| Modern wireless communication uses complex signal modulation to improve spectral efficiency,but it also degrades the peak-to-average ratio(PAPR)of the signal,which negatively affects the power efficiency of the transmitter.In addition,multi-carrier aggregation technology is also commonly used to improve spectral efficiency.Compared with single-band systems,the nonlinear distortion of multi-band systems becomes more complicated.Envelope tracking(ET)technology can improve the efficiency of the transmitter in the fallback area,but the ET power modulator itself,which is the core component of ET technology,also has a certain impact on the efficiency and nonlinearity of the transmitter system.Digital predistortion(DPD)technology can improve the nonlinearity of the system very well,but this technology usually only focuses on the linearity performance of the transmitter system.Therefore,this thesis pays attention to the research of the efficiency and nonlinearity of the dual-band concurrent ET transmitter,and explores the relationship between the transmitter's average output power and linearity,and uses digital predistortion technology to improve the global performance of the ET transmitter system.The main research contents of this thesis are as follows:1.In order to reduce the requirement of the ET power supply modulator for the bandwidth of the envelope signal,this thesis proposes an envelope bandwidth reduction algorithm based on iterative filtering,gives the algorithm principle,and compares and analyzes the algorithm compared with the traditional bandwidth reduction through simulation.Algorithmic advantages.In addition,in order to correctly track and amplify the dual-band envelope signal,this thesis proposes an improved bi-band power amplifier two-dimensional peak clipping algorithm,which introduces dual piecewise constants for peak clipping,which has an EVM improvement of 1.2%.The relevant principles of the algorithm are expounded and verified by simulation.2.The ET power modulator based on the digital open-loop structure has a simple structure and its delay is easier to control.Based on this structure,this thesis designs a high-efficiency wideband ET power modulator.A two-stage switch is used to improve the equivalent bandwidth of the circuit,and a two-stage LC filter network structure is used to balance the switching ripple and filter bandwidth.The switch part uses a Ga N-based EPC8010 transistor to improve the switching rate of the switch.The input of the ET power supply is provided by the FPGA,and the delay of the circuit can be controlled by the FPGA.The experimentally measured output voltage error NMSE is-34.22 d B.3.The nonlinearity of the double-band ET system is very complex,and the number of parameters of the model is large.Therefore,in order to reduce the computational complexity of model parameter identification,this thesis improves the 3D-DMP model,and proposes an improved 3D model by simplifying and merging memory items and nonmemory items.The model has a smaller number of coefficients and the single-band ACPR specification can reach-50 d Bc.4.In this thesis,the multi-objective optimization algorithm is used to take the output power of the power amplifier and the linearity index NMSE or ACPR as the optimization goals at the same time,which can achieve better DPD global performance.This thesis expounds the method of introducing multi-objective optimization algorithm into DPD,and firstly builds a test platform for verification in single-band and single-band ET system.This thesis analyzes the nonlinear components and DPD architecture in the dual-band ET system,introduces multi-objective optimization into the dual-band ET digital predistortion,and uses the surrogate model method to reduce the experimental complexity.According to the test results,the relationship between linearity and output power in the dual-band ET system is analyzed,and the appropriate optimal solution is selected,so that the dual-band ET system can ensure the output power after DPD,and the ACPR can reach-47.7 dBc. |
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