WLAN signal strength - good or bad ?

Andy Green andy at openmoko.com
Sun Oct 5 11:11:21 CEST 2008

Hash: SHA1

Werner Almesberger wrote:

> The rest of the access points are all reported with very weak signal
> strengths, so I'm not surprised the Neos don't see them.

It might be educational to stick say the laptop in Monitor mode and
tcpdump it.  The beacons go out at 1Mbps always, it means they have the
longest reach, it's quite common to be able to see many more beacons
from ESSIDs you don't recognize in a crowded place than are reported in

I think the WLAN devices routinely filter what they're seeing on the
basis that of you only see one 1Mbps beacon a minute from somewhere that
pumps out ten a second, there is no point trying to authenticate to it.
 So then it can mean the result in firmware was filtered rather than not
seen -- unfortunately with no Monitor mode (yet?) on AR6001 there's no
way to check up on it.

BTW A lot of confusion is caused by this 4/94 type report in iwconfig,
if there is no valid information driven by bit error rate floating
around for that maybe an interesting patch would be to take the dBm
figure and say add 100 to it or something and report / 100, so at least
the figure here is sane.

- -Andy
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