On line rates, information rates, and spectral efficiencies in probabilistically shaped QAM systems

We carefully revisit the definitions of line rates, information rates; and spectral efficiencies in probabilistically shaped optical transmission systems. Generally accepted definitions for uniform quadrature amplitude modulation (QAM) systems arc extended to more generally apply to systems with probabilistically shaped QAM, as well as to systems using pilot symbols of different QAM order than the information symbols. Based on the proper definitions, we correct erroneous claims in a recently reported work. (C) 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement