Models and Information Rates for Multiuser Optical Fiber Channels with Nonlinearity and Dispersion

TL;DR

This paper develops two discrete-time interference channel models for multiuser optical fiber channels considering nonlinearity and dispersion, introducing a novel interference focusing technique that enhances capacity pre-log factors.

Contribution

It introduces a new interference focusing method for multiuser optical channels that achieves higher capacity pre-log factors compared to traditional approaches.

Findings

Interference focusing doubles the pre-log to 1 for two users.

All three users can simultaneously achieve pre-log 1 with interference focusing.

Models incorporate key nonlinear effects while ignoring some dispersion phenomena.

Abstract

Two discrete-time interference channel models are developed for information transmission over a single span of optical fiber using wavelength-division multiplexing (WDM) and lumped amplification. The models are derived from the nonlinear Schroedinger (NLS) equation by including the nonlinear phenomena of self-phase modulation (SPM) and cross-phase modulation (XPM) but ignoring four-wave mixing (FWM), polarization effects and group velocity dispersion (GVD) within WDM bands. The first model also ignores GVD across WDM bands, referred to as group velocity mistmatch (GVM). For the case of two users, a new technique called "interference focusing" is proposed where each carrier achieves the capacity pre-log 1, thereby doubling the pre-log of 1/2 achieved by using conventional methods. For three users, interference focusing is also useful under certain conditions. The second model captures GVM and the effect of filtering at the receivers in addition to SPM and XPM. In a 3-user system, it is shown that all users can achieve the maximum pre-log factor 1 simultaneously by using interference focusing, a time-limited pulse and a bank of filters at the receivers.