Wide-range, accurate frequency offset compensation algorithm based on LDPC for space coherent optical communication

In this paper, we introduce a wide-range, accurate LDPC coded-aided frequency offset compensation algorithm based on both EM algorithm and M&M algorithm in space coherent optical communication systems. The proposed approach can overcome the shortcoming of the existing frequency offset compensation algorithms which are employed in space coherent optical communication systems directly. It allows performing reliable frequency estimation with respect to the ideal frequency estimation for the signal-to-noise ratios down to a few decibels, and without need phase-locked loops (PLL). The simulations show that the approach can increase the synchronization range about ±50% of the symbol rate. Furthermore, its accurate is close to the Modified Cramer-Rao bound (MCRB) in low signal- to-noise ratio.