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Journal of Electrical and Computer Engineering
Volume 2015 (2015), Article ID 736267, 12 pages
Research Article

Maximum Likelihood Sequence Detection Receivers for Nonlinear Optical Channels

1Laboratorio de Comunicaciones Digitales, Universidad Nacional de Córdoba, CONICET, Avenida Vélez Sarsfield 1611, Córdoba X5016GCA, Argentina
2ClariPhy Communications, Inc., 7585 Irvine Center Drive, Suite 100, Irvine, CA 92618, USA

Received 25 July 2014; Revised 12 November 2014; Accepted 14 January 2015

Academic Editor: Martin Haardt

Copyright © 2015 Gabriel N. Maggio et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


The space-time whitened matched filter (ST-WMF) maximum likelihood sequence detection (MLSD) architecture has been recently proposed (Maggio et al., 2014). Its objective is reducing implementation complexity in transmissions over nonlinear dispersive channels. The ST-WMF-MLSD receiver (i) drastically reduces the number of states of the Viterbi decoder (VD) and (ii) offers a smooth trade-off between performance and complexity. In this work the ST-WMF-MLSD receiver is investigated in detail. We show that the space compression of the nonlinear channel is an instrumental property of the ST-WMF-MLSD which results in a major reduction of the implementation complexity in intensity modulation and direct detection (IM/DD) fiber optic systems. Moreover, we assess the performance of ST-WMF-MLSD in IM/DD optical systems with chromatic dispersion (CD) and polarization mode dispersion (PMD). Numerical results for a 10 Gb/s, 700 km, and IM/DD fiber-optic link with 50 ps differential group delay (DGD) show that the number of states of the VD in ST-WMF-MLSD can be reduced ~4 times compared to an oversampled MLSD. Finally, we analyze the impact of the imperfect channel estimation on the performance of the ST-WMF-MLSD. Our results show that the performance degradation caused by channel estimation inaccuracies is low and similar to that achieved by existing MLSD schemes (~0.2 dB).