A joint frequency offset estimation algorithm based on training symbol and virtual subcarriers for CO-OFDM systems

In this paper, we propose a joint method of frequency offset estimation based on training symbol and virtual subcarriers for coherent optical orthogonal frequency division multiplexing(CO-OFDM) system. In the proposed method, the integer frequency offset is estimated through subtraction between the mode got form the first data subcarriers´ position in OFDM symbols and the number of virtual subcarriers inserted in each side of the OFDM symbol, in which the first subcarrier´s position can be found at the maximum slope of the fitting curve to virtual subcarriers; While the fractional frequency offset is estimated by periodic characteristic of the training symbol. Theoretical analysis and simulation results show that the estimation accuracy is improved by the proposed method in the additive white Gaussian noise(AWGN) and the dispersive channel. Simultaneously, estimation range of the proposed algorithm is about [−5GHz, +5GHz], satisfying the practical application requirement, and when the optical signal-to-noise ratio(OSNR) is low, it can still operate properly.