Hybrid digital analog (HDA) beamforming has attracted considerable attention in practical implementation of millimeter wave (mmWave) multiuser multiple-input multiple-output (MU-MIMO) systems due to the low power consumption with respect to its fully digital baseband counterpart. The implementation cost, performance, and power efficiency of HDA beamforming depends on the level of connectivity and reconfigurability of the analog beamforming network. In this paper, we investigate the performance of two typical architectures that can be regarded as extreme cases, namely, the fully-connected (FC) and the one-stream-per-subarray (OSPS) architectures. In the FC architecture each RF antenna port is connected to all antenna elements of the array, while in the OSPS architecture the RF antenna ports are connected to disjoint subarrays. We jointly consider the initial beam acquisition and data communication phases, such that the latter takes place by using the beam direction information obtained by the former. We use the state-of-the-art beam alignment (BA) scheme previously proposed by the authors and consider a family of MU-MIMO precoding schemes well adapted to the beam information extracted from the BA phase. We also evaluate the power efficiency of the two HDA architectures taking into account the power dissipation at different hardware components as well as the power backoff under typical power amplifier constraints. Numerical results show that the two architectures achieve similar sum spectral efficiency, while the OSPS architecture is advantageous with respect to the FC case in terms of hardware complexity and power efficiency, at the sole cost of a slightly longer BA time-to-acquisition due to its reduced beam angle resolution.

中文翻译：

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用于毫米波 MU-MIMO 的全连接/部分连接混合波束成形架构

混合数字模拟 (HDA) 波束成形在毫米波 (mmWave) 多用户多输入多输出 (MU-MIMO) 系统的实际实现中引起了相当大的关注，因为与其全数字基带对应物相比具有低功耗。HDA 波束成形的实施成本、性能和功率效率取决于模拟波束成形网络的连接性和可重构性水平。在本文中，我们研究了两种可以被视为极端情况的典型架构的性能，即完全连接 (FC) 和每个子阵列一个流 (OSPS) 架构。在 FC 架构中，每个 RF 天线端口都连接到阵列的所有天线单元，而在 OSPS 架构中，RF 天线端口连接到不相交的子阵列。我们联合考虑初始波束获取和数据通信阶段，使得后者通过使用前者获得的波束方向信息发生。我们使用了作者先前提出的最先进的波束对齐 (BA) 方案，并考虑了一系列 MU-MIMO 预编码方案，它们非常适合从 BA 阶段提取的波束信息。我们还评估了两种 HDA 架构的功率效率，同时考虑了不同硬件组件的功耗以及典型功率放大器约束下的功率回退。数值结果表明，两种架构实现了相似的总频谱效率，而 OSPS 架构在硬件复杂度和功率效率方面相对于 FC 情况具有优势，