A fast beam training scheme for the massive antenna arrays is a key to frequency division duplex (FDD) mmWave systems, as channel reciprocity between the down-link (DL) and up-link (UL) channels does not hold in general, requiring feedback mechanism for DL beam selection. Due to the large number of antennas in a massive array, it is not very practical to conduct an exhaustive search, especially when considering the small angular coverage of one directional narrow beam (hence the number of candidate beams). To address such a challenge, we consider the 3D beam matching problem for a multi-user massive multiple-input multiple-output (MIMO) system, and propose a two-stage hierachical codebook along with the corresponding fast beam training scheme. The proposed codebook contains a primary codebook for hierarchical beams and an auxiliary codebook for narrow beams following the limited resolution of the phase shifters (PSs). The fast beam training scheme based on the codebook not only reduces beam training overhead, but also is applicable to the scenario where there exist multiple propagation paths for one mobile station (MS). Numerical results show that the proposed scheme not only enjoys a lower beam matching complexity (i.e. the training overhead), but also achieves a comparable performance to the exhaustive search scheme.

中文翻译：

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具有有限移相器分辨率的 FDD 多用户大规模 MIMO 系统的快速波束训练


大规模天线阵列的快速波束训练方案是频分双工 (FDD) 毫米波系统的关键，因为下行链路 (DL) 和上行链路 (UL) 信道之间的信道互易性通常不成立，需要反馈DL 波束选择机制。由于大规模阵列中的天线数量较多，进行详尽的搜索不太实用，特别是考虑到一个定向窄波束的小角度覆盖范围（因此候选波束的数量）。为了解决这一挑战，我们考虑了多用户大规模多输入多输出（MIMO）系统的3D波束匹配问题，并提出了一种两级分层码本以及相应的快速波束训练方案。所提出的码本包含用于分层波束的主码本和用于遵循移相器（PS）的有限分辨率的窄波束的辅助码本。基于码本的快速波束训练方案不仅减少了波束训练开销，而且适用于一个移动站(MS)存在多个传播路径的场景。数值结果表明，该方案不仅具有较低的波束匹配复杂度（即训练开销），而且实现了与穷举搜索方案相当的性能。