The Design And Implementation Of Broadband Power Amplifier Digital Predistortion

As the final stage of the transmitter chain, high efficiency power amplifier(HEPA) is used to amplify transmit signal power. However, with the development of communication technologies, new communication patterns challenge the HEPA.First, the increasing business demand changes modulation mode from constant envelope to non-constant envelope, improving the signal peak to average ratio and affecting the quality of communication system. Then, the growing transmission bandwidth makes demands on linearization techniques. In order to make full use of spectrum resources, new modulation and demodulation modes(i.e., QPSK, 64 QAM, OFDM, etc.)are used, which requires improving the power amplifier nonlinear distortion. Finally, the mathematical modeling of power amplifier increases the complexity of project implementation. When the Volterra series model is used, the complex implementation and computational cost increase with the model’s order.In view of the above problems, a digital predistortion distortion(DPD) implementation with simplicity, low cost, strong linear compensation capacity and high efficiency for wideband PA is proposed. And the details are as follows.(1) According to the key technology of broadband power amplifier digitalpredistortion, put forward and analyze the demand of broadband digitalpredistortion power amplifier system, and then design analysis solutions, fromthe model identification algorithm(LMS algorithm, LS algorithm, RLSalgorithm), the amplifier model(Volterra series, MP model, SRPV model),lookup table structure and other aspects.(2) Design a broadband power amplifier digital predistortion with the FPGA. Inaccordance with the FPGA development process, dividing the whole project intofive modules to be designed, including signal generation, the output poweradjustment, digital predistortion calculation, generating polynomial parametersand high-speed data acquisition interface design, and give block diagrams ofcommunication between modules and interfaces pseudo-code representation, alsogive analysis of the FPGA resource usage.(3) Performance measurement and analysis of broadband power amplifier digitalpredistortion. Build broadband power amplifier digital predistortion systemmplementation platform, including baseband board, the RF board, high powermplifier box and spectrum tester. And then give the testing and analyzinginstrictions of digital predistortion performance results. After testing ADCnterface and DAC interface, testing the system with 100MHz-bandwidth and20MHz-bandwidth source, and both meet the technical requirements.This study verifies the use of FPGA chip can complete the calculation of digital predistortion, achieve the goal of improving power amplifier nonlinear distortion and provide a basis for the feasibility and effectiveness of engineering application. In the digital part, predisortion has reduced the engineering complexity and operated cost.