CMA misconvergence in coherent optical communication for signals generated from a single PRBS

Abstract

In the experimental study of modulators for coherent optical communications, it is common to generate multilevel signals using a single pseudo-random binary sequence. This simple experimental realization leads to symbol correlation. When modulators are studied in combination with adaptive receiver algorithms that rely on independent data, misconvergence may result. In this contribution, we investigate the impact of such correlation on a standard blind equalization method and provide guidelines to avoid misconvergence. Our results indicate that care needs to be taken when using a single PRBS sequence and that decorrelation delays must be chosen appropriately. We present simulation and theoretical results for 16-QAM, and show how our results can be applied to other multi-level constellations.