Electronic – How does sender and receiver clock time periods synchronize in data communication

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In asynchronous data communication, Initiation of data communication between two stations(sender and receiver) involves synchronizing their clocks to ensure both stations are agreed upon same bit times. How does this process takes place? How do sender and receiver agrees on same clock period? If possible point me to some resources too.

Best Answer

This clock sync doesn't necessarily happen before; it often happens before, and during transmission.

The things you might want to read in the usual literature (especially: Sklar and Proakis, imho) is timing synchronization.

How to implement that depends on a lot of unknowns, so I can't give you one answer. In reality, there's literally hundreds of approaches to synchronize timing, and which one you choose depends, among a lot of other things, on

  • physical relation of symbol rate and carrier frequency
  • modulation
  • signal model
  • statistical noise model
  • statistical interference model
  • receiver imperfection models (nonlinearities, I/Q imbalances, clock drifts, sampling jitter, …)
  • length of transmission
  • coherency time of your channel (which is closely linked to)
  • doppler bandwidth of your channel
  • statistical model of the clock offsets
  • affordable overhead for CSI acquisition vs. payload data rate
  • receiver operation characteristics, ARQ vs robustness trade-off etc
  • memory available at receiver
  • computing power available at receiver
  • power consumption limits and tradeoffs
  • MIMO necessity
  • receiver cost vs BER tradeoff
  • Channel coding used (effect of SER, in the end)
  • multi-user capabilities

If you pick any of these books, they'll probably introduce some classical synchronizer – and you can still find those in application very often! But all of these are already relatively application-specific. For example, a control loop that stabilizes a QPSK reception doesn't necessarily (and usually: won't, because a few mathematical tricks don't work here) work for 8PSK.

If you're really just interested in timing estimation happening before actual payload transmission, you're after preambles. Those are known sequences that the receiver looks for to estimate the parameters of the channel and transmission – timing is one of these parameters.

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