Pilot-aided Kalman filter scheme with high robustness for joint equalization of PMD, RSOP, and RCD in ultra-high-speed coherent fiber-optic communications systems

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We propose a pilot-aided Kalman filter (PA-KF) scheme based on the pilot symbols designed in the OIF 400ZR. The leveraging of pilot symbols simplifies the exhaustive search across all rings into a single-ring determination, which substantially enhances performance and robustness, and to a lesser degree, reduces complexity compared to the ordinary extended Kalman filter (EKF). To verify the performance of the proposed PA-KF, we built a 140 Gbaud PDM simulation platform for 16QAM, 32QAM, and 64QAM. Simulation results show that under a rotation of state of polarization (RSOP) from 2 to 10 Mrad/s, a differential group delay (DGD) from 1 to 5 times the symbol period, and a residual chromatic dispersion (RCD) of 0 to ±300 ps/nm, considering the BER threshold of 2 × 10 −2 for soft-decision forward error correction (SD-FEC), the proposed PA-KF reduces up to approximately 3 dB of OSNR requirement for 16QAM compared with the ordinary EKF. For 32QAM and 64QAM, the PA-KF achieves excellent performance, while the ordinary EKF completely fails under such impairments. Meanwhile, when jointly equalizing the three impairments, the PA-KF reduces computational complexity by 2%, 6%, and 17% for 16QAM, 32QAM, and 64QAM, respectively. In addition, the PA-KF is a modulation-format transparent, requiring no separate adaptation across formats.

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