Capacity Region Bounds for the K user Dispersive Nonlinear Optical WDM Channel with Peak Power Constraints

TL;DR

This paper analyzes the capacity limits of a K-user dispersive nonlinear optical WDM channel with peak power constraints, proposing bounds and strategies to improve achievable data rates by treating interference as a channel rather than noise.

Contribution

It introduces a multiuser information theoretic framework for the nonlinear optical WDM channel and derives new outer bounds and achievable rate regions using genie-aided and time-sharing techniques.

Findings

Time-sharing strategies outperform treating interference as noise.

Achievable rate increases from 1.67 to 6.33 bits/sym with time-sharing.

Outer bounds on capacity region are established for the simplified model.

Abstract

It is known that fiber nonlinearities induce crosstalk in a wavelength division multiplexed (WDM) system, which limits the capacity of such systems as the transmitted signal power is increased. A network user in a WDM system is an entity that operates around a given optical wavelength. Traditionally, the channel capacity of a WDM system has been analyzed under different assumptions for the transmitted signals of the other users, while treating the interference arising from these users as noise. In this paper, we instead take a multiuser information theoretic view and treat the optical WDM system impaired by cross-phase modulation and dispersion as an interference channel. We characterize an outer bound on the capacity region of simultaneously achievable rate pairs, assuming a simplified K-user perturbative channel model using genie-aided techniques. Furthermore, an achievable rate region is obtained by time-sharing between certain single-user strategies. It is shown that such time-sharing can achieve better rate tuples compared to treating nonlinear interference as noise. For the single-polarization single-span system under consideration and a power 4.4 dB above the optimum launch power, treating nonlinear interference as noise results in a rate of 1.67 bit/sym, while time-sharing gives a rate of 6.33 bit/sym.