Adaptive Methods for Joint Compensation of Power Amplifier Nonlinearity and Quadrature Modulator IQ Imbalance

The power amplifier (PA) linearization performance of adaptive digital predistorter (PD) are degraded by the imperfections in quadrature modulator (QM) such as in-phase and quadrature (IQ) imbalance in the direct up-conversion transmitter chain. In this paper, we first propose a new adaptive algorithm to estimate and compensate the IQ imbalance in QM. The effectiveness of the proposed IQ imbalance compensator is validated by MATLAB simulations. The results clearly show the performance of the MOP PD is enhanced significantly by adding the proposed IQ imbalance compensator. Then, based on the previously presented method, we propose a modified joint adaptive algorithm to compensate the IQ imbalance of QM in conjunction with the nonlinearity of PA. The computer simulations results clearly demonstrate that the proposed method has excellent linearization performances similar to the previous method, while has lower computational complexity than previous method.