Over-the-Air Linearization of Phased Array Transmitters Affected by Load Modulation

Abstract

Unlocking the potential of millimeter-wave (mmWave) phased array systems demands robust nonlinear transmitter modeling and digital pre-distortion (DPD) techniques. In this article, we present a novel behavioral modeling approach and the corresponding linearization solution for beamforming antenna arrays comprising multiple and mutually interacting nonlinear power amplifier (PA) units. Our non-recursive transmitter model simplifies numerical evaluations across diverse phased array/multiple-input multiple-output (MIMO) configurations under crosstalk-induced load modulation. We introduce a novel, nonlinear forward model parameter identification algorithm tailored for crosstalk-prone array systems and applicable in arbitrary MIMO transmitter configurations, enabling precise modeling and characterization using over-the-air (OTA) observations. Furthermore, we propose an offline direct learning architecture based DPD method, harnessing the estimated nonlinear array forward model and specific beam-sweeping procedure, for linearizing phased arrays under severe load modulation. Numerical assessments across various scenarios demonstrate superior performance, while physical validation on a measurement test bench reinforces our methodology’s real-world applicability. Overall, this work paves the way for advanced nonlinear array transmitter optimization and linearization, vital for next-generation wireless communication networks.