OTA-Based Data Acquisition and Signal Separation for Digital Predistortion of Multi-User MIMO Transmitters in 5G

In this paper, a non-interruptive over-the-air (OTA) data acquisition method is presented to characterize system nonlinearity and calibrate digital predistortion (DPD) in multi-user (MU) multiple-input multiple-output (MIMO) transmitters with low hardware complexity. Based on a unified system model for fully-digital and hybrid MU-MIMO transmitters, the requirements and difficulties of data acquisition for MU-MIMO DPD are outlined first. A versatile OTA data acquisition technique, featuring a multi-observation forward modelling procedure, is thereby developed to obtain power amplifier (PA) output without interrupting the operation of the MIMO transmitters. By using this method, the output of each PA can be reconstructed instead of directly measuring each PA's output, even when the output signals of PAs are correlated. DPD can therefore be effectively constructed to mitigate the distortions. Experimental results demonstrate that DPD method with the proposed OTA data acquisition can accurately estimate each PA output and linearize all PAs in the array.