Wireless Communication
Typically a known sequence is transmitted (often as a preamble) that has properties to aid in determining the channel characteristics (by spreading its energy across all frequencies within your signal bandwidth) and in determining the symbol clock (many transitions at the symbol clock boundary). Both can be accomplished by using pseudo-random sequences which also have the desirable property of an autocorrelation that approximates an impulse function (useful for establishing a timing boundaries under low SNR conditions). When shorter sequences are sufficient for  acquisition and channel estimation, Barker codes also have the desirable autocorrelation and signal energy spreading properties mentioned (these go hand in hand: the autocorrelation of white noise is an impulse).

The details on estimating the channel (or equalizing your signal to remove the channel distortions) for single-carrrier modulation schemes are identical to the operations detailed in this post here:  Compensating Loudspeaker frequency response in an audio signal