Patent ID: 7386073

Claim:
An AFC (Automatic Frequency Control) device of a QPSK (Quadrature Phase Shift Keying) modulation system comprising: a frequency discriminating unit for calculating a real part peak value based on a frequency discrimination between adjacent I and Q signals in a received sequence, and for calculating an imaginary part peak value based on a frequency discrimination between adjacent I signals and adjacent Q signals in the received sequence; an error detecting unit for detecting an error symbol based on the real part peak value and the imaginary part peak value; a switching unit for removing the detected error symbol under the control of the error detecting unit; and a frequency difference average calculating unit for calculating an average of real part peak values and an average of imaginary part peak values output from the switching unit, the frequency difference average calculating unit further calculating a frequency difference average of the received sequence based on the averages of the real part and imaginary part peak values, wherein automatic frequency control is performed based on the frequency difference average calculated by the frequency difference average calculating unit.