Training sequences are used for synchronization between the transmitter and the receiver, signal detection, automatic gain control convergence, diversity selection, timing and frequency acquisition and channel estimation, in GSM, OFDM, LTE etc.

A poly-phase (complex valued, not like the real valued spread spectrum sequences) sequence is a finite complex sequence with discrete time phases and constant amplitude. The constant amplitude of the sequences, provides the sending and receiving of the signals to be easy and without any correction. Since the poly-phase sequences have desirable periodic and aperiodic autocorrelation and cross-correlation properties, they are used for applications in system identification and spread spectrum communications.

A Constant Amplitude Zero Auto Correlation (CAZAC) sequence is a periodic complex-valued sequence with the amplitude equals to one and out-of-phase periodic autocorrelation equal to zero. It is used in wireless communication systems like 3GPP Long Term Evolution for synchronisation. With having zero auto correlation property, it ensures the correlative variance between the users is zero, and this provides that there is not any interaction or interference between the users. A well known type of CAZAC sequences are the Zadoff–Chu sequences.