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Behavioral Modeling and Digital Predistortion for Fully-Connected Hybrid Beamforming Massive MIMO Transmitters

In this paper, a new digital predistortion (DPD) scheme is proposed to model and linearize the fully-connected hybrid beamforming (HBF) transmitters. In order to address the implementation issue of conventional DPD architecture in HBF array, the proposed DPD scheme allows to estimate and linearize the beam signals instead of the individual PAs. Different from the single-input single-output (SISO) DPD solutions in sub-array based HBF array, the proposed technique constructs a series of multi-input DPD blocks parallel for each RF chain to model and eliminate the complicated cross-channel intermodulation and inner-channel distortion specifically in fully-connected HBF array. Experimental results on a 2-stream 4-element fully-connected beamforming array show a 13 dB ACPR improvement of the proposed DPD than the conventional SISO DPD solutions. To the best of our knowledge, this is the first time that the DPD solutions for linearizing the FC HBF (b) array are investigated.