>
> On Fri, Dec 06, 2019 at 02:27:47PM -0800, Matthew Wang wrote:
> > We saw that on certain platforms in certain places we keep switching
> > between two APs and eventually get the same RSSI.
> > Debugging showed that we have a very big difference between the two
> > antennas.
> >
> > Ant A can hear AP A very well (-60) but AP B very bad (-80) Ant B can
> > hear AP B very well (-60) but AP A very bad (-80)
> >
> > When the device associates to AP A, it'll learn to use Ant A.
> > If the device uses one single antenna to receive the scan results, it
> > may hear the AP it is currently associated to on the second antenna
> > and get bad results. Because of that, the wpa_supplicant will roam to
> > the other AP and the same scenario will repeat itself:
> >
> > Association to AP A (Ant A reports -60).
> > Scan on Ant A: AP A: -60, AP B: -80
> > Scan on Ant B: AP A: -80, AP A: -60 ==> ROAM.
> >
> > Association to AP B (Ant B reports -60) Scan on Ant A: AP A: -60, AP
> > B: -80 ==> ROAM
> >
> > Etc...
> >
> > Fix this by querying the signal of the current AP using
> > drv_signal_poll() instead of relying on the signal that we get from
> > the scan results.
>
> Thanks, applied with some cleanup.
>
> > diff --git a/wpa_supplicant/events.c b/wpa_supplicant/events.c
> > +static int wpas_get_snr_signal_info(const struct wpa_signal_info *si)
> > +{
> > + int noise = IS_5GHZ(si->frequency) ?
> > + DEFAULT_NOISE_FLOOR_5GHZ :
> > + DEFAULT_NOISE_FLOOR_2GHZ;
> > +
> > + /*
> > + * Since we take the average beacon signal, we can't use
> > + * the current noise measurement (average vs. snapshot),
> > + * so use the default values instead.
> > + */
> > + return si->avg_beacon_signal - noise; }
>
> This use of hardcoded default values resulted in significant increase in
> undesired roaming in my test setup since the driver-reported noise floor was
> about 5 dB lower than the hardcoded values and that resulted in the current
> BSS being seen as significantly worse than another BSS that had the same
> signal level. That comment does not sound correct either since the noise
> floor from the driver is likely to be from some kind of calibration operation
> and not an instant snapshot. As such, I applied another change to use the
> noise floor value from the driver, if available, and use those default values
> only if the driver does not report a noise floor value.
>
Fine by me. I have to say that I can't remember all the details, but I do seem to remember that our device doesn't support the SURVEY command which means that I couldn't check that on our devices.
Thanks for fixing this!
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