Modulation-Format-Independent Carrier Phase Estimation for Square M-QAM Systems

A modulation-format-independent or universal carrier phase estimation (U-CPE) technique is proposed for square 4-, 16-, and 64-ary quadrature amplitude modulation transmission systems for future elastic optical networks. The proposed U-CPE is based on a feedback architecture and eliminates the need to know the signal modulation format (MF) by using a cost function in the phase estimation update that is common to all square-shaped constellations. Compared with standard decision directed phase lock loop (S-DD-PLL) that requires the knowledge of the MF, the U-CPE method maintains close OSNR performance and linewidth tolerance. When MF is agnostic, the proposed U-CPE outperforms a modulation format oblivious (MFO)-DD-PLL in which QPSK decision rules are always used irrespective of actual MF of the signal.