Research On Digital Pre-distortion Techniques Of The Power Amplifiers

In order to make use of the limited frequency resource,the modulation techniques such as quadrature amplitude modulation(QAM)and orthogonal frequency division multiplexing(OFDM)are widely applied to the modern communication.However,the signals produced by those modulation techniques have the problem of high peak-to-average power ratio(PAPR).When those signals pass through the radio frequency power amplifiers(PAs),they would suffer from the PA's nonlinearity,leading to the demonstrable degradation of overall performance in communications systems.Among all kinds of exist linearization techniques,digital pre-distortion(DPD)technique is one of the most promising linearization techniques,for the reason that it could achieve excellent performance with low cost.This dissertation focuses on behavioral modeling,loop delay estimation and reduction of sampling rate these three aspects,for the project that digital pre-distortion of power amplifiers.For the digital pre-distortion models parts,the general implementation methods of digital pre-distortion are presented and discussed.In order to avoid the instability of memory polynomial(MP),a piecewise MP model is proposed to suit the strong nonlinear systems with memory,and the new model needs less computation complexity.To reduce the random access memory(RAM)storage of memory look-up tables(LUTs),the memory LUTs technique based linear interpolation is also proposed,and it is able to provide better linearization performance with the limited size of LUTs.For the misalignment between sending signals and feedback signals,the DPD system will not work with convergence.Based on the inverse process of Newton iteration method,the author proposes a novel robust loop delay estimation algorithm with low complexity,which reduces the iteration times of interpolation.In order to improve the stability and accuracy of delay estimation further,two average operation schemes are proposed to smooth the estimation values,based on the conventional data smoothing treatment.For the high speed sampling devices with high prices,we study two DPD methods with low sampling rate for broadband communication.For the mismatch between existing DPD models and the band-limited signals,we put forward the band-limited version of generalized memory polynomial(GMP)model,which is based on the fundamentals of band-limited models.For the characteristics of static nonlinearity parts of PA's behavior,the united sheme that LUT is cascaded with linear interpolation MP/LUT is proposed,which is based on the two-box structure model by separating static nonlinearity from memory effect.