Compensation of frequency-dependent gain/phase imbalance in predistortion linearization systems

Impairments in the analog quadrature modulator can adversely impact the performance of a digital predistortion linearization system. In this paper, we focus on modeling and compensation of frequency-dependent gain/phase imbalance and dc offset when the input and output of the direct upconverter are available. We first propose channel models to describe the effects of these impairments on transmitted I/Q data streams. We then develop algorithms to estimate the parameters of these channel models and to construct I/Q compensators. Performance of the algorithms and the I/Q compensators is shown in conjunction with digital predistortion.