RX signal level calculation

don don
Fri Feb 21 16:40:23 PST 2003

It is very difficult to determine the signal strength using a wireless
lan card as a receiver. There is an Intersil (windows) utility that
sends out packets with no gaps between them so that the card is
effectively in continuous transmit mode. This enables signal strength
measurements to be done with any receiver capable of receiving 2.4ghz. I
use a Drake C band converter and a standard vhf receiver with a signal
strength meter for the purpose. But I don't know of a similar utility
that works with linux.

If you use a laptop with a wireless lan card it gives you no information
at all if there is not enough signal to associate. 

Don Magee

On Fri, 2003-02-21 at 12:53, Ricardo Galli wrote:
> On Friday 21 February 2003 13:01, Location Proj shaped the electrons to 
> shout:
> > 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:
> http://mnm.uib.es/~gallir/80211tracking/
> 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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