On Thursday 03 April 2008 04:27:31 Luis R. Rodriguez wrote:
> > so in the "unspecified" case we really don't know much about the units,
> > in the worst case we can't even assume that 1/2 the value will mean 1/2
> > of the received signal strength. it's very hard to work with this values,
> > but it's better than nothing.
> >
> > other cards might not have noise, so no absolute (dBm) measurement, but
> > a form of RSSI which is measured in dB (that is a logarithmic
> > difference). in this case we might not know which reference point the
> > measurement is taken to, but we know how it behaves: -3 dB means half of
> > the signal strength. if you add a 6dB gain antenna you can expect to see
> > the signal reading to increase by 6dB. it's not strictly SNR (because we
> > don't know the noise) but quite close to it.
> >
> > i think it's important to know the difference between this 3 cases i
> > order to make some sense of the values in userspace gui, roaming agents,
> > mesh link metrics, etc...
>
> Agreed, but can you give me an example of a card which does provide
> RSSI in db for values we don't know and that UNSPEC cannot handle? Is
> this what is assumed of the rt2x00 cards?
i currently assume that for rt2x00 and zd1211 cards - but i'm really just
guessing here. feedback from driver authors or people who have more knowledge
about the hardware would be greatly appreciated!
here's the current table:
DRIVER SIGNAL MAX NOISE QUAL
-----------------------------------------------------------------
adm8211 unspec(?) 100 n/a missing
at76_usb unspec(?) (?) unused missing
ath5k dBm dBm percent rssi
b43legacy dBm dBm percent jssi(?)
b43 dBm dBm percent jssi(?)
iwl-3945 dBm dBm percent snr+more
iwl-4965 dBm dBm percent snr+more
p54 unspec 127 n/a missing
rt2x00 percent rssi+tx/rx frame success
rt2400 dB(?) 100 n/a
rt2500pci dB(?) 100 n/a
rt2500usb dB(?) 100 n/a
rt61pci dB(?) 100 n/a
rt73usb dB(?) 100 n/a
rtl8180 unspec(?) 65 n/a (?)
rtl8187 unspec(?) 65 (?) noise(?)
zd1211 dB(?) 100 n/a percent
bruno
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