Generalized Rational Functions for Reduced-Complexity Behavioral Modeling and Digital Predistortion of Broadband Wireless Transmitters

In this paper, we present and analyze rational-function-based digital predistortion (DPD) of transmitters for broadband applications where system noise and prominent memory effects contribute to the overall nonlinearity of the system. The performance is reported for simulation and measured results for gallium nitride (GaN)-based class-AB and laterally diffused MOS (LDMOS)-based Doherty power amplifiers (PAs) using three different wideband code division multiple access signals with peak-to-average-power ratios of around 10 dB. The performance of the proposed model, in terms of normalized mean-square error, adjacent channel power ratio, matrix condition number, and coefficient dispersion, is compared against those of a memory polynomial (MP) model and a previously proposed rational-function-based model. It is shown by simulation and measurement that the previously proposed absolute-term denominator rational functions have limitations in the inverse modeling needed for DPD. A new variation of the rational function is proposed to alleviate this limitation. Depending on the type of PA and signals, a floating-point operation reduction of 8%-38% is reported as compared with a low-complexity MP model.