Joint calibration of frequency selective time variant I/Q-imbalance and modulator DC-offset error in broadband direct-conversion transmitters

Recently, much attention has been paid to frequency selective I/Q-imbalance, which can seriously limit the performance of broadband direct-conversion transceivers and degrade the baseband pre-linearization of the power amplifier in the transmitter. This paper addresses the issue of joint calibration of frequency selective I/Q-imbalance and modulator DC-offset error in the transmitter. The presented parameter estimation requires no pilot signal, making the calibration "semi-blind" and standard-independent. The proposed digital pre-equalization is very simple. Moreover, the I/Q-imbalance is modeled as slowly time-variant and a seamless I/Q-imbalance and DC-offset error parameter tracking algorithm is developed. The effectiveness of the proposed algorithms is verified by numerical simulations.