Efficient mitigation of power amplifier (PA) nonlinear distortion in multi-user hybrid precoding based broadband mmWave systems is an open research problem. In this article, we carry out detailed signal and distortion modeling in broadband multi-user hybrid MIMO systems, with a bank of nonlinear PAs in each subarray, while also take the inevitable crosstalk between the antenna/PA branches into account. Building on the derived models, we adopt and describe an efficient closed-loop (CL) digital predistortion (DPD) solution that utilizes only a single-input DPD unit per transmit chain or subarray, despite crosstalk, providing thus substantial complexity-benefit compared to the state-of-the art multi-dimensional DPD solutions. We show that under spatially correlated multipath propagation, each single-input DPD unit can provide linearization towards every intended user, or more generally, towards all spatial directions where coherent propagation is taking place, and that the adopted CL DPD system is robust against crosstalk. Extensive numerical results building on practical measurement-based mmWave PA models are provided, demonstrating and verifying the excellent linearization performance of the overall DPD system in different evaluation scenarios.

中文翻译：

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毫米波多用户混合 MIMO 的数字预失真

在基于多用户混合预编码的宽带毫米波系统中有效缓解功率放大器 (PA) 非线性失真是一个开放的研究问题。在本文中，我们在宽带多用户混合 MIMO 系统中进行了详细的信号和失真建模，每个子阵列中有一组非线性 PA，同时还考虑了天线/PA 分支之间不可避免的串扰。在派生模型的基础上，我们采用并描述了一种高效的闭环 (CL) 数字预失真 (DPD) 解决方案，尽管存在串扰，但该解决方案在每个传输链或子阵列中仅使用一个单输入 DPD 单元，与最先进的多维 DPD 解决方案。我们表明，在空间相关的多径传播下，每个单输入 DPD 单元可以为每个预期用户提供线性化，或者更一般地说，向发生相干传播的所有空间方向提供线性化，并且采用的 CL DPD 系统对串扰具有鲁棒性。提供了基于实际测量的毫米波 PA 模型的大量数值结果，展示并验证了整个 DPD 系统在不同评估场景中的出色线性化性能。