The Design And Implementation Of Adaptive Predistortion Device

With the development of the broadband wireless communication technology, the limited frequency resource has become the binding constraint of the future development. Orthogonal frequency division multiplexing (OFDM), broadband code division multiple access (WCDMA), Orthogonal amplitude modulation (QAM) and Quadrature Phase Shift Keying (QPSK), are widely used in the modern wireless communication systems. However these no constant envelope modulation technologies have a high peak-to-average power ratio. The power amplifier’s inherent nonlinear characteristics will result in severe spectrum regeneration out-of-band and distortion in-band. And it will cause adjacent interference, the increase of bit error rate, and then influence the quality of communications. Therefore, except for high output power level, the power amplifier’s linearity should to be considered in order to meet the needs of modern wireless communication.Power amplifier linearization technique is one of the effective ways to improve power amplifier’s efficiency with no effect to the modulation. Pre-distortion technology has become the most promising linearization technique because the advantages of its simple structure, stabilization, high efficiency of linearization and so on.Based on some researches on the amplifier measurement and modeling, this paper puts forward pre-distortion structure and adaptive algorithms and designs an adaptive pre-distortion structure for the broadband RF power amplifier.1. Design a kind of power amplifier measuring platform to measure the nonlinear characteristics of the broadband power amplifier. This dissertation mainly focuses on the memory polynomial model of the power amplifier and the parameter identification method, and then the behavioral model of the power amplifier based on the measurement results is built, and finally the accuracy of the behavioral model of the power amplifier is tested.2. Study the lookup table, polynomial pre-distortion method and the RLS and LMS adaptive algorithm and compare the differences between the orthogonal polynomials and general polynomial. Then the adaptive pre-distortion structure based on orthogonal polynomials and the LMS algorithm is designed and simulated.3. Implement the design into hardware and give a specific introduction of the key module, such as error signal generator, polynomial generator, the memory unit and RF signal processing. The digital parts are implemented with FPGA and DSP.4. Debug the hardware of the pre-distortion system. The results of the experiments show that this adaptive pre-distortion structure can effectively alleviate signal adjacent channel leakage with15dB when fed with OdBm power, single-carrier WCDMA signal. Compared with other linearization technique, this adaptive pre-distortion structure has the following advantages:fast operation, low system complexity, less costs of the hardware and high design efficiency.