Design And Implementation On Predistortion Of Wideband Power Amplifier

The demands of people for radio spectrum resources are rapidly increased.In order to utilize to scarce radio spectrum resources,some modulation methods and transmission techniques of the high spectral efficiency such as multi-level quadrature amplitude modulation(M-QAM),orthogonal frequency division multiplexing(OFDM)and wideband code division multiple access(WCDMA)have been widely used.But they have common drawbacks:envelope signal fluctuations,high peak-to-average power ratio(PAPR)and other serious distortions due to the nonlinearity of power amplifier.The distortions lead to in-band distortion and out-of-band spectral regrowth.The in-band distortion damages the signal quality,consequently degrading the overall communication performance within the user's own frequency band,while the out-of-band spectral regrowth causes adjacent channel interference(ACI)and other undesired interferences.With the rapid development of wireless communication techniques,the linearity of modern communication system for PA becomes increasing demanding.Among lots of linearization techniques,because of the flexibility and excellent linearization performance of digital predistortion(DPD),it has become one of the most preferred choice for linearizing PAs and tends to be a fundamental component in current and next-generation wireless communication systems.The paper studies DPD techniques in the context of OFDM signals,covering aspects of DPD system structure,the PA mathematical model and the adaptive DPD algorithms.What's more,the combined method of DPD techniques and PAPR reduction are studied deeply.The main works and contributions are summarized as follows:1.The new method of combining DPD with companding transform to compensate nonlinear distortion is proposed.Companding transform module embeds in polynomial predistortion system structure,and the structure is simple and easy to implement.The proposed predistorter uses memory polynomial adaptive DPD techniques to reduce the out-of-band spectrum interference and nonlinear distortion.PA model is Wiener model,the memoryless nonlinear part is Saleh model.Companding transform is a technique of reducing PAPR of OFDM signal,and it is a signal predistortion method based on numerical value transformation,essentially.Simulation results show that the method maximizes the PA linearization,and effectively reduces PAPR of OFDM signal.2.The improved design of combining DPD with clipping and filtering is proposed.In the context of polynomial model,the paper studies the whole process of signal processing.Firstly,the system limits the signals which exceed the threshold by clipping and filtering module.Then the signals pass through polynomial predistortion module by utilizing adaptive algorithm to adjust coefficient.Finally,the output signal is amplified into the PA.The design solves the problems of the PA predistortion slow convergence and high PAPR.MATLAB simulation results show that the method improves BER performance and compensates the nonlinear distortion.Then,the design which associates lookup table predistortion with clipping and filtering is analyzed.Based on lookup table DPD,the method improves the system bit error rate and reduces system PAPR.MATLAB simulation results illustrate the effectiveness of this method.