Integrated MAP equalization and turbo product coding for optical fiber communications systems

We propose an integrated maximum a posteriori equalization and turbo product coding (IMAP-TPC) scheme for optical fiber communications systems (OFCS). The scheme uses accurate probabilistic characterization of electrical current in the presence of polarization mode dispersion (PMD)-induced intersymbol interference (ISI) and amplified spontaneous emission (ASE) noise. In the new IMAP-TPC scheme, TPC decoding is integrated with a symbol-by-symbol maximum a posteriori (MAP) detector. The MAP detector calculates the log-likelihood ratio (LLR) of a received symbol using the estimated conditional pdfs, and hence, obtains a much more accurate reliability measure for use in the TPC decoder. Similar to the case in the recent hardware implementation of TPC decoder for optical systems, we generate TPC by serial concatenation of two Bose, Chaudhuri, and Hocquenghem codes with low overhead. Simulation results with all-order PMD and ASE noise demonstrate both the practicality and the effectiveness of the IMAP-TPC scheme for OFCS.