Mobile radios make intranet

By Kimberly Patch, Technology Research News

There are times when being able to log onto the Internet to send a quick message or find key information would be useful but impractical, like when a firefighter is trapped in a burning building and needs to let someone know exactly where he is, or during war games, which regularly coordinate large, mobile groups of people over wide areas.

Researchers from ITT Industries are working on a scheme to bring Internet-like communications to groups of field radios. The researchers' scheme would allow radios to form a self-contained wireless network that could pass along voice and data signals, boosting the distances they could cover. The scheme would also allow for radio access to data on networks like the Internet.

Internet radio islands could eventually be useful in military applications, firefighting and in the trucking and construction industries, said Joe Visvadoer, a senior scientist for technical communications at ITT industries. A firefighter connected to an Internet radio island could, for instance "report back where he is, what his situation is, what the field situation is, and be able to communicate anything he needs to [even eventually] including video images. And if a man goes down people know where he is and they could help," he said.

Mobile networks could also prove useful in keeping track of equipment, said Visvadoer. "You'd be surprised how often a truck is lost for... days... because it's parked on one construction site and somebody forgot it was there," he said.

There are several challenges to corralling radios into a coherent network, said Visvadoer. The central problem is the nature of the radios -- battery-powered and mobile. "As people move around the quality of the communications is going to vary [and] we're talking about very low-power pieces of equipment," he said.

A network whose nodes vary both in location and power needs a lot of adjusting, said Visvadoer. "Most networks measure changes in minutes, hours, or days. We're measuring [them] in hundreds of milliseconds."

The Internet radio islands use the same networking software -- Internet Protocol (IP) -- that links computers to each other over the Internet. The software theoretically allows any radio in an Internet radio island to communicate with any host computer in the world.

The radio frequency network is considerably different even from other networks that include wireless communications equipment because the entire radio network is mobile. In a cell phone network, for example, the wireless phones transmit data packets directly to immobile base stations, said Visvadoer. "A cellphone [network] communicates with one hop directly to the handheld platforms. We have to communicate across multiple hops," he said. For long-range communications cellphone data packets go to a base station and then across telephone wires. In contrast, the handheld radios in the field form a self-contained network.

The key to making the scheme work is two underlying layers of software -- a link layer and a radio network layer -- that manage and hide from the Internet Protocol the many adjustments needed to make mobile radios into a seemingly stable network.

"The link layer finds what radios are in range, measures the quality of the connectivity with those radios, and it adapts communications as those links change," said Visvadoer. The link layer automatically adjusts three variables: power levels, in order to use battery power efficiently and avoid detection; the route that packets of voice data are traveling as radios move in and out of range or are turned on or off; and the speed data travels through the network.

There could be as many as 12,000 adjustments in a five-minute conversation between two people who are far enough apart that the signals must hop from the originating radio through two intervening radios before reaching their target, said Visvadoer. "We're going to send about one voice packet every 90 milliseconds, so that's about 10 a second and about 600 a minute. [In] five minutes, that's about 3,000 packets," he said. Each of the four radios can change the power, data rate or path of every packet, adding up to the 12,000 potential adjustments. In a typical five-minute conversation, there are likely to be about 2,000 adjustments, said Visvadoer.

Most of those adjustments are to adapt power; a smaller number are to change the path the packets take to get from one radio to another. Changing the data rate -- usually slowing down to boost power when more power is available and there's no alternative path -- is done least often, said Visvadoer.

The radio layer manages the radio frequency environment as a whole, said Visvadoer. "Who can I see, what radios can I communicate with and how well can I communicate with them? The radio software provides that information to the [Internet Protocol] networking software and makes it appear to the networking software like it's a more stable environment than it really is. The radio environment forms subnetworks and then connects those subnets up together based on information that the radio provides them," he said.

The software also manages the transmission frequencies the radios use in order to avoid congestion, prevent eavesdropping, and maximize power efficiency. The radios can transmit information over waves ranging from 30 megahertz to 2.5 gigahertz. That range is typically divided up into local, medium haul and long haul tiers, said Visvadoer. The shortest radio waves -- 900 megahertz to 2.5 gigahertz -- provide very high data rate connections between radios less than two kilometers apart. The midrange 300 to 500 megahertz waves allow for larger hops of 9 or 10 kilometers at lower data rates. The 30 to 50 megahertz range is reserved for long haul connections of up to 15 kilometers at the lowest data rates.

The researchers are working with two types of military radios and can make Internet radio islands of either or both types. The smaller model can support two simultaneous conversations and act as a conduit for four more. The larger model allows for four conversations and eight additional links.

In theory, the Internet radio network could link up to 2,000 radios, said Visvadoer. The difficulty of linking more radios is the network becomes less efficient as it gets larger. "There's more overhead -- it takes more resources to keep track of 2,000 radios than it does to keep track of 50. But if you have 2,000 radios they're going to be spread out over a fairly large area. So the capacity of the network increases dramatically at the same time," he said.

The researchers have also looked at ways to eventually extend the network to 10,000 radios, said Visvadoer. "We believe there are ways of building upon this basic software to get to 10,000 radios," he said.

The concept is interesting, and the researchers have some interesting ideas for implementation "but the level of wishful thinking is high," said Charles Bostian, a professor of electrical and computer engineering at the Virginia Institute of Technology.

The way the researchers are making radios aware of their neighbors at the network link level, and the algorithms they're using to form islands of radios are interesting concepts, he said. It may be difficult to extrapolate the scheme to 10,000 users, however, he said. If they are able to make it work, "it would be useful for ad hoc tactical networks," he added.

The researchers are currently testing prototype hardware, and they have networking software running, said Visvadoer. "We've built the first set of islands -- it's working," he said. There are preliminary military tests scheduled for this fall and operational tests scheduled for the end of the year, said Visvadoer. The radio network scheme could be practical in two or three years, he said.

Visvadoer's research colleague is Larry Williams of ITT. Williams published the research in the April, 2001 issue of International Electronic and Electrical Engineers (IEEE) Spectrum. The research was funded by the Defense Advanced Research Projects Agency (DARPA) and ITT Industries.

Timeline:   2-3 years
Funding:   Government
TRN Categories:  Internet; Wireless Communications
Story Type:   News
Related Elements:  Technical paper, "Technology Advances from Small Unit Operation Simulation Awareness System Development," April, 2001, International Electronic and Electrical Engineers (IEEE) Spectrum.


October 10, 2001

Page One

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Mobile radios make intranet

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