A Combined Approach of DPD and CFR in F-OFDM System

Abstract

The nonlinear distortion of the power amplifier (PA) is studied for Filtered Orthogonal Frequency Division Multiplexing (F-OFDM) systems, which will be adopted in the fifth generation (5G) mobile communication systems. The peak to average power ratio (PAPR) of F-OFDM signal may make the PAs work in the saturation region and result into extremely serious nonlinear saturation distortion, and the nonlinear saturation distortion is usually compensated by predistortion technology. A digital predistortion (DPD) structure is designed to compensate the nonlinear characteristics of the PA in the article. Firstly, repeated iterative clipping revision (RICR) algorithm is used to reduce the PAPR, which makes the working region of PA infinitely close to the saturation region, and as a result, the efficiency is improved. Furthermore, an integrated structure combining crest factor reduction (CFR) and DPD is employed. The experimental results show that the performance of the proposed CFR joint adaptive DPD lowers the PAPR of the predistorted signal by 2dB. The combined CFR & DPD reduces the ACPR of the transmitter by 3dB compared with the unlinearized PA.