Adaptive IQ Mismatch Compensation in Time-Domain Using Frequency-Domain Observations

The imbalance between in-phase (I) and quadrature (Q) branches of quadrature down-conversion receivers creates interference between the mirror frequencies in baseband. We introduce two new adaptive algorithms for compensating frequency-dependent IQ imbalance in orthogonal frequency-division multiplexing (OFDM) systems. The proposed algorithms utilize frequency-domain observations to update filter weights of a time-domain IQ mismatch compensator (IQMC) based on a mini-batch gradient descent search approach. The update rule in the first algorithm is based on the kurtosis criterion, which is a blind adaptation method. The second algorithm is based on minimizing the Euclidean distance (ED) between the frequency-domain impaired signal and the known received reference signal, which is a pilot-aided method. A low-complexity method is introduced to obtain the gradient of cost functions that are only based on the IQMC coefficients and the frequency-domain observations. Numerical results demonstrate that the proposed algorithms reduce IQ imbalance considerably. The proposed adaptation schemes outperform conventional time-domain IQMC schemes in high signal-to-noise ratio region and also use a much smaller number of adaptation parameters than the previous frequency-domain IQMC methods.