Adaptive iterative detection: a performance comparison of closed-loop and open-loop phase synchronization

In this paper we consider iterative detection over bandpass channels which introduce an unknown phase rotation in the transmitted signal. We first introduce a unified formulation of adaptive forward-backward algorithms for channels with parametric uncertainty, including both recursive and non-recursive estimation strategies, and then apply this framework to a phase noncoherent channel. Two main classes of adaptive forward-backward algorithms are then considered and compared: closed-loop algorithms, which use explicit recursive phase estimation, and open-loop algorithms, which use implicit non-recursive phase estimation. We consider schemes with combined detection and decoding. Pilot symbols are inserted in order to cope with the unknown time-varying channel phase.