Investigation On Signal Characteristics-based Linearization Of Transmitter

With the development of mobile communication,massive data and terminals have caused serious energy consumption and spectrum resource shortage.The next generation communication systems put forward ‘intelligent network' to alleviate these problems.For example,to reduce unnecessary power consumption,the dynamic power strategy requires the transmitter adjusts the average power in real-time with the environment and user needs.And the spectrum reconstruction mechanism that dynamically adjusts and redistributes the signal bandwidth is applied to make full use of the limited spectrum resources.As the main source of power consumption and nonlinearity in the transmitter,the power amplifier needs linearization technology to alleviate the contradiction between energy efficiency and nonlinearity.Digital predistortion is the most widely used technology in macro base stations.In contrast,analog predistortion plays an important role in linearizing scenes requiring low power consumption,such as small and mediumsized base stations.When the signal characteristics such as power and bandwidth change,the nonlinear characteristics of the power amplifier will change rapidly.Traditional digital predistortion can not track its nonlinearity quickly because of the complexity of parameter extraction.And the current analog predistortion is difficult to realize adaptation.Therefore,for digital predistortion,by decoupling the dynamic and static distortion of power amplifiers,predistortion models with power adaptability and bandwidth adaptability are proposed,which reduces the complexity of adaptation.For analog predistortion,this dissertation realizes the transformation of analog predistortion through low-cost digital processing technology.The main innovations of this dissertation are as follows:1.A power adaptive digital predistortion model based on dynamic and static distortion decoupling is proposed,which reduces the complexity of adaptive parameter extraction.The static and dynamic distortions of the power amplifier are decoupled by static post compensation technology to realize the quantitative comparison of these two kinds of distortions affected by dynamic power.Thanks to the independent compensation of the static and dynamic distortions by the two-box model,the proposed model realizes an adaptive method that only needs to update the static term and keep the dynamic term unchanged under the dynamic power.Based on the regularity of model parameters under different power levels,a power-related parameter interpolation method is given to improve the adaptive process' s convergence speed.Adaptive digital predistortion experiments are verified on a continuous-mode power amplifier at 12 power levels.The results show that the performance of the proposed method is close to that of the traditional method,and the adjacent channel power ratio can be reduced to-49 dBc,but the number of parameters to be extracted is only 19% of that of the traditional method.2.A power adaptive digital predistortion model based on amplitude transformation is proposed.To further improve the power adaptability of the model,this dissertation focuses on the static distortion of power amplifiers with dynamic power and realizes the consistency of the static distortion trend through signal amplitude transformation.Based on these analyses,an adaptive method that only needs to update the static term in the low amplitude section of the model with power is given.To extract and change the model coefficients of different amplitude segments of the signal independently,an affine function model based on amplitude selection is used to compensate for the static distortion of the power amplifiers.In power adaptive digital predistortion experiments,the proposed model can reduce the adjacent channel power ratio to-48 d Bc.The multiplier required in the adaptive process is only 8% of the traditional model.3.A bandwidth adaptive digital predistortion model with dynamic structure is proposed.This dissertation presents a method to study the correlation between the power amplifier's distortion and the signal bandwidth from three dimensions: static distortion,linear dynamic distortion,and nonlinear dynamic distortion.The time-frequency analysis of the static post compensated output signals is carried out.The frequency-related signal amplitude distortion diagram is obtained using the short-time Fourier transform,which intuitively reveals that the uneven in-band gain of power amplifiers is one of the reasons for the dynamic effect.At the same time,the direct relationship between the in-band gain fluctuation and the linear dynamic distortion is studied by using the pseudo-transfer function method of a nonlinear system.Based on the analysis results,the optimization direction of the general model under dynamic bandwidth is given,and an adaptive bandwidth method in which the structure and coefficients of the narrowband model can be directly applied to the wideband model is proposed.The adaptive modeling experiments of 20 MHz,40 MHz,and 100 MHz signals are carried out on the continuousmode and Doherty power amplifiers.The results show that the number of parameters of the proposed model is only 18% of that of the traditional model on the premise that the modeling accuracy is similar to that of the conventional model.4.An adaptive analog predistortion method is proposed based on low-cost digital processing.By studying the causality between the analog linearizer's parameters and the nonlinearity of the predistortion signal,an amplitude segmentation method based on peak to average power ratio of the input signal is proposed,and an algorithm for parameter adaptive optimization based on piecewise statistical error is proposed.At the same time,a signal feedback method of reduced bandwidth and sampling rate is designed to further reduce the cost and power consumption of the adaptive system.The effects of feedback bandwidth,signal data flow variation,and multi stream signals on the statistical error are analyzed,providing a theoretical basis for applying the proposed analog adaptive method in the practical communication architecture.In the experiment of adaptive analog predistortion excited by a 40 MHz bandwidth signal,the error vector magnitude is reduced to 1.27% with only 5 MHz feedback bandwidth,which is only 0.01% higher than that of the traditional method,and the adaptive convergence speed is 8.5 times that of the conventional method.