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We're Gonna Have to Wait a Year for White Spaces

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istock_000005540809xsmallThe votes have been cast, the winners and losers have spoken, and the euphoria of yesterday will now give way to the realization that a lot of hard work lies ahead. We’re not talking about the U.S. presidential race, but the even longer slog to use the spectrum between digital television channels for unlicensed wireless broadband.

For years, broadband proponents such as Google, (s GOOG), Motorola, Dell (s DELL) and Microsoft (S MSFT) have pushed to use this spectrum, which will be opened up next February, for some type of unlicensed wireless broadband following the model Wi-Fi uses today. Yesterday, the Federal Communications Commission approved plans to make that happen. Proponents of the technology rejoiced, issuing congratulatory statements heralding the dawn of a new age of broadband for all Americans. Opponents, meanwhile, such as the National Association of Broadcasters and users of wireless microphones — including Dolly Parton — vowed to continue the fight.

More requirements, more work

And they will. But that won’t be the only thing making white spaces a grey issue. When the FCC approved the technology, it included some interesting caveats. Among them, low-power devices that use geolocation to avoid interference with television channels and microphones will be required to undergo the typical FCC certification process to get a seal of approval for devices. This is great for Motorola, which manufactures geolocation sensing products, but makes consumer deployment more complicated because someone has to host the database and keep it up to date.

The low-power requirement is also limiting for proponents of white spaces. Rob Kenney, a spokesman for the FCC, says devices transmitting in an “open channel” that isn’t adjacent to a broadcast channel can broadcast at up to 100 mW, while those that are operating in an adjacent channel have to operate below 40 mW.

There are two issues with this. First the “open channels” will commonly be found in rural areas where there aren’t as many television stations, so more channels are empty. Broadcasting in an open channel requires two empty channels on either side of the data signal. In urban areas with more stations, finding the five channels necessary to broadcast at that higher power will be difficult if not impossible. That means a device maker needs to create two classes of device — one for rural areas and one for urban areas — if it wants to take advantage of the highest power settings. That’s costly.

The lower the power, the more involved a network buildout will be, because lower-power devices can’t shout as loudly to talk to a tower. This means more towers or access points in the network, and puts a damper on portable white spaces devices for the time being.

The FCC also gave a tentative nod to devices that use spectrum sensing rather than geolocation sensing, and it left the door open to higher-powered devices. Spectrum-sensing devices, which would scan the spectrum before broadcasting a signal to it, will have to undergo a more rigorous testing and approval process, one that includes public approval (you can bet opponents will make their voices heard) as well as a vote from the commissioners. That’s a lot of bureaucracy for what should presumably be a low-cost broadband-enabled device. The FCC will review higher-powered devices through a separate inquiry later.

The long road ahead

Aside from the limits put on the technology, it’s going to take at least a year to roll out devices, according to Steve Sharkey, senior director of spectrum and regulatory policy at Motorola (s MOT). The prototype devices used in the tests are clearly not ready for consumer use and deployment. Businesses will also have to build a network and figure out business models.

However, devices will take the most time to come to fruition, as networks can be set up using existing models and infrastructure. He points to Motorola’s Canopy network products as an example. Backhaul could be delivered by fiber, landline broadband or even through piggybacking on a different white spaces channel to get back to the Internet. As for business models, different companies have different plans.

One model, similar to the way Wi-Fi is deployed, involves a consumer shelling out for the device and providing their own broadband. This obviously doesn’t help rural deployments much, since they don’t have access to broadband to serve as the backhaul. Other models would have operators setting up a white spaces network to which consumers subscribe.

So now that the celebrations are over, it’s time to get to work. We need business models, devices, networks and likely new ways for technology to squeeze the most broadband out of these limits. It’ll take time, but if white spaces can deliver speeds of 13 Mbps that Sharkey says it can, that’s nothing to scoff at — especially in rural parts of the country.

13 Responses to “We're Gonna Have to Wait a Year for White Spaces”

  1. Jesse Kopelman


    With spectrum sensing you don’t pick a clear channel and stick with it indefinitely, you keep scanning every few seconds and hop to a new channel as needed. This allows you to not only avoid interfering with other devices but also always be on the channel with the best RF characteristics. The overall mechanism would be very similar to frequency hopping in GSM. When the user device is powered on it scans through all channels and associates with the base-station that it can receive the best. If it doesn’t find any base stations, it will continue to periodically rescan until it does. Channel hopping will be controlled by the base station. When it decides there is a need to change channel it will first broadcast a message to all user devices informing them of the new channel. Even if this message is missed by a particular device, after a period of no control messages being received it will re-enter scanning mode and eventually rediscover the base-station (by eventually, I mean some fraction of a second). A primary factor in the success of this strategy is that user devices will have to be limited to no more power than devices like wireless mikes, so that you will never have a situation where the base-station cannot “hear” such devices in the proximity of the White Spaces user device. In spectrum starved markets, dynamic power control can also be employed to reshape the service area on the fly as wireless mikes and whatnot are detected — sucks for users near those wireless mikes, but at least the rest of the network is unaffected. These techniques have all been used to various degrees in digital radios for a very long time, so we are not talking about anything hard or costly to implement in prospective White Spaces devices (although standardizing things for guaranteed interoperability between vendors could take years).

  2. Robert A. Rosenberg

    With Spectrum-sensing devices how does the receiver know what channel to listen to (ie: The sender finds an available channel and uses it but how does it tell the receiver where to listen). Also what happens when someone else fires up on the channel that is in use (such as wireless mikes/etc. who assume that they can use the channel without bothering to check or use Spectrum-sensing). I can see a scenario where the White Space device does the check and selects a channel that is not in use at that point in time only to have some wireless mike user fire up and then complain about interference. The only solution that will handle this is to assign a channel for wireless mikes/etc. and tell the White Space device it is off limits. This is what currently is done for medical monitors where that have their assigned channel and that channel and the guard bands are not allowed to be allocated to TV Stations.

  3. Geolocation devices were considered in the specification of standards for this application (IEEE 802.22 WRAN). So — while not the simplest or cheapest of technologies, it was anticipated technically and is not a significant surprise. Comapred to other barriers to entry, that one is by no means a show stopper!

  4. Bill Seymour

    As a service provider for rural customers in coastal Oregon communities, all I can say this is great news! It is very difficult to get signals into remote areas using the existing open channels, even 900MHz doesn’t particularly care for trees (especially wet trees), and dirt stops it cold. These frequencies should work much better for those fringe areas we’ve been unable to serve so far.