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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.
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My cell phone battery goes dead soon enough without transmitting data for other people.
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 .
According to the article it seems that their only real selling feature is to increase the robustness of a cell network without having to add additional towers. There might be other reasons to have P2P enabled phones but this one is just plain silly.
First, this would only really work in well-populated areas with high densities of regular cell phone users. But these cities are already very likely to have a strong saturation of cell coverage, and it is probably relatively economical to install new network towers in such high density areas.
Second, if an emergency occured, a la 911, where the load is exceptionally high, I can't imagine this system of low powered devices holding up anywhere near as well as a decently saturated network of towers (that also have a lot more power). The decentralized network might be theoretically more robust, but not if everybody's trying to make a call at the same time and not when the device range only allows for a very limited number of localized connections to form.
Wireless P2P and multi-hop) systems are really cool, but it's not going work for everything or solve every problem. One day they may become ubiquitous, but are likely to be first employed for niche applications only. Cell phone applications and benefits will probably be limited to local network communications.
Maybe such a system could one day be used to help improve coverage deep within buildings, or for very localized load balancing, but I doubt that they will or should be trusted technically as an alternative to building an independently robust network of towers etc. And, if they are only proposing the technology as an adjunct for increased reliability, then I just don't see a very strong business case.
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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
Basic truth: for reliable low-power communication, at least one end of the link needs to be well-sited. That's why cell phone towers are positioned carefully. Even setting up an 802.11b network requires that the base stations be positioned in reasonable locations.
You can blast your way out of that limitation with power (the military solution), or only expect it to work in areas with very dense node populations (the urban WiFi solution).
This idea was looked at back when mobile phones were attached to cars. Back then, power levels were higher, battery life wasn't a problem, and antenna locations were better. Even then, it wasn't that attractive.
Amateur packet radio works something like this, but even there, what makes it all go are VHF repeaters sited on high places.
GMDSS, the Global Marine Distress and Safety System, really does work this way. Marine radios, since 1999, have had a big red "DISTRESS" button. Pushing this sends out a message that gets forwarded by every other ship that has GMDSS gear. But that's a specialized, low-bandwidth application.
I've seen several comments pointing out that reduced battery life as a serious issue...
Here's another one: Signal degradation.
Anyone with experience in networking knows that while repeaters can be used to extend the maximum length of an Ethernet run, you can only repeat the signal so many times (4, for Ethernet, IIRC) before data error become an issue.
I paid for a Motorola Startac back in the day... $250 for a cell phone, and even with such a nice cell phone, loss of quality is pretty noticeable when compared to a landline... Wouldn't hoping the signal through 3 or 4 of these make for pretty horrible reception?
It's possible the loss of quality due to some other aspect of cell technology that I'm not aware of (digital signals and compression, perhaps?) I'd love to hear from someone who knows more about cell technology.
The major stumbing block, and why this idea cannot immediately go to cell phones, is the notion of band-split and the fact that the cell-phone network is fundamentally circuit-switched (as alluded in the article).
Mobile devices are licenced to transmit on certain frequencies and receive on another set. The base station (at the tower) has the opposite band-split. That's how a full-duplex connection is made. One can listen and talk without having to push a button like a walkie-talkie since there are two separate radio connections used together simultaneously. Mobiles typically transmit on the low side of the band and base stations on the high side.
In order for a mobile to act as a base station (for the purposes of repeating or P2P), it would have to implement the radio hardware to do listen to other phones, like a base station does. Besides the licensing issues, cell phones do not offer this extra-cost (and potentially bulky) RF hardware.
The P2P cellphone idea demonstrated on 802.11 has a fundamentally different RF architecture, where one band is shared in a multiple-access fashion. It's also inherently a packet-switched technology. In 802.11 band-split is not an issue for P2P.
Anybody want a peanut?
My cell phone is often on a charger, either at home or in the car, so no problem with battery drainage. No doubt being used as a relay would be an opt in proposition with many settings like your laptop sleep and idle modes. For instance, only relay while on a charger, only relay while over 50% charge, only relay 50% as many calls (power equivalent) as actual usage. Etc...
Users to be rewarded by relay discount points in their bills (think frequent flyer miles).
Encryption no more (or less) needed than regular phone. Why hack your relay phone, when you can just buy a scanner?
Maybe my phone will work in this near underground apartment, relaying though the phones above, then out.
More available bandwidth, more calls can get through, by using smaller, but more numerous relay towers, that are closer together, or hop around a tower that is saturated, like often happens Friday nights in this College town.
Huge events (or disasters) less likely to completely jam network (continue hopping until getting to an unsaturated tower).
Mini towers possible, by tying phones into land-lines or cable modems. Again, a customer discount or credit option.
With a diffuse enough network, and mbone like simulcasting, 4G services like mobile HDTV.
Cellphone network compatible laptops should hardly notice the relay drainage, compared to regular greedy CPU use.
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