This paper presents a hybrid beamforming design for millimeter-wave (mmWave) orthogonal frequency division multiplexing (OFDM) distributed antenna systems (DASs). First, we derive a downlink signal transmission model that considers the delay spread differences (DSDs) caused by the distributed nature of the network. We then propose a cooperative wideband hybrid beamforming method under the transmitting power constraints of each remote access unit. In a simulation study, the proposed method performed comparably to fully-digital beamforming, even when operated with practical finite-resolution phase shifters. We further confirm that the DSDs are the dominant cause of performance degradation in mmWave OFDM DASs.

本文提出了一种用于毫米波（mmWave）正交频分复用（OFDM）分布式天线系统（DAS）的混合波束成形设计。首先，我们导出一个下行链路信号传输模型，该模型考虑了由网络的分布式特性引起的延迟扩展差异（DSD）。然后，我们提出了在每个远程访问单元的发射功率约束下的协作宽带混合波束成形方法。在仿真研究中，即使使用实际的有限分辨率移相器，所提出的方法也可以与全数字波束形成相比。我们进一步确认，DSD是mmWave OFDM DAS中性能下降的主要原因。