Research On Digital Predistortion Technique In LTE System

LTE system adopts OFDM as the modulation mode, which is an inconstant envelope modulation; and so on impose higher requirements on the linearity of power amplifiers. To improve the efficiency and linearity of PA, linearization technique is employed to suppress the out-of-band distortion to reduce the adjacent channel interference and in-band distortion to improve the BER performance.This paper analyses the models used by theoretical analysis for PAs, then lists out the advantages and disadvantages of these models. Based on these models, the paper analyses the effect that the PA nonlinear produced on the LTE transmitting signals.As for the predistortion techniques, the paper focuses on the digital baseband adaptive predistortion technique, which is stable, adaptive and suitable for wideband communication. There are two important types of techniques for digital predistortion, the first one is based on look-up table, and the other one is based on polynomials. This paper points out the advantages, disadvantages and applications of the two types of technique.In terms of polynomials based predistortion, memory polynomials are often adopted in memory polynomials based predistorter. This paper improves a predistorter which is based on memoryless polynomials and indexed in two-dimensional table. The predistorter has the better performance and saves the memory resources. Based on the improved theory, a hardware system is implemented to verify the performance of the theory.