Volterra based nonlinear equalizer with reduced complexity

Abstract

A model for a reduced complexity nonlinear electrical equalizer based on the Volterra theory is presented which can be utilized to mitigate dispersion and other distortions in optical communication systems. In recent years several electronic equalizers like the feed forward equalizer (FFE), the decision feedback equalizer (DFE) and the maximum likelihood sequence estimator (MLSE) were intensively investigated in optical communication systems. Also, nonlinear FFE/DFE structures based on the Volterra theory were proposed. These nonlinear equalizers can mitigate the effects of dispersion much better than the classical FFE/DFE but are more complicated to build. In a practical system the Volterra nonlinearity is therefore limited to second and third order. However, the number of filter coefficients for such a nonlinear FFE of appropriate order (e.g. 5 taps) is still very high for the nonlinear parts. This results in a very high effort in the equalizer control and optimization algorithm and makes a practical implementation questionable. In this Paper we present a reduced model for Volterra based nonlinear equalizers were the order of the nonlinear parts can be set separately from the linear order. This results in less complex filter structures as the number of coefficients is reduced drastically.