A Fast Digital Predistortion Algorithm for Radio-Frequency Power Amplifier Linearization With Loop Delay Compensation

Abstract

An adaptive, digital, baseband predistortion (PD) algorithm that compensates for the memoryless nonlinearities of radio-frequency (RF) power amplifiers (PAs) for wireless systems using non-constant-envelop modulation schemes is presented. Compared with the conventional, complex-gain predistorters based on lookup tables (LUTs), the proposed direct-learning, multilevel lookup table (ML-LUT) approach assisted by a hardware-efficient loop delay compensation scheme achieves a significant reduction in convergence time and an improvement in linearization accuracy in the presence of an unknown loopback delay. The experimental results in an FPGA prototyping platform show that the fast adaptation speed enables the predistorter to track time-varying PA nonlinearities as fast as in the tens of kilohertz range, constituting a potential solution for highly efficient PAs in mobile handsets.