Subject: [Geopriv] WLAN Positioning

From: Hannes Tschofenig <[email-masked]>
Date: Tue, 27 Nov 2007 16:46:50 +0100

Hi all,

I just had a chat with Guenther Retscher (author of the paper Carl 
distributed in one of his previous mails).
http://www.mycoordinates.org/testing-indoor-environment.php

I asked him about his experience with WLAN positioning techniques. In 
particular I have asked him about the quality of his measurements in an 
outdoor environment.
(He uses a technique call fingerprinting, as explained in the article.)

Here is the short summary:
a) When there are multiple access points then they got the location of 
an end point with +/- 1 to 3 meters.
b) When there is only one access point available then there is obviously 
a problem because then you can essentially only provide the coverage 
area of the WLAN. He said that a circle is typically sufficient to 
describe the area.

For (a) I would argue that we just need lat/long[/alt]. Nothing more.

For (b) there are essentially a couple of approaches:
- argue that this cannot be used for some applications (e.g., emergency 
services). Hence, the "problem cases" essentially go away with better 
location determination techniques.
- return only the location information (civic or geodetic) of the access 
point itself
- try to approximate the coverage area of the WLAN using the available 
techniques (namely "resolution" or "uncertainty" parameter for DHCP) and 
then translate them into a polygon for transport in a PIDF-LO.
- define a new way of representing the area (for usage with DHCP; we 
already have the necessary tools in PIDF-LO).

Ciao
Hannes

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