An algorithm to remove the modulated phase is further investigated to make the algorithm be suitable for the coherent systems of higher-order modulation format.In the algorithm

the absolute operation is respectively implemented on the real part and imaginary part of received complex signals to remove their modulated phases.The performance of the proposed algorithm in a 28 GBaud coherent 64 ary Quadrature Amplitude Modulation（64QAM）system is investigated through simulation.The simulation results show that the proposed algorithm requires no multiplier and reaches the approximate performance as the Mth-power operation in the frequency offset estimation.Therefore

the algorithm reduces the complexity with similar performance compared with Mth-power operation.