Millimeter-wave (mmWave) communications promise Gigabit/s data rates thanks to the availability of large swaths of bandwidth between 10–100 GHz. Although cellular operators prefer the lower portions of the spectrum due to popular belief that propagation there is more favorable, the measurement campaigns to confirm this – conducted by ten organizations thus far – report conflicting results. Yet it is not clear whether the conflict can be attributed to the channel itself – measured in different environments and at different center frequencies – or to the differences in the organizations’ channel sounders and sounding techniques. In this paper, we propose a methodology to measure mmWave frequency dependence, using the 26.5–40 GHz band as an example. The methodology emphasizes calibration of the equipment so that the measurement results represent the channel alone (and not the channel coupled with the channel sounder). Our results confirm that free-space propagation is indeed frequency invariant – a well understood phenomena but to our knowledge reported nowhere else at mmWave to date. More interestingly, we found that specular paths – the strongest after the line-of-sight path and so pivotal to maintaining connectivity during blockage – are the least invariant compared to weaker diffracted and diffuse paths.

中文翻译：

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跨毫米波频谱测量多径信道频率相关性的方法

由于 10–100 GHz 之间的大带宽可用，毫米波 (mmWave) 通信承诺千兆位/秒的数据速率。尽管由于普遍认为那里的传播更有利，蜂窝运营商更喜欢频谱的较低部分，但迄今为止由十个组织开展的测量活动报告了相互矛盾的结果。然而，尚不清楚冲突是否可以归因于频道本身——在不同环境和不同中心频率下测量——或组织的频道探测仪和探测技术的差异。在本文中，我们提出了一种测量毫米波频率依赖性的方法，以 26.5-40 GHz 频段为例。该方法强调设备的校准，以便测量结果仅代表通道（而不是与通道测深仪耦合的通道）。我们的结果证实，自由空间传播确实是频率不变的——这是一个很好理解的现象，但据我们所知，迄今为止在 mmWave 的其他任何地方都没有报道过。更有趣的是，我们发现镜面反射路径——在视线路径之后最强，对于在阻塞期间保持连通性至关重要——与较弱的衍射和漫反射路径相比，其不变性最小。