[clug] WiFi Direction Finder

Paul Wayper paul.wayper at anu.edu.au
Fri May 6 00:39:37 GMT 2005

Hi all,

The Register has an article today on a new device from Cisco which can 
track the location of a WiFi device - even an 802.11 RFID tag - down to 
about five metres (which is about 16 nanoseconds).  It only works with 
certain base stations and costs USD$15,000 or so.

Strangely, I was thinking of this problem (it bothers me that someone 
can set up a rogue access point and get away with it) the other day.  
The basic kit would consist of two WiFi aerials a known distance apart, 
connected to a machine that could timestamp them to nanosecond 
accuracy.  A separate machine or process could then analyse the timing 
between the occurrences of each packet on the two aerials out-of-band.  
Sweep the stick around, and when the timing difference was exactly the 
same as the distance between the aerials (or, more generally, approached 
a maximum), your stick points to the access point.  Further improvements 
would be to include further aerials for triangulation, and change it to 
a bunch of access points of known location - longer baselines equal 
better accuracy.

Anyone interested in working on such a project?  Please contact me on 
this email address or at home on paulway at mabula.net.

Have fun,


-- Paul Wayper at ANU - +61 2 6125 0643

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