On the channel capacity of multilevel modulation schemes with coherent detection

Abstract

We describe a method to determine the channel capacity of an arbitrary multilevel modulation scheme by modeling the fiber-optic channel as a dynamical nonlinear ISI channel with memory. We also propose a multilevel turbo-equalization scheme that is able closely to approach the channel capacity. We show that with this scheme we are able straightforwardly to upgrade currently installed 10 Gb/s optical transmission systems to 100 Gb/s, and even with small memory assumption we are able to achieve 100 Gb/s per DWDM channel transmission over 9600 km.