Online Method of Determining the Nonlinear Characteristics of a PA with Short Updating Intervals for LTE-Advanced System

This paper proposes a method for measuring the rapidly varying parameters of a power amplifier (PA) characterized by a memory polynomial model in less time than in the symbol period of the orthogonal frequency-division multiplexing (OFDM) signal of a long-term evolution-advanced (LTE-Advanced) system. The method fulfills the dual-updating scheme that we proposed in our previous papers, which described a method of determining slowly varying parameters. We used the dependence of bandwidth on the order of nonlinearity to distinguish the contributions from different orders of nonlinearities in the frequency domain. We assumed that fast Fourier transforms (FFTs) with shorter fundamental periods than the symbol period attain shorter measuring times. We conducted a computer simulation to confirm the applicable range of the described method for varying the speed of the model parameters. We assumed sinusoidal variations for the parameters of the PA, and used the proposed method to trace the varying parameters and used the traced results in a predistorter (PD). We estimated the improved spectrum for the PD to confirm the accuracy of the determined coefficients. The simulation shows that our method traces changes accurately up to a variation in amplitude of 20%. We also confirmed that the method can trace the sinusoidal variation frequency up to half of the symbol period.