Compensation of frequency-selective I/Q imbalances in wideband receivers: models and algorithms

To achieve satisfactory performance in analog I/Q (inphase/quadrature) processing-based wireless receivers, the matching of amplitudes and phases of the I and Q branches becomes vital. In practice, there is always some imbalance and the image attenuation produced by the analog processing remains finite. Especially in wideband receivers, where the existence of strong image band signals makes the attenuation requirements extremely stringent, analog processing is incapable of providing adequate image rejection. We derive a general frequency-dependent signal model for an imbalanced analog front-end and present two alternative methods utilizing digital processing to enhance the analog front-end image rejection. Based on the obtained results, the proposed methods provide adequate image signal rejection with very few assumptions, even in the difficult cases of frequency-selective and/or time-varying imbalances.