Mobile Sands

September 27, 2010

White Space Spectrum Becomes Available With Simplified Rules

Filed under: Uncategorized, white space — Tags: , , — AJ @ 12:33 am

White Spaces Officially Available for Unlicensed Use

On 9/23/2010, the FCC officially made unused TV channels (so called “white space” spectrum) available for unlicensed use and resolved several open technical and legal issues. Most importantly, in its Second Memorandum Opinion and Order, it eliminated the requirement that TV bands devices that incorporate geo-location and database access must also include sensing technology. This is a big change that simplifies the development of devices that use this spectrum.

The FCC had first voted to approve unlicensed use of white spaces in Nov 2008 and issued a “Notice of Proposed Rule Making”. This started a a consultation process that culminated in last week’s order. The Nov 2008 required unlicensed TV Band Devices (TVBDs) to not only incorporate geo-location and access a FCC-mandated database but also to include sensing technology to detect TV transmitters and wireless microphones. Fixed unlicensed white space devices (li.e. base stations) had to do spectrum sensing with a 10m high omni-directional antenna! These rules effectively made the spectrum useless for both – providing broadband access or local area networking (see posts from last year). Though I am skeptical of the FCC’s “Super Wi-Fi” claims, I do think the revised rules make the spectrum more interesting for both these applications.

TV Band Devices and a TV Band Database

The FCC order defines two kinds of TV band devices: Mode I (or personal/portable) and Mode II (fixed), and a TV bands database. Mode II (fixed) devices must either have geo-location capability (50 m accuracy) or be professionally installed. In both case, these devices report their location to a TV bands database and get a list of permissible channel on which these devices and the Mode I devices connected to them can operate. Mode I devices operate on channels provided by Mode II devices.

Simple White Space Network

Several companies, including Google, are interested in building a TV Bands Database. This database would contain information on channels used by protected services by geographical location. Details of this database are still being worked out and the FCC has to select database providers. The FCC does leave the door open for personal/portable devices that have spectrum sensing capability. Such devices can work without a Mode I device to form, say, a mesh network, and it will be interesting to see how companies that have done considerable amount of research in cognitive radios will react.

Not Much White Space Spectrum in Major Metro Areas

Still, the real barrier to the development of commercial white space devices is the availability of white space spectrum. FCC rules still bar the use of Mode II devices in both channels occupied by TV broadcasters and in adjacent channels. As a result, there are often just one or two 6 MHz channels available for Mode II devices in major metro areas. Mode I devices are allowed to operate in adjacent channels if the transmit power is less than 40 mw.

Spectrum Bridge, one of the companies that want to provide a TV band database, offers a free online service that allows one to check the channels available for white space spectrum.

Super Wi-Fi. Really?

It is still not clear to me how white space spectrum will unleash super Wi-Fi. Compared to a Wi-Fi router, a TV band wireless router will have to share 6 MHz of spectrum with other similar routers in major metro areas and will require an in-building GPS receiver. Still, lots of other applications may be possible, and any tie-in with Wi-Fi helps in promoting new unlicensed band technologies (remember WiMAX?)!


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