Re: [PATCH] wl12xx: Increase scan channel dwell time for passive scans

[Juuso Oikarinen <juuso.oikarinen@nokia.com>]

On Mon, 2011-01-17 at 14:33 +0200, ext Kahn, Gery wrote:
> Does it worth to have different value for 5GHz?
> 

I guess the 100ms value benefits 2.4GHz passive scanning as well, does
it not? In 2.4GHz band there are usually very few channels passive
scanned (mostly channels 12 and 13 in the 00 region) so the cost of this
increased wait time is quite little.

-Juuso

> On Mon, Jan 17, 2011 at 13:32,  <juuso.oikarinen@nokia.com> wrote:
> > From: Juuso Oikarinen <juuso.oikarinen@nokia.com>
> >
> > The passive scan channel dwell time currently used is 30ms-60ms. A typical
> > beacon interval for AP's is 100ms. This leads to a ~30% worst-case probability
> > of finding an AP via passive scanning.
> >
> > For 5GHz bands for DFS frequencies passive scanning is the only scanning
> > option. Hence for these, the probability of finding an AP is very low.
> >
> > To fix this, increase the passive channel scan dwell times (also the early
> > leave value, as 5GHz channels are still typically very silent.) Use a value
> > of 100ms, because that covers most typical AP configurations.
> >
> > Based on testing the probability of finding an AP (102.4ms beacon interval) on
> > a single scan round are as follows (based on 100 iterations):
> >
> > dwell min/max (ms)   | probability
> > ---------------------+------------
> > 30/60                | 35%
> > 60/60                | 56%
> > 80/80                | 77%
> > 100/100              | 100%
> >
> > Total scan times now and after the change:
> >
> > Region | Before (s) | After (s)
> > -------+------------+----------
> > 00     | 0.77       | 1.48
> > FI     | 0.95       | 2.01
> > US     | 0.91       | 1.76
> >
> > Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
> > ---