Complexity of DPD linearization in the full RF-band for a WiMAX power amplifier

摘要

In this paper, the influence of channel frequency in the RF-band on digital predistortion (DPD) is investigated empirically. A class-AB GaN-HEMT power amplifier targeting the 3.5 GHz band for WiMAX is used with a 20 MHz OFDM signal. It is found that frequency dependent memory effects in the band have a strong impact on the amount of memory taps needed for the DPD predistorter model. The overall characteristic is dominated by the non-linear behavior of the transistor, the memory effects, and the IQ imbalance introduced by the low cost modulation hardware. Using DPD models with memory that can handle IQ imbalance the EVM is improved by at least 12 dB in backed-off operation.