Special relativity without distant clock synchronization
  Observers at rest in two inertial reference frames are located within the propagation space of the same electromagnetic wave. Raising receiving antennas in a suitable way, these observers use the electromagnetic oscillations in the wave as an electromagnetic clock. The invariance of the wave phase ensures that the observers of the two frames detect the same phase of the oscillation when they are located at the same point in space and consequently theirs synchronization proceeds automatically. Because the Doppler Effect is free of any clock synchronization, we use the formula that accounts for this effect for deriving the basic formulas of relativistic kinematics. 
Bernhard Rothenstein, Stefan Popescu, George J. Spix