The Research Of Transmitter Behavior Model And Predistortion In Wideband Communication System

In the transmitter system,in addition to the non-linear distortion of the power amplifier,the analog components at the front end of the transmitter also cause problems such as IQ imbalance and leakage of the local oscillator.These distortions seriously affect the performance of the transmitter.Therefore,in order to make the transmitter meet the linearity requirement,the distortion must be compensated.In general,the distortion generated by the transmitter front-end and power amplifier will be corrected separately,but this compensation method is more complicated.This article will mainly study how to use digital pre-distortion technology to jointly compensate the distortion in the transmitter system,which is mainly composed of ADI's RF evaluation board FMCOMMS1,Xilinx's high-performance FPGA development board VC707 and a class AB amplifier whose working frequency from 1.7GHz to 3.5GHz.The main works of this paper can be divided in the following three parts.Firstly,the article analyzes the distortion of RF evaluation board and PA in the transmitter system,and the causes of which are introduced.Then through the experiment to research the impacts caused by IQ imbalance?LO leakage and nonlinear distortion in transmitter.Secondly,this paper studied the behavior model of the FMCOMMS1 evaluation board and power amplifier.Then the transmitter's behavioral model – PMP model is further derived.In order to reduce the complexity of this model,a new dual-box model with low complexity is proposed in the paper,which is to model the transmitter by distributed modeling,and the corresponding coefficient identification algorithm is given.In addition,through simulating and analyzing of the complexity of the transmitter's model,the complexity of the dual-box model is relatively low.Thirdly,basing on the digital pre-distortion structure presented in this article,different transmitter's models are used to jointly compensate the distortion in the transmitter system.The experimental results show that when 20 MHz LTE signal is used as the excitation signal,both the PMP model and the twin-box model can improve the ACPR of the output signal by at least 16 d B,the ACPR from the original-35.8dBc to below-51 dBc,which meets the requirement of the communication standard that lower than-45 dBc.In addition,compared to the PMP model,the complexity of the twin-box model is reduced by approximately 35% when achieving the same linearization effect that the ACPR drop to-53 dBc.