Optimal Electrical Processing in Multilevel Optical Systems Insensitive to GVD and PMD

The optimal receiver processing based on maximum-likelihood sequence detection (MLSD) is employed with high-order phase and amplitude modulations in optical transmission systems affected by typical channel impairments such as group velocity dispersion (GVD), polarization mode dispersion (PMD), and phase uncertainties due to phase noise. A couple of widely known front ends, with proper modifications, can be used to extract the required sufficient statistics from the received signal. Receiver adaptivity and complexity reduction are also discussed. It is demonstrated that, as long as a sufficient receiver complexity is employed, GVD and PMD entail no performance degradation with respect to the case of no channel distortions (the back-to-back case).