Real-world deployments of WiFi-based indoor localization in large public venues are few and far between as most state-of-the-art solutions require either client or infrastructure-side changes. Hence, even though high location accuracy is possible with these solutions, they are not practical due to cost and/or client adoption reasons. Majority of the public venues use commercial controller-managed WLAN solutions, %provided by Aruba, Cisco, etc., that neither allow client changes nor infrastructure changes. In fact, for such venues we have observed highly heterogeneous devices with very low adoption rates for client-side apps. In this paper, we present our experiences in deploying a scalable location system for such venues. We show that server-side localization is not trivial and present two unique challenges associated with this approach, namely \emph{Cardinality Mismatch} and \emph{High Client Scan Latency}. The "Mismatch" challenge results in a significant mismatch between the set of access points (APs) reporting a client in the offline and online phases, while the "Latency" challenge results in a low number of APs reporting data for any particular client. We collect three weeks of detailed ground truth data ($\approx 200$ landmarks), from a WiFi setup that has been deployed for more than four years, to provide evidences for the extent and understanding the impact of these problems. Our analysis of real-world client devices reveal that the current trend for the clients is to reduce scans, thereby adversely impacting their localization accuracy. We analyze how localization is impacted when scans are minimal. We propose heuristics to alleviate reduction in the accuracy despite lesser scans. Besides the number of scans, we summarize the other challenges and pitfalls of real deployments which hamper the localization accuracy.

中文翻译：

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使用现有基础架构进行服务器端WiFi室内本地化的经验与挑战

在大型公共场所中，基于WiFi的室内本地化的实际部署很少，而且相差甚远，因为大多数最新解决方案都需要客户端或基础架构方面的更改。因此，即使使用这些解决方案可以实现较高的位置精度，但由于成本和/或客户采用原因，它们并不实用。大多数公共场所使用由Aruba，Cisco等提供的商业控制器管理的WLAN解决方案，这些解决方案既不允许更改客户端，也不允许基础架构更改。实际上，对于这样的场所，我们已经观察到高度异构的设备，客户端应用的采用率非常低。在本文中，我们介绍了在此类场所部署可扩展位置系统的经验。我们证明了服务器端本地化并非易事，并提出了与此方法相关的两个独特挑战，即\ emph {Cardinality Mismatch}和\ emph {High Client Scan Latency}。“不匹配”挑战会导致在脱机阶段和联机阶段报告客户端的一组访问点（AP）之间存在严重的不匹配，而“延迟”挑战会导致报告任何特定客户端的AP的数量较少。我们从已经部署了四年以上的WiFi设置中收集了三周的详细地面真实数据（约200美元的地标），以提供证据证明这些问题的严重程度和影响。我们对实际客户端设备的分析表明，客户端的当前趋势是减少扫描，从而不利地影响其定位精度。我们分析了最小化扫描时对本地化的影响。尽管扫描次数较少，我们建议采用启发式方法来减轻准确性的降低。除了扫描数量之外，我们还总结了实际部署的其他难题和陷阱，这些难题和陷阱会影响定位的准确性。