On Fri, Feb 04, 2005 at 11:10:46AM -0500, Dan Williams wrote: > On Fri, 2005-02-04 at 10:53 -0500, Sven wrote: > > iwlib.c in WEXT says (in the example) > > * 2) value is -54dBm. noise floor of the radio is -104dBm. > > * qual->value = -54 = 202 ; range->max_qual.value = -104 = 152 > > i'm confused. why is the max value the noise floor??? in Atheros chips, > > given the value in dBm comes from RSSI, should max_qual.value not be > > MAX_RSSI (converted into dBm)? > > I think this is actually wrong... What I _think_ it should say is: > > * 2) level is -54dBm. noise floor of the radio is -104dBm. > * qual->level = -54 = 202 ; range->max_qual.noise = -104 = 152
Doh ! Stupid bug ! You are right. > Noise levels _do_ change dynamically, which is something else that the > drivers don't do (ahem, atmel, madwifi, and airo for starters). When > you turn on your microwave, that totally screws the 2.4GHz frequency > range and impacts 802.11 communications. Since the microwave is random > energy, it is extra noise and therefore decreases the Signal to Noise > ratio (ie, the noise value increases, say from -95dBm -> -85dBm, due to > the extra energy from the microwave, while the signal may stay the > same). Yes. > You _always_ have a noise floor, which is the normal value where in good > conditions the card can no longer distinguish the usable radio energy > from background energy, but most drivers at this time use that noise > floor level in the "qual.noise" field and not the "max_qual.noise" > field, because they evidentally don't sample noise on each channel > dynamically, or don't know how to pull that value off the card. You are correct about the definition of noise floor. This is a characteristic of the radio and the frequency band, and usually in the spec (you can't read it from the hw). I don't believe any driver use the noise floor in qual.noise, that would not make sense. > Jean: can you give some clarification on that statement in iwlib.c? MAX_RSSI converted to dBm is some totally uninteresting value. It's going to be close to 0 dBm, and a value that has nothing much to do with real operation but just an arbitrary limit on the A->D converter used for RSSI sampling. On the other hand, MIN_RSSI is very relevant, so that's why we use that. > Dan Jean _______________________________________________ NetworkManager-list mailing list NetworkManager-list@gnome.org http://mail.gnome.org/mailman/listinfo/networkmanager-list