Am 18.12.2019 um 03:37 schrieb Ben Greear:
On 12/17/2019 06:12 PM, Sebastian Gottschall wrote:
i dont know what you want to compare here.
1. you compare 2 different wifi chipsets. both have different
sensititivy and overall output power spec
2. both have different amount of antenna chains. which does make a
difference in input sensitivity
3. the patch ben made has no effect on qca9880 chipsets. it only
takes effect on 10.4 based chipsets like 9984
The part of my patch that sums secondary frequencies should apply to
wave-1 as well, but I have
not verified that yet.
yeah. right. sorry i was just looking at total signal sum which uses
rssi_comb_ht
about noise floors in general. noise floors of -108 are bogus. there
is a physical limit a noise level can be.
since drivers like ath9k are doing a cyclic calibration, the noise
value might indeed change. but this calibration is
not running in realtime. its cyclic. i'm not aware if chipsets like
qca988x are going the same way, but since qca988x
has sime similaries with ath9k chipsets unlike the newer 9984
variants, it could be. the 30 seconds mentioned
in the bug report fits to my expectations of the early noisefloor
calibration which has a short delay and after success
turning to use a long delay. anyway. in this early calibration phase
signals might change and will stabilize after. this isnt a issue
since your connection will work anyway even if it might take a little
bit longer if you have poor signal levels
@ben. am i wrong or what do think?
I don't know enough about how the noise floor calculations are done or
how the apply to settings
to know the answer.
I will be happy in general if ath10k wave-1, wave-2, and ath9k report
similar RSSI for similar
setups.
that will not work. you compare different chipsets and depending on the
implementation by the card vendor
rf sensitivity can be very diffent. the same goes for output power.
some
vendors are using additional rf amps
for enhancing output power (ubiquiti is best example here). this these
amps also may have influence to sensitivity.
on these cards you set 10 db output power, but in fact it outputs 18
db.
so there is a bias offset on these cards or devices. (the offset is
depending on the device model)
what you measure is what the chip receives, but not what was lost on
the
pcb layout. (or was even generated in case of noise)
and when it comes to calibration data. correct would be if each
individual card is calibrated before shipment. in reality manufactures
are doing calibration on a single reference card and clone it on all
following cards to save time. the result depends on day or week of
production
and current position of the moon and sun. errors of +- 2 db are common
here. (this is not a fact for all card or device vendors)
If you look at the tx-rate-power table in ath10k, for instance, you
can see different MCS are transmitted
at different signal levels. So, some change from initial conditions
might be because higher MCS is
being transmitted after rate-ctrl scales up?
yes. this is modulation related. as higher the rate goes as lower the
power will be. thats princible of QAM.
and the rate control itself isnt signal but error rate based. so high
packet loss triggers the rate control to lower the rate which results
in increased output power and vice versa. but as mentioned. at card
startup a noise floor calibration starts which may succeed or fail.
if it succeeds it will turn into a long delay phase. so cyclic
calibration. the calibration time is exactly 30 seconds (minimum)
and if
it fails it can
exceed to 60 seconds. after that time it will sleep for 300 seconds and
will check for recalibration conditions. (there are rules like high
noise floor changes etc.)
a recalibration is also triggered at channel changes and if chipset
temperature changes at a certain level.
from what i have seen the procedure in the qca9880 firmware is exactly
the same as in ath9k.
anyway. while this calibration is running, the signal and noise floor
might be unstable or even bogus until this is finished and rate control
might not be optimal
under stress conditions like long range links with low signals. with
standard wifi usage you should not notice it that much since signal to
noise ratio is high enough anyway
Lots of moving parts...
Thanks,
Ben
Sebastian
Am 18.12.2019 um 00:37 schrieb Tom Psyborg:
also noticed now that the noise floor changes with signal
strength as
described in this bug report:
https://www.mail-archive.com/ath10k@lists.infradead.org/msg11553.html
after wifi restart
iwinfo:
signal: -59dBm noise: -108dBm
then goes to
signal: -52dBm noise: -103dBm
and finally drops to
signal: -59dBm noise: -103dBm
