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This paper presents a combinational synchronization method including symbol timing synchronization, fractional frequency estimate and integer frequency estimate applied to an OFDM system based on FPGA. An estimator for OFDM symbol timing synchronization and fractional frequency offsets is proposed based on conjugate multiplication, Cordic algorithm and autocorrelation properties of PN (pseudo noise) codes. All the sub-modules of synchronization circuit are described in Verilog HDL or constructed by MegaCore supplied by Altera. The results of computer simulation show that the receiver of the OFDM system applying the algorithm can find the right symbol timing point in the guard interval, meanwhile the fractional frequency offset can be caught and then compensated by a feedforward method, at last, the integer frequency offset that exists in the data stream can also be compensated by integer frequency estimation module.