Digital Predistortion Algorithm Analysis And Implementation Of Power Amplifier

Power amplifiers(PA) are inherently nonlinear, and have memory effects. The nonlinearity and memory effects of PA lead to in-band distortion and out-of-band spectrum expansion. In addition, the nonlinearity and memory effects of PA is particularly evident to high peak-to-average-ratio and high-band-width input signal. However, with the rapid development of communication technology, there has been a variety of new modulation schemes(including QAM, OFDM, etc), which requires communication system can properly handle high peak-to-average-ratio and high-band-width signal. These propose new challenges to power amplifier linearization technologies.Early linearization technologies, include Feedforward, Envelope Elimination and Restoration, LINearization techniques using Non-linear Components, mostly use analog circuits, so there is a low controllability, poor flexibility and high cost. In recent years, digital pre-distortion technology is widely used because of its simple structure, good flexibility, and it can implemented using digital chips.This paper discusses the function and performance requirements of digital predistortion(DPD) based on the analysis of the key technologies of DPD. Then, design the schemes of DPD according to the requirements, and finish the implementation and verification of the schemes based on the DSP&FPGA platform.Firstly, this paper discusses the current technologies of DPD, analyzes the function and performance requirements, design the DPD scheme which meet the requirements, and verify the scheme through Matlab simulation. Finally, select the memory polynomial model as the model of predistortor, and design the LS algorithm which based on the Cholesky decompsition. In addition, this paper employs the look-up-table method to compute the result of DPD.Secondly, according to the schemes designed before, this paper finish the detail design and implementation based on the DSP&FPGA hardware platform. This paper divides the function modules of the DPD system, introduces the workflow of the DPD, and gives the detailed design and implementation of the modules.Finally, use the predistortion model and identification algorithm determined by simulation, the design and implementation of digital predistortion is finished by the aid of hardware platform based on DSP and FPGA. The adaptive model identification algothrithm is done by DSP, and the calculation of predistortion results is implemented in FPGA using look-up-table. In order to verify the validation of the design, we use 9-carrier TD-SCDMA signal as signal source to test the system. The results of the test prove that the design can significantly improve the nonlinearity of the power amplifier, inhibite the out-of-band spread spectrum, and reduce the in-band signal distortion.