Fig. 1. Flexible-rate grid-less optical transport network

Fig. 2. Communication system block diagram based on FEC code^[30]

Fig. 3. Multi-rate hierarchical encoding QAM and demodulation principle diagram^[39]

Fig. 4. Diagram of THDM^[49]

Fig. 5. Diagram of signal generation structure^[53]. (a) TDHM; (b) PAS

Fig. 6. AIR curves of various modulation schemes in AWGN channel^[53]

Fig. 7. Flow of singular value decomposition (SVD) scheme^[56]

Fig. 8. Flow of feature extraction algorithm of signal constellation diagram^[57]

Fig. 9. Schematic diagram of modulation format recognition based on LSTM ^[70]

Fig. 10. LSTM modulation format identification performance^[70]. (a) Confusion matrix for identifying four modulation formats; (b) classification accuracy of modulation formats under different OSNRs

Fig. 11. Schematic diagram of MIMO equalizer based on Bayes-Adam algorithm^[87]

Fig. 12. Processing scheme for continuous signals with different modulation formats^[89]

Fig. 13. Gridless optical transmission principle^[91]. (a) Comparison of traditional fixed grid and gridless frequency spectra; (b) operation of optical switching nodes

Fig. 14. Control plane and interface of flexible rate gridless optical transmission network^[95]

Fig. 15. Composition of OXC system^[96]

Fig. 16. Principle of WSS^[98]