Modified synchronization scheme for coherent optical OFDM systems

We propose a series of modified methods covering timing and frequency synchronization in the coherent optical orthogonal frequency-division-multiplexing (CO-OFDM) system. The modified timing synchronization method eliminates the ambiguity of Park´s method, and the modified frequency synchronization method employs only one training symbol without any loss of accuracy compared to Schmidl´s method. The proposed synchronization scheme is tested in a 20 Gb/s CO-OFDM simulated system, with the result that the modified synchronization scheme gives a more accurate timing estimation and a more economical frequency offset estimation with a wide estimation range in the relatively short transmission distance. Meanwhile, chromatic dispersion compensation added before the synchronization keeps the modified scheme´s performance stable over longer distances and makes better subcarrier recovery with the optical signal-to-noise ratio improved by 3 dB at the bit-error rate of 10^-3.