Linearization of power amplifiers by baseband digital predistortion for OFDM transmitters

For the signals with high peak-to-average ratio (PAR), such as WiMax OFDM, power amplifiers need to operate in a compression mode. It results in a nonlinear distortion of the output signal. To compensate for this distortion, linearizers are used. However, they decrease efficiency of amplifiers. This paper proposes to use a digital predistortion of baseband signals, which is characterized by a small impact on efficiency and a good linearizing performance, for linearization of OFDM transmitters. The paper describes design of a baseband predistorter and verifies its performances by WiMax OFDM simulations in ADS. Proposed predistorter brings significant improvements in AM/AM characteristic, eliminates spectrum re-growth, decreases adjacent channel power ratio (ACPR) and error vector magnitude (EVM).