Non-parametric Estimation of Mutual Information with Application to Nonlinear Optical Fibers

This paper compares and evaluates a set of non-parametric mutual information estimators with the goal of providing a novel toolset to progress in the analysis of the capacity of the nonlinear optical channel, which is currently an open problem. In the first part of the paper, the methods of the study are presented. The second part details their application to several optically-related channels to highlight their features.Comment: This work has been submited to IEEE International Symposium on Information Theor

Nonlinearity Mitigation in WDM Systems: Models, Strategies, and Achievable Rates

After reviewing models and mitigation strategies for interchannel nonlinear interference (NLI), we focus on the frequency-resolved logarithmic perturbation model to study the coherence properties of NLI. Based on this study, we devise an NLI mitigation strategy which exploits the synergic effect of phase and polarization noise compensation (PPN) and subcarrier multiplexing with symbol-rate optimization. This synergy persists even for high-order modulation alphabets and Gaussian symbols. A particle method for the computation of the resulting achievable information rate and spectral efficiency (SE) is presented and employed to lower-bound the channel capacity. The dependence of the SE on the link length, amplifier spacing, and presence or absence of inline dispersion compensation is studied. Single-polarization and dual-polarization scenarios with either independent or joint processing of the two polarizations are considered. Numerical results show that, in links with ideal distributed amplification, an SE gain of about 1 bit/s/Hz/polarization can be obtained (or, in alternative, the system reach can be doubled at a given SE) with respect to single-carrier systems without PPN mitigation. The gain is lower with lumped amplification, increases with the number of spans, decreases with the span length, and is further reduced by in-line dispersion compensation. For instance, considering a dispersion-unmanaged link with lumped amplification and an amplifier spacing of 60 km, the SE after 80 spans can be be increased from 4.5 to 4.8 bit/s/Hz/polarization, or the reach raised up to 100 spans (+25%) for a fixed SE.Comment: Submitted to Journal of Lightwave Technolog

Performance Evaluation of a Low-Complexity Digital Backpropagation Method for Optical Fiber Communications

To compensate for linear and nonlinear distortions, several optical and digital techniques have been proposed. However, the significant performance improvement due to the combination of coherent detection with Digital Signal Processing has resulted in an almost complete abandonment of optical techniques. Consequently, digital nonlinear compensation has prevailed; this technique includes digital back propagation, perturbation-based techniques, and a combination of these two. All of these digital methods rely on numerically solving the nonlinear Schrödinger equation. Despite the well-known potential of digital back propagation, this method has an Achilles heel: its computational complexity. The aim of the current study is to analyze and investigate on the performance obtained using a low-complexity numerical method that can be used in DBP to solve the NLSE. Such a method is the Enhanced split-step Fourier method suggested by Secondini, Marsella and Forestieri

Non-parametric Estimation of Mutual Information with Application to Nonlinear Optical Fibers

This paper compares and evaluates a set of nonparametric mutual information estimators with the goal of providing a novel toolset to progress in the analysis of the capacity of the nonlinear optical channel, which is currently an open problem. In the first part of the paper, the methods of the study are presented. The second part details their application to several optically-related channels to highlight their features