Beam-Oriented Digital Predistortion for Hybrid Beamforming Array Utilizing Over-the-Air Diversity Feedbacks

In this paper, a novel beam-oriented digital pre-distortion (DPD) is proposed for linearizing the hybrid beamforming large-scale array. Utilizing the over-the-air (OTA) diversity feedbacks, the proposed DPD can solve the hardware implementation issue of conventional DPD architecture in hybrid beamforming array by estimating and linearizing the main beam signal while avoiding the complex feedback configurations. Mathematical analysis proves that it is possible to derive the main beam signal from the OTA feedback information directly. The predistorter can then be identified based on the estimated main beam signal. Furthermore, the OTA diversity feedback configuration is suggested to address the problem of insufficient nonlinear information occasionally appearing on the single OTA feedback. The experimental tests were performed on a 4-antenna array using two OTA observations, and a more than 13 dB ACPR improvement has been realized with the proposed DPD.