The Shrinking Wireless Spectrum

Believe it or not, one of the hottest AV products in the consumer market right now is the TV antenna. The antenna's surprise return to the tops of sets and roofs is a harbinger of problems that will 10/23/2007 6:45 AM Eastern

The Shrinking Wireless Spectrum

Believe it or not, one of the hottest AV products in the consumer market right now is the TV antenna. The antenna's surprise return to the tops of sets and roofs is a harbinger of problems that will become increasingly common over the next few years.

Believe it or not, one of the hottest AV products in the consumer market right now is the TV antenna. The antenna's surprise return to the tops of sets and roofs is a harbinger of problems that will become increasingly common over the next few years.

The TV antenna's resurrection is fueled by the U.S. broadcast industry's continued migration toward digital, a migration that ends Feb. 17, 2009. On that day, all full-power TV stations must shut off their analog broadcasts and use only digital.

The switch will be expensive for broadcasters, but it's non-negotiable — this change is government-mandated. And it has its positives. Going digital will let stations have multiple feeds, creating more opportunities to sell advertising than with a single analog channel. Broadcasters also will have to switch frequencies, a change that forces them to increase their signal strength.

Meanwhile, the federal government is considering allowing unlicensed consumer wireless devices to move into the TV spectrum. All of those changes will directly impact pro AV products, such as wireless mics, by creating interference, potentially enough to render some wireless AV products unusable.

“There are going to be problems,” says Gary Gunn, market development manager for installed and touring sound at the U.S. division of AKG Acoustics.

Bet the Farm

To understand how pro AV got pulled into this situation, go back to 1997, when the Federal Communications Commission opened what is known as the DTV (digital TV) proceedings. These meetings started a decade-long process of “refarming” the very high-frequency and ultra-high-frequency bands for use by other technologies, such as wireless Internet service providers. (For an overview of what frequencies fall where in the spectrum, see the figure on the next page.)

FCC began by reallocating 24 MHz of the UHF band (TV channels 63, 64, 68, and 69) for public safety services. The commission also decided that much of the rest of the UHF band — 698-806 MHz, also known as the 700 MHz band — would be auctioned off to companies that want to offer services such as mobile TV for consumers, similar to what's available today from cellular operators.

“The public safety broadcasts will squash anything in the 746 to 806 MHz [range],” says James Stoffo, a wireless consultant in Portland, Ore., who specializes in pro AV deployments. “There will be 500-watt police repeaters in major cities throughout this band.”

It is expected that public safety will move quickly its new home, partly because many agencies already have a large base of compatible radios. “There are 500,000 to 600,000 public safety radios out in service that have the capability to operate in that band,” says Edgar Reihl, a technology director in advanced development at Shure in Niles, Ill.

Why auction off the 700 MHz band? In a word: money. For more than a decade, governments worldwide, including the United States, have used spectrum auctions as a major revenue source. For instance, a September 2006 cellular auction netted about $13.9 billion for the U.S. government.

Credit: Courtesy of Sure

The effects of the spectrum refarming are already out there, according to some AV pros. Digital TV is energizing the airwaves from 512 to 698 MHz, says Stoffo. “This has increased congestion throughout the bulk of what the professional audio community has known as the wireless microphone band,” he says.White Spaces, White Noise

As part of the spectrum refarming, the government also is allowing unlicensed wireless devices to inhabit the so-called white spaces between the new digital TV channels.

In October 2006, FCC decided to let stationary unlicensed wireless devices begin using the white spaces as soon as the digital TV migration is complete in February 2009. The agency is still hashing out technical rules for mobile unlicensed wireless devices in the white spaces. Those devices could be similar to 802.11 Wi-Fi PC card modems for laptops, in the sense that they'd be designed to provide low-cost broadband access for consumers. Another similarity is that, like a Wi-Fi modem, the new devices could turn up literally anywhere, making it difficult for AV pros to avoid interference they would create. Another concern is their power, which would be four-tenths of a watt under current proposals.

“That's higher than the maximum permitted for a wireless audio transmitter, and considerably higher than most wireless mics, which generally are 10 to 50 milliwatts,” says Edgar Reihl, a technology director in advanced development at Shure, which has been meeting with FCC about technical parameters.

Because they're designed for the consumer market, mobile white space devices have to be inexpensive. One way for consumer electronics vendors to keep costs low is to cut corners, such as by making the devices unable to identify frequencies in use and avoid them, a technique referred to as frequency hopping.

“At this point, we haven't seen a single compliant, unlicensed device that can sense wireless mics in order to protect incumbent users from interference,” says Riehl. “There's a lot of work left to be done.”

Other pro AV vendors share Shure's concerns about the impact of unlicensed white space devices, but they are cautiously optimistic about the ability to design products that can work around the interference.

“Wireless microphones will be more difficult to coordinate and use,” says Karl Winkler, director of business development at Lectrosonics in Rio Rancho, N.M. “However, I don't think it's correct to say that our systems will be wiped off the map. Digital signals tend to look like noise to an FM (analog) system. FM systems are good at digging the intended signal out of the noise.”

Broadband, and Noise, for All?

FCC's technical studies could conclude that allowing for unlicensed mobile consumer devices would raise the band's noise floor to unacceptable levels. But that doesn't mean those devices won't be allowed, because Congress could overrule FCC. Two bills under consideration would do just that, forcing the agency to open the entire digital TV band for use by unlicensed consumer devices.

Many members of Congress are concerned about the so-called digital divide, where people in poor or rural areas lack affordable broadband access. Creating a new band for broadband wireless devices and services is one way for Congress to take action.

That begs a question: Why not just auction off the white spaces? Doing so would mean more revenue for the federal government. The catch is that the companies that want to offer consumer broadband wireless services would have to pay billions for spectrum licenses. Those costs then would be passed on to customers, many of whom might not be able to afford the service — which is the opposite of Congress' broadband-for-all intent. Hence the preference for unlicensed devices and services.

One wild card is whether the 2.4 GHz band, home to many Wi-Fi services, will remain popular despite being crowded. Consumer electronics vendors prefer bands that are available worldwide, so they don't have to build separate products for each country's unique spectrum requirements. “Many of the wireless consumer AV devices are moving to 2.4 GHz or 5 GHz bands to provide a worldwide market for products,” says Ralph Mason, CTO of Kleer, a Cupertino, Calif., semiconductor manufacturer that specializes in wireless audio products for unlicensed bands.

If that turns out to be the case, it would affect pro AV in at least two ways. First, it could mean a small market for consumer AV and broadband devices in the white spaces, and thus less interference for pro AV gear. Second, more devices at 2.4 GHz and 5.8 GHz means possibly more interference with, for example, projectors that use Wi-Fi.

Time will tell whether service providers and consumer electronics vendors will flock to the white spaces or stick with other bands. Some analysts think the 700 MHz band will be popular. In March, Stifel Nicolas analyst Blair Levin predicted that the auction “will be one of the most significant telecom events of the coming year.”

Preparing for Change

The pro AV industry has several options for dealing with increased interference from the digital TV migration. For vendors, one option is to design wireless equipment to be more resistant to interference, such as through better filtering and frequency agility. For vendors, one silver lining to the growing interference cloud is that it creates another opportunity to differentiate their products.

“The systems that are not well-filtered will not operate nearly as well when the general background noise level rises,” says Lectrosonics' Winkler. “There are systems on the market with good filtering, and customers will likely gravitate toward them first, as manufacturers ramp up their abilities in this area and then introduce new products as a response. Frequency agility is a must, and most systems offer this.”

The ultimate in agility would be transmitters and receivers that can be upgraded in the field for new bands or interference-mitigating techniques. “With all of our new systems, especially on the higher end, it's simply a firmware change” to switch bands, says AKG's Gunn. Chaning firmware rather than hardware also is less expensive, so vendors wouldn't be saddled with huge costs that have to be passed on to customers. “Changes don't have the cost impact they used to,” says Gunn.

Then there is gear that is more interference-prone and could be nearing the end of its useful life by the February 2009 deadline. In those cases, it might be possible to make a business case for replacing it, thereby reducing the interference problem. The trick is to steer budget-constrained clients away from bargains over the next year or so.

“There could be a lot of blow-out [sales] of VHF,” says Gunn. “I could see people thinking they're getting really good deals on stuff that has a very limited lifetime.”

Over the next two years, AV pros also should keep an eye on digital TV and other wireless services in the market. For example, when a large tower starts rising on the horizon, it's a good sign that at least one local TV station is close to going digital; digital TV antennas frequently require new, tall towers. Spectrum analyzers, which give a view of signals in a particular swath of a band, also could become necessary.

“The spectrum environment that we all operate in is fluid,” says Shure's Reihl. “The fact that you used a certain frequency for the past five or 10 years doesn't mean you'll be able to use that for another 10 years. That's going to be very difficult for people to adjust to.”

Tim Kridel is a freelance writer and analyst who covers telecom and technology. He's in Kansas City, Mo., and can be reached at

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