Linearization Angle Widened Digital Predistortion for 5G MIMO Beamforming Transmitters

To reduce the demand for frequently adjusting phase shifts in the fifth-generation (5G) multiple-input multiple-output (MIMO) beamforming transmitters, in this article, a novel digital predistortion (DPD) technique is proposed, which employs multiple predistortion boxes to shape the pattern of nonlinear distortions in space in order to linearize multiple targets simultaneously. By using this approach, the linearization angle is widened and thus the communication quality can be kept when the user moves off the main beam direction. As a proof of concept, two DPD boxes, namely main and auxiliary boxes, are used to realize the 2-target linearization. A new model extraction method is also proposed with a dedicated over-the-air (OTA) feedback post-processing stage. Simulation and experiment are demonstrated on a 4-path beamforming transmitter. The results show that the proposed DPD method can effectively widen the linearization angle with reasonable additional complexity.