The relationship between modulation format, reach distances, and error is described in GNPy literature

[alittleice]

Question:
I have seen a paper published in the Journal of Optical Communications and Networking in 2020: GNPy: 《an open source application for physical layer aware open optical networks》Then, there is a place in the literature that I do not understand very well, and I hope to get your answer. The specific questions are as follows:
In the B.Results section of 4. VALIDATION in Chapter 4, there is a passage in the literature: “Moreover, as the QoT estimator is based on the GGN model, it neglects the impact of the modulation format on the NLI generation. For this reason, the QoT estimator predicts the same GSNR when only the modulation format changes. This assumption is validated because the modulation format has a negligible impact on the measured GSNR. ". Does this mean that only a single modulation format change in the GNPy framework will not change the value of the output GSNR?
However, in Figure 13b at the back of the document: "Error distribution-Modulation Format", it is shown that different modulation formats have different error distributions. Is this in different with the above?

[alittleice]

Answer:
The error distribution of each modulation format doesn’t correspond to the same average reach (fig13.a). The 16QAM format is suitable for shorter reaches with larger errors, while the QPSK format can be applied to longer reaches with reduced errors. This is why the different formats have different error distribution: this is related to their dependency on reach distances.

This answer was written by Prof. Esther Le Rouzic and Prof. Vittorio Curri. Thanks to both professors for their answers.