I/Q Imbalance Estimation for Direct Conversion Receivers by Jointly Using the Existing Preambles and Blind Estimation

In this paper, we study the baseband estimation of the frequency- dependent imbalance between the in-phase and quadrature branches (I/Q imbalance) of a direct-conversion receiver, by exploiting the preambles which is not specially designed for I/Q imbalance estimation. We propose an in-service estimation method which consists of two stages: the first stage utilizes the existing preambles in a standard-compliant system to estimate the frequency-independent component of the I/Q imbalances on only a subset of subcarriers; in the second stage, a blind estimation method is proposed to estimate the frequency-dependent component of I/Q imbalances on all subcarriers, based on the result of the first stage and the second-order statistics of the received signal. The proposed estimation method is applicable to commonly used multi-carrier systems.