One of the biggest problems in phase modulated communication is discovering when your signal has arrived. High accuracy in this area is important, as even a quarter wavelength error can cause the estimated data bit to be completely wrong. One solution to this problem is to use a preamble code, which is a waveform whose autocorrelation has a very tight mainlobe and low sidelobes.
My question is, are preamble codes actually used in practice? If so, which ones? How is it that such a high accuracy of quarter wavelength is achieved in the real world using a preamble code? If this bound isn't correct, what bound do we really need to achieve synchronization using say BPSK?