A Frequency-Selective I/Q Imbalance Analysis Technique

Digital approaches concerning the I/Q imbalance problem in zero-intermediate frequency (zero IF) mixing scheme have one of two main objectives: the first one is knowing the parameters of a widely-linear system (WLS) that models this problem with the purpose of devising a compensation scheme (calibration). The second one is estimating the system gain and phase imbalance values before and after calibrating the system to determine the quality of the manufacturing and calibrating processes (testing). State-of-the-art techniques for both objectives should involve three main aspects to be optimized: computational complexity, reliability and performance. In addition, a framework to use a single technique for both calibration and testing has not been proposed yet. This paper presents a low-complexity and statistically-efficient WLS parameters estimation technique based on the auto-correlation property of Golay complementary sequences (GCS). The proposed technique allows for disregarding the power amplifier (PA) nonlinearities affecting the model, making it reliable. In addition, a framework to extract the phase and gain imbalances in the I/Q branches from the WLS estimations is presented. The low complexity operations of the proposed estimator allow for a cheap hardware implementation. The performance of this technique is illustrated under extreme test cases.