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.