From: M. Thomas Eastham <god@an...> - 2001-12-13 23:44:21
So what you guys are saying is that I can turn my cisco card into a
wattmeter? Anybody worked on this and negated to need for a $300+ Bird 43?
[mailto:aironet-admin@...]On Behalf Of Jean Tourrilhes
Sent: Thursday, December 13, 2001 4:52 PM
To: Aironet mailing list
Subject: [Aironet] Re : Understanding reported signal strength
Douglas S. J. De Couto wrote :
> 2) Signal quality (SQ)
> This is ``The SQ of the DSSS PHY PN code correlations''.
We have that with the old Wavelan driver. It works only with 1
and 2 Mb/s rate and is totally useless as a quality indicator (I've
only ever seen the max value).
I believe everybody has forgotten about that in new hardwares.
> I have seen two or three techniques shown on the list this month:
> 1) (posted by someone who was reading intersil docs)
> dBm = 100 - RSSI
Please don't assume that Intersil and Aironet are the same
beast, the Intersil and Aironet firwares are *very* different, so it
is expected for each hardware to do the translation differently.
With Wireless Extensions, the responsability of doing the
conversion from the raw value from the hardware to dBm is left to the
driver. Therefore, the values shown by "iwconfig" are dBm and you can
use them without worrying about the hardware (which is the whole point
of Wireless Extensions).
> 2) (derived by Javier? by observing the ACU program)
> dBm = (RSSI' / 2) - 95
> where RSS' = RSSI / 255 (i.e. convert to percentage)
> 3) posted by Javier
> Lookup dBm <-> RSSI conversion in firmware table where available.
Was discussed on the list earlier. The second method is more
accurate, the first is a good aproximation.
> Okay, finally, can I turn the ``quality'' number into a S/N ratio, and
> use it together with the signal strength to get a noise estimate?
If it was possible, Javier, that does an excellent job on the
driver, would have already done that and iwconfig would report the
My understanding is that ``quality'' is an agregate indicator,
factoring various different stats (like signal strength, missed
beacons and others).
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