Research On Adaptive Digital Predistortion Technology For Broadband Power Amplifiers

Digital predistortion is the most effective way to compensate the nonlinearity and memory effects of wideband power amplifiers.In recent years,the digital pre-distortion technology of wideband power amplifier has gained great attention of scholars all over the world.Therefore,it's imminent to carry out the pre-distortion technology research for its characteristic.This paper focuses on the power amplifier modeling and predistortion techniques applicable to wideband power amplifiers.Firstly,the behavior model of power amplifier is introduced.The orthogonal polynomial model and its improvement for the deep memory power amplifier model are demonstrated.Secondly,the digital predistortion technique for power amplifier and the parameter extraction algorithms for the pre-distorter,such as Least Squares(LS),Recursive Least Squares(RLS),Least Mean Squares(LMS),are presented.It is provedthat by using the orthogonal polynomial model,the conditional number increasing of the input matrix in RLS algorithm,caused by the memory effect of the broadband power amplifier,can be effectively avoided.Then a new parameter extraction algorithm based on multi-model data fusion method is proposed,which using the maximum likelihood function to achieve data fusion,and is suitable for wideband power amplifier.Simulation results show that the root mean square error(RMSE)is reduced by 4.2dB.At last,a brand new digital predistortion scheme for wideband power amplifier based on orthogonal polynomial model and data fusion parameter extraction algorithm is presented.The simulation results show that the proposed scheme is effective and the performance of the system is verified by the experimental verification platform.The bandwidth of excitation OFDM signal used for measurement is 100MHz,and the test power amplifier is a 1.95GHz Doherty wideband power amplifier.Measurement results show that the output ACPR can be improved from-31.29dBc-41.16dBc by using normal predistortion scheme,meanwhile,by employing the new predistortion scheme,the output ACPR of power amplifier can be further improved to-44.37dBc.