchronization has been an extremely important
topic in wireless sensor networks, required in applications ranging from
distributed beam forming to precision localization and navigation. However, it
is very challenging to realize, in particular when the required accuracy should
be better than the runtime between the nodes. This work presents, to our
knowledge for the first time, an experimental timing synchronization scheme
that achieves a timing accuracy better than 5ns rms in a network with 4 nodes.
The experimental hardware is built from commercially available components and
based on software defined ultra wideband transceivers. The protocol for
establishing the synchronization is based on our recently developed blink
protocol that can scale from the small network demonstrated here to larger
networks of hundreds or thousands of nodes.
