Low-Complexity Residual Carrier Frequency Offset Mitigation Based on Spectrum Symmetry for CO-OFDM Systems

In this paper, a low-complexity residual carrier frequency offset compensation (RCFOC) approach based on spectrum symmetry is proposed for coherent optical orthogonal frequency division multiplexing systems. A closed-form expression of spectrum symmetry is derived, which shows the dependence of spectrum shape of carrier phase on the residual carrier frequency offset (RCFO). Compared with our previous proposal, the computational complexity of the new method is dramatically reduced by avoiding excessive times of discrete Fourier transform operations in calculating the degree of symmetry. The complexity analysis shows that the required number of complex-valued multiplications in the new algorithm is only 3.4% of that with the previous one. The performance of the proposed RCFOC method is evaluated by Monte Carlo simulations in a 16 QAM modulated system. Numerical results verify that high accuracy RCFO estimation is achieved by our algorithm with optimal parameters of moderate values. The mean square error analysis indicates that the proposed algorithm is very robust to different combinations of laser linewidth, transmission distance, and optical signal-to-noise-ratio in metro/long-reach access applications.