Re: problem on ACS

On Mon, Jul 25, 2011 at 1:32 PM, Luis R. Rodriguez [off-list ref] wrote:

quoted

On Thu, Jul 21, 2011 at 8:13 PM, MingAnn Ng [off-list ref] wrote:

quoted

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..

quoted

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.

quoted

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;