[OZAPRS] APRS HF beacon rates

[Robert Bruninga]

>>> amcdade at iprimus.com.au 07/08/06 8:33 PM >>>
>I think perhaps we need to look at creating a standard set 
>of options for those people running Smart beaconing 

Actually, I hope that future designs will consider Proportional
Pathing option instead.  It doesnt have as many potential set-up 
errors, and actually reduces the load on the network.

http://www.ew.usna.edu/~bruninga/aprs/ProportionalPathing.txt

If the user selected (in the USA) PROPORTIONAL PATHING = 2, 
Here is what he would get every minute:

- Except as below, each packet goes DIRECT path (no digi)
- Every 2nd minute it would use the WIDE1-1 path
- Every 4th minute it would use WIDE1-1,WIDE2-1

If set PROPORTIONAL PATHING = 3 he would get the above plus
- Every 8th minute it would use WIDE1-1,WIDE2-2

If he set PROPORTIONAL PATHING = 4 he would get the same 
plus a 4 hop path once every 16 minutes, WIDE1-1,WIDE3-3 
and so on.  Though in the USA, nothing greater than 3 would 
ever be recommended for routine ops.

DECAYED BEACONING:  Also, APRS was never designed for 
fixed rates.  The design was that only new-changed data was 
transmitted now, and that if the data did not change, then 
the time to the next transmission of that data would double.  
So, for positions for example, set to a 1 minute rate, if the 
mobile stopped for any reason, then the next packet would 
go out 2, then 4, then 8 then 16 and then 30 minutes 
later.  As soon as the position changed (new data) then the 
rate was reset back to the selected rate (1 minute).  Too 
many APRS clones and follow-on devices simply used fixed 
rates for simplicity even when the data is not changing.

Trackers should compare position data, and if unchanged, 
double the period to the next packet (to a max of 30 mins).
If changed, go back to the initial rate.

RESULTS of PROPORTIONAL PATHING AND DECAYED BEACONING:
The result is that for close in work or meeting someone or local 
events  or whatever, the tracker gets good smooth high rate 
tracking (1 minute for example) and minimum QRM to anyone 
else.  For the local area (each  digi he can hit), he gets a 
comfortable 2 minute rate.  For a region and  those watching 
out 2 hops, he gets a 4 minute rate.  And for observers
a long distance away, he gets an 8 minute rate.  And with 
decayed algorithm, if he stops, he also generates less QRM too.

This resolves the tradeoff between too high a rate (QRM)and 
too low a rate (LATENCY, and LOW TRACK QUALITY)...

PROPORTIONAL PATHING / Decayed Beaconing would cut the 
QRM from each  mobile by a factor of 8 or more while moving, 
and 30 to 1 when stopped.  And since mobiles are the largest 
load on the network, this would make a HUGE difference to 
the network while still providing good  local tracking.

HUMAN INTERFACE:

The options for setting up a mobile APRS unit (tracker) in 
my opinion  should be a menu where the user enters the path 
for each period, something like this.  These would be the 
defaults.

15 sec path*:  none            (means none transmitted)
30 sec path*:  none      
 1 min Path*:  DIRECT          (transmitted but no path)
 2 min Path:   WIDE1-1         (might be RELAY in Europe)
 4 min Path:   WIDE1-1,WIDE2-1
 8 min Path:   WIDE1-1,WIDE2-2
16 min Path:   none
32 min Path:   none

Decay when stopped   ON

If the user selects anything other than "DIRECT" in the 
first three, then he gets a "QRM.  ARE YOU SURE?" WARNING.  
He also gets it if he sets any path with 3 or more hops in it.

This is just a continuation of the original APRS decay-algorithm 
which causes older duplicate packets to be transmitted less and 
less often and new data to be updated quickly.  In the case with 
Proportional Pathing, it makes NEAR data more important than 
FAR data as well as NEW data versus old duplicate data.

Also, since the WIDE1-1,WIDEn-N should work everywhere, this 
one-size-fits-all appproach would make setting up a mobile 
tracker trivial, and help make the network immune to user 
set-up errors.

de WB4APR, Bob

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