Efficient Mitigation of Frequency-Selective I/Q Imbalance in OFDM Receivers

I/Q imbalance is one of the main practical obstacles in the implementation of direct-conversion receivers. This paper presents novel DSP-based techniques for the estimation and compensation of frequency-selective receiver I/Q imbalances in OFDM systems. The estimation is based on a special pilot or preamble structure, and frequency-domain smoothing is utilized to effectively reduce the effect of noise. Reliable estimation is attained with a minimum of two OFDM symbols. Further, it is shown that estimation of frequency-selective I/Q imbalance and the frequency-selective radio channel can be decoupled, which is beneficial from the computational complexity point of view. Simulation analysis shows impressive performance with fast convergence.