No noise: researchers at Microsoft use an echo free (anechoic) chamber to prove that an HD movie can be streamed over the same frequency as used by a wireless microphone.
Chandra and colleagues are working on ways to cram more connections into the white spaces than the FCC has decreed it will allow, in the hopes of influencing it and other regulators to make more space available. One strand of research has shown that an HD movie stream can be transmitted over the same channel being used by a wireless microphone (which use frequencies close to TV broadcasts) without causing any noticeable degradation to the sound recorded. That shows that the current rules may be too conservative, says Chandra. Currently white spaces devices must avoid any channel in use by a wireless microphone as well as the channels on either side of a TV broadcast. “We’ve found that you really don’t need to vacate the entire channel,” says Chandra.
“We intend to leverage all of the work that we’ve done, even if there are some we can’t implement under the FCC rules so far,” says Paul Garnett, Microsoft’s director of interoperability and standards. “The U.S. rules may change in the future, or different countries may take fuller advantage of the capabilities of white spaces networking.”
The SenseLess system has already been modified for use in other countries, including Finland, Singapore, and the U.K., in preparation for white spaces initiatives expected from regulators there. Microsoft has also made it possible for certain devices, such as wireless microphones, to ask SenseLess to reserve them a channel and ask other devices using the database to make room.
This kind of dynamic functionality hints at the broader potential for using a central, dynamic system to manage wireless spectrum beyond just TV white spaces. Kevin Werbach, who researches Internet and communications policy at the Wharton Business School, University of Pennsylvania, says a database that managed more than just white spaces could enable more efficient use of the limited radio spectrum.
“A database system like this could be the basis of a new system of access control, a universal intermediary between devices that want wireless connections and those with the capability,” says Werbach. Like the DNS system that directs Internet traffic to the correct destinations, such a service could direct requests for wireless access to vacant pieces of spectrum, he says, a method that could use available bands more efficiently than the current system that allocates fixed blocks to certain companies and uses.