Linearization Technology For Massive MIMO Transmitters

The massive multiple-input multiple-output(MIMO)transmitters have played a very important role in the fifth-generation(5G)wireless communication systems.A large number of channels and antenna units will be employed in such systems,which can not only improve the performance but also introduce many challenges.Among them,the nonlinear distortion of power amplifiers(PAs)is particularly prominent.Based on digital predistortion(DPD)techniques,this thesis innovatively proposes several linearization solutions for hybrid,analog and fully digital massive MIMO transmitters,which can achieve the good linearization performance based on the experimental verifications.For the hybrid subarrays/fully digital single-beam transmitters,a novel full-angle DPD technique is developed,which is achieved by first compensating the PA differences in multiple radio-frequency chains with low-complexity tuning boxes and then linearizing all PAs by using a single-shared DPD block.A test on one single-beam transmitter with four channles has been carried out for experimental verification and the results have shown that the method can realize excellent linearization performance.In addition,the concept of power amplifier characteristic tolerance is proposed,which can reduce resource consumption with satisfactory performance.The above research results have been published in IEEE Transactions on Microwave Theory and Techniques and 2018 IEEE International Conference on Microwave and Millimeter Wave Technology(ICMMT).Aiming at the analog multibeam transmitters,a novel multibeam digital predistortion(MBDPD)technique is developed to linearize multiple beams simultaneously.It is achieved by effectively constructing the predistorted signal for each beam to remove both the intrinsic nonlinear distortion of PA and the multibeam interference.To validate the proposed technique,a two-beam test on an analog beamforming transmitter with Butler matrix has been carried out and the measurement results have shown that the proposed method can effectively realize the multibeam linearization.The above research results have been published in IEEE Microwave and Wireless Components Letters and 2019 European Microwave Conference in Central Europe(Eu MCE).A novel DPD technique is proposed to linearize the fully digital multi-beam transmitters.It is achieved by first modeling outputs of PAs and then linearizing them with decomposed vector rotation-based model.The measurement results based on a three-beam transmitter with digital beamforming network have shown that the proposed method can effectively realize linearization of all beams with correct beamforming.This work has been published in 2019 IEEE MTT-S International Wireless Symposium(IWS).