On Achievable Rates for Long-Haul Fiber-Optic Communications

TL;DR

This paper derives lower bounds on mutual information for long-haul fiber-optic systems, providing practical formulas and simulations to evaluate how system modifications influence achievable data rates, emphasizing the benefits of mutual information over traditional metrics.

Contribution

It introduces ready-to-use expressions for mutual information calculation and analyzes the impact of various system parameters on achievable rates in optical communications.

Findings

Mutual information bounds are derived for different modulation formats.

System modifications like channel spacing and digital back-propagation significantly affect achievable rates.

Mutual information offers advantages over Q-factor as a performance metric.

Abstract

Lower bounds on mutual information (MI) of long-haul optical fiber systems for hard-decision and soft-decision decoding are studied. Ready-to-use expressions to calculate the MI are presented. Extensive numerical simulations are used to quantify how changes in the optical transmitter, receiver, and channel affect the achievable transmission rates of the system. Special emphasis is put to the use of different quadrature amplitude modulation formats, channel spacings, digital back-propagation schemes and probabilistic shaping. The advantages of using MI over the prevailing $Q$-factor as a figure of merit of coded optical systems are also highlighted.