A new research project from Microsoft and Harvard could pave the way for long-range wireless networking

Aug 18, 2009 07:24 GMT  ·  By

Wireless Internet is quickly becoming a strict necessity both in developed parts of the world but also in emerging regions. Current Wi-Fi technology is reaching its limits and is only suited for short-to-medium ranges with relatively small amounts of bandwidth. One of the best prospects for the future is the opening up of “white spaces,” unused parts of the spectrum between assigned frequencies, especially in the lower frequencies used until now by analog TV broadcasts. One of the most advanced research projects in the area will be presented today at the ACM SIGCOMM 2009 communications conference held in Barcelona, Spain by a team of researchers at Microsoft and Harvard.

Regular Wi-Fi operates at 2.4 GHz and has a small number of channels with only three that don't overlap (four in Europe). The high frequency allows for more channels in a smaller slice of the spectrum (84.5 MHz); however, the biggest disadvantage of operating at this frequency is the limited range, which is typically 32m indoors and 95m outdoors, and which can be extended in some circumstances using specialized equipment. These are enough for crowded city locations but don't provide a real alternative for long-range connections. Operating in the lower frequencies left open by the transition from analog to digital TV broadcasting, which is being carried out in most parts of the world, provides a much bigger range and also potentially more bandwidth as there are bigger chunks of the spectrum to be used.

With the frequencies now left open the FCC ruled last November that the white spaces were open to any device and company, something in which Google was instrumental, as long as these didn't interfere with existing devices or broadcasts operating in the same frequency range. The new research project, backed by the Networking Research Group at Microsoft Research, uses the UHF spectrum (512 MHz to 698 MHz), which was originally sliced into 30 TV channels (21 to 51). The project, dubbed “White Fi,” is one of the most advanced in the field, both dealing with the hardware side but also creating the networking protocols to handle the specific challenges.

"It's a totally different paradigm for wireless networking," Ranveer Chandra, a member of the Networking Research Group, told MIT's Technology Review. "Until now, in wireless networks, you were given a spectrum, and you would share it with everyone else. Everyone was an equal stakeholder. Now, you have this spectrum where there are certain people who are primary users."

Because there are other devices in the spectrum and the networking is given the lowest priority a big challenge was setting up the protocol so the communications could switch between available channels on the fly if the one being used was suddenly occupied by other broadcasts. The infrastructure is similar to Wi-Fi, with a central access point and peripheral devices connecting to it. The devices connected to the network work together to find a channel that is suitable for all. The researchers also designed a way for new devices to find an available signal, which is also more problematic because of the wider range of channels and the fact that they could change at any point.

The strict requirements of the FCC meant that a greater focus was on avoiding interference with other transmissions that would have priority over the networking. A wireless microphone operating at this frequency would be affected by the White Fi communications so the protocol was designed with a backup channel in mind. As soon as a device is detected as using the same channel, the access point along with all of the devices connected switch to the backup. A more detailed description of the research can be found here.

There are a number of universities and big tech companies working on this kind of technology which, while still several years off, could make wireless Internet a much better and cheaper alternative while also offering greater bandwidth. While the first devices will be expensive and only suitable for the more developed parts of the world, as the technology matures, it would allow poor or remote regions in which fiber optics or other connections aren't feasible to have a reliable and fast Internet connection.

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Current Wi-Fi technology has a very limited range
The KNOWS hardware prototype used in the White Fi project
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