SDM Optical Systems with MMSE Equalizers: Information Rates and Performance Monitoring

TL;DR

This paper develops analytical models for MMSE equalizers in SDM optical systems affected by MDG and MDL, providing new solutions for information rates and monitoring techniques validated by simulations.

Contribution

It introduces the first analytical solutions for information rates under MMSE equalization with co-channel interference in coupled SDM systems.

Findings

Analytical models accurately predict information rates.

Monitoring techniques effectively track MDG and SNR.

Solutions validated by Monte-Carlo simulations.

Abstract

The information rate of coupled space-division multiplexing (SDM) transmission systems is impaired by the stochastic effects of mode-dependent gain (MDG) and mode-dependent loss (MDL), turning it into a random variable and reducing its average value. In systems operating with minimum mean squared error (MMSE) equalizers and no channel-state information (CSI), co-channel interference further reduces the instantaneous and average information rates. Analytical solutions for the average information rate in MDG- and MDL-impaired systems under strong coupling have been presented in early studies assuming ideal maximum-likelihood (ML) equalization. However, to the best of our knowledge, a solution encompassing co-channel interference under MMSE equalization has not been presented yet. In this work, we derive statistical models for the MMSE equalizer coefficients and develop analytical solutions for the post-filtering information rate. We also use these statistical models and analytical solutions to carry out MDG and signal-to-noise ratio (SNR) monitoring in coupled SDM systems. The derived analytical solutions and monitoring techniques are validated by Monte-Carlo simulations, exhibiting a suitable accuracy within practical operational values.