Digital perdistortion technique for compensating memory effects of power amplifiers in wideband applications

Abstract

The application of digital predistortion in base band signal is an extended method of amplifier linearization to reduce the Adjacent Channel Interference (ACI) in those systems in which a varying envelope modulation scheme like OFDM and MQAM is used. Digital baseband predistortion is a highly cost-effective way to linearize Power amplifiers (PAs), but most existing architectures assume that the PA has a memoryless nonlinearity. For wider bandwidth applications such as wideband code-division multiple access (WCDMA), wideband orthogonal frequency-division multiplexing (W-OFDM) and worldwide interoperability for microwave access (WiMAX), PA memory effects can no longer be ignored. In this paper a novel technique for compensating such effects is proposed. This technique is a combination of two techniques, memory polynomial predistortion and the gain based predistorter method. This method is compared with the other technique, memory polynomial method and validated using a Mini-Circuit power amplifier and QPSK signal with 1 MHz bandwidth. Simulations and results show improvement in ACLR reduction and EVM with applying this method. K e y w o r d s: digital predistortion, memory effects, ACLR, power amplifier, WCDMA