Research And Implementation On Digital Predistortion Technology In Mobile Communication

In order to achieve high spectrum efficiency, non-constant envelopemodulation schemes, such as M-QAM, QPSK and OFDM are often used inmobile communication systems. This leads to the high Peak to Average PowerRatio characteristic of the signal. Power amplifier is very sensitive to the PAPRcharacteristic. We know that when the amplitude of the input signal exceeds PA’slinear working region, it will enter the saturation region. This will generatenonlinear distortion. Which will result inter symbol interference and adjacentchannel interference. As the bandwidth goes wider, PA’s memory effect becomesmore and more obvious. The distortion caused by memory effect may evenexceed which caused by PA’ nonlinearity. A lot of achievements have been madeon research of linearization technology. And a number of techniques have beenreported in recent years.Thanks to the development of digital predistortion technology and devices.Digital predistortion is becoming a promising way to compensate PA’snonlinearities. Cost-effective, reliable and easy to implement are the mayadvantages of digital predistortion. The main idea is to insert a nonlinear blockin the digital domain to compensate PA’s nonlinearity. In this paper, we focus onseveral key issues in dgital predistortion. First we summarize the existedalgorithms about digital predistortion in literature. Then we propose our improved algorithms. We have also done some FPGA logical design andsimulations. This paper mainly focuses on three key issues, which are loop delayestimation, PA model identification and predistorter construction.As the bandwidth goes wider, PA’s memory effect will become more andmore obvious. The distortion caused by memory effects may even exceed whichcaused by PA’s nonlinearity. So research on how to do digital predistortion withstrong memory effects will be more and more meaningful in the future.