Nearpoints

Craig Mathias

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What's Holding Up the White Spaces?

We should have more spectrum available soon - unless $600 is worth more than billions (and it may be)

By Craig Mathias on Fri, 06/18/10 - 10:32am.

. What's this?

I had the privilege this week of speaking at the TV White Spaces Summit, sponsored by the Wireless Innovation Forum, which is the new name of the trade association formerly known as the Software Defined Radio Forum. As you might guess, this group is on the leading edge of radio technology, and this event was designed to gather key players from the regulatory (including an FCC Commissioner and the Head of the FCC's Office of Engineering Technology) and technical sides together to evaluate the state of the White Spaces effort that will bring new and very important spectrum to both fixed and mobile wireless broadband applications across the board, from government to consumer broadband access. And, as you might guess from the provocative title of this blog entry, action is required if this reallocation of spectrum, already so far along that the FCC (and other international) regulations are already in effect, is going to succeed. Yes, there's a risk that nothing will happen here, which, if so, would rise to the status of a Greek tragedy pretty quickly.

The beauty of the White Spaces is their relatively low frequencies, in the UHF band of a few hundred megahertz. This means that the propagation characteristics will allow for good range, good throughput (megabits per second), and good in-building penetration. The bad news is that the White Spaces are in fact television channels that are unused, which means there will be a lot more of this spectrum available in less-populated areas than in urban settings - not all bad considering the underserved populations in these areas, the cost to serve these populations with higher-frequency, line-of-sight wireless solutions, and the many other applications (like all manner of machine-to-machine) that are also economically unfeasible in the middle of nowhere without appropriate wireless solutions. Regardless, if it were only a matter of TV transmissions, this issue, while politically sensitive (the broadcasters will protest this no matter what, for obvious reasons, but they're going to lose regardless) would be resolved - all we need to know is what TV channels are licensed and in use and where, and the transmit power for each, and off we go. Instead, the roadblock lies elsewhere - wireless microphones, to be precise, believe it or not.

I am a huge fan of wireless mics. I insist on them in public presentations, as I really can't stand still behind a podium, and, as an amateur musician, I love both the freedom of mobility and electrical decoupling (musicians have been killed by ground faults in those classic amps we all love) inherent in wireless mics in that application. Wireless mics come in many different forms and work in many different frequency bands - including, unfortunately for our purposes here, UHF TV channels. And these are protected devices operating under FCC part 74 rules, not unlicensed devices that could be blown off (although lots of wireless mics do in fact operate in the ISM bands just fine). So, Washington, we have a problem.

The proposed solution is to have new White Spaces devices sense the presence of energy and avoid channels where such energy is present. This could work in some cases, but non-linearities in radio propagation could produce all manner of false positives and negatives. One vendor of radio chipsets told me that spectrum-sensing is essentially a non-starter, and they won't proceed to production if this requirement remains in place. Wow! But there's a better solution - a database of licensed users of this band. And such a database is in fact required under the FCC rules. The wireless mic guys still aren't happy, but they should be. After all, the FCC recently issued regulations that flat-out banned wireless mics formerly allowed in the now-auctioned 700-MHz. band, even those (formerly) licensed under Part 74. It's unreasonable for wireless microphones, which require perhaps only 200 KHz. of spectrum and yet occupy, for White Spaces purposes, an entire 6-MHz. TV channel, to hold up what could literally be success measured in the billions of dollars for those producing new White Spaces devices, along with numerous other benefits, like basic broadband service where such otherwise would not be technically or economically feasible.

I expect this issue to be resolved by the FCC in the next quarter of this year, as they continue their work and take up the remaining petitions for reconsideration of their rules. Let us hope this effort bears fruit. And it's my hope that this new database-driven approach to cognitive radio will eventually become the dominant metaphor for making use of the spectrum everywhere - and in many more bands than the White Spaces alone. More on this later. In the meantime, anyone want to get to work on a trunked-radio-style digital wireless mic system?