In this paper, a phase-noise-tolerant two-stage carrier recovery concept for arbitrary quadrature amplitude modulation (QAM) constellations is presented. Possible implementations are evaluated in simulations of square 16-QAM, 64-QAM, and 256-QAM transmission systems, considering fourth-power and decision-directed carrier recovery for the first stage. The second stage uses QAM feedforward carrier recovery. It is shown that the two-stage concept achieves the same phase noise tolerance as the original QAM feedforward carrier recovery concept, but reduces the required hardware effort by factors of 1.5-3 depending on the order of the QAM constellation.
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Pfau et al. (2009) studied this question.
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