White Space Coalition members Dell, Google, HP , Intel , Microsoft , Philips, Earthlink, and Samsung hope to develop a type of radio frequency chip that can be embedded into portable devices in much the same way that today's Wi-Fi chips are added to laptops.

Although the concept has immense potential as an alternative to other wireless broadband initiatives, including WiMax, the National Association of Broadcasters (NAB) -- which represents the nation's TV channel operators -- is worried that white-space devices could interfere with TV broadcasts.

The FCC's latest tests "confirm what NAB and others have long contended, that the portable, unlicensed devices proposed by high-tech firms can't make the transition from theory to actuality without compromising interference-free television reception," said NAB executive vice president Dennis Wharton in a prepared statement.

Not Ready for Prime Time?

To prevent two or more TV channels operating within the same market from interfering with one another, the adjacent channels are always left unoccupied. But just which of these channels actually go unused can vary from one area to the next. White-space devices, therefore, must be able to determine whether the channel is in use before making a transmission.

Theoretically, at least, this check could be accomplished through the use of either a "detect and avoid" or "listen before talk" strategy. "This approach would use 'spectrum sensing' techniques that listen for the signals of TV stations, wireless microphones, and perhaps other incumbent services," the FCC said.

In preliminary trials of two prototypes submitted by the White Space Coalition, however, researchers at the FCC's Office of Engineering and Technology found that the samples "submitted to the Commission for initial evaluation do not consistently sense or detect TV broadcast or wireless microphone signals." Moreover, the researchers found that "the transmitter in the prototype device is capable of causing interference to TV broadcasting and wireless microphones," just as broadcasters had long feared.

Still, the FCC noted that its results were preliminary, indicating that it remains willing to continue to explore the matter. For its part, the White Space Coalition told media representatives that it intends to continue to work with the FCC to come up with a workable solution.

Pressure Mounting

The FCC already has established that fixed white-space devices will be allowed into the TV spectrum once the final transition from analog to digital television broadcasts takes place in early 2009. And it is also clear that the FCC would like to approve the use of unlicensed mobile units for the same spectrum to foster more broadband competition.

But the Association for Maximum Service Television, which also represents the nation's broadcasters, said that all of the billions of dollars being spent to make the transition from analog to digital TV will be wasted if new digital TV sets and other new digital TV products and services receive interference, causing "the picture to become unwatchable."

The White Space Coalition must therefore make its technology interference-free if it is ever to become ready for prime time.