Data-Aided I/Q Imbalance Estimation and Compensation in OFDM Systems

We propose a novel approach for data-aided estimation of the mixer gain and phase imbalances in the analog front-end of direct-conversion receivers. We estimate the inphase and quadrature imbalance (IQI) parameters isolated from the fading channel estimate and use the estimated IQI parameters for time-domain compensation. The motivation behind this approach is the scenario where the training symbols used for IQI estimation are transmitted from different antenna ports than those used for data transmission. In this scenario, the conventional composite IQI and channel estimate cannot be used for signal detection because the training and data symbols experience different channels. An example of this scenario is the long-term evolution (LTE) standard where the synchronization and broadcast signals are transmitted from different antenna ports than those used for data transmission. Numerical results show that our approach achieves up to 10 dB improvement using only two training symbols.