Design And Implementation On Digital Predistortion Of Power Amplifier In IMT-Advanced System

With rapidly improvement of the people living standards,people has higher requirement for wireless communication.It not only demands connected anytime and anywhere but also demands high quality voice services and Internet data services.The application of the IMT-advanced system is constantly adapt and meet to people's growing demand of communication.Since 3G generation,the rapidly growth of data and multimedia communication business have intensified spectrum resources exploitation,in order to effectively use the limited spectrum resources,some effective patterns such as M-QAM modulation and OFDM have been applied.In IMT-Advanced system,these modulation methods have unsteady signal envelope and high peak ratio characteristics,the power amplifier easily working on the saturating zone after the signal through,it bring the nonlinear distortion affect the quality of communication.The IMT-Advanced communication system high efficiency and high speed are based on the reliable communication quality,thus it requirements reducing the system nonlinear distortion as far as possible.Power amplifier as the main source of nonlinear of communication system,it become the key research of linearization in IMT-Advanced system.The digital predistortion technology with its high flexibility and good linearization performance become the optimal scheme of power amplifier linearization techniques.In IMT-Advanced system,power amplifier is working in saturated zone and the nonlinear distortion of PA caused in-band signal distortion and out-of-band spectrum extension.At the same time,with vigorously promote energy-saving green communication,the power amplifier efficiency is important to energy saving.On the basis of give consideration to both PA's linearization and efficiency,a new method of combined adaptive DPD and crest factor reduction(CFR)is proposed.It mainly embedded a peak clipping module in the predistortion system,the module used in fusion algorithm of select mapping method and the pressure transformation method.Through the combined structure,the transmission of signal's PAPR greatly reduced,making the power amplifier working under the saturation point,effectively eliminate the influence of power amplifier saturation nonlinear distortion and improve the efficiency of the power amplifier.The fusion algorithm of select mapping method and the pressure transformation method is superior to the single reduction PAPR method can effective reducing the introduction of clipping noise,to reduce the system BER.In order to improve the digital predistrtion linearization performance,the paper proposed improving adaptive digital predistortion with indirect learning structure.firstly,an improve convergence algorithm adaptive module is proposed,LS-LMS algorithm,it combines the LS algorithm converges fast and LMS algorithm is simple and smooth,can make the system fast and stable convergence,in fast response to the changing of the iteration surrounding at any time.Predistortion behavior model of fractional generalized memory polynomial model is put forward,which effectively improve the ability to resist memory effects and model nonlinear precision,so as to improve the digital predistortion linearization performance.