Hybrid beamforming can effectively reduce the cost of millimeter wave multiple-input-multiple-output (MIMO) system. However, the analog beamformer realized by the unit-norm phase shifters makes the design of the hybrid beamformers a complicated non-convex optimization problem, and prior works suffer from high computational complexity. In this letter, we focus on the single-user scenario and propose a two-step procedure for the low-complexity hybrid beamforming design. The first step employs a codebook-based algorithm to provide an initial setting of the hybrid beamformers. The second step employs the AltMin-based algorithm to refine the hybrid beamformers. In particular, we also modify the loss function used in the AltMin algorithm for complexity reduction. Simulation results show that the proposed codebook-assisted AltMin (CA-AltMin) reduces the complexity by 96% and achieves better performance than the state-of-the-art algorithms from different technical aspects.

中文翻译：

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用于低复杂度混合波束成形设计的两步码本辅助交替最小化 (CA-AltMin)

混合波束成形可以有效降低毫米波多输入多输出（MIMO）系统的成本。然而，由单位范数移相器实现的模拟波束形成器使混合波束形成器的设计成为一个复杂的非凸优化问题，并且先前的工作具有很高的计算复杂度。在这封信中，我们专注于单用户场景，并为低复杂度混合波束成形设计提出了一个两步程序。第一步采用基于码本的算法来提供混合波束形成器的初始设置。第二步采用基于 AltMin 的算法来细化混合波束形成器。特别是，我们还修改了 AltMin 算法中使用的损失函数以降低复杂性。