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
.