Adaptive Maximum Likelihood Sequence Detection for QPSK Coherent Optical Communication System

A novel Viterbi-type adaptive maximum likelihood sequence detection algorithm is developed and investigated in coherent optical communication systems in the presence of both laser phase noise and nonlinear phase noise. Compared with the nonadaptive version, it can self-adjust the effective memory length of the phase estimator and automatically deliver the optimum bit-error rate performance without requiring any prior statistical knowledge of the optical channel. The phase error variance of the estimator is also analytically investigated.