RX signal level calculation
gallir at uib.es
Fri Feb 21 07:53:23 EST 2003
On Friday 21 February 2003 13:01, Location Proj shaped the electrons to
> Im also trying to determine indoor position using signal strength
> values. We are seeing a small fairly predictable variance. Our cards
> are 1.4.2 or 1.4.9 with the ram upload, both give a signal readings of
> between 1 and 100. Id prefer cards that gave a higer resolution but we
> have had good results with these (1-2 meters) so far.
> How high is the variance you are seeing? ours is approx 5 vaues (ie
> 40->45 or 60-65 etc..)
It depends on the antenna, and if your are using diversity ot not, and the
txpower of the transmitters.
By fixing the txpower and enabling just one of the antenna (even if the
card has an external antenna they have a second one, which is not
disabled by default), I've got a variance of 1, with diversity antennas
up to 65.
With variable txpower, you will see a "low frequency" variation.
Check some of the plots in:
The first image in http://mnm.uib.es/~gallir/80211tracking/data3.png
(three different locations) is the signal coming from a Prism2 on a
Windows machine. The second one if from a hostap in master mode.
In http://mnm.uib.es/~gallir/80211tracking/data4.png (four different
locations) I put an external (omni) antenna in the receiver. The fiorst
image is from the same AP as before. The second is from a iBook with
Linux and the kernel airport driver (default configuration).
ricardo galli GPG id C8114D34
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