Research And Verification Of Digital Predistortion Technique In Broadband Communication

As a key component of the communications system,power amplifier(PA)has attracted the attention of many researchers.With the increasing bandwidth of communication signal,the non-linear distortion of PA has become more and more serious.At present,the digital pre-distortion(DPD)technique has become the mainstream technology to improve the distortion of the PA.This thesis focuses on the DPD technique in broadband communication systems,including the behavioral model and the pruning algorithm for model coefficients.To extract the behavior of power amplifiers in broadband communication system,this thesis presents a feature extraction platform for single-input and single-output RF device.This platform works in wide frequency range(400MHz-4GHz)with 125 MHz channel bandwidth(14-Bit 250 MSPS ADC,16-Bit 1GSPS DAC).This thesis adopt ADI's FMCOMMS1 RF evaluation board and Xilinx's high-performance FPGA development board VC707,and implements a broadband and efficient zero-IF Tx & Rx unit.The key factor of interest,such as LO leakage and I/Q imbalance in the transmitting and receiving path,delay calibration in the establishment of behavior model,has been analyzed in detail,as well as corresponding compensation techniques.In broadband communication system,the behavioral model of PA needs more nonlinear terms.This leads to an increase of computational complexity.The behavioral model of the power amplifier is effectively pruned by compressed sensing reconstruction algorithm,such as the OMP(Orthogonal Matching Pursuit)algorithm and VS-SAMP(Variable Step-size Sparsity Adaptive Matching Pursuit)algorithm in this thesis.The simulation results show that both OMP and VS-SAMP can effectively reduce the number of model coefficients while ensuring the modeling capabilities.Even though the number of coefficients(sparsity)of the PA's model is unknown,VS-SAMP algorithm can reach the requirement of the modeling accuracy by using as few coefficients as possible.Finally,this thesis verifies the distortion improvement of the mixed power amplifier through DPD which uses VS-SAMP algorithm.The experimental results show that the ACLR(Adjacent Channel Leakage Ratio)of the PA's output signal improved by 16 dB to below-45 dBc when tested by 20 M and 40 M LTE signals,and achieved the desired target.Compared to the traditional LS identification algorithm,VS-SAMP algorithm uses fewer coefficients.