Multi-dimensional demappers for optical fiber systems with soft-decision forward error correction

We study the impact of demappers using various channel statistics, including circularly symmetric and multi-dimensional Gaussian, in fiber-optic communication systems. In nonlinear dispersion-managed fiber systems, an improvement in achievable information rate (AIR) and bit error ratio (BER) after decoding is obtained from using multi-dimensional non-circularly symmetric Gaussian statistics at the demapper. For fiber systems without in-line dispersion compensation, only minor gains are obtained.