Analog TV spectrum is prime real estate, the wireless equivalent of Hawaiian beachfront property and a Park Avenue brownstone in New York all rolled into a single package. The reason is simple: signals in the analog TV spectrum travel very well because of their low (sub-700MHz) frequencies, and they can easily be received indoors. Back in 2006, engineers began to realize that, in any given market, plenty of the TV channels were empty. Given the terrific signal propagation in these frequencies, the engineers came up with a plan: why not run wireless broadband services in empty TV channels?
The White Spaces Coalition was born, and it began to lobby hard for the idea at the Federal Communications Commission, which had been pondering what to do with these “white spaces” since 2003. This debate, which might sound purely technical, quickly became both political and acrimonious. TV broadcasters saw no upside to this experiment but plenty of downside; their TV signals might soon be subject to interference. Wireless microphone operators also complained; what happened if churches and Broadway shows had their productions disrupted by someone accessing the Internet from a nearby apartment?
The debate took years, but in late 2008, the FCC finally voted unanimously to approve unlicensed wireless broadband in empty TV channels. To address interference concerns, the Commission adopted a “belt and suspenders” approach that required white space devices to query a geolocation database before transmitting. The gadgets would also have to use “spectrum sensing” to scan the selected frequency for signs of a TV station or wireless microphone before transmission could begin. (The spectrum sensing requirement was later dropped.)
Test networks using white space devices have been operating for years at places like the Microsoft campus, but white space routers still remain absent from the shelves of big box electronics retailers. Some of this has been due to foot-dragging at the FCC, where the necessary geolocation databases have only just been approved for buildout by private operators.
Still, though they have yet to come to market, white space devices have shown serious potential. Real-world testing by a Rice University team in Houston has shown stable signal ranges of at least one mile in urban environments, with further distances possible in rural areas. If white spaces devices truly do live up to their potential, they may well do so as a last-mile technology for rural communities.