Integrated MAP equalization and coding for optical-fiber-communication systems

In this paper, an integrated maximum a posteriori equalization and turbo product coding (IMAP-TPC) scheme for optical-fiber-communication systems (OFCS) is proposed. The scheme uses a probabilistic characterization of the electrical current in the presence of intersymbol interference (ISI) and noise to compensate their effects and improve the bit error rate. In the new IMAP-TPC scheme, TPC decoding is integrated with a symbol-by-symbol MAP detector. The MAP detector calculates the log-likelihood ratio of a received symbol using the conditional probability-density information and, hence, obtains a much more accurate reliability measure than the traditional measure used in the TPC decoder. The TPC was generated by serial concatenation of two Bose, Chaudhuri, and Hocquenghem codes with low overhead, which is a structure similar to a recently proposed hardware implementation of TPC decoder for optical systems. Simulation results with all-order polarization mode dispersion and amplified spontaneous emission noise demonstrate both the practicality and the effectiveness of the IMAP-TPC scheme for OFCS.