Mitigating nonlinear interference through constellation shaping
Sebastiaan Goossens defended his PhD thesis at the Department of Electrical Engineering on January 22nd.
Nonlinear interference noise (NLIN), caused by the optical Kerr effect and chromatic dispersion, is one of the primary limitations in optical fiber communication systems. Although computationally intensive digital signal processing (DSP) techniques, such as digital backpropagation (DBP), can partially compensate for NLIN, they cannot fully address the issue due to model inaccuracies and unpredictable signal-noise interactions. To mitigate NLIN, optimizing the transmitted modulation format through constellation shaping is a promising strategy. In his research Sebastiaan Goossens focused on two forms of constellation shaping: probabilistic shaping (PS), which adjusts the probabilities of constellation points, and geometric shaping (GS), which alters the geometry of the points.
Key contributions
Four main contributions are presented in his thesis. First, the performance of two finite-blocklength PS algorithms was experimentally evaluated in a long-haul wavelength division multiplexing (WDM) setup, confirming a theoretical observation about blocklength dependency on nonlinear tolerance. Second, a framework was developed to optimize 4D GS constellations for nonlinear optical channels, reducing the optimization space through energy shell discretization and symmetry constraints. Third, GS techniques were optimized for high cardinality (up to 17 bit/4D symbol) in finite signal-to-noise ratio (SNR) additive white Gaussian noise (AWGN) channels. Finally, the thesis optimized 4D GS constellations (up to 12 bit/4D symbol) for realistic optical communication system models, addressing current and future standards for transceivers supporting 1.6 Tbps and 3.2 Tbps links.
Title of PhD thesis: . Supervisors: Prof. Alex Alvarado, and Dr. Chigo Okonkwo.