If its only a a pulse that to be used in the determination then we go further back in time were at LORAN-A. LORAN-C used multi pulses to provide transmitter identification in each burst with phase comparison to complete the fix.
Now if the clocks are used to provide an ultra precise frequency, DECCA is back with lane counting.
Having worked at and on a Differential GPS site all I will honestly say is that the Velocity Factor varies in both the micro term and the long and any radio derived fix must receive the signals from several sources not local and with different frequencies. Omega was good but highly vulnerable to hostile intent.