Pilotless carrier phase-synchronization via LDPC code feedback

This paper addresses the carrier-phase estimation problem under the low SNR conditions often encountered in turbo and LDPC-coded applications. In a decision-directed carrier synchronization (DDCS) circuit that uses soft information from an iterative LDPC decoder was presented for BPSK and QPSK constellations with constant phase offsets. In this work, we present a method that is able to handle arbitrary constellations with a random-walk phase noise process. Loop SNR equations are derived and the performance for different constellations is shown. An extension of the DDCS algorithm is described that uses a search and tracking method based on measuring the number of satisfied LDPC constraint-node equations equations at the decoder and is able to track arbitrary carrier phase.