Upper Bound on the Capacity of a Cascade of Nonlinear and Noisy Channels

TL;DR

This paper derives an upper bound on the spectral efficiency of cascaded nonlinear noisy channels, relevant to optical fiber communications, highlighting the fundamental limits imposed by channel nonlinearities and noise.

Contribution

It introduces a theoretical upper bound on capacity for cascaded nonlinear channels using the split-step Fourier model, advancing understanding of optical fiber channel limits.

Findings

Spectral efficiency is at most log(1+SNR).

The bound applies to optical fiber channels.

Bandwidth definition affects the interpretation of the bound.

Abstract

An upper bound on the capacity of a cascade of nonlinear and noisy channels is presented. The cascade mimics the split-step Fourier method for computing waveform propagation governed by the stochastic generalized nonlinear Schroedinger equation. It is shown that the spectral efficiency of the cascade is at most log(1+SNR), where SNR is the receiver signal-to-noise ratio. The results may be applied to optical fiber channels. However, the definition of bandwidth is subtle and leaves open interpretations of the bound. Some of these interpretations are discussed.