Disclosed is method of computing a round trip delay between a pair of nodes, the method comprising transmitting at least one beacon at a known transmit time from each of the nodes; measuring the times-of-arrival of the beacons at other of the nodes; and estimating a round trip delay between the nodes from the measured times-of-arrival and the transmit times; and correcting the round trip delay for either or both of a frequency offset between the nodes and relative motion between the nodes.