Estimation and Compensation of Frequency-Dependent I/Q Imbalances in OFDM Systems over Fading Channels

In this paper, the estimation and compensation of frequency-dependent in-phase/quadrature-phase (I/Q) imbalances in an OFDM-based communication system is studied over fading channels. The input-output relation of this system is derived in closed-form in the frequency domain. Based on the result, two novel approaches are proposed to jointly estimate and compensate the distortion coefficients. The first method utilizes least square algorithm, while the second employs an adaptive normalized least mean square algorithm. The simulation results show that both approaches can almost reach the performance of the system without I/Q imbalances in the time-invariant multipath channels. By utilizing decision feedback scheme, the adaptive method outperforms the least square method in the time-varying fading channels at high signal-to-noise ratios.