A white space device is an FCC-certified wireless device that can be used without an exclusive broadcast license in the RF spectrum below 700 MHz. White space devices can access the Internet at wireless broadband speeds. The devices use underutilized, unlicensed portions of the spectrum called white space. Characteristics of signals in those spectrum ranges -- such as greater range and penetration of objects -- are expected to lead to better and cheaper wireless service.
In the not-too-distant future, WSDs may be found in all of the electronics and computer hardware categories that currently have WiFi built into them, including routers, tablets, video game consoles, cameras, servers or smartphones.
On November 4, 2008, the FCC formerly approved the use of unused spectrum for WSDs. There were two types of WSDs under consideration. According to an FCC statement released in October 2008:
The first category consists of low-power "personal/portable” WSDs that will function similar to WiFi transceivers in laptop computers, and wireless in-home local area networks (LANs). The second category consists of higher-powered "fixed/access" WSDs that would typically be operated from a fixed location and might be used to provide a commercial service such as wireless broadband access. As established previously by the Commission, fixed white space devices will be allowed into the TV spectrum upon completion of the transition from analog to digital television broadcasts on February 17, 2009.
Members of the White Space Coalition, including Philips, Motorola, Google and Microsoft, submitted white space devices to the FCC over the course of two years. These low power transmitting devices were tested for potential interference with the signals for TV stations, wireless microphones and other incumbent services. The FCC has indicated that it will allow conditional unlicensed use of vacant frequencies only for white space devices that include spectrum sensing and geolocation capabilities. Spectrum sensing is a form of "smart radio" that scans for unused channels nearby. Geolocation is a technology that combines GPS with cross-referencing locations with a database of licensed spectrum users to identify active services nearby.
See a simple introduction to white space technologies: