Maximum-likelihood sequence estimation in dispersive optical channels

Abstract

This paper discusses the investigation of maximum-likelihood sequence estimation (MLSE) receivers operating on intensity-modulated direct-detection optical channels. The study focuses on long-haul or metro links spanning several hundred kilometers of single-mode fiber with optical amplifiers. The structure of MLSE-based optical receivers operating in the presence of dispersion and amplified spontaneous emission (ASE), as well as shot and thermal noise, are discussed, and a theory of the error rate of these receivers is developed. Computer simulations show a close agreement between the predictions of the theory and simulation results. Some important implementation issues are also addressed. Optical channels suffer from impairments that set them apart from other channels, and therefore they need a special investigation. Among these impairments are the facts that the optical channel is nonlinear, and noise is often non-Gaussian and signal dependent. For example, in optically amplified single-mode fiber links, the dominant source of noise is ASE noise, which after photodetection is distributed according to a noncentral chi-square probability density function. In addition, optical fibers suffer from chromatic and polarization-mode dispersion (PMD). Although the use of MLSE in optical channels has been discussed in previous literature, no detailed analysis of optical receivers using this technique has been reported so far. This motivates the study reported in this paper.

Advanced Modulation Formats and MLSE Based Digital Signal Processing for 100Gbit/sec Communication Through Optical Fibers

“…Another case of interest is ASE limited channel. As stated above the noise in such a channel becomes signal dependent and the functional form of the conditional PDF of the received sample n x , given that k  is transmitted, can be approximated by a non-central Chi-square distribution with  degrees of freedom (Agazzi et al, 2005):…”

“…It is clear that in (3.2) 0 N and  need to be estimated. More information about parametric estimation is given in (Agazzi et al, 2005;Foggi et al, 2006).…”

Performance Bounds of Optical Receivers With Electronic Detection and Decoding

“…Therefore, bounds and algorithms are based on the same statistical mismatch and thus the determined bounds are the lower bounds of the investigated algorithms. Some of the considered algorithms are BCJR detection [27], maximum-likelihood sequence estimation (MLSE, Viterbi equalizer) [29], [30], sum-product-algorithm (SPA) LDPC decoding [31], decoding of RS codes [32], turbo equalization [2], [4], and others. None of them consider the noise correlation.…”

Architecture and Experimental Evaluation of a 10Gb/s MLSD-Based Transceiver for Multimode Optical Fibers

“…Maximum-likelihood sequence detection (MLSD) has attracted considerable interest in recent literature as an electronic dispersion compensation (EDC) technique for single mode optical fibers (SMF), particularly for long-haul or metropolitan area network applications [2], [3], [4]. However, most of the literature on EDC for multimode fibers (MMF) is based on the decision-feedback equalizer [5], [6].…”