Re: problem on ACS

[Christian Lamparter <chunkeey@googlemail.com>]

On Tuesday, July 26, 2011 01:35:07 AM Luis R. Rodriguez wrote:
> On Mon, Jul 25, 2011 at 1:32 PM, Luis R. Rodriguez <mcgrof@gmail.com> wrote:
> > On Thu, Jul 21, 2011 at 8:13 PM, MingAnn Ng <devil_eddie01@hotmail.com> wrote:
> >> Hi Luis,
> >>
> >> I am thinking of using the ACS application for channel selection on IBSS
> >> network. I had run a test with the current git. But the result is not so
> >> convincing.
> >>
> >>    10 surveys for 2412 MHz: 11.382248 12.847997 13.223471 13.403065
> >> 13.454694 13.529891 12.556324 13.573309 13.616969 13.645601
> >>    10 surveys for 2417 MHz: 12.678072 10.299560 -inf -inf 9.678072 -inf -inf
> >> -inf -inf -inf
> >>    10 surveys for 2422 MHz: -inf -inf -inf -inf -inf -inf -inf -inf -inf
> >> -inf
> >>    10 surveys for 2427 MHz: -inf -inf 12.192645 -inf -inf -inf -inf -inf
> >> -inf -inf
> >>    10 surveys for 2432 MHz: -inf 9.192645 12.777608 12.192645 12.192645 -inf
> >> 12.192645 -inf 10.093109 12.192645
> >>    10 surveys for 2437 MHz: 11.192645 -inf 11.000000 10.093109 10.093109
> >> 11.192645 -inf 11.192645 -inf -inf
> >>    10 surveys for 2442 MHz: 10.192645 10.093109 -inf 10.061401 11.192645
> >> -inf -inf -inf 11.192645 10.093109
> >>    10 surveys for 2447 MHz: -inf -inf -inf 11.777608 -inf 10.192645 -inf
> >> -inf -inf -inf
> >>    10 surveys for 2452 MHz: 11.192645 -inf -inf 11.192645 -inf -inf -inf
> >> 13.777608 11.337035 10.830075
> >>    10 surveys for 2457 MHz: 10.192645 -inf -inf -inf -inf -inf -inf -inf
> >> -inf -inf
> >>    10 surveys for 2462 MHz: 9.540568 9.192645 10.283793 8.476438 -inf -inf
> >> -inf -inf 10.192645 -inf
> >>    10 surveys for 2467 MHz: -inf -inf -inf -inf -inf -inf 9.752072 -inf -inf
> >> -inf
> >>    10 surveys for 2472 MHz: -inf -inf 10.192645 -inf -inf -inf -inf -inf
> >> 7.714598 -inf
> >>    10 surveys for 5180 MHz: 2.000000 1.830075 1.000000 0.678072 2.000000
> >> 2.000000 2.000000 0.678072 2.000000 2.000000
> >>    10 surveys for 5200 MHz: 2.000000 1.678072 2.000000 2.000000 2.000000
> >> 2.000000 1.678072 2.000000 0.678072 0.678072
> >>    10 surveys for 5220 MHz: 2.000000 1.415037 2.000000 0.000000 2.000000
> >> 2.000000 1.678072 2.000000 2.000000 2.000000
> >>    10 surveys for 5240 MHz: 3.000000 3.000000 3.000000 1.245112 3.000000
> >> 3.000000 3.000000 2.678072 2.000000 3.000000
> >>    10 surveys for 5260 MHz: 3.000000 2.000000 3.000000 3.000000 3.000000
> >> 3.000000 2.000000 2.678072 2.000000 2.678072
> >>    10 surveys for 5280 MHz: 3.000000 1.415037 3.000000 1.415037 1.678072
> >> 2.000000 1.245112 3.000000 3.000000 2.678072
> >>    10 surveys for 5300 MHz: 3.000000 3.000000 3.000000 1.415037 3.000000
> >> 3.000000 3.000000 2.000000 3.000000 3.000000
> >>    10 surveys for 5320 MHz: 3.000000 3.000000 3.000000 3.000000 3.000000
> >> 2.678072 3.000000 1.415037 3.000000 2.000000
> >>    10 surveys for 5500 MHz: -1.000000 -2.000000 -1.000000 -2.321928
> >> -1.321928 -1.321928 -1.000000 -2.321928 -1.000000 -2.459432
> >>    10 surveys for 5520 MHz: -2.392317 -1.169925 -1.169925 -0.807355
> >> -1.906891 -1.169925 -1.169925 -1.169925 -1.700440 -0.807355
> >>    10 surveys for 5540 MHz: -1.169925 -2.643856 -1.169925 -2.087463
> >> -1.169925 -1.169925 -2.523562 -1.169925 -1.169925 -1.169925
> >>    10 surveys for 5560 MHz: -1.169925 -1.169925 -2.643856 -1.169925
> >> -1.321928 -1.169925 -1.459432 -1.700440 -2.087463 -1.169925
> >>    10 surveys for 5580 MHz: -1.169925 -1.700440 -1.169925 -1.906891
> >> -1.321928 -1.169925 -1.169925 -1.169925 -1.169925 -1.169925
> >>    10 surveys for 5600 MHz: -1.169925 -1.169925 -1.169925 -2.643856
> >> -0.807355 -2.459432 -1.459432 -1.169925 -1.169925 -1.169925
> >>    10 surveys for 5620 MHz: -1.169925 -1.321928 -2.087463 -1.169925
> >> -1.169925 -1.321928 -0.807355 -2.392317 -1.169925 -1.169925
> >>    10 surveys for 5640 MHz: -2.643856 -1.321928 -1.169925 -2.857981
> >> -1.169925 -0.584963 -1.169925 -1.169925 -1.169925 -3.643856
> >>    10 surveys for 5660 MHz: -2.169925 -1.584963 -2.169925 -2.857981
> >> -1.169925 -1.169925 -1.169925 -1.169925 -1.459432 -1.169925
> >>    10 surveys for 5680 MHz: -1.169925 -1.169925 -2.643856 -2.700440
> >> -1.169925 -1.169925 -1.169925 -1.169925 -0.807355 -1.700440
> >>    10 surveys for 5700 MHz: -2.087463 -1.169925 -1.169925 -1.000000
> >> -2.459432 -1.169925 -1.169925 -1.169925 -1.169925 -1.169925
> >> 2412 MHz: 13.123357
> >> 2417 MHz: -inf
> >> 2422 MHz: -inf
> >> 2427 MHz: -inf
> >> 2432 MHz: -inf
> >> 2437 MHz: -inf
> >> 2442 MHz: -inf
> >> 2447 MHz: -inf
> >> 2452 MHz: -inf
> >> 2457 MHz: -inf
> >> 2462 MHz: -inf
> >> 2467 MHz: -inf
> >> 2472 MHz: -inf
> >> 5180 MHz: 1.618622
> >> 5200 MHz: 1.671229
> >> 5220 MHz: 1.709311
> >> 5240 MHz: 2.692318
> >> 5260 MHz: 2.635614
> >> 5280 MHz: 2.243133
> >> 5300 MHz: 2.741504
> >> 5320 MHz: 2.709311
> >> 5500 MHz: -1.574714
> >> 5520 MHz: -1.346398
> >> 5540 MHz: -1.544436
> >> 5560 MHz: -1.506274
> >> 5580 MHz: -1.311873
> >> 5600 MHz: -1.438962
> >> 5620 MHz: -1.378062
> >> 5640 MHz: -1.690221
> >> 5660 MHz: -1.609185
> >> 5680 MHz: -1.487164
> >> 5700 MHz: -1.373637
> >> Ideal freq: 2417 MHz
> >>
> >>
> >> The ideal channel is 2417MHz. But there are many interference in 2.4G at my
> >> testing place. the result for that channel is -inf.
> >
> > Right..
> >
> >> I did not understand the
> >> outcome, maybe you can describe about -infinity and why that this result
> >> occurs.
> >
> > Sure, so -inf means the calculation resulted in a value out of bounds
> > by the used data type. The issue lies in the wide range of values that
> > we run into for analysis in very noisy environments. One alternative I
> > considered was to use __float128 instead of long double for the
> > interference_factor but I was unable to figure out how to print these
> > correctly.
> >
> >> will it be causing by scanning time for particular channel is too
> >> short?
> >
> > Can you test with the latest ACS patches I posted for hostapd with
> > debugging and see the values you get there?
> 
> Or you can try to split up the computation by using logarithm
> identities as follows:
> 
> 
> diff --git a/survey.c b/survey.c
> index ef47f95..13defc8 100644
> --- a/survey.c
> +++ b/survey.c
> @@ -274,10 +274,9 @@ static long double
> compute_interference_factor(struct freq_survey *survey, __s8
>  {
>         long double factor;
> 
> -       factor = survey->channel_time_busy - survey->channel_time_tx;
> -       factor /= (survey->channel_time - survey->channel_time_tx);
> -       factor *= (base_to_power(2, survey->noise - min_noise));
> -       factor = log2(factor);
> +       factor = log2(survey->channel_time_busy - survey->channel_time_tx);
> +       factor -= log2(survey->channel_time - survey->channel_time_tx);
> +       factor += survey->noise + min_noise;
							^^^^^ that "+" should a "-" right?

btw, base_to_power can go as well. [now if only acs would stop freezing]

Regards,
	Chr