The Design And Implementation Of Dual-band Digital Predistorter Based On FPGA

Mobile communications is the most significant part of communications.After four generations innovation of mobile communications,nowadays,China has entered the era of 5G.In order to implement multi-services better,a system which supports multi-standard coexistence is needed,that is,a system which meets the requirements for transmission of a concurrent multi-frequency communication,and a concurrent dual-band communication transmission system is most commonly used.With the purpose of realizing this system,the power amplifier needs to be able to support the transmission of signals of two frequency bands at the same time,namely,the concurrent dual-band power amplifier.As we known,the transmission signals which through the power amplifier could produce nonlinear distortion,as well as concurrent dual-band band power amplifier without exception.In order to solve this problem,this paper intends to study the digital predistortion technology which has low complexity,high precision and suitable for broadband communication,after that finally designing and realizing the digital predistorter behavioral model and structure through FPGA(Field-Programmable Gate Array).The major research contents and innovations are as follows:1.A 2D-CPWL model is proposed.The CPWL(Canonical Piecewise-Linear Function)model will be decomposed by the decomposed vector rotation(DVR)method,and extended to the dual-band to create a 2D-CPWL model that meets the requirement of a concurrent dual-band digital predistorter model.The 2D-CPWL model will be simplified and the specific methods for calculating the coefficients of the model will be given,while analyzing the computational complexity of the model.However,the improved 2D-CPWL model and the original 2D-CPWL model will be verified by instrument test platform,hardware test platform and Matlab software simulation.Considering the indicators such as NMSE,ACPR and computational complexity,and compared with the original concurrent dual-band digital predistorter model.The ACPR(Adjacent Channel Power Ratio)of the 2D-CPWL model is-56.19dBc/-55.04dBc for the low frequency band and-59.93dBc/-59.57dBc for the high frequency band.The NMSE(Normalized Mean Square Error)is-44.24dB/-45.14dB;Computational complexity is 54(nonlinear order is 7,memory depth of 3).2.A novel 1D-LUT(Look-up Table)structure is proposed.Taking 2D-MP model as an example,a novel 1D-LUT structure is proposed that based on the analysis of 2D-LUT structure.Compared with the original 1D-LUT structure,this structure uses inter-band look up table instead of in-band look up table by adding pre-synchronization,divider,multiplier and radio frequency filter modules in the communication system,to eliminate inter-band cross-intermodulation distortion,out-of-band cross-intermodulation distortion and some in-band cross-intermodulation distortion.Through the instrument test platform,hardware test platform and Matlab software simulation comparing to the original structure.The ACPR(Adjacent Channel Power Ratio)of the 2D-MP model based on the novel 1D-LUT structure is-45.27dBc/-46.20dBc for the low frequency band and-45.25dBc/-47.14dBc for the high frequency band.The NMSE(Normalized Mean Square Error)is-38.72dB/-40.28dB;Compared with 2D-LUT structure to save 50%of the hardware resource space.3.After each innovation,this paper carries on the instrument test platform,hardware test platform and Matlab software simulation,verifing the model and the structure,and finally achieves the expected result.