Research On Behavioral Modeling And DPD Of Wideband Power Amplifiers In MIMO Systems

As an important part of the fifth-generation(5G)mobile communication,Massive Multiple-Input Multiple-Output(MIMO)technology can effectively improve the spectrum efficiency and the channel capacity.In MIMO systems,the crosstalk may be introduced between the multiple RF channels which are placed close to each other.When such crosstalk passes through the power amplifiers(PAs),new nonlinear distortions will be generated.Digital predistortion(DPD)technology is widely used in linearization of transmitters,and has been successfully verified in multi-channel systems.This thesis focuses on the research on behavioral modeling and DPD technology of the wideband PAs in the 2×2MIMO system.Firstly,two basic models in 2×2MIMO system,the CODPD model and the 2×2PH model are studied.In order to improve the accuracy of the basic MIMO PAs model,the G-PH model and the PHEC model are proposed.Compared with the basic 2×2PH model,the model accuracy can be improved and the moderate model size can be maintained because some special forms of cross-terms are added to the G-PH model and the PHEC model.In addition,in terms of reducing the model complexity,four new models are proposed when using different optimization methods.The COMP model and the COMP-CPWL model are based on the traditional MP model.The OMP-PHEC model and the SOMP-PHEC model are based on the compressed sensing algorithm.The complexity of four models can be reduced while the modeling accuracy can be maintained.The above models are verified on the instrument platform when-15 dB nonlinear crosstalk is introduced.The test results show that,compared with the 2×2PH model,the modeling accuracy of the G-PH model and the PHEC model will be increased by 1.1dB and 1.57 dB,and the number of coefficients will be reduced by 28.3%and 26.7%,respectively.Compared with the 2×2PH model,the modeling accuracy of the COMP model and the COMP-CPWL model is decreased by 0.5dB and 1.52 dB,respectively,and the number of model coefficients is reduced by 66.7%.Compared with the PHEC model,the modeling accuracy of the OMP-PHEC model and SOMP-PHEC model is decreased by0.67 dB and 0.14 dB,respectively,and the number of model coefficients is reduced by 71.6%.Secondly,a dual-channel wideband RF transceiver system is built,and the system supports over 2GSPS sampling rates.With the help of a high-performance arbitrary waveform generator and a wideband signal analyzer,multi-tone signal excitation and frequency stitching technology are used to measure and compensate the wideband linear frequency responses of the DAC,the ADC and the transceiver loop.The test results show that the performance of the DAC and the ADC after compensation is improved significantly.For the 16 QAM signal with the carrier frequency of 2.7648 GHz and the symbol rate of 552.96Msym/s,the demodulation EVM in the transmitting and receiving loop is reduced to 3.78%.Finally,DPD experiments for single and dual channel PAs are completed in the wideband RF transceiver system.The DPD test results of the single-channel system show that for the16 QAM signal with the symbol rate of 138.24Msym/s,the ACPR improvement exceeds 13 dBc.In the two-channel DPD experiment,both-20 dB nonlinear crosstalk and linear crosstalk are introduced,the test results show that for 20 MHz and 100 MHz OFDM signals,the ACPR of the predistorted signal is lower than-50 dBc and-45 dBc,respectively.