Research On Digital Predistortion Technology In ROF System

With the development of communication technology,people more and more high to the requirement of future 5G communication rate,in order to meet the requirements of 5G communication rate,5G communications in the future will be distributed in the small cellular or micro cellular network mode,support multiple standard,multiple formats,multiband coexistence of heterogeneous networks.In order to reduce the complexity and cost of remote terminal RRU,the ROF technology is proposed for 5G communication.ROF system is composed of ROF link and Amplifier.Like other electronic devices,ROF system suffers from nonlinear problems.Therefore,it is necessary to solve the nonlinear problem in ROF system.Most of the previous literature separate research ROF link and power amplifier nonlinear problem,few will regard as ROF link and power amplifier as a whole.In this article,regard ROF link and power amplifier as a whole system,take the single band and dual band transmission of nonlinear problems to studied.For single band ROF system nonlinear problem,this article chose several commonly used power amplifier model of ROF system modeling,the modeling results obtained from analysis on the model precision contribution larger items,by removing the contribution model precision small items,a generalized memory polynomial model is simplified.Under the strong nonlinear and model accuracy of similar cases,the simplified model of relative polynomial model coefficient reduced by 50%,relative to the enhanced generalized fractional model coefficient reduced by 25%.The linearized results show that the proposed model is better for the adjacent channel power than the suppression effect.For dual-band ROF system,third-order intermodulation signal surpression is a problem,this article based on dual band model,proposed a methed for strengthening the third order intermodulation suppression predistortion structures,modified the injection technology,and propose a new model of the third-order intermodulation.The preinjection technology before improvement needs to know the characteristics of the nonlinear system,then generate the suppression signal of the third-order intermodulation signal according to the system characteristics,otherwise the surpression effect is poor.In this paper,the improved pre-injection technology through partition acquisition ROF system output signal,reduces the signal bandwidth required sampling,and through the third-order intermodulation signal characteristic coefficient instead of the system,enhances the range of application in the process of the injection technology.The simulation results show that the improved pre-injection technology and the new third-order intermodulation model have significantly enhanced the inhibition of the dual band model to the third-order intermodulation.