Improved FFT-Based Frequency Offset Estimation Algorithm for Coherent Optical Systems

Algorithms of frequency offset (FO) estimation based on fast Fourier transform of the sample signal's argument have been investigated, in which the FO estimation range is $[-R_{s}/12, R_{s}/8]$ ($R_{s}$ is the symbol rate). In this letter, an improved algorithm is proposed with the sign of FO being determined by means of an improved judging method. The estimation range of the proposed algorithm can be up to $[-R_{s}/8,R_{s}/8]$, with the same accuracy as that of the previous algorithms being obtained, yet at the same time requiring very little additional computational burden.