Patent ID: 7068593

Claim:
A frequency synchronization apparatus for an orthogonal frequency division multiplexing (OFDM) communication system, the frequency synchronization apparatus comprising: a radio frequency (RF) receiver for receiving an OFDM signal; an analog/digital (A/D) converter connected to the RF receiver, the A/D converter converting the OFDM signal into a digital signal; a frequency synchronizer connected to the A/D converter, the frequency synchronizer synchronizing a carrier frequency; a Fast Fourier Transformer (FFT) connected to the frequency synchronizer, the FFT performing fast Fourier transformation to symbols from the frequency synchronizer; a channel estimator connected to the FFT, the channel estimator estimating a carrier channel; an equalizer connected to the FFT and the channel estimator, the equalizer configured for equalizing a channel; a residual phase tracker connected to the equalizer, the residual phase tracker configured for tracking a residual phase; a demodulator connected to the residual phase tracker, the demodulator configured for demodulating; and a controller connected to the frequency synchronizer, the controller controlling the frequency synchronizer, wherein if the received signal contains both short and long training signals, the frequency synchronizer estimates the frequency offset of the short training signal so as to compensate the long training signal with the frequency offset of the short training signal in a coarse mode, and re-estimates the frequency offset of the compensated long training signal so as to re-compensate the long training signal in a fine mode.