Research On Digital Predistortion Of Power Amplifier

With the rapid development of mobile communication technology,mobile communication devices are widely used in our daily life.Power amplifier,as a key part of the transmitter,is an important component in the communication system.The inherent nonlinear characteristics of power amplifier lead to the in-band distortion of the output signal and the out-of-band spectral regrowth,which seriously affect the performance of the communication system.At the same time,modern communication system make efficient modulation signals,such as QPSK and M-QAM,as the input signal.With the high characteristics of PAPR,these signals will reduce the performance of communication system.Linearization of power amplifier becomes popular in our field.Linearization of power amplifier includes power back,feed-back,feed-forward,predistortion and so on.Because of its simple structure,stable system,adapting algorithm,digital predistortion becomes the most popular technique in the linearization of power amplifier.In this paper,the behavior model of power amplifier,the structure of digital predistortion and adaptive algorithm are introduced.And then,we propose a piecewise-linear memory polynomial(PWL-MP)model for DPD technique.Because the high order terms by multiplying is not stable in the implementation,we convert the high order terms by multiplying in the GMP model to the summation of PWL functions in the PWL-MP model.As the threshold can adjust in the PWL-MP model,it is more flexible and accuracy in the DPD technique.The measurement results show that the proposed model can provide a better performance than the GMP model while requiring 40% less coefficients.The adjacent channel power ratio(ACPR)and the normalized mean square error(NMSE)can be improved 1dB and 8 dB respectively.So the PWL-MP model can achieve a relatively good performance in the DPD technique.