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I/Q imbalance has been identified as one of the key challenges in the practical implementation of the direct-conversion receiver architecture. This holds in particular at the reception of multi-carrier signals, such as OFDM. While allowing highly integrated and low-cost solutions, direct-conversionmay cause serious signal distortions due to an imbalanced I/Q down-conversion. This paper shows how blind, i.e. non reference-based, signal processing techniques can be applied for a digital estimation and compensation of I/Q imbalance. Further enhancements of the blind estimator can be achieved through the application of Kalman filtering, including tracking and compensation of time-varying and frequency-selective I/Q imbalance.