Group Digital Predistortion With Step Uniformization for Hybrid Beamforming Transmitters

Abstract

This letter proposes a group digital predistorter with step uniformization (SU-GDPD) for massive multi-input multi-output (MIMO) transmitters with hybrid beamforming architecture. Analog predistorters (APDs) are employed to iteratively adjust the nonlinear character of the power amplifiers (PAs) that are sharing one radio frequency (RF) chain. The shared digital predistortion (DPD) parameter and the APD control voltage (ACV) are optimized alternately to achieve the best linearity. This step optimization process avoids extensive search of the ACV combination, which causes much time and calculation resource consumption. Furthermore, SU-GDPD has the adaptability to handle the nonlinearity variation of each PA. Two class-AB PAs with the peak output power of 42 dBm are tested to verify the validation of the proposed SU-GDPD. With the stimulation of the 100-MHz long-term evolution advanced (LTE-A) signal, the two PAs have an average output power of 31 dBm. The adjacent channel power ratio (ACPR) of the two PAs is improved by 19.8-22 dB simultaneously by the proposed SU-GDPD.