Estimation and Compensation of CFO and I/Q Imbalance in OFDM Systems Under Timing Ambiguity

This paper proposes a joint carrier frequency offset (CFO) and In-phase/Quadrature-phase (I/Q) imbalance estimation and compensation method for orthogonal frequency-division-multiplexing (OFDM) systems under timing uncertainty. A matrix representation of the received signal with CFO, timing offset (TO), and I/Q imbalance is first derived. Then, a least-square CFO estimator robust against TO and I/Q imbalance is proposed. The Cramér-Rao bound (CRB) for CFO is also derived. With the estimated CFO and equivalent channel, a compensation method for both frequency-dependent and frequency-independent I/Q imbalances is presented. Simulation results are provided to verify the performances of the proposed methods.