Complexity-Reduced Joint Calibration for Nonlinearity and I/Q Imbalance in Direct-Conversion Transmitters.

A novel joint compensator with reduced complexity is proposed to address nonlinearity and in-phase and quadrature (I/Q) imbalance in the direct conversion transmitters (DCT). Parallel I and Q-data are fed to the same joint real-I/Q imbalance and memory polynomial structure. Compared to conventional complex conjugate joint model, the model significantly reduces complexity, while maintaining calibration performance. In addition, a third-order nonlinear predistortion block is added to both the I and Q path to cancel out the third-order counter-intermodulation (CIM3) products caused by baseband nonlinearity in modulators. Theoretical analysis and simulation are carried out to verify the efficacy of the proposed model. The results demonstrate that the complexity is reduced by nearly 50%. Meanwhile, the adjacent-channel-power-ratio and image-rejection-ratio are respectively increased by more than 20dB and 40dB indicating that the model efficiently mitigates nonideal effects in DCT and can be implemented at a lower cost.