Communications and Signal Processing Lab (ComSP)

Title	Receptores lineales MIMO para comunicaciones ópticas sobre canales con atenuación dependiente del modo
State	Finished
Author	Luis Manuel Torres Cantón
Director/s	Francisco Javier Cañete Corripio ,  Luis Díez Del Río
University	Universidad de Málaga
Center	Escuela Técnica Superior de Ingeniería de Telecomunicación
Department	Ingeniería de Comunicaciones
Reading date	21/03/2024

Spatial multiplexing optical systems (SDM) are postulated as an interesting solution in terms of spectral efficiency and aggregate transmission rates to face the physical limitation that long-haul optical communication systems based on single-mode fibers exhibit.

The ability of the SDM technique to transmit múltiple data streams simultaneously using modes or groups of modes over multimode or multi-core fibers, combined with the use of wavelength multiplexing and coherent MIMO receivers, brings the aggregate rate of long-haul optical systems to experimental data rates cióse to 1000 Tb/s over a distance of 2000 km based on multi-core fiber using SDM-specific intermedíate amplifiers.

However, the MIMO channel for long-haul optical SDM systems presents particular characteristics due to the unequal amplification of the modes that occurs in the intermedíate amplifiers, called MDL (mode-dependent loss). When the MDL level in the channel is not negligible, the performance of an ideal linear MIMO equalizer based on mean squa-re error minimization (MMSE) criteria begins to depend on the realization of the optical channel. In other words, the equalizer performance becomes random and gives results in terms of bit error rate (BER) to be described by a probability density function.

This thesis addresses this phenomenon and its impact on the design of the Communications system in three distinct stages, and each one has resulted in a sepárate publication.

In the first stage, we show why the ideal MIMO MMSE equalizer in the presence of MDL in the optical channel is no longer the optimal receiver in the sense of minimum error probability and that, in such a case, it offers performances that are random. We will analyze how the ideal MIMO MMSE equalizer fails to be the channel matched filter in the presence of MDL. We will also perform nurnerical simulations to quantify the degradation in terms of SNDR due to a certain amount of MDL for a MIMO system based on a multicore fiber and intermedíate amplifiers with varying MDL level.

In the second stage, we will statistically analyze the residual inter-symbol interference (ISI) and crosstalk that appear after the ideal MIMO MMSE equalizer, as well as its BER probability density functions, all in the presence of MDL in the channel. We will verify that these probability density functions depend on both the MDL level in the channel and the SNR at the equalizer input. Furthermore, we will propose an approximation of