Convergence characteristics of iterative phase synchronization and detection

Serially concatenated systems with rotational invariance can tolerate certain phase ambiguities and, therefore, for these systems coherent detection is robust even when cycle slipping, false-lock and hangup exist during phase synchronization. In this paper, we present a simplified phase model to analyze convergence of iterative receivers with/without occurrence of phase rotations. Particularly, an oscillatory convergence behavior due to cycle slipping is explained by means of density evolution. Moreover, based on per-survivor processing (PSP) and single-estimator processing (SEP) techniques, a family of adaptive soft-input soft-output algorithms are employed to implement joint phase tracking and demodulation in the context of maximum a-posteriori symbol detection. Both analytical and simulation results show that the convergence performance of SEP method is more robust than that of PSP method when carrier phase has high and random dynamics.