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High-Precision AFC Circuit Applied to 64QAM Point-to-Multipoint Burst Communications
Yushi SHIRATO Kazuji WATANABE
IEICE TRANSACTIONS on Communications
Publication Date: 2006/12/01
Online ISSN: 1745-1345
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Transmission Systems and Transmission Equipment for Communications
FWA, AFC, 64QAM, burst communication,
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In this paper, we propose a novel open-loop Automatic Frequency Control (AFC) circuit suitable for 64QAM point-to-multipoint (P-MP) burst communications. The proposed AFC contains two frequency offset detectors. One estimates the phase rotation over long intervals to obtain accurate estimates at the cost of phase ambiguity. The other estimates the phase rotation over short intervals and its output is used to resolve the ambiguity in the following phase ambiguity compensator. Thus, the proposed AFC circuit calculates the phase rotation over sufficiently long periods to yield accurately estimate the carrier frequency offset while suppressing the phase-unwrapping problem. The proposed AFC approaches the Cramer-Rao bound (CRB) and so achieves very small residual frequency offset. The proposed AFC circuit can be implemented with much smaller circuit scale than the conventional devices. Computer simulations and experiments confirm that its residual frequency error is less than of 10-5 for the frame format considered; this performance is sufficient for the 64QAM -40 Mbaud system targeted.