Blind I/Q imbalance parameter estimation and compensation in low-IF receivers

The rejection of the image signal is a problem inherent to all receiver architectures. One of the benefits of the low-IF receiver is, that image rejection is realized by I/Q signal processing instead of a fixed analog filter, making it highly reconfigurable and cost-efficient. However, unavoidable imbalances between the I- and Q-branch lead to a limited image attenuation. In this paper a novel I/Q imbalance compensation scheme is presented, in which the unknown analog imbalance parameters are estimated digitally without the need for any calibration or training signal. Based on these estimates the interference by the image signal is effectively compensated, upgrading the vulnerable ordinary low-IF receiver to a powerful advanced receiver architecture, where the mean value of the image-to-signal ratio never exceeds a pre-defined maximum value, regardless of the image signal power.