Blind joint estimation of carrier frequency offset and I/Q imbalance in OFDM systems

This paper proposes a blind estimator of the carrier frequency offset (CFO) and in-phase/quadrature (I/Q) imbalance in orthogonal frequency-division multiplexing (OFDM) systems, which does not require any prior knowledge of training symbols or channel side information. The key element behind this algorithm is the null sub-carriers commonly existed in many OFDM systems. This blind joint estimation is carried out in a sequential manner that the frequency offset is estimated first and then based on which, the I/Q imbalance estimation is performed. Important issues including the identifiability problem of the CFO estimator involving whether minimizing the cost function would yield a unique and exact estimate of the frequency offset, performance analysis of the I/Q imbalance estimator and complexity analysis are addressed. Furthermore, this algorithm is proved to be applicable in multiple-input multiple-output (MIMO) systems. Finally, numerical simulation results are presented to validate the effectiveness of the proposed scheme and carry out performance comparison with other existing approaches. (C) 2014 Elsevier B.V. All rights reserved.