Research On The Linearization Technique For Power Ampliifer With Memory Effects Based On Digital Predistortion

With the rapid development of wireless communication radio frequency resources arebecoming more and more scarce.To enhance spectrum efficiency, linear modulation and multicarriertechniques are widely used in the modern wide-band wireless communication systems. Poweramplifier(PA) in the wireless communication systems has to be designed to operate near itssaturated area, so as to provide higher system power efficiency. Accordingly, the PA ends up witheither high efficiency, but bad linearity. However, the complicated modulation schemes ofwide-band wireless communication systems which lead to a nonconstant envelope and largePeak-to-Average Power Ratio (PAPR) will result in out-of-band spectral regrowth and in-banddistortion when modulated signals pass a power amplifier with nonlinear range. In order to resolvethe conflict between spectrum efficiency and power efficiency different linearization techniques,such as feed-forward, feedback, and predistortion, have been proposed to satisfy the linearityrequirement while operating the PA at its nonlinear area.Among the various linearization techniques,digital baseband predistortion is one of the most promising and cost-effective linearizationtechniques due to its digital implementation that offers significant accuracy and flexibility. Aresearch method is proposed in this paper, which is combined theory with practice based on ADS,MATLAB, VSA89600, an electronic signal generator(ESG E4438C) and a spectrum analyzer(PSAE44400A) to discuss and study the following contents step by step, including PA nonlinearcharacteristic, extraction of PA nonlinear characteristic, behavioral modeling of PA, PA memoryeffect identification and digital predistortion system.And it has an extremely practical value for thetheoretical research of the digital predistortion system, hardware platform design and systemdevelopment. The main tasks in this paper can be summarized as follows:1. The nonlinear characteristics of PA, basic modeling theory and linearization techniques aredescribed. The effect of the EVM and ACPR which results from the nonlinear distortions of PA incommunication systems is analyzed.2. A testbench used for PA nonlinear characteristic extraction under the broadband digitalmodulation signal excitation is established after an overview of some typical measurement setupsused for testing amplifier characterization.With connected simulation from Agilent Technologies,the testbench consists not only of test equipment, but also includes the ADS for simulation ofsystem. The nonlinear characteristic of PA under the broadband signal excitation is tested byADS-ESG-VSA connected solution, and the measured data of the input signal and the output signalof PA is captured. Then the effect of broadband signal in terms of ACPR is analyzed. 3. In broadband communication systems, memory effects of PA are strong. After analyzing thephenomena and the causes of PA memory effects, a method based on the memoryless predistortiontechnique to identify accurately and measure quantitatively the memory effects in wideband PA isproposed. The behavioral model based on the measured data is established and used in the postsystem simulation.4. The basic principles of digital predistortion techniques are introduced.After the effect oftime delay estimation in terms of behavioral modeling and the design of digital predistortion systemis analyzed, a method based on FIR time delay estimation is proposed.And workfunction basedpredistorter and a recursive batch least square algorithm are applied to implement the digitalpredistortion system. Finally, the feasibility of the proposal is validated through computersimulations.5. After computer simulations a real-world adaptive digital predistortion system based onADS-ESG-VSA connected solution and memory polynomial is designed.The performance ofalgorithm and system is tested by the WCDMA TEST1 excitation.