A new IEEE standard designated 802.19.1 aims to fix what for now is a minor flaw in TV white spaces broadband technology, but which could become more problematic in the future as the technology is more widely deployed.
When technologists figured out how to use database technology to keep track of where TV broadcast spectrum was in use by licensed broadcasters, it paved the way for wireless ISPs and others to use vacant broadcast spectrum to support broadband wireless connectivity. But as deployed today, the database technology doesn’t keep track of where other unlicensed users are using vacant spectrum. And considering that most, if not all, TV white spaces equipment requires at least one TV channel and that signals can travel as far as 100 kilometers, it’s easy to see how that limitation could eventually be a problem.
The New TV White Spaces Standard
“Co-existence is important,” said Dr. Apurva Mody, chairman of the IEEE 802.22 working group and the White Space Alliance, who believes TV white spaces database administrators in the U.S. eventually will agree to share information with one another about where TV white spaces equipment is already operating on an unlicensed basis. The 802.19.1 standard details how they could do that.
The U.S. has at least four FCC-approved TV white spaces database administrators – including Spectrum Bridge, Microsoft, Google, and iconectiv (formerly a unit of Telcordia and now a unit of Ericsson). Currently all four get the same information from the FCC about where TV channels are vacant – information that they communicate to TV white spaces devices when the equipment is installed so that the equipment can automatically tune itself to use vacant channels.
The database administrators aren’t allowed to charge for providing that information, explained Mody. But potentially a database administrator could charge for supplying information about where other unlicensed users are using TV white spaces, Mody said.
He also noted that the FCC has indicated that it does not plan to get involved in database administration beyond tracking licensed users but that he expects to see regulators in some other countries seeking to enhance the database of licensed broadcast spectrum users so that it also includes information about where unlicensed users are operating.
802.22 and 802.11af
A potential complicating factor is that there will be at least two different types of TV white spaces equipment. Wireless ISPs use equipment based on the 802.22 standard to deliver fixed broadband wireless at DSL data rates over great distances even where line of sight is not available. In addition, equipment based on the 802.11af standard will use vacant spectrum in the same TV broadcast band to provide higher-bandwidth shorter-range mobile Wi-Fi connectivity.
This means that to be effective, the database technology will need to track where both types of users are using spectrum – and it will need to know which type of technology each user is using. Those people using 802.11af equipment will use spectrum over a considerably smaller geographic area than those using 802.22 equipment.
Mody believes the industry will see broader deployment of TV white spaces technology after the upcoming voluntary auction of TV broadcast spectrum. The amount of spectrum in the TV broadcast band dedicated to licensed use is likely to increase as a result of the auction, but some spectrum in that band will be reserved for unlicensed use.
After the auction, the exact mix of licensed and unlicensed spectrum will be known. And with uncertainty removed, Mody says that’s when TV white spaces technology will see broader deployment – and when the need will arise for the new coexistence technology to be implemented.
