Fig. 1. Algorithm diagram of cascaded EKF and LKF

Fig. 2. BER versus different block lengths and parameter Q

Fig. 3. (a) BER versus linewidth when frequency offset of 1 GHz; (b) BER versus FO when linewidth of 100 kHz

Fig. 4. Case of tracking different FO drifts. (a) FO drift velocity of 40 MHz/μs; (b) FO drift velocity of 320 MHz/μs

Fig. 5. BER versus frequency offset drift velocity

Fig. 6. 12 Gbaud dual polarization QPSK signal system

Fig. 7. Frequency offset tracking. (a) Frequency offset estimation with different block lengths; (b) frequency offset estimation with different OSNRs