Received signal strength

Eduard Garcia eduardg at
Fri May 14 05:59:50 EDT 2004

(please, I need help with this) all power statistics returned by iwconfig/iwpriv or stored in
/proc/net/wlan0, etc. are in RSSI format which can be transformed to dBm
using dBmAdjust (multiplying?, dividing?...?). Am I wrong? can I read the value of dBmAdjust and in general, any RID word?
More: the value of CommsQuality is referred to the quality of the signal
received with the AP I'm associated to?

And last: what do you suggest me to do to set the txpower? iwconfig ...
txpower...? iwpriv...writemif? With hostap 0.0.3 version and firmware 1.3.6
should I upgrade to
1.5.6 and install patch from

Please, I need a reference to RID words and mifs
( is broken)!! Or
somebody explain-me.

Sorry, but maybe this is a very-newbie question :((


----- Original Message ----- 
From: "Pavel Roskin"
To: "Christopher Dobbs"
Cc: "Anand S. Katti"
Sent: Monday, May 10, 2004 11:02 PM
Subject: Re: Received signal strength

> On Mon, 10 May 2004, Christopher Dobbs wrote:
> > I dont know about rssi but mabey this
> > will help.
> No, we are talking about conversion between two logarithmic scales, dBm
> and the scale used in the card, known as RSSI (received signal strength
> information).  The table you posted the link to converts between dBm and
> Watts, a linear scale.
> Firmware 1.3.1 and newer has RID 0xfd51 (dBmCommsQuality), which is
> supposed to give the information in dBm.  HostAP uses RID 0xfd43
> (CommsQuality), which uses its own scale.  That scale was also changed in
> 1.3.1 firmware.
> Also, RID 0xfc46 (dBmAdjust) contains a constant that should be used for
> conversion between RSSI and dBm.
> If dBm values are needed, I suggest using dBmCommsQuality instead of
> CommsQuality.  Even then, I don't expect the data to be very accurate, but
> it's probably the best data the card can provide.
> I'm working on a patch for Orinoco driver that would use dBmCommsQuality
> if possible and provide reliable data in its absence.  Once I'm satisfied
> with it I plan to submit similar patch to HostAP.
> > > I have a Harris Semiconductor Prism 2.5 Wavelan Chipset.I want to
convert the
> > > parameter rxdesc->signal into dBm.
> > >Is  (rxdesc->signal-100) the right way to do it?.
> I don't think so.  You can print dBmCommsQuality and CommsQuality to the
> kernel log and try to find the dependency.  I think it should be linear.
> > > Will this conversion hold good even if I am using this card in managed
> > >mode and use an alternate driver like orinoco?
> I suggest that you don't trust drivers too much at this point.  There is
> some work that need to be done before you can trust the drivers, both
> Orinoco and HostAP.  Sorry for inconvenience.
> -- 
> Regards,
> Pavel Roskin
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