hi, here are some suggestions and food for thought (see below for a
"patch" proposal). i appreciate any comments and feedback.
for the FAQ, a better (more detailed and informative) version of the
whitepaper i referred to earlier is actually this:
http://www.connect802.com/download/techpubs/2004/you_believe_D100201.pdf
as far as i can tell, there _are_ some (admittedly vague) guidelines as
to what the "Link Quality" as displayed in iwconfig should be: have a
look at wireless.h and iwlib.c in and Wireless Tools or just man
iwconfig. what various wireless drivers are reporting is a different
issue, but at least one could make an effort to (try to) comply with the
standards set in WExt (IMHO they need to be clarified a bit, though).
what i have to say is mainly based on the current guidelines in WExt and
man iwconfig, and it is restricted to quality stuff. ie, man iwconfig
says:
Link quality
Overall quality of the link. May be based on the level of
con-
tention or interference, the bit or frame error rate, how
good
the received signal is, some timing synchronisation, or
other
hardware metric. This is an aggregate value, and
depends
totally on the driver and hardware.
Signal level
Received signal strength (RSSI - how strong the received
signal
is). May be arbitrary units or dBm, iwconfig uses driver
meta
information to interpret the raw value given
by /proc/net/wire-
less and display the proper unit or maximum value (using 8
bit
arithmetic). In Ad-Hoc mode, this may be undefined
and you
should use iwspy.
Noise level
Background noise level (when no packet is transmitted).
Similar
comments as for Signal level.
FAQ 4.3 states that madwifi currently reports as the link quality RSSI /
noise floor. but RSSI is not measured in dBm, and thus the
interpretation of "20/96" as "An RSSI of 20dBm relative to a noise floor
of 96dBm" is technically incorrect. if i understand Sam (RSSI MAX is 60
or 63) and the whitepaper (Atheros recipe: Subtract 95 from RSSI to
derive dBm) correctly, an RSSI of 20 corresponds to 20 - 95 = -75dBm and
MAX RSSI is 63 (or 60) - 95 = -32dBm (-35dBm). IMHO a more useful (and
currently implementable) specification of "Link Quality" would be
"20/60", i.e. RSSI/RSSI_MAX (or % values, ie scaled to 100, but i prefer
RSSI/RSSI_MAX), but not dBm values.
what the driver really should be reporting, according to my
understanding of WExt (and my own opinion), is the "quality of the
link," which probably should be the "signal quality." the "signal
quality" is very different from the "signal strength" and from SNR
(signal-noise-ratio). while either can in some sense be used to give a
"Link Quality," signal quality is probably the closest to what is meant
by "Link Quality."
signal quality is hard to determine, you need to take into account not
only the noise level, but also the amount of corruption in the
environment between the access point and the client (see above paper for
an excellent discussion of this issue). i understand that getting the
"signal quality" is difficult and probably currently not really
measurable with madwifi (one would have to have a better measure of the
noise, errs/corrupted/discarded packages transmitted, data rates...).
next best to signal quality is signal strength, which is RSSI / MAX
RSSI. given that we _do have_ a relative value, IMHO the driver should
report the RSSI / MAX RSSI value instead of a dBm value as qual. i am
told the ipw2200 driver does augment this value with things like, ie
receive packet errors, link speed, etc. to get a more realistic signal
quality. figuring out an "improved" way of getting eg the qual or the
level would be a future challenge.
in the above example, for quality the driver should be reporting
absolute values:
iq->qual = 20 (=RSSI) and range->max_qual.qual = 60 (= MAX RSSI). as
WExt prefers dBm values (and not RSSI) for level and noise (see below
for WExt specs), what should be reported by the driver (as in
net/ieee80211_wireless.c) is
iq->qual = rssi; /* or some calibrated RSSI value */
if (iq->qual > 63) /* this should be the MAX RSSI ... so it might be 60
for some cards */
iq->qual = 63;
iq->noise = -95; /* noise floor in dBm, should be + real noise (needs to
be determined) */
iq->level = rssi - 95; /* -95 because that converts rssi to dBm. does
noise belong here? */
max values should also be set:
range->max_qual.qual = 63; /* relative, MAX RSSI ... 60 for some cards
*/
range->max_qual.level = -32; /* in dBm, MAX RSSI - 95, = -35 for some
*/
range->max_qual.noise = -95; /* noise floor */
i know this is very crude, but IMHO this would make madwifi get closer
to complying with WExt standards.
Sven
FYI:
/* Quality of link & SNR stuff */
/* Quality range (link, level, noise)
* If the quality is absolu
