Image: Paul Wearing
In Brief
- Ad-hoc wireless networks require no fixed infrastructure. Instead they pass information from device to device, forming a web of connections.
- These networks can be used in places where building traditional mobile network infrastructure would prove too unwieldy or expensive—for example, in remote areas and combat zones.
- Because any ad-hoc network is constantly in flux, innovative strategies must be employed to avoid data loss and mitigate interference.
In this era of Facebook, Twitter and the iPhone, it is easy to take for granted our ability to connect to the world. Yet communication is most critical precisely at those times when the communications infrastructure is lost. In Haiti, for example, satellite phones provided by aid agencies were the primary method of communication for days following the tragic earthquake earlier this year. But even ordinary events such as a power outage could cripple the cell phone infrastructure, turning our primary emergency contact devices into glowing paperweights.
In situations such as these, an increasingly attractive option is to create an “ad-hoc” network. Such networks form on their own wherever specially programmed mobile phones or other communications devices are in range of one another. Each device in the network acts as both transmitter and receiver and, crucially, as a relay point for all the other devices nearby. Devices that are out of range can communicate if those between them are willing to help—passing messages from one to the next like water in a bucket brigade. In other words, each node in the network functions as both a communicator for its own messages and infrastructure for the messages of others.
This article was originally published with the title The Rise of Instant Wireless Networks.
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9 Comments
Add CommentWas Michelle Effros, Andrea Goldsmith and Muriel Médard in a hurry to go on their coffee break? With that many people working on an article, you'd think it would have more detail. SciAm did not get their money's worth this time.
Reply | Report Abuse | Link to thisJames, did you purchase and read the entire article? I think the above is just a teaser for a larger body of work.
Reply | Report Abuse | Link to thismy iPhone only gets a little over a day's worth of charge. The last thing I want my "emergency communication device" to do is make calls for other people, and die when I need to. This is a great idea for emergencies, but linking back to the actual web could go though over 10 devices, draining power from all of them.
Reply | Report Abuse | Link to thisI didn't read the article, but the thought of dynamic battlefield networks brings to mind an interesting board game - how to deceive enemy nodes into transmitting our critical command & control info without revealing same...
Reply | Report Abuse | Link to thisCitizens could also do it for themselves with a cheap open-mesh router for $25 which lets them share their internet and secure the home network at the same time. The more plugged in, the more they mesh up. No fuss no programming just plug em in. Open-mesh allows restricting the amount of bandwidth available to neighbors. Contributors can also require logins, resell it if desired, restrict on mac addresses, and boot heavy users.
Reply | Report Abuse | Link to thisIf people with enlightened social attitudes or a just a dislike of the phone company, switched to open-mesh WiFi routers from their junk easily compromised equipment Big Telecom sells, Big Telecom would be taking a serious beating and the FCC's goal of universal broadband would be in sight.
Reply | Report Abuse | Link to thisTwenty-something years ago, I studied queuing theory at Dr. Effros' institution. I then went on to design telecom equipment. In that time, I tried to use queuing theory only once. Perhaps that experience will be of use to the authors.
The basis for analytical queuing theory is that the system be "memoryless." That is, the result does not depend on the order in which events are added to the queue. (The concept is highly related to, although slightly different from, the idea of a "stateless" system.) On my one attempt to use the theory, I failed almost immediately because the system was dependent on call order. That, in fact, was why they needed someone to analyze it!
Ultimately, I solved the problem through Monte Carlo simulation -- through the brute force of sending thousands of random cases through a simulated system to see what would happen. Interestingly, the result was a simple derating of the system relative to a memoryless system... except foe extreme cases. Never published that result -- perhaps I should have.
The same applies here. The analytical solutions are impossible to derive for all but trivial ad hoc networks. Further, since the ad hoc network changes configuration constantly (not stateless), the order in which packets are sent matters (not memoryless). The only answers, then, based on my experience are:
1) Brute force simulation: simulate a lot of cases with a lot of configurations that occur in a lot of different orders. This has academic merit to be sure.
2) Brute force in bandwidth: put a lot of bandwidth out there and see what happens. Apply heuristic policies (like "no video traffic if the network is loaded") and call it a day. Just as in my case, knowing that there is a specific derating factor is not as useful as simply building a system with a huge safety margin and ignoring the problem.
Lord save us from the military, its use of IWN's, and these three yokels/nitwits, obviously beholden to its largesse!
Reply | Report Abuse | Link to thisLord save us from the military, its use of IWN's, and these three yokels/nitwits, obviously beholden to its largesse!
Reply | Report Abuse | Link to thisthanks for sharing useful information with us...
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