Turbo Equalization in Fiber-Optics Communication Systems

Abstract

In order to adapt to the ever-increasing demands of telecommunication needs, the network operators already consider 100 Gb/s per dense wavelength division multiplexing (DWDM) channel transmission. At those data rates, the performance of fiber-optic communication systems is degraded significantly due to intra- and interchannel fiber nonlinearities, polarization mode dispersion (PMD), and chromatic dispersion [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11]. In order to mitigate the signal distortions at ultra-high bit rates, some new technologies have been proposed and deployed in optical systems, and they represent a distinctive new trend in optical fiber communications. These new technologies include digital signal processing (DSP)-aided optical channel equalization, digital coherent receiving, multilevel modulations and optical polarization multiplexing (or optical multiple-input multiple-output technologies) [1, 2, 3, 4, 5, 6]. To deal with chromatic dispersion and PMD a number of channel equalization techniques have been proposed recently including digital-filtering approach [1] and maximum likelihood sequence detection/estimation (MLSD/E) [2]. To simultaneously suppress chromatic dispersion and PMD, orthogonal frequency division multiplexing (OFDM) has been proposed [4, 5]. On the other hand, to deal with intrachannel nonlinearities someone may use either constrained coding [6].