Joint estimation of QAM carrier phase with block turbo decoding

The paper concerns a new synchronizing scheme designed for block turbo coded systems. Phase estimation relies on the feedback of reliability information from the output of the turbo decoder. It is based on the fact that the power of the lower reliability values is strongly dependent on the carrier phase offset. A near optimum version of the algorithm based on a Pyndiah-like block turbo decoder allows easy implementation. We display various results showing that the proposed algorithm is able to track frequency shifts and that it works very well in the case of general quadrature amplitude modulation (QAM) constellations. We also show that this turbo synchronizer works at low signal-to-noise ratios (SNR), taking complete advantage of the turbo coding possibilities.