Robust Frequency Offset Estimation in the Presence of Time-Varying DC Offset

Umut YUNUS  Hai LIN  Katsumi YAMASHITA  

IEICE TRANSACTIONS on Communications   Vol.E92-B    No.8    pp.2577-2583
Publication Date: 2009/08/01
Online ISSN: 1745-1345
DOI: 10.1587/transcom.E92.B.2577
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Transmission Systems and Transmission Equipment for Communications
carrier frequency offset,  DC offset,  direct-conversion receiver,  OFDM,  

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In OFDM systems, the estimation/correction of carrier frequency offset (CFO) is crucial to maintain orthogonality among subcarriers. However, the CFO estimation suffers from DC offset (DCO) generated in low-cost direct-conversion receivers (DCRs). More seriously, in practice, DCO is time-varying due to the automatic gain control. In this paper, a novel CFO estimator in the presence of time-varying DCO is proposed. It is shown the residual DCO after high-pass filtering varies in a linear fashion. Based on this observation and the periodicity of the training sequence, we derive a CFO estimator independent of DCO. Also, the residual DCO can be estimated, using the obtained CFO. The validity of the proposed estimation method is demonstrated by simulations.