Low-Complexity Carrier Phase Recovery for Square M-QAM Based on S-BPS Algorithm

Minimum distance blind phase search (BPS) algorithm has good tolerance to laser linewidth but with high computational complexity. In this letter, a novel substitution algorithm, i.e., symmetry BPS (S-BPS) is proposed for arbitrary square M-ary quadrature amplitude modulation (M-QAM) coherent optical systems. Based on the symmetry of square M-QAM, it can reduce the complexity directly by simplifying the phase error detection in the real plane and without multiplication. Taking square 4-QAM, 16-QAM, and 64-QAM as examples, the effectiveness of the proposed S-BPS algorithm is demonstrated by numerical simulations.