Patent ID: 7133479

Claim:
A frequency synchronization apparatus for OFDM systems, comprising: a digital mixer for acquiring a baseband signal by means of a local frequency and adjusting the local frequency in response to an integer frequency offset and a fractional frequency offset; a first synchronizer for taking a sequence of received samples derived from the baseband signal in a time domain, estimating the fractional frequency offset, and feeding the fractional frequency offset back to the digital mixer, comprising: a first buffer for storing N previous samples of the received sample sequence to provide an Nth previous sample, where N is a first positive integer; a second buffer for storing L previously calculated products to provide an Lth previously calculated product, where L is a second positive integer and L≦N; and a controller for taking a current sample from the received sample sequence, multiplying the current sample by a conjugate of the Nth previous sample to yield a current product, writing the current sample to the first buffer to keep as a previous sample, computing a moving sum of L most recently calculated products from the current product and the Lth previously calculated product, writing the current product to the second buffer to keep as a previously calculated product, and estimating the fractional frequency offset based on the moving sum; a second synchronizer for taking a sequence of demodulated symbols derived from the baseband signal in a frequency domain, obtaining the integer frequency offset through a coarse search stage and a fine search stage, and feeding the integer frequency offset back to the digital mixer.