Wifi 三角测量 - 从 AP 到 iPhone 的距离
我正在尝试计算从 AP（接入点）到 iPhone 的粗略距离。几个常量：
1）我已经解决了查找和确定附近 AP 信号强度的问题（必须使用私有 API，不用担心这不会出现在 App Store 中）
2）所有 AP 都是同一品牌&模型
现在给定 AP RSSI，我怎样才能获得粗略的距离？
示例：RSSI 为 -60，我还需要哪些其他信息才能到达一定距离？
谢谢！
I'm trying to calculate a rough distance from an AP (Access Point) to an iPhone. A couple of constants:
1) I've already solved the problem of finding and determining signal strength of nearby APs (had to use private APIs, don't worry this isn't going in the App Store)
2) All the APs are the same brand & model
Now given a APs RSSI, how can I get a rough distance?
Example: RSSI is -60, what other info would I need to get to a distance?
Thanks!
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补充一下andynormancx：
真正要了你的命的不是衰减，而是干扰：
我知道我们校园里有足够多的房间，在满信号和无信号之间只有20厘米的距离。
您所能做的就是查看是否看到某个 AP。如果是这样，那就很好地表明您距离它大约不到几十米。
如果您没有看到某个 AP，您就只能知道您没有看到某个 AP。你不知道的是，如果它……
编辑：
顺便说一下，这是当没有 GPS 信号时，核心位置会做什么...至少，它可以告诉我这台笔记本电脑在哪里，精度为 +/- 70 米。
也就是说，当您拥有正确数量的接入点、在相当大的间隔信道中运行并知道它们的位置时，您可能能够比核心位置好一个数量级 — 如果您所在的建筑物的地板和主体结构是用钢筋混凝土建造的，具有相对较薄的“可移动”墙壁，您应该能够找到用户位于这些“单元”中的哪个。
如果您在大型会议厅，那么希望现场的出口标志足够好;-)
Adding to andynormancx:
The thing that is totally going to kill you isn't attenuation as much as interference:
I know more than enough rooms on our campus where there are a mere 20cm between full signal and none at all.
All you can do is look whether you see a certain AP. If so, that's a good indication that you're approximately less then a few ten meters away from it.
If you don't see a certain AP you only know, that you don't see a certain AP. What you don't know is if it's...
Edit:
This, by the way, is what core location does, when there is no GPS signal... At least, it can tell me where this laptop is with an accuracy of +/- 70 meters.
That said, when you have the right number of APs, operating in considerably spaced-out channels and know where they are, you might be able to get better than core location by one order of magnitude — if the building you are in is built out of reinforced concrete for the floors and main structure with comparably thin, "removable" walls, you should be able to locate in which of these "cells" the user is.
If you are in a large conference hall, well then hopefully your exit signs on site are good enough anyway ;-)
你不能，除非所有这些接入点都在没有任何障碍物的完全开放的空间中运行。接收到的信号强度将根据距离以外的其他几个因素而变化。
墙壁、树木、窗户、门等都会显着减弱信号。当然，即使是不同类型的墙壁也会有非常不同的衰减水平（对于某些类型/厚度的墙壁来说几乎是完全衰减）。我预计这些相同物体的反射也会产生类似的效果。
You can't, not unless all these access points are running in a completely open space with no obstructions. The received signal strength will vary depending on several other factors other than distance.
Walls, trees, windows, doors etc will all attenuate the signal significantly. And of course even different types of walls for example will have very varying levels of attenuation (almost total for some types/thicknesses of walls). I expect reflections off of those same objects will also have a similar effect.
您可以应用简单的信号传播损耗模型，并假设您知道源功率（接入点发出多少能量），您可以估算出距离。避免复杂化是很棘手的——墙壁之类的东西会减弱功率，因此计算会认为接入点比实际距离更远。
You can apply a model of simple signal propagation loss, and assuming you know the source power (how much energy the access point is putting out) you could approximate the distance. It would be tricky to avoid complications - things like walls will attenuate the power and so the calculation will think the AP is farther away than it actually is.