A Blind $I/Q$ Imbalance Compensation Technique for Direct-Conversion Digital Radio Transceivers

Although the quadrature mixing radio front-end offers an attractive way to perform frequency translation, its image-rejection capability is severely affected by the gain and phase imbalances (I/Q imbalances) between its two analog signal paths. Digital signal processing techniques have widely been proposed to compensate for these mixer imperfections. Of these techniques, the class of blind compensation techniques seems very attractive since no test signals are required. This paper presents a novel I/Q imbalance extraction technique that uses a Cholesky decomposition of the received signal´s covariance matrix to extract the exact imbalances of the front-end. An analysis is also presented on extracting and separating the imbalances of a cascaded imbalanced modulator and demodulator. Both a block-based and an adaptive variant of the technique are proposed, and a performance evaluation over multipath channels is presented.