Carrier recovery
![Example of QPSK carrier recovery phase error causing a fixed rotational offset of the received symbol constellation, X, relative to the intended constellation, O.](/Images/godic/202501/05/QPSK_Phase_Error.svg1338.png")
![Example of QPSK carrier recovery frequency error causing rotation of the received symbol constellation, X, relative to the intended constellation, O.](/Images/godic/202501/05/QPSK_Freq_Error.svg1338.png")
A carrier recovery system is a circuit used to estimate and compensate for frequency and phase differences between a received signal's carrier wave and the receiver's local oscillator for the purpose of coherent demodulation.
In the transmitter of a communications carrier system, a carrier wave is modulated by a baseband signal. At the receiver the baseband information is extracted from the incoming modulated waveform.