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[aprssig] APRS needs...

Scott Miller scott at opentrac.org
Tue May 27 01:59:22 UTC 2008

I *really* don't like the idea of just moving traffic to 9600 baud 
without implementing some kind of intelligent channel access scheme. 
ALOHA just isn't going to cut it for efficient channel utilization.

It's a really nasty problem in APRS because the links are more 
asymmetrical than you normally find in mobile mesh networks, the hidden 
transmitter problem is worse, and many nodes are highly mobile.  You 
can't rely on any consistent central coordination (like the cellular 
network), but I think there are still a lot of possibilities.

Just switching to slotted ALOHA based on GPS time synchronization would 
effectively double the capacity of the network.  If wide digis could be 
configured to give some 'hints' about time slot availability, even in 
areas of overlapping digi influence and where they might not be 
coordinating with each other, you'd still be better off than with no 
coordination at all.

I haven't kept up on the literature in a couple of years, and I'm sure 
more work has been done in the field.  I'll have to catch up at some point.

But back to the $99 laptop thing - I don't see fitting a transceiver and 
TNC in a volume much smaller than a deck of cards, so I don't think an 
internal device is really an option.  Not to mention some potential 
interference issues with cheap consumer electronics.  Maybe some kind of 
backpack unit to clip on would be workable...


Tom Hayward wrote:
>> For a while, I was getting into hacking the ZipIt IM
>> device.
>> http://www.linuxdevices.com/articles/AT8107883197.html
>> Decent sized graphic PCD, QWERTY keyboard, built-in
>> Wifi and even has a serial port with the addon of an
>> ST202 IC.  The really cool part...it runs on embedded
>> linux.  However, I am too crummy of a programmer to do
>> anything with it on my own.
> Cool. If someone can pack a VHF or UHF 9k6+ data transceiver and a GPS
> into this package, I'll write the software. I'm not sure if APRS is
> worth implementing though. I could talk to Scott about an Opentrak
> implementation. I'm working solo on an embedded linux project at work
> so I'm getting very familiar with this type of programming.
> In response to "build it and they will come": APRS is already
> saturated in my area. 1200 baud is a no-go for any new device. The UHF
> network at 9k6 seems to have plenty of growing room, but I wouldn't
> want to encourage any growth on 144.390. I already can't get packets
> out with portable trackers.
> Tom KD7LXL
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