3 ms·

> ...it requires triangulation + accurate timestamps... This system does not do round-trip time measurements (RTT) which I believe you are referring. RTT is di

by qrv3w 9y ago

> ...it requires triangulation + accurate timestamps... This system does not do round-trip time measurements (RTT) which I believe you are referring. RTT is different because it uses actual triangulation, whereas this system merely classifies a given point in space based on surrounding electromagnetic waves (WiFi/Bluetooth/etc.). RTT is superior, what I would call extreme precision, because it is capable of cm-level precision. (I say high-precision as compared to GPS which I tried to do this with before years ago). I love RTT, except that it is not a solution that is widely available yet. This FIND system is nice because anyone can use on their phone right now, and you don't know need any specialized hardware or need to buy any equipment. And the signal generators are already there (your WiFi, your neighbors WiFi, Bluetooth devices, etc.). > How many devices to coordinate the location discovery? In the active mode (where you do the scanning) it will use every device it sees in the vicinity. In a place like an apartment in the city, this would include all WiFi+Bluetooth points in your home and your neighbors, which could be dozens. > There's no mention of hardware or system requirements. Thanks, I'll fix this. It really depends on how you use FIND - in active mode you only need a computer or a Android smartphone. For passive mode you need some small computers and WiFi cards.

gricardo99 9y ago
Thanks! Much appreciated response. +1
cesarb 9y ago
If you're connected to an AP via Wifi, can't you ping the router? That would give you a single RTT data point, which you could combine with the non-RTT measurements to enhance the precision. The router is often either the AP itself, or linked to it through a wired connection. Thinking more about it, you could even use an ARP ping (like the "arping" tool) to try to ping the AP directly, even if it's not the router.
- qrv3w 9y ago
  Yes you can do that but that runs up against the problem of "processing time" in the router. A router might process a simple echo request for +/- 1 millisecond. Since 1 nanosecond = 1 foot, this variability already makes the distance measurement meaningless for indoor positioning. The way to do it accurately requires using something like 802.11mc [1] which can vary accurately measure time using frame collisions. [1] http://ieeexplore.ieee.org/document/6805649/ http://ieeexplore.ieee.org/document/6805649/

by qrv3w 9y ago

gricardo99 9y ago

Thanks! Much appreciated response. +1

cesarb 9y ago

If you're connected to an AP via Wifi, can't you ping the router? That would give you a single RTT data point, which you could combine with the non-RTT measurements to enhance the precision. The router is often either the AP itself, or linked to it through a wired connection. Thinking more about it, you could even use an ARP ping (like the "arping" tool) to try to ping the AP directly, even if it's not the router.

qrv3w 9y ago
Yes you can do that but that runs up against the problem of "processing time" in the router. A router might process a simple echo request for +/- 1 millisecond. Since 1 nanosecond = 1 foot, this variability already makes the distance measurement meaningless for indoor positioning. The way to do it accurately requires using something like 802.11mc [1] which can vary accurately measure time using frame collisions. [1] http://ieeexplore.ieee.org/document/6805649/ http://ieeexplore.ieee.org/document/6805649/