Research On Digital Predistortion Technology For RF Power Amplifiers

In modern communication systems, due to the dual pressures of high-speed data transmissionneeds and the limited spectrum resources, unconstant envelope modulation technologies, such as theQAM and OFDM, are widely applied for their higher spectral efficiency. But the inherentnon-linear feature of RF amplifiers have a serious impact on the modern wireless communicationsystems, Non-linear distortion leads to the increase of in-band BER and out-band adjacent channelinterference.So the linearization of power amplifiers becomes the major issue of moderncommunication. Digital predistortion is considered the most promising technology of alllinearization techniques because of various advantages, such as good linearity, wide bandwidth,high efficiency, full adaptation and so on. So the core of this paper is the technology of poweramplifier linearization of digital predistortion. Base on this technology, non-linearity, memoryeffects, behavioral model and linearization of the RF power amplifier are researched.The mainachievements are as follows:1. Power amplifier nonlinear distortion theory and technical index are extensively researched,Then the main nonlinear characteristics of PA are analyzed with ADS software, includingintermodulation distortion, the influence of frequency band signal and memory effects of PA.2. The most common behavioral models of power amplifiers are introduced in detail.Theprinciple, advantages and disadvantages of various linearization techniques are discussed at thesame time.3. The power amplifier is modeled by combining the ADS and MATLAB software skillfully.The sampled data is obtained via ADS simulation and the model coefficients are estimated byMATLAB. The test results show the ADS software can get data approximate to that in realenvironment and can be applied in the behavioral modeling for power amplifier. Applying thepower amplifier model, which is estimated from MATLAB, in the analysis of digital predistortion,the result is good.4. The adaptive structures of predistortion and the basic principles of adaptive algorithm arediscussed, what’s more, some structures and algorithms of predistortion have been validated byprogramming in MATLAB software as well. The two common predistortion techniques, lookuptable and polynomial, are analyzed and simulated. On the polynomial predistortion technique, formemory power amplifier models in broadband communication systems, this paper creativelyproposes a power amplifier linearization technique, which combined with power back-off, PAPRsuppression technology and adaptive algorithms. 5. Builds the digital predistortion system in SystemVue circumstance, EVM、ACLR and thefrequency spectrum are simulated and analyzed, and the results show the system can get the effectof predistortion.6. A method for using digital predistortion in ADS is described,in which vector signalgenerator, spectrum analyzer and series vector signal analysis software are connected to build asoftware/hardware connected system, This system allows an actual hardware power amplifier to beoptimally linearized in wireless system.