US Patent 7133479 Frequency synchronization apparatus and method for OFDM systems

A frequency synchronization apparatus and method for OFDM systems. The frequency synchronization apparatus is comprised of a digital mixer, a first synchronizer and a second synchronizer. The digital mixer acquires a baseband signal by means of a local frequency and adjusts the local frequency in response to an integer frequency offset and a fractional frequency offset. The first synchronizer takes a sequence of received samples derived from the baseband signal in a time domain to estimate the fractional frequency offset. The fractional frequency offset is fed back to the digital mixer. After that, the second synchronizer takes a sequence of demodulated symbols derived from the baseband signal in a frequency domain. The second synchronizer yields the integer frequency offset through a coarse search stage and a fine search stage. Then, the integer frequency offset is fed back to the digital mixer.