Efficient Compensation of Frequency Selective TX and RX IQ Imbalances in OFDM Systems

Radio frequency impairments such as in-phase/quadrature-phase (IQ) imbalances can result in a severe performance degradation in direct-conversion architectures. In this paper, a training based equalizer is developed to estimate and compensate the effects of these IQ imbalances along with channel distortions in an OFDM system. The proposed scheme provides a decoupling mechanism to estimate all the three frequency selective distortions in the communication system, namely the transmitter IQ imbalance, the receiver IQ imbalance and the channel dispersion. Once the IQ imbalance parameters are estimated, the proposed scheme then utilizes a standard one tap frequency domain equalizer to estimate and compensate the channel variations in the system. Simulation results show that the resulting calibrated equalizer requires a very small training overhead for an efficient, post-FFT equalization with performance very close to the ideal case.