List-Encoding CCDM: A Nonlinearity-Tolerant Shaper Aided by Energy Dispersion Index

Abstract

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Probabilistic Amplitude Shaping and Nonlinearity Tolerance: Analysis and Sequence Selection Method

“…It is insightful to compare the LSAS metric with the EDI metric from [18]. For this purpose, we show how the latter can be derived as a simplified version of the former.…”

“…The parameters for the two simulation setups are adopted from [18] and [21] and shown in Tables I and II, respectively. a) Setup 1 [18]: A multi-span WDM transmission with 11 channels, 32 GBd baud rate, and 50 GHz channel spacing is simulated using the SSFM. The modulation is 256 QAM with root raised cosine pulse shaping (roll-off 0.1).…”

“…We start with 256 QAM transmission in Setup 1 to compare the effectiveness of the LSAS metric for sequence selection with that of the EDI metric from [18]. Figure 8 shows the AIR as a function of the number of flipping bits v for PAS with different blocklengths and EDI and LSAS metrics for sequence selection.…”

“…Figure 8 shows the AIR as a function of the number of flipping bits v for PAS with different blocklengths and EDI and LSAS metrics for sequence selection. EDI uses a window length of w = 100, as suggested in [18]. For the LSAS metric, we distinguish two cases: (i) C = {c}, i.e., only SPM is considered ("LSAS (SPM)"), and (ii) C = {c−1, c, c+1}, i.e., XPM from adjacent channels is considered ("LSAS (SPM+XPM)").…”

“…The first pairs a conventional AS with a selection module, in which the latter chooses from a candidate set of shaped amplitude sequences generated by the AS. The selection is aided by a criterion that accounts for the nonlinearity of the optical channel, such as the EDI in the list-encoding CCDM (L-CCDM) of [18] or the effective SNR obtained from channel emulation using the split-step Fourier method (SSFM) in [19]. The generation of candidate sets can be integrated into the operation of a conventional AS by inserting additional flipping bits into each information block that is input to the AS.…”