Decoding metrics for multistage bit-wise coded modulation in optical communications

A fiber-optic communication system employing a multistage bit-wise coded modulation scheme is considered as it enables the efficient utilization of higher-order modulation formats in combination with binary forward error correction (FEC) coding. Since modern FEC schemes employ soft-decision decoding, soft information on coded bits is required. In this paper, the decoding metric for the multistage bit-wise receiver structure is reviewed. Both numerical as well as experimental results are provided for the proposed decoding metrics using coded transmission over dispersion-unmanaged and dispersion-managed links.