Robin Berger of TVTechnology.com has written a good summary of the current (9th April 2008) state of White Spaces. She details the status of device testing at the OET and the recent proposal by Google on spectrum sensing, noting that Google’s embracing of geolocation puts them at odds with the rest of the Wireless Innovation Alliance.

She lists the main advocacy groups on each side of the issue, and summarizes their positions. Among the people apparently interviewed for the article are Stu Overby, Motorola’s senior director of Global Spectrum Strategy, Ed Thomas of the White Spaces Coalition and Ahren Hartman, Shure’s director of Platform Engineering. Also quoted in the article are David Donovan of the MSTV and statements from the NAB and the Broadway League, which is interested in wireless microphones.

In the discussion of the testing, the article covers the wireless microphone issue in depth, with an interview with Ahren Hartman.

An April 8th 2007 article in PC Magazine gives some background on ads from the NAB and the WIA.

The forthcoming transition to digital TV transmissions will free up about half the spectrum currently allocated to TV broadcasters. This freed-up spectrum was the subject of the FCC’s just-concluded 700MHz Auction, which yielded about $20 billion in license fees to the government. The fate of the other half of the TV spectrum, the part that will remain assigned to TV broadcasts after the digital transition, remains in contention.

This spectrum will be shared by licensed TV broadcast channels and wireless microphones, but even so much of it will remain mostly unused. These chunks of spectrum left idle by their licensees are called “White Spaces.” The advent of “spectrum sensing” radio technology means that it is now theoretically possible for transmitters to identify and use White Spaces without interfering with the licensed use of the spectrum.

The FCC has issued a Notice of Proposed Rulemaking and a First Report and Order to explore whether this is a good idea, and if so, how to handle it.

The potential users of the White Spaces have formed roughly two camps, those who see it best suited for fixed broadband access (similar to the first version of WiMAX), and those who see it as also suited for “personal/portable” applications (similar to Wi-Fi).

Google, along with Microsoft and some other computer industry companies, advocates the personal/portable use. The FCC’s Office of Engineering and Technology (OET) is currently lab-testing some devices from Microsoft and others to see if their spectrum-sensing capabilities are adequate to address the concerns of the broadcast industry, which fears that personal/portable use will cause interference.

Google filed an ex-parte letter with the FCC on March 24th, weighing in on the White Spaces issue. The letter is well worth reading. It concedes that in the introductory phases it makes sense to supplement spectrum sensing with other technologies, like geo-location databases and beacons. The letter asserts that these additional measures render moot the current squabble over a malfunction in the devices in the first round of FCC testing, and that the real-world data gathered in this introductory phase would give the FCC confidence ultimately to repeal the supplemental measures, and perhaps to extend open spectrum-sensing uses to the entire radio spectrum, leading to a nirvana of effectively unlimited bandwidth for everybody.

The kicker is in the penultimate paragraph, where Google recycles an earlier proposal it made for the 700MHz spectrum auction, suggesting a real-time ongoing “dynamic auction” of bandwidth. Google now suggests applying this dynamic auction idea to the white spaces:

For each available spectrum band, the licensee could bestow the right to transmit an amount of power for a unit of time, with the total amount of power in any location being limited to a specified cap. This cap would be enforced by measurements made by the communications devices. For channel capacity efficiency reasons, bands should be allocated in as large chunks as possible. The airwaves auction would be managed via the Internet by a central clearinghouse.

Current expectations are for spectrum-sensing use of the whites spaces to be unlicensed (free, like Wi-Fi). Now Google appears to be proposing “sub-licensed” rather than unlicensed spectrum use. The word “auction” implies that this could be a revenue producer for TV broadcast licensees, who received their licenses free from the government. This is a very different situation than the original context of the dynamic auction proposal, which applied to spectrum for which licensees paid $20 billion. Depending how it is implemented, it could fulfill the telcos’ dream of directly charging content providers for bandwidth on a consumer’s Internet access link, a dream that Google has opposed in the network neutrality wars. Google may ultimately regret opening the door to this one, even though it presumably sees itself cashing in as the ideal candidate to operate the “central clearinghouse.”

Update April 10th: Interesting related posts from Michael Marcus and Sascha Meinrath.

It took a while, and 261 rounds of bidding, but its over. Click here for the write-up from Wired.

The attractive thing about the 700 MHz spectrum that was freed up by the move to digital TV broadcasting is that transmissions at these frequencies pass through walls. The unusual thing about the “C Block” of this spectrum is that the FCC attached “open access” conditions to the license. This was at the behest of the computer industry, spearheaded by Google, who may even have made a bid on this block. But as the Wired story points out, Google had already won their victory with the imposition of the open access rules - winning the spectrum would have been more of a headache for them than losing it.

Don’t confuse the spectrum licensed in this auction with the White Spaces spectrum. The White Spaces spectrum is the spectrum that the TV broadcasters retained for their transition to digital transmissions in February 2009. The White Spaces issue is still unresolved by the FCC. The FCC is deliberating over whether to allow unlicensed use of the digital TV spectrum when it is not being used by a TV broadcast (hence “White Spaces.”) This use depends on effective functioning of “cognitive radio,” which lets transmitters sense by listening (and other means) when spectrum is available for use. If the FCC allows it, they still have to decide whether to allow only fixed broadband replacement like 802.22, or to allow “Personal and Portable” use as well.

It’s an amazing idea. Radio signals at less than 1 GHz pass easily through buildings. TV broadcast signals are below 1 GHz so you can use an indoor antenna. Anywhere in the US about half the TV channels are idle, so why not use these empty channels (White Spaces) for wireless broadband Internet access? The FCC has been pushing this idea since 2004. The IEEE has a workgroup (802.22) hammering out the technical details, and some of the mightiest companies in the technosphere are banding together to make it happen.

Even the broadcasting industry sees the merit of this idea - in a letter to Senators Stevens and Inouye, David Donovan, the president of MSTV (the Association for Maximum Service Television) says:

Ensuring that the United States is a global leader in the provision of broadband services is a worthy goal. We believe this goal can be accomplished, especially in rural markets, without causing interference to new digital television receivers and converter boxes… Our desire is to find a solution that will bring broadband to underserved Americans while ensuring that consumers’ and broadcasters’ investments in the DTV transition are protected.

Did you spot the catch? The broadcasters are worried that unlicensed use of their spectrum will interfere with their broadcasts. The chief executives of Disney, News Corporation, NBC and CBS sent a letter to the FCC saying:

As you know, current proposals based on “sensing” to avoid interference could cause permanent damage to over-the-air digital television reception.

There are two main categories of issue here: technical and compliance. Both must function correctly to avoid the outcome feared by the broadcasters.

On the technical side, if technologies can be developed that effectively eliminate the potential for interference, and regulations can be crafted that require the use of such technologies, the broadcasters have nothing to fear. This technical issue is relatively easy to debate, and while the broadcasters may seem overly cautious to some, their position is reasonable:

It has taken nearly a decade for government and industry to deploy digital television across this nation. A rush to place millions of unlicensed devices in the TV band without extensive real-world testing should not undermine these efforts.

But technical issues yield to engineers in time, and we can confidently expect cognitive radio to work properly in the end. Credible proponents argue that it is working correctly already. The FCC tested devices from Microsoft and Philips in July 2007 expecting to close this issue with hard data, but in a catastrophic blunder one of the tested devices was defective and failed the tests, leaving the issue open. The broadcast industry seized on this mistake and used it to characterize the technology in general as unripe. But the technical argument will eventually yield to conclusive experimental results, showing that cognitive radio works, and that unlicensed use of this spectrum as proposed by the FCC will not interfere with TV broadcasts.

The compliance and enforcement issue is far tougher to resolve, but it is separate from the White Spaces issue, and should be debated separately. This issue is actually more important, since it concerns not only the TV broadcast frequencies but the utility of the entire radio spectrum in the US. If devices that transmit on radio frequencies are badly engineered, defective or designed in such a way that they don’t conform to the regulations, it is possible that they might interfere with legitmate uses. As things stand, there is no guarantee that this will not happen, since the enforcement arm of the FCC is weak. Michael Marcus, in his “Spectrum Talk” blog goes into this issue and proposes some actions.