Threshold-based Identification of Non-Gaussian Distortion in Optical Constellations Using Clustering Validity Metrics

Eduardo Avendano Fernandez; Henry Montaña Quintero; Lely Adriana Luenghas Contreras

doi:10.14482/inde.44.01.985.544

Autores/as

Eduardo Avendano Fernandez Universidad Pedagógica y Tecnológica de Colombia (UPTC) https://orcid.org/0000-0003-0910-8539
Henry Montaña Quintero Universidad Distrital Francisco José de Caldas https://orcid.org/0000-0003-0752-6315
Lely Adriana Luenghas Contreras Universidad Distrital Francisco José de Caldas https://orcid.org/0000-0002-3600-4666

DOI:

https://doi.org/10.14482/inde.44.01.985.544

Palabras clave:

Agrupamiento, k-means, fuzzy c-means, Gustafson-Kessel, distorsión no-Gaussiana, ruido de fase no lineal

Resumen

En este trabajo, los autores demuestran experimentalmente una estrategia de demodulación basada en umbrales para constelaciones 16-QAM y 4+12 PSK afectadas por distorsiones no gaussianas, utilizando índices de validez de agrupamiento como métrica de decisión. Al aplicar fragmentación mediante algoritmos de clustering—k-means, fuzzy c-means (FCM) y Gustafson-Kessel FCM (GK-FCM)—lograron identificar distorsiones elipsoidales en los clústeres externos de símbolos de datos y seleccionar dinámicamente estrategias de demodulación apropiadas. El enfoque propuesto, basado en agrupamiento, no requiere correcciones de desbalance en las ramas IQ ni de desfase, ya que redefine las regiones de decisión en función de los centroides de los clústeres. Los autores introducen el uso de índices de validez de agrupamiento (Coeficiente de Partición, Separación, Xie y Beni, y el Índice de Dunn) para caracterizar los niveles de distorsión de los símbolos en los diagramas de constelación y establecer umbrales de desempeño. La combinación de DI y XB proporciona un criterio para definir el umbral de distorsión no gaussiana. En particular, XB ? 10.7 y DI ? 0.015 pueden servir como indicadores empíricos de que la constelación en sistemas ópticos de radio sobre fibra (RoF) ha transitado hacia un régimen más estructurado en el que los centroides de clúster son utilizados para la demodulación. Los resultados experimentales muestran que, en condiciones de alto ruido (OSNR = 16 dB), el índice XB alcanza su valor mínimo, confirmando la sensibilidad del método a la distorsión inducida por ruido. Se observaron mejoras en la relación señal-ruido óptica (OSNR) de hasta 2.1 dB para 16-QAM y 0.7 dB para 4+12 PSK en un umbral de BER de 10?² en una transmisión sobre 78.8 km de fibra. La combinación de los índices DI y XB proporciona un criterio sólido para definir el umbral de distorsión no gaussiana. Estos hallazgos experimentales sugieren que las métricas de validez de agrupamiento pueden servir como umbrales efectivos para la demodulación adaptativa, permitiendo la identificación en tiempo real de distorsiones no gaussianas en sistemas de comunicación RoF.

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