LAA和Wi-Fi共存的隐藏节点：实际部署的测量研究
Hidden-nodes in coexisting LAA & Wi-Fi: a measurement study of real deployments
摘要：
LTE授权辅助接入（LAA）网络开始在美国的主要大城市区域中在未授权的5GHz频带中广泛部署，其具有现有的密集部署的Wi-Fi。这为研究LAA和Wi-Fi之间的隐藏节点场景造成的问题提供了现实机会。隐藏节点问题已经在重叠Wi-Fi AP的上下文中得到了很好的研究。然而，当Wi-Fi与LAA共存时，隐藏节点问题加剧，因为LAA不能使用公知的请求发送（RTS）/清除发送（CTS）机制来解决竞争，导致Wi-Fi的吞吐量下降。在本文中，我们描述了详细的测量和芝加哥大学校园实验的结论，提出了一个完美的隐藏节点的情况下，由我们控制的Wi-Fi接入点（AP）和由AT&T部署的LAA基站（BS）彼此隐藏，但客户端不是。我们在共存区域的三个不同区域中进行了仔细的实验：（i）LAA和Wi-Fi之间的中间客户端;（ii）靠近Wi-Fi AP的客户端;以及（iii）靠近LAA BS的客户端。我们的结果表明，在LAA使用与80 MHz Wi-Fi传输重叠的三个未授权信道（60 MHz带宽）的集合的情况下，客户端设备的Wi-Fi吞吐量会受到相当大的影响。总体而言，Wi-Fi性能受到隐藏节点问题的影响比LAA更严重。在最佳室外条件下，与另一系统不存在时相比，LAA和Wi-Fi共存时的吞吐量分别降低了35%和97%。此外，我们得出结论，当LAA和Wi-Fi都使用多个20 MHz信道，并且在同一组信道上有多个Wi-Fi AP与LAA共存时，Wi-Fi主信道的选择可能会对LAA吞吐量产生重大影响。
英文摘要：
LTE-Licensed Assisted Access (LAA) networks are beginning to be deployed widely in major metropolitan areas in the US in the unlicensed 5 GHz bands, which have existing dense deployments of Wi-Fi. This provides a real-world opportunity to study the problems due to hidden-node scenarios between LAA and Wi-Fi. The hidden node problem has been well studied in the context of overlapping Wi-Fi APs. However, when Wi-Fi coexists with LAA, the hidden node problem is exacerbated since LAA cannot use the well-known Request-to-Send (RTS)/Clear to-Send (CTS) mechanism to resolve contentions, resulting in throughput degradation for Wi-Fi. In this paper, we describe detailed measurements and conclusions from experiments on the campus of the University of Chicago which presents a perfect hidden node scenario where Wi-Fi access points (APs) controlled by us and an LAA base-station (BS) deployed by AT&T are hidden from each other, but the clients are not. We performed careful experiments in three different regions of the coexistence area: (i) clients midway between LAA & Wi-Fi; (ii) clients close to the Wi-Fi AP; and (iii) clients close to the LAA BS. Our results show that in a situation where LAA uses an aggregate of three unlicensed channels (60 MHz bandwidth) which overlap with an 80 MHz Wi-Fi transmission, the Wi-Fi throughput at client devices suffers considerably. Overall, Wi-Fi performance is impacted by the hidden node problem more severely than LAA. In the best outdoor conditions, the throughput of LAA and Wi-Fi is reduced by 35% and 97% respectively when coexisting with each other as compared when the other system is not present. Furthermore, we conclude that when both LAA and Wi-Fi use multiple 20 MHz channels and there are multiple Wi-Fi APs coexisting with LAA on the same set of channels, the choice of Wi-Fi primary channels can have a significant impact on LAA throughput.
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