Mathematical model for amplitude distortion in nonlinear HPA

Abstract

A piecewise mathematical expression with one parameter was proposed for the amplitude (AM) distortion in nonlinear high power amplifiers (HPA). Its performance was assessed by the predistortion effects in terms of NMSE, RMSE and ACEPR yielded by its inverse function, namely AM predistorter (PD) in HPA digital predistortion (DPD). The use of this PD allows the HPA DPD to be implemented by only taking into consideration the compensation for the distortion signals, while the ones in the linear region of HPA don't need to process, thus greatly reducing the required memory storage capacity for the AM LUT. Moreover, the PD makes it feasible to implement HPA DPD by manually adjusting the parameter values, therefore the complexity can be avoided due to a feedback loop and the iterative predistortion algorithm. Simulation results show the PD can admirably balance between predistortion accuracy and implementation complexity. Accordingly, it is testified that the proposed AM model provides a good tradeoff between the precision and complexity in approximating the AM nonlinearity in TWTA driven by OFDM signals.