Investigations On Digital Predistortion For RF Power Amplifier

With the emergence of various non-constant envelope modulation methods, high linear RF power amplifiers are required in modern communication systems. The back-off method is usually used to obtain linear amplification. However, the back-off method reduces the efficiency dramatically. Hence, the research of power amplifier linearization is of great importance for next generation wireless communication systems. In different kinds of linearization technologies, the digital predistortion method is one of the most attractive ways due to its stability, convenience and flexibility.This thesis concentrates on the software and hardware implementation of the digital predistortion method. The nonlinear model of the power amplifier is extracted with the closed-loop method. The linearization algorithm is carried out based on the extracted power amplifier model. The whole system includes an RF part and a baseband part. This thesis focuses on the design of the baseband board. The LUT architecture is used in the DPD implementation. At first, a training signal is sent to the RF part and the feed-back AD gets the distorted signal. Then, after synchronization and phase adjustment, new LUT values are updated in the RAM according to the predistion algorithm with Matlab. Thus, an optimization iteration is done. More optimization iterations can be carried out to obtain better improvement of linearity.The performance of the DPD system is excellent according to the tested results. For the pilot cdma2000 signal, more than 10dB ACPR improvement is obtained. Although the PAR of the WCDMA signal is much higher than that of the cdma2000 signal, more than 7dB and 6dB improvement in the near band are obtained for the 1DPCH and the 64DPCH WCDMA signal respectively. When the two-carrier 64DPCH WCDMA signal is applied on this DPD system, more than 7dB and 6dB improvement are obtained for the inter-modulation and the in-band spectrum.