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Peer-to-Peer Cellular
Phos writes: "A cool article over at the O'Reilly Network outlines a possible solution to cellular network outages in the event of an emergency. A P2P SMS technique where individual handsets act as autonomous SMS relays."
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No way! your battery would die within minutes... Think about how much SMS messaging there is, and imagine your phone relaying just 0.01% of that. That would be about 10 messages a minute... Sending and receiving, with verification packets to boot... Battery life would drop big time on any phone implementing this scheme.
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Programming is like sex... Make one mistake and support it the rest of your life.
This article examines the task of creating a wireless communication system that can survive a catastrophic failure, and still provide basic communication services to its users.
It's called Amateur or 'ham' radio - every year they have an event called 'field day' which is an exercise in taking your gear out and operating on generators, etc. 2 Meter handy talkies can work thru a repeater or direct simplex (peer-to-peer) if the repeater is down.
I'll never forget listening to a ham during hurricane floyd, w/o power, operating on emergency backup power, 80 meter band, crouched in his garage on the NCarolina cost reporting the fierce winds in the night.
try { do() || do_not(); } catch (JediException err) { yoda(err); }
It is called a Mobile Ad-hoc Network (manet) and the IETF has a working group which has come up with some protocols and such.
. ht ml
http://www.ietf.org/html.charters/manet-charter
The first based on the way cellular systems work. The major cost of the system is centred in those parts of the network that are shared between the users, namely the base stations. This makes the handsets (which each user must have) cheaper and thus lowers the system cost by sharing the cost of the expensive parts between users. Great, but why is that relevant? It is relevant because the maximum range between a cell and a base station is primarily determined by the low noise (read: expensive) receiver and high power (read: expensive) transmitter at the base station. So the range of cell-to-cell communication will be MUCH less than the base station-to-cell range. So much so that it is possible that the distance between a cell that can see a base station and a cell that can't will be no more than a few metres. This means that a large number of hops will be required in most cases clogging up the system bandwidth and meaning that each cell will need to be able to store a large number of messages. These problems will be even worse in an emergency when everyone and their dog are sending messages. Also, cell-to-cell communication will require much more power from the cell than base station-to-cell communication because the reciever in a cell is not nearly as good as that in a base station.
The second problem has to do with battery life. The battery life of cell phones is rather short when the transmitter is used. As explained previously, the power needed for cell-to-cell communication is rather high, aggravating the problem. This could cause major problems when people's batteries start going flat because the person in the next office likes sending lots of messages and is out of range of a base station (quite possible in buildings).
I think this is a great suggestion, but it assumes that the cellular environment is the same as the internet, which it is not.
Interested readers should probably read A Performance Comparison of Multi-Hop Wireless Ad Hoc Network Routing Protocols to find out why this is difficult.
According to the article, phones would have to exchange and update their routing information all the time, even while everything was working normally (because by definition a phone can not know if a neighboring base station that's just out of reach is still working or not). Every phone would continuously keep broadcasting a list of every other phone and base station in it's reach.
This overhead alone (just to update the routing tables) would consume a big chunk of the bandwith all the time. Since a base station dropout or overload is an exception (hopefully), a dynamic on-demand routing protocol would make much more sense in this case.
Idempotent operation: Like MS software, wether you run it once or often, that doesn't make it any better.
Wow, a network that would still be on after a major disaster... Noone has ever thought about that I'm sure.n d. htm
s ed .html
l #a dhoc_software
e se arch/routes-sigmobile/sigmobile/
Oh but wait, maybe the army is not that bad after all:
http://www.mitre.org/pubs/edge/november_98/seco
and maybe there is something called ad-hoc networks. And maybe it's actually not that easy at all to implement in the real world:
http://citeseer.nj.nec.com/mcdonald99mobilityba
http://www.ee.cornell.edu/~haas/wnlprojects.htm
http://www.cs.ucla.edu/NRL/wireless/papers.html
http://nelson.www.media.mit.edu/people/nelson/r
Moral of the story. Not everything that is on O'reilly's website is gold. And for the author of the original article, he should really do some research before he claims he has a brand new idea that is "so cool..." he'll look less foolish next time!
I think I recall this ....
Typical cellphones are a few hundred milliWatts.
A tower can punch out power (in some cases) up to 60 Watts or more, though it doesn't usually.
At least that was how it worked for cell data systems such as CDPD. Cellphones are probably analogous. I think when they try to either acquire a channel or when they are broadcasting, they can amp the power up (I'm not sure quite at what starting level they use) up to 200 or 300 mW max. If you have one of the in-car systems, you can go up to 2 or 3 W. (Considerable increase in range, and the big ass antennae helps receiving fainter signals). Towers can pretty much always reach a phone that can reach them. Usually it is the phones returning signal that drops below the noise threshold rather than the signal from the tower.
FYI... (from memories a couple or four years old).
Tomb
-- Mal: "Well they tell you: never hit a man with a closed fist. But it is, on occasion, hilarious."
No, it doesn't. Rather than try to explain why not, I suggest you read Ad Hoc Networking by Charles Perkins (editor) or the papers and references from the IETF MANET working group, or some of the stuff from CMU or Cornell. In short, an end-node usually only needs to know about its immediate neighbors, plus a modest amount of information regarding location (either physical or abstract).
Absolutely not.
Wrong again. Both end-to-end and in-network retransmission and acknowledgement can be used to prevent such loss even in the face of multiple failures. That's just basic networking, not even specific to mobile networks.
The problems you mention are real, but don't assume that solutions do not or cannot exist just because you weren't able to see them after a few minutes' worth of independent thought. Some pretty bright people have been working on them for twenty years or more, not without success, and before you assume "it won't work" you owe it to yourself to find out whether you've been proven wrong already.
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Your battery life transmitting SMS messages should be no worse than simply being out of contace with a tower.
If you have lost connection to the main network, then battery life is going to be short anyway. Currently, your phone operates at the lowest power possible to be able to communicate with a cell tower. (And if you think your phone only transmits when you are using it, try putting it on top of a computer monitor, they transmit quite frequently). When there is no tower available, your phone will increase power until it successfully contacts a tower or hits the max power.
The longer you are out of the area, the shorter the time your phone's battery lasts.
For good peer to peer mobile phone systems it's best to use systems based on Time Division Duplexing rather than Frequency Division Duplexing. TDD is used in Japan's Personal HandyPhone System (PHS) and the early models had peer to peer voice. FDD is used mostly on all other digital networks (GSM/CDMA/TDMA etc.), this means that the base station talks to mobiles on one band and all mobiles talk back to the base on another. They're not designed in hardware to support transmissions in bands they don't normally use. Further, the base sends out all kinds of extra data to mobiles: timing control, paging info, frequency channel allocation, etc. It'd take WAY more than a software upgrade to support that.
Also, mobile phones get away with small antennas and relatively low power transmissions because the place they're talking to is usually a HUGE antenna sitting on top of a hill somewhere, high up or on top of a building. That system gives you reasonable cell size. If you had to have mobile to mobile it'd shrink the distance that you could send to quite considerably.
Finally, sad to say it but in North America you basically have 3 different and incompatible digital systems, in addition to the analog one. That'd cut down the possible intermediate hop hosts.
I'm not saying this is a bad idea but given the current cellular technology it is infeasible. Didn't the cell sites for the most part stay up in NY though? Heard on the radio this morning how there's been a huge increase in cell phone sales since then.