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Wide-Range and Fast-Tracking Non-Data-Aided Frequency Offset Estimator for QAM Optical Coherent Receivers
Tadao NAKAGAWA Takayuki KOBAYASHI Koichi ISHIHARA Yutaka MIYAMOTO
IEICE TRANSACTIONS on Communications
Publication Date: 2016/07/01
Online ISSN: 1745-1345
Type of Manuscript: PAPER
Category: Fiber-Optic Transmission for Communications
optical fiber communication, optical receivers, quadrature amplitude modulation, digital signal processing, frequency offset estimation,
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This paper describes a blind frequency offset estimator (FOE) with wide frequency range for coherent quadrature amplitude modulation (QAM) receivers. The FOE combines a spectrum-based frequency offset estimation algorithm as a coarse estimator with a frequency offset estimation algorithm using the periodogram as a fine estimator. To establish our design methodology, each block of the FOE is rigorously analyzed by using formulas and the minimum fast Fourier transform (FFT) size that generates a frequency spectrum for both the coarse and fine estimators is determined. The coarse estimator's main feature is that all estimation processes are carried out in the frequency domain, which yields convergence more than five times faster than that of conventional estimators. The estimation frequency range of the entire FOE is more than 1.8 times wider than that of conventional FOEs. Experiments on coherent optical 64-ary QAM (64-QAM) reveal that frequency offset estimation can be achieved under a frequency offset value greater than the highest value of the conventional estimation range.