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Peer-to-Peer Cell Phones?
Mike writes "This Wired article mentions that research firm SRI International has come up with a nifty way to lessen the need for the ugly cell towers that you see popping up everywhere (I love the ones here in Atlanta that are oh-so-cleverly dressed up to look like pine trees). Their PacketHop software would create a sort of peer-to-peer network, utilizing the unused power in phones in the vicinity as miniature relays, with your voice/data hopping from one phone to the next until it reaches a relay tower and its final destination."
Let me just say that these people would have to provide some pretty serious security credentials before I'd let my calls hop along other people's phones. Maybe they could PGP each person's phone. That'd be cool.
This tagline is umop apisdn.
If the number of cell towers were reduced and relied on proximity to other cell phones for a signal, would'nt that reduce the likleyhood of someone getting a connection in someplace like a national park or the Mojave Desert? People away from people need to talk to other people too!
Yeah, it's possible. Of course, it'd mean your cell phone's battery would run down within a matter of hours as it relayed other people's conversations around. I'd guess a lot of people would "hack" their phones to not act as relays, so as to conserve battery life. The result would be a breakdown of the network.
The multiple relay idea isn't such a bad idea, though, if you move the relays out of the phones and onto the power grid. How 'bout if everyone who got a phone also plugged in a base station at their house? That piece of hardware would do the relaying instead. Then battery life wouldn't be a problem. Offer a few people free service if there are dead spots in the neighborhood.
Add on another feature; plug the relay into your phone line, and when you're at home or near it, your cell phone becomes a cordless phone (like in L. Neil Smith's book Hope .
Anyone who's done any cellphone programming will know that there aren't an awful lot of spare CPU cycles going begging when the phone is idle, and there are hardly any at all when you're in a call.
Unless your phone has more CPU power than you need for normal use, and why on earth would the phone manufacturer do that?? - it'll just eat battery and make the phone uncompetitive.
Sorry, but you can't get this sort of system for free. It will cost, in more expensive handsets and/or reduced battery life. Not to mention a re-run of all the safety research as the things will be transmitting on a higher duty cycle even when you aren't deliberately making a call.
[Disclaimer: The above is all true for GSM systems as used in 199 countries of the world. I gather things may be a bit different in the USA.]
If you only need enough power to reach the nearest peer, instead of enough to reach the tower, your battery might last longer.
Covering distance in multiple hops is more power-efficient overall than going all the way in one hop. The math is easy to see for inverse-square, and cellphone signals drop off faster than inverse-square due to absorption.
If you're not mathematically oriented, imagine the battery drain if there were only one tower in your city and your phone had to reach it from everywhere.
Heh.
Yes, it sends packets every once in a while.
Thing is, your battery has a standby time of 48 hours, but a talk time of what? 1 hour? 90 minutes? Most of that power isn't going to sound circuitry, it's going to the radio, and if your phone is busy relaying a call that radio will be pulling just as much power.
Each one supports the other cell callers further from the nearest cell, extending in a chain of small spheres back to the tower, rather than one large sphere that wastes all kind of energy sending random radiation off in all directions as far as it can reach.
The biggest factor in power expenditure is the ability to put the device into standby mode. The transmission power has relatively little relevance. If the device has be a routing node in a mesh network, it can never go into standby. Even if there is no traffic to forward, it will have to keep exchanging routing information with its neighours, in order to be *able* to forward traffic. This will suck the battery dry in a matter of hours.
Not to mention the other equally inexplicable down sides:
1) security - intermediate nodes can tap your calls
2) security - intermediate nodes can reroute or prevent your calls
3) quality - packet loss for a number of consequtive wireless links would be stupendous
4) quality - cumulative delay from a number of consequtive links would be disastrous (more so, if link layer retransmissions were used to improve packet loss)
5) you've got no neighbours, you've got no calls - where do you get the people who are willing to stand in a chain between you and the tower, while you yabber on with your girlfriend?
6) would you pay for that service? Would you trust the intermediate nodes to meter your call? Might be a few surprises in store when the bill arrives...
"I have opinions of my own, strong opinions, but I don't always agree with them." -- George H. W. Bush
P2P packet radio is an old idea. Check out the old Aloha and AX25 protocols. One of the best sites for amature packet radio is Tucson Amateur Packet Radio or Packet Primer.