Apparatus and method for synchronizing frequency in orthogonal frequency division multiplexing communication system

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 receiver signal contains one of both short and long training signals, the frequency synchronizer estimates frequency offset of the training signal and compensates the training signal and data symbol with the estimated frequency offset.

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 freauency 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 confiqured 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 the frequency synchronizer comprises:
• an estimator for estimating frequency offset and residual phase of a received signal;
• a first demultiplexer for selectively outputting the frequency offset and residual phase estimated in the estimator;
• an adder for adding the frequency offsets from the first demultiplexer;
• a frequency offset compensator for compensating the received signal and data symbol using the frequency offsets from the first demultiplexer and the adder;
• and
• a second demultiplexer for selectively outputting a compensated signal from the frequency offset compensator.

A freguency synchronization apparatus for an orthogonal freguency division multiplexing (OFDM) communication system, the freguency synchronization apparatus comprising:

• a radio freauency (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 freguency synchronizer connected to the A/D converter, the freguency synchronizer synchronizing a carrier freguency;
• a Fast Fourier Transformer (FFT) connected to the freguency synchronizer, the FFT performing fast Fourier transformation to symbols from the freguency synchronizer;
• a channel estimator connected to the FFT, the channel estimator estimating a carrier channel;
• an egualizer connected to the FFT and the channel estimator, the egualizer configured for egualizing 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 the residual phase tracker comprises:
• a pilot extractor for extracting a pilot signal from a data symbol transformed by the FFT and sending the pilot signal to the frequency synchronizer;
• a residual phase compensator for compensating the data symbol with the residual phase of the data symbol estimated at the frequency synchronizer.

A frequency synchronization method for an orthogonal frequency division multiplexing (OFDM) communication system comprising:

• estimating a frequency offset of a training signal;
• compensating a frequency of the training signal with the estimated frequency offset;
• performing fast Fourier transformation on the frequency;
• compensating a data symbol of an input signal with the estimated frequency offset;
• performing fast Fourier transformation on the data symbol;
• compensating the data symbol with the estimated channel obtained by performing the fast Fourier transformation;
• tracking a residual phase of the estimated data symbol;
• and
• compensating the residual phase.