Gradient-based blind iterative techniques for I/Q imbalance compensation in digital radio receivers

This paper considers the radio implementation related I/Q imbalance problem and its digital compensation in direct-conversion and low-IF type radio receivers. In general, I/Q imbalances result in mirror-frequency interference and can severely limit the receiver dynamic range and sensitivity, if not taken properly into account. Here the compensation algorithm developments build on the so-called circular nature of complex-valued communications waveforms which is known to hold only under perfect I/Q balance. A well-behaving non-circularity measure is first formed which is then minimized iteratively using gradient-descent type approach. The derived compensator is computationally simple and operates blindly on the received signal, meaning that no known training or pilot data is needed. The compensation performance of the proposed method is analyzed using extensive computer simulations and is shown to outperform the state-of-the-art adaptive reference techniques by several dB´s, when measured in terms of the obtained overall mirror-frequency attenuation.