On the Mitigation of the Differential Decoding Penalty in 100G PDM-QPSK Digital Coherent Receivers for Multirate WDM Transmission

We evaluate the performance of nonredundant differential decoding schemes under linear and nonlinear channel conditions with various neighbor channels based on measured data. Each method is analyzed with respect to its systematic back-to-back performance, its nonlinear tolerance, its implementation complexity, and its compatibility to soft-decision (SD) forward error correction (FEC). All schemes successfully avoid large error-bursts due to residual phase ambiguity after digital carrier recovery. Only the complex implementation of the recursive multisymbol phase estimation provides SD samples to subsequent SD-FEC and reaches substantial recovery of the differential penalty at the same time. None of the schemes can overcome the hard-decision differential penalty.