Sequence Selection With Dispersion-Aware Metric for Long-Haul Transmission Systems

Sequence selection (SS) potentially offers a pragmatic way to unlock nonlinear shaping gains in coherent optical fiber communications beyond those offered by probabilistic constellation shaping (PCS). We introduce a novel sign-dependent metric: the energy dispersion index (EDI) of sequences that endured chromatic dispersion, denoted as D-EDI, which exhibits more accurate opposite variations with the transmission performance compared to the standard EDI metric. Then, by applying D-EDI and EDI to the SS process, we present two signaling approaches denoted as D-SS and E-SS respectively. These approaches are designed to minimize rate loss and enhance transmission performance in nonlinear optical fiber transmission systems, catering to both short-distance and long-haul scenarios. With enumerative sphere shaping (ESS) as distribution matcher (DM), our simulation results reveal significant performance gains over ESS without SS, with improvements up to 0.4 bits/4D-symbol. These improvements were observed over a 205-km single-span standard single mode fiber link in wavelength-division multiplexing (WDM) transmission, with five dual-polarization channels, each operating at a net rate of 400 Gbit/s. Furthermore, we demonstrate that D-SS surpasses ESS without SS by 0.03 bits/4D-symbol in achievable information rate over a
$30\times 80$
 km link in a single- wavelength, with 8 discrete multi-band (DMB) transmission, and an 880 Gbit/s net rate. Notably, our proposed D-SS scheme achieves similar performance to a sequence selection based on a full split-step Fourier method (SSFM) simulation and it consistently delivers throughput enhancements across various block lengths and selected sequence lengths.