Cycle slip mitigation scheme aided blind carrier phase recovery algorithms

In coherent optical communication systems, phase noise—caused by the finite linewidth of both transmitter and receiver lasers—induces random rotations of the signal constellation points, which significantly impedes signal demodulation. Carrier phase recovery/estimation (CPR/CPE) effectively mitigates phase noise and is thus a critical digital signal processing (DSP) technology in such systems. Blind carrier phase recovery (BCPR) algorithms are widely used and contribute to improving key performance metrics such as generalized mutual information (GMI), bit error rate (BER), and error vector magnitude (EVM) in high-order quadrature amplitude modulation (QAM) coherent optical communication systems. However, BCPR algorithms are inherently susceptible to cycle slips (CS), which can cause catastrophic error propagation and reduce system robustness. Existing BCPR algorithms—such as blind phase search (BPS) and principal component-based phase estimation (PCPE)—are unable to completely eliminate CS. To address this issue, we propose a phase pilot-aided (PPA) scheme, a CS mitigation method based on signal phase labeling and amplitude mapping. By converting phase variations into detectable amplitude changes, the PPA scheme effectively suppresses the impact of CS. Numerical simulations demonstrate that the proposed PPA scheme significantly mitigates the effects of cycle slips and improves GMI performance for QAM coherent optical communication systems.