Carrier recovery system and carrier recovery method

A carrier recovery system, comprising:

• a compensation signal generator, generating a compensation signal based on a coherent demodulated signal;
• a mode selector, switching the carrier recovery system from a first mode to a second mode when an estimated frequency offset satisfies a first criterion;
• and
• a compensation device, wherein, when the carrier recovery system is in the first mode, the compensation device generates the coherent demodulated signal for the compensation signal generator by compensating an output of an equalizer with the compensation signal, and, when the carrier recovery system is in the second mode, the compensation device compensates an output of a synchronizer with the compensation signal to generate an input of the equalizer while the output of the equalizer is received by the compensation signal generator as the coherent demodulated signal;
• wherein the compensation signal generator comprises:
• a polarity detector, generating a detector output based on an input thereof;
• a first switch, coupling the coherent demodulated signal to the polarity detector as the input of the polarity detector when the first switch is turned on;
• a power detector, turning on the first switch when magnitude of the coherent demodulated signal is greater than a threshold magnitude;
• a divider and an imaginary portion extractor, dividing the coherent demodulated signal by the detector output and extracting an imaginary portion of an output of the divider to generate a phase error signal;
• a loop filter, filtering the phase error signal and having a plurality of coefficients;
• a coefficient controller, setting the coefficients;
• and
• a numerical controlled oscillator, receiving an output of the loop filter and outputting the compensation signal.