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[aprssig] APRS for One-Laptop-Per-Child

Scott Miller scott at opentrac.org
Mon Nov 12 01:20:16 UTC 2007


I have my reservations about the OLPC project as a whole, but as long as 
the hardware is out there, yeah, it would be a good idea to design to it.

The PSK31 link is something I've thought about for disaster response for 
awhile.  I don't know about scaling it to thousands of users, but I 
suppose the main limitation is available spectrum.

The primary purpose of the network I've envisioned would be text 
messaging, both one-to-one and one-to-many, with support for multiple 
levels of traffic priority.

A fixed network of relatively high-powered stations connected by a 
separate backbone (possibly Internet, but not necessarily) would form 
the basis of the system.  Individual stations would function basically 
like two-way pagers, listening during assigned timeslots to determine if 
and when incoming messages need to be received.  Assuming a fixed 3 kHz 
RX passband, you could decode several incoming channels at once (a la 
Digipan).  The coordinating stations would manage uplink channels and 
timeslots to avoid collisions among remote stations.

Assuming a total of 300 bps available for uplink, with reasonable 
compression and allowing for some overhead, you could handle maybe 3000 
messages of 2k bytes each per day if your channel access scheme and 
uplink scheduling are efficient enough to keep it running constantly. 
It might not be instantaneous (especially not for low-priority traffic) 
but waiting an hour or two for a message to get through is better than 
having no connectivity at all.

Scott
N1VG

Bob Bruninga wrote:
> At the AMSAT meeting (or was it DCC?), it was announced that the $100 laptops-per-child mass production gets underway in Novermber for every kid on the planet.  In my mind, this is a UNIQUE opportunity for HAM radio and should be the ham-radio target machine for just about everything we do.
> 
> I can think of no better investment in ham radio, than making sure our stuff can run on these machines.  And thereby get kids involved in HAM radio.  As they come, they have 802.11g wireless for a self-building network from nothing.  Out of the box, they will network, and the ads say, the 802.11 is more powerful than conventional wireless lans.  Ham radio can bring some RF expertise to these networks.
> 
> Because the laptop is supposed to be able to form this peer-to-peer social network throughtout a villiage as is.  We can add some longer links...  Basically it is APRS out of the box...
> 
> My first thought is a USB PSK-31 device that links that laptop, not just to he next hut in the villiage, but can use 5W radios on PSK-31 to reach the world.  I think the target power for the whole laptop is around 1 watt.  So it can be recharged on solar power.
> 
> This thing just jumps out at me as a fundamental building block for ad-hoc emergnecy comms and funn coms and just about everything else we do with ham radio.  Then we overlay on top of that, all the neat things we do in ham radio.  As tom points, out, AMSATS etc.  (And of course APRS) Winlink and all our other EMCOMM toys...
> 
> Of course until they get to the millions of quantities, they are now costing $200 each, and you have to buy two for a total of $400 to get yours (the other one goes to a kid)...
> 
> But its a great way to get one... and start developing code...  Actually get two (4), so you can play both ends...
> 
> WB4APR, Bob
> 
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