Blind Nonlinearity Equalization by Machine-Learning-Based Clustering for Single- and Multichannel Coherent Optical OFDM

• Published in: Journal of lightwave technology Vol. 36; no. 3; pp. 721 - 727
• Main Authors: Giacoumidis, Elias, Matin, Amir, Wei, Jinlong, Doran, Nick J., Barry, Liam P., Wang, Xu
• Format: Journal Article
• Language: English
• Published: New York IEEE 01-02-2018; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Algorithm design and analysis; Algorithms; Artificial neural networks; Binary phase shift keying; Clustering; Clustering algorithms; Coherence; coherent detection; coherent optical OFDM; Equalization; Frequency division multiplexing; Fuzzy logic; machine learning; Multichannel communication; Neural networks; Nonlinearity; nonlinearity mitigation; OFDM; Optical fiber amplifiers; Optical fiber networks; Orthogonal Frequency Division Multiplexing; Phase shift keying; Support vector machines; Transfer functions; Wave division multiplexing; Wavelength division multiplexing
• ISSN: 0733-8724; 1558-2213
• DOI: 10.1109/JLT.2017.2778883

Fiber-induced intra- and interchannel nonlinearities are experimentally tackled using blind nonlinear equalization (NLE) by unsupervised machine-learning-based clustering (MLC) in ∼46-Gb/s single-channel and ∼20-Gb/s (middle-channel) multichannel coherent multicarrier signals (orthogonal frequency-division multiplexing (OFDM) based). To that end, we introduce, for the first time, hierarchical and fuzzy-logic C -means (FLC)-based clustering in optical communications. It is shown that among the two proposed MLC algorithms, FLC reveals the highest performance at optimum launched optical powers (LOPs), while at very high LOPs, hierarchical can compensate more effectively nonlinearities only for low-level modulation formats. When employing binary phase-shift keying and quaternary phase-shift keying, FLC outperforms K-means, fast-Newton support vector machines, supervised artificial neural networks, and NLE with deterministic Volterra analysis. In particular, for the middle channel of a QPSK wavelength-division multiplexing coherent optical OFDM system at optimum −5 dBm of LOP and 3200 km of transmission, FLC outperforms Volterra-NLE by 2.5 dB in Q-factor. However, for a 16-QAM single-channel system at 2000 km, the performance benefit of FLC over inverse Volterra-series transfer function reduces to ∼0.4 dB at a LOP of 2 dBm (optimum). Even when using novel sophisticated clustering designs in 16 clusters, no more than additional ∼0.3-dB Q-factor enhancement is observed. Finally, in contrast to the deterministic Volterra-NLE, MLC algorithms can partially tackle the stochastic parametric noise amplification .