Impact of 4D channel distribution on the achievable rates in coherent optical communication experiments

TL;DR

This paper experimentally examines how different four-dimensional channel distribution assumptions affect the achievable information rates in coherent optical communication systems, highlighting the benefits of sophisticated models especially with inline dispersion compensation.

Contribution

It investigates the impact of 4D channel distribution assumptions on achievable rates in optical systems, demonstrating gains with more complex models in certain scenarios.

Findings

Circularly symmetric Gaussian approximation works for WDM without dispersion compensation.

More sophisticated 4D distributions improve achievable rates with inline dispersion compensation.

Estimating mean values in 4D can enhance information rates for nonlinear channels.

Abstract

We experimentally investigate mutual information and generalized mutual information for coherent optical transmission systems. The impact of the assumed channel distribution on the achievable rate is investigated for distributions in up to four dimensions. Single channel and wavelength division multiplexing (WDM) transmission over transmission links with and without inline dispersion compensation are studied. We show that for conventional WDM systems without inline dispersion compensation, a circularly symmetric complex Gaussian distribution is a good approximation of the channel. For other channels, such as with inline dispersion compensation, this is no longer true and gains in the achievable information rate are obtained by considering more sophisticated four-dimensional (4D) distributions. We also show that for nonlinear channels, gains in the achievable information rate can also be achieved by estimating the mean values of the received constellation in four dimensions. The highest gain for such channels is seen for a 4D correlated Gaussian distribution.