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[aprssig] Fundamental APRS capacity

Robert Bruninga bruninga at usna.edu
Mon Oct 4 13:35:50 UTC 2004


>>> needhame1 at plateautel.net 10/4/04 9:55:57 AM >>>
>> > Here is the algorithm to exactly (in real time) determine what
>> > the ALOHA circle range is for any user:
> >
>>Great explanation, and the algorithm seems reasonable, 
>>but... How do you use this information to come up with
>>a reasonable path.  Should it be 'RELAY, WIDEC-C'?

>1.  If there's a hamfest in your area, do you shorten your path to 
>fit the closest 60 stations?  What if there are 60 hams using 
>APRS in the  lot next door?

Yes, to be good stewards of the channel, then shorten your
path.  If there are 60 people in one mile of you then the
1200 baud channel will be totally saturated within that one
mile.  Hence, no one can expect any form of reliable 
cpommunications beyond that area and should reduce their
path (QRM) for everyone's benefit.

>2.  I notice that when I look at [the nearest 40 stations]
>http://www.findu.com/cgi-bin/near.cgi?call=KD5XB-2 
>a number of those stations are in Amarillo, but we don't 
>have a  path to Amarillo.  How do we adjust for this?  

PHG, Aloha, the APRSdos HOPS display, the FINDU "nearest"
displays are all tools to help the user evaluate his channel 
situation.  There is no magic "right answer".  But the user 
should be using these to be constantly aware of the network
channel situation in his area...

Amarlilo may be un-linkable, but the digis you are trying to use 
in your area might probably hear those packets and so they 
do contribute to the channel loading in your area even if
not reliably decodable.  Maybe they dont.  In that case, it 
looks like your ALOHA circle is over 90 miles.  This is good
news to most people.

>Surely I'm not the only one in the country in this situation.  

Right  Everyone is in a different situation.  Hence they should
use the tools to properly assess that local situation...

>(I guess the algorithm Bob posted operates on packets 
>received, right?)

Yes, so I have APRSdos re-compute an ALOHA circle at any
time the user wants to see his usable range by just hitting
three keys.   This is because during commute hours there
are more mobiles and this loads the channel heavily...

de Wb4APR, Bob





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