WiFi 运动，心跳，跌倒监测 (一)

（参考文献：Wi-Fi Can Do More: Toward Ubiquitous Wireless Sensing. IEEE Commun. Stand. Mag. 6(2)
: 42-49 (2022)）

WiFi作为最大的基础网络架构，遍布于大大小小的家庭。传统WiFi主要应用于communication以及networking功能，而现在增加了一个新的属性sensing，并构建世界最大的"sensorless" sensing network。目前，最新修订IEEE 802.11bf协议正是为WiFi sensing建立标准，预期于2024年公布。并且不仅仅是WiFi，其他如UWB,毫米波，都在未来成为研究sensing方向重要的手段。

使用WiFi做sensing所面临的的三个挑战：

1. Wi-Fi transceivers are not synchronized, and therefore the measured channel information contains significant phase distortions.
2. Commercial Wi-Fi has limited channel bandwidths （20MHz–80MHz）.
3. Only a small number of antennas (e.g., typically one to three on IoT devices), producing poor spatial resolution to differentiate multipath signals arriving from different angles. 
4. How do we deploy Wi-Fi sensing solutions by integrating on top of commodity devices without affecting the primary networking functionality?

针对以上挑战的结论是：

1. While there is a considerable number of multipaths in the complex indoor environments, the multipath resolvability of Wi-Fi signals is greatly and fundamentally constrained, making traditional two-ray reflection models and phased array signal processing techniques impractical for Wi-Fi sensing.
2. Purely software-based solutions running on top of legacy Wi-Fi devices, which will then serve both networking and sensing concurrently, a true integrated communication and sensing solution.

基于以上作者不再采用原来的two-ray model，而是基于电磁波原理提出了一种新的方法，新方法利用尽可能所有多径并进行统计分析。采用了channel state information (CSI)+ auto-correlation function (ACF)来进行特征提取（往后的文章用了同样的方法）。具体可以实现以下功能：

1.  Motion. (参考论文 widetect)
2.  Periodicity (breathing rate). (参考论文 Smars) a predominantly periodic chest movement.
3.  Speed. (参考论文 wispeed 和 gaitway)

以下是几个APP和WEB端界面，Origin Tracking （the world’s first indoor tracking
technology with centimeter accuracy even underNLoS conditions）以及HEX