Patent ID: 7103332

Claim:
An apparatus for estimating a frequency offset to compensate for the frequency offset of the I and Q channel signals, in a receiving apparatus of a mobile communication system, said receiving apparatus for receiving a signal containing training symbols of a predetermined pattern inserted in a data symbol sequence, downconverting the received signal by a predetermined carrier frequency, and outputting in-phase (I channel) and quadrature-phase (Q channel) signals, comprising: an adder for adding I and Q channel training signals and outputting a sum channel signal containing one of a cosine component or a sine component, the I and Q channel training signals being obtained by downconverting the training symbols; a subtractor for subtracting the Q channel training signal from the I channel training signal and outputting a difference channel signal containing one of the sine component or the cosine component in correspondence with the sum channel signal; and a frequency offset estimator for receiving a first sum channel signal and a first difference channel signals at a first point in time, receiving a second sum channel signal and a second difference channel signal at a second point in time, calculating a first phase value using the first sum channel signal and the first difference channel signal, calculating a second phase value using the second sum channel signal and the second difference channel signal, and estimating the frequency offset by determining the slope of a second-order line derived from the first and second phase values.