The performance of a feed-forward carrier frequency recovery algorithm for 16-quadrature amplitude modulation (QAM) optical coherent systems is investigated using the quaternary phase-shift keying (QPSK) partition scheme. The frequency estimation technique, which employs only a subset of the 16-QAM symbols with the QPSK partition, is demonstrated to be effective when applied prior to the carrier phase recovery. Frequency offset of 10-1times the symbol rate is shown to be tolerable at a bit-error rate (BER) of 10-3with combined linewidths symbol duration products of 10-4.
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Fatadin et al. (2011) studied this question.
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