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A multistage carrier phase estimation (CPE) scheme for anym-ary quadrature amplitude modulation (QAM) formats is proposed and analyzed in coherent optical communication systems. The scheme is based on the crossed constellation transformation algorithm that is transparent to all modulation formats whose constellations are on the square grid. Simulation results show that the hardware complexity of the proposed CPE scheme can be significantly reduced by the group factors of 6.1/8.6, 4.7/6, and 2.6/3.3 (in the form of multipliers/adders) for 32-QAM, 64-QAM, and 128-QAM compared with the single-stage blind phase search algorithm. In 32-QAM, 64-QAM, and 128-QAM, coherent optical communication systems with 1-dB SNR penalty at bit error rate is1× 10⁻², the comparable linewidth symbol duration can be reached with the values of6× 10⁻⁵,4× 10⁻⁵, and8× 10⁻⁶, respectively.
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Su et al. (2014) studied this question.
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