Single-PA-feedback digital predistortion for beamforming MIMO transmitter

In this paper, a simplified method of digital predistortion (DPD) based on the feedback for single power amplifier (PA) is proposed to linearize beamforming Multiple-Input Multiple-Output (MIMO) transmitter. In MIMO beamforming transmitter, a couple of radio frequency (RF) channels are paralleled to transmit signals simultaneously, it is almost impractical to perform linearization for each channel individually. The proposed method can not only achieve good linearization effect, but also greatly simplifies the system structure. A simple MIMO system with 2×4 beamformer is constructed to evaluate the proposed method. The experiment is based on two Long Term Evolution (LTE) signals with different bandwidth and peak-to-average power ratio (PAPR) operating at 2.12 GHz and 2.18 GHz, respectively. With a two dimensional memory polynomials (2-D-MP) model, the nonlinearity of the transmitter is compensated, and the adjacent channels power ratio (ACPR) can reach lower than -45dBc, which has been compressed 9-21 dB in the results.