Recently the FCC opened empty TV channels to wireless networking and Microsoft’s Research Division wants to replicate the success of WiFi except with three times the coverage radius, much greater bandwidth and the ability to permeate solid structures with much more ease.
Welcome to “WhiteFi.”
WhiteFi would have to be commercially viable first, however, and you would need some sophisticated engineering as the FCC has imposed two critical conditions on WhiteFi development: whitespace devices must sense local transmissions from televisions and wireless microphones in order to avoid transmitting on those frequencies, and the devices must also access a geolocation database of known transmitters as a backup solution in case spectrum sensing failed. So Microsoft proposed to create a WiFi-style system in which multiple clients can connect to a local access point operating in the UHF TV band.
Microsoft’s team tackled mesh networking first; where each whitespace device connects to its neighbors, which connected to their neighbors, to create a spontaneous spiderwebbing local network. After that the team decided to replicate the traditional WiFi model of a central access point with multiple client devices connected to it,but there’s a catch (isn’t there always a catch?)
The aforementioned access point needs to query all of the client devices when negotiating its data channels, making the system more complex than WiFi and creating two distinct problems: a WhiteFi system on a WiFi model needs to worry about interference but doesn’t have to hop off any particular channel because of it and the ability to vary the data channels over time. To Illustrate this, imagine a wireless access point broadcasting across a coffeehouse. Everything is going great until the guy hired to play guitar that night switches on a wireless microphone- the access point must immediately drop its signal on that channel and find a way to notify all of its clients about a move to some new channel-one that isn’t already occupied.
So the team crafted an efficient way to detect “variable-bandwidth signals,” called SIFT. They tackled spectrum assignment algorithms and how to handle that pesky wireless mic problem. To this end they devised a brilliant method of “chirping.” Whenever an access point or a client device detects a TV or wireless mic signal on a channel it is using, it stops transmission immediately and sends out a series of “chirps” on a backup channel. All access points and client devices check this channel every few seconds, and the chirps will help all the devices work out where to transmit next.
So now the groundwork for the next age of wireless is laid. In part two we’ll look at what WhiteFi means for businesses, and how it can actually help the Earth. Be sure and check back!
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