The United States was the first country to broadcast digital TV, in 1998, and its mechanism was basically followed by other countries in their own systems. So the U.S. experience is illustrative.

In the late 1990s, the Federal Communications Commission (FCC) loaned each TV broadcaster a second channel in the existing broadcast bands, 54 through 806 MHz. Interspersed among the broadcast channels are some spectrum gaps that minimize interference between them. To further minimize interference, the FCC skipped certain channels in a geographic region; for example, if channel 4 is assigned in one metropolitan area, the nearest channel 3 broadcaster is in a different metropolitan area. The skipped channels are known as taboo channels.

Each channel occupies 6 MHz, and that hasn't changed. Rather, because digital transmission is less interfering and also less subject to interference, and because digital channels operate at lower power levels than their analog counterparts, the FCC assigned second channels into analog taboo channels. The FCC deemed the modest increase in the overall level of interference acceptable during the transition.

At the time of the bandwidth loan, Congress set year-end 2006 as the date when analog service would officially cease and the extra channels would be "returned." At that point, the digital channels, with their low interference characteristics, could be repacked into less bandwidth\ufffda swath between 54 and 698 MHz. The move would free 108 MHz of spectrum\ufffdthe upper end of the UHF band, or TV channels 52 to 69\ufffdfor other uses. To put the potential value of that 108 MHz in perspective, note that the entire AM radio spectrum is less than 1.2 MHz. All local area networks using IEEE 802.11b and 802.11g, the most common forms of Wi-Fi, occupy just 83.5 MHz. Congress looked forward to a lucrative spectrum auction to help balance the federal budget.

The 2006 date, however, came with a caveat: on a market-by-market basis, at least 85 percent of households would have to own at least one television that could receive digital signals.

It has been clear for months that the 85 percent criterion will not be met next year, so the U.S. plan will be delayed [see sidebar, "Countdown to the End" But for how long? Now, many of the affected players\ufffdconsumer electronics and computer manufacturers, along with communications and other companies interested in using the recaptured spectrum\ufffddo not want a "soft date." Instead, they have been agitating for a hard one, with no further chance of delay.

Although Congress has yet to pass legislation to set such a date, both the House of Representatives and the Senate seemed in late summer 2005 to be converging on 1 January 2009.

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"Beachfront Spectrum" is what analysts are calling that soon-to-be-auctioned upper 108 MHz, because it is ideal for cellular services. Signals at those frequencies propagate farther and penetrate buildings better than signals in today's cellular bands, which go up to 1.9 gigahertz. Best of all, cellphone system operators expect infrastructure costs to be reduced by 90 percent, because fewer cells will be required, given the longer distances signals will travel.

Thanks to such advantages, the cellular phone companies are likely to compete hard for this valuable bandwidth. Exactly what they would do with it is a closely guarded secret, at least until winning bidders are selected. Nevertheless, it's not hard to imagine the winners launching third-generation services, including mobile video and wide-band Internet access, which would enable cellphone users to receive video programming and e-mail on the run.

The FCC's huge menu of allowable uses for the new frequencies identifies "[f]lexible fixed, mobile, and broadcast uses, including mobile and other digital new broadcast operations; fixed and mobile wireless commercial services, as well as fixed and mobile wireless uses for private, internal radio needs. Could also include two-way interactive, cellular, and mobile television broadcasting services."

Perhaps the best early indicators of what will happen with the freed-up bandwidth are recent events in Berlin\ufffdthe first city to turn off analog television\ufffdand in the United States, where a couple of preemptive auctions gave developers access to segments of spectrum on the condition that they not interfere with broadcasters still using them.

The "Berlin Switch" is an intriguing novelty. It was possible because the region affected is relatively small, with 1.8 million households in the TV market, and because an overwhelming number of those households\ufffdall but 160 000\ufffdsubscribe to cable or satellite television. Nonsubscribers each coughed up at least $200 to buy a set-top converter, and for less than $1 million, the government subsidized the purchase for families on welfare.

What the switch gave Berliners, mainly, was an increase in the number of broadcast stations\ufffdfrom 12 to 27. Multiplexing allows four digital channels to fit in the space previously allotted to a single analog channel. (This excludes HD broadcasts, because they require more bandwidth.) The switch also gave the government 35 MHz to use\ufffdor sell\ufffdfor new services.

With more channels, viewers of broadcast television in Berlin have access to niche programming and channels previously available only to cable or satellite subscribers. Programming now includes Eurosport; Arte, with art movies, documentaries, poetry, and theater; Phoenix, with political news; Viva II, with pop culture for people in their 20s; and several new local channels.

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Two auctions held so far accounted for just 24 MHz of the 108 MHz that will eventually be sold. Of the 84 MHz remaining, in 1997 the FCC reserved 24 MHz for public-safety communications, such as police and fire services\ufffdthose located at four of today's UHF TV channels, 63, 64, 68, and 69. Since the 9/11 attacks on the United States, Congress has been paying a lot of attention to the public-safety communications plan, originally with little fanfare. In fact, congressional eagerness to reallocate the swath of spectrum is the main impetus behind a drive to set a firm date for the transition to digital television. The Save Lives Act of 2005, introduced in the Senate in June, calls for expediting the reassignment of the spectrum for public-safety purposes and requires spectrum to be taken back from broadcasters by 1 January 2009.

Although Congress is driving the agenda to free portions of spectrum for public-safety use, local governments will decide how they will be used. Metropolitan-area governments, for example, would like to alleviate the congestion that plagues existing emergency services. They are concerned with voice and text transmission, already in use, and are looking to add wideband transmission of images. On-the-scene images can help emergency responders and their dispatchers. With broadband access to stored records, fire or police teams could review building plans and blueprints.

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