In this paper, a novel multi-stream spatial digital predistortion (DPD) technique is proposed to model and linearize the fully-connected (FC) hybrid beamforming (HBF) transmitters. The proposed scheme solves the DPD implementation issue in the FC HBF array by estimating and linearizing the beam signals instead of the individual PAs. In FC HBF systems, significant intermodulation (IMD) between different transmit signals will be generated due to the analog beamforming and combining network upstream of the power amplifiers (PAs). The IMD beams will end up being radiated in different directions and some of them might fall in the linear beam directions. Therefore, multi-input DPD blocks using a practical multi-variable model are constructed for each RF chain to eliminate the complicated inner- and cross-channel IMDs of the beam signals. Simulations on a 4-stream 64-element FC HBF array and experimental tests on a 2-stream 4-element system are carried out to benchmark the proposed DPD technique against the conventional techniques. Better than 13 dB adjacent channel power ratio (ACPR) improvement and 12 dB normalized mean square error (NMSE) improvement have been achieved by the proposed DPD technique.

中文翻译：

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全连接混合波束成形大规模 MIMO 发射机的多流空间数字预失真

在本文中，提出了一种新颖的多流空间数字预失真 (DPD) 技术来对全连接 (FC) 混合波束成形 (HBF) 发射机进行建模和线性化。所提出的方案通过估计和线性化波束信号而不是单个 PA 来解决 FC HBF 阵列中的 DPD 实现问题。在 FC HBF 系统中，由于功率放大器 (PA) 上游的模拟波束成形和组合网络，将在不同发射信号之间产生显着的互调 (IMD)。IMD 光束最终会向不同方向辐射，其中一些可能会落在线性光束方向。因此，为每个 RF 链构建了使用实用多变量模型的多输入 DPD 模块，以消除波束信号复杂的内通道和跨通道 IMD。对 4 流 64 单元 FC HBF 阵列进行了模拟，并在 2 流 4 单元系统上进行了实验测试，以将所提出的 DPD 技术与传统技术进行基准测试。所提出的 DPD 技术已经实现了优于 13 dB 的相邻信道功率比 (ACPR) 改进和 12 dB 归一化均方误差 (NMSE) 改进。