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[aprssig] ALOHA Circle Calculation

Bob Bruninga bruninga at usna.edu
Mon Aug 2 13:06:21 UTC 2010


> ... [the ALOHA circle] is the circle that contians 
> a FULL [APRS channel].

> Thanks Bob... well, using Visual Basic 6.0, I...
> calculate the distance from my station to each of
> the stations heard [that] transmits a POSIT packet.
> I can sort them in ascending order [of distance]...
> ...I total them into Mobiles, Weather, Digi's and 
> Home stations... From there, the directions in
> your algorithm get blurry...

Ah, now the fun begins.  You want to know how many packets each of those stations puts on the network per 30 minutes.  So we assume 2 for a home station, 6 for WX, 3 per digi and so on (this is from memory so I may not have exact numbers here).  

Then we need to know how many copies each of those generates.  So we start at own-station and go outward.  Multiply each station's number by 1 until you get to the first digi.  From then on, multiply each stations numbers by 2, and so on until the third digi, multiply by 3 and so on.  Once  this total number reaches 1800, (30 minutes of seconds), then the channel is 100% saturated.

That range defines the aloha circle.

>   Now, when you say, "digi-copies" (variable of "c"
>   initialized to 1), do you mean to count any packet
>   that was digipeated as opposed to a packet
>   heard"direct" and then of course, increment "c"
>   accordingly? 

No,  you increment C only when you get to another digi as you work outward in range down the list.

Bob, WB4APR




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