Fig. 1. Data frame structure of the proposed joint scheme

Fig. 2. Schematic block diagram of the proposed joint scheme

Fig. 3. Simulation platform for 64 Gbaud PM-16QAM FTN-WDM coherent systems

Fig. 4. S-curves of timing error detection output based on SGPD under different AF

Fig. 5. RMS curves of timing error detector under different schemes. (a)(d) Gardner algorithm; (b)(e) conventional discrete scheme; (c)(f) proposed scheme

Fig. 6. Comparison of convergence cost among the proposed scheme, conventional discrete scheme and SGPD algorithm under different DGD. (a) AF is 0.90 and LLW is 50 kHz; (b) AF is 0.85 and LLW is 50 kHz; (c) AF is 0.90 and LLW is 100 kHz; (d) AF is 0.85 and LLW is 100 kHz

Fig. 7. System performance comparison under different schemes. (a) AF is 0.90 and LLW is 50 kHz; (b) AF is 0.85 and LLW is 50 kHz; (c) AF is 0.90 and LLW is 100 kHz; (d) AF is 0.85 and LLW is 100 kHz

Fig. 8. Offline experimental platform of three-carrier 40 Gbaud PM-16QAM FTN coherent transmission system

Fig. 9. RMS curves of timing error detection under transmission distance of 800 km. (a) With conventional discrete scheme; (b) with the proposed scheme

Fig. 10. Comparison of convergence cost between the proposed scheme, conventional discrete scheme and SGPD algorithm under transmission distances. (a) AF is 0.90; (b) AF is 0.85

Fig. 11. Offline experiment performance. (a) AF is 0.90; (b) AF is 0.85