Monday, January 9, 2012
Microsoft has developed a new kind of Wi-Fi network that performs at its top speed even in the face of interference. It takes advantage of a new Wi-Fi standard that uses more of the electromagnetic spectrum, but also hops between the narrow bands of unused spectrum within television broadcast frequencies.
In 2008, the U.S. Federal Communications Commission approved limited use of "white spaces"—portions of spectrum adjacent to existing television transmissions. The ruling, in effect, expanded the available spectrum. Microsoft developed the new network partly as a way to push Congress to allow much broader use of white spaces, despite some concerns over interference with some other types of wireless devices, such as wireless microphones.
The fastest Wi-Fi networks, which can transmit data at up to a gigabit per second, use as much spectrum as possible, up to 160 megahertz, to maximize bandwidth. Krishna Chintalapudi and his team at Microsoft Research have pioneered an approach, called WiFi-NC, which makes efficient use of these white spaces at these speeds.
Rather than using a conventional Wi-Fi radio, it uses an array of tiny, low-data rate transmitters and receivers. Each of these broadcast and receive via a different, narrow range of spectrum. Bundled together, they work just like a regular Wi-Fi radio, but can switch between white-space frequencies far more efficiently.
That means the system is compatible with existing equipment. "The entire reception and transmission logic could be reused from existing Wi-Fi implementations," says Chintalapudi.
The team calls these transmitters and receivers "receiver-lets" and "transmitter-lets." Together, they make up what's known as a "compound radio."
The resulting wireless network doesn't increase data rates in specific ranges of spectrum above what's currently achieved with latest-generation technology. It does, however, make more efficient use of the entire range of spectrum, and especially the white spaces freed up by the FCC.
The new radio integrates with a previous Microsoft project that provides a wireless device with access to a database of available white-space spectrum in any part of the United States. That system, called SenseLess, tells a device where it can legally broadcast and receive. WiFi-NC then chooses the bands of spectrum that have the least interference, and broadcasts over them.
By sending its signal over many smaller radios that operate in slivers of the available spectrum, WiFi-NC suffers less interference and experiences faster speeds even when a user is at the intersection of overlapping networks. This is important because the white spaces that may be authorized for commercial use by the FCC are at the lower ends of the electromagnetic spectrum, where signals can travel much further than existing Wi-Fi transmissions.
Whether or not Microsoft's WiFi-NC technology gets commercialized depends on Congress, says Kevin Werbach, a professor at the University of Pennsylvania's Wharton Business School, and an expert on the FCC's effort to make more spectrum available for wireless data transmission.
"The problem is that many of the Congressional proposals to give the FCC [the authority to auction off currently unused bandwidth] also restrict it from making available white spaces for devices around that spectrum," says Werbach.
Microsoft hopes WiFi-NC will persuade Congress to approve wider use of white spaces.
"It is our opinion that WiFi-NC's approach of using multiple narrow channels as opposed to the current model of using wider channels in an all-or-nothing style is the more prudent approach for the future of Wi-Fi and white spaces," says Chintalapudi. The team's ultimate goal, he adds, is to propose WiFi-NC as a new wireless standard for the hardware and software industries.