Massive multiple-input multiple-output (MIMO) systems operating at millimeter-wave (mmWave) frequencies promise to satisfy the demand for higher data rates in mobile communication networks. A practical challenge that arises is the calibration in amplitude and phase of these massive MIMO systems, as the antenna elements are too densely packed to provide a separate calibration branch for measuring them independently. Over-the-air (OTA) calibration methods are viable solutions to this problem. In contrast to previous works, the here presented OTA calibration method is investigated and optimized for subarray-based hybrid beamforming (SBHB) systems. SBHB systems represent an efficient architectural solution to realize massive MIMO systems. Moreover, based on OTA scattering parameter measurements, the ambiguities of the phase shifters are exploited and two criteria to optimize the beam pattern are formulated. Finally, the optimization criteria are examined in measurements utilizing a novel SBHB receiver system operating at 27.8 GHz.

中文翻译：

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基于子阵列的混合波束成形系统的波束方向图优化方法

以毫米波（mmWave）频率运行的大规模多输入多输出（MIMO）系统有望满足移动通信网络中对更高数据速率的需求。出现的实际挑战是这些大规模MIMO系统的幅度和相位校准，因为天线元件过于密集，无法提供单独的校准分支来独立测量它们。空中（OTA）校准方法是解决此问题的可行方法。与以前的工作相比，本文介绍的OTA校准方法已针对基于子阵列的混合波束成形（SBHB）系统进行了研究和优化。SBHB系统代表了实现大规模MIMO系统的高效架构解决方案。此外，基于OTA散射参数测量，利用了移相器的模糊性，并制定了两个优化光束方向图的准则。最后，使用在27.8 GHz下运行的新型SBHB接收机系统在测量中检查了优化标准。