Frequency Offset Estimation With Multi-Steps Interpolation for Coherent Optical Systems

We investigate a frequency offset estimation (FOE) algorithm based on improved fast Fourier transform (FFT) for coherent optical systems. The algorithm implements FFT operation with a small number of samples and then adopts multi-steps interpolation with the increasing number of samples to improve the estimation accuracy gradually. In a 28-GBd coherent quaternary phase-shift keying system, simulation results show that the proposed algorithm reaches the same estimation accuracy with least-squares FOE algorithm that utilizes 64 time spans (LS-64) under the same total number of samples L. But the number of complex multiplications required by the proposed algorithm is just 7.26% and 6.75% of that required by LS-64 at L = 1024 and L = 2048, respectively.