Heavenly Music (continued 3/4)

In the United States, Edward Fritts, the president of the National Association of Broadcasters, has made this an issue. His comments have roused the fears of local broadcasters, who have demanded a response from the FCC. They are not alone. Protests have also come from big providers of mobile-phone services, including AT&T, WorldCom and BellSouth, who claim that the terrestrial repeaters could interfere with reception of future data services planned for their wireless networks. There have even been grumblings from the Ultra Wide Band (UWB) community—developers of a new wireless broadband technology—who argue that the repeaters could disrupt their own 2.5 gigahertz transmissions.

For the time being, the FCC has sided with XM Radio and Sirius. Last September, the regulatory agency granted both companies temporary licences to operate their repeaters in areas where a satellite signal might be blocked. A final ruling was due as this issue of TQ went to press. Most expect XM Radio and Sirius to get a permanent green light.

In the meantime, radio operators in the AM and FM bands are supporting their own brand of digital broadcasting, from iBiquity Digital. The company's core technology, called In-Band On-Channel (IBOC) broadcasting, lets station owners add a digital signal to the same chunk of spectrum that they already use for their analogue transmissions. With a solution to hand, iBiquity has quelled many of the local broadcasters' fears about satellite radio. If anything, Mr Struble views XM and Sirius as clients rather than competitors. That is because the audio compression technology used by the satellite operators is licensed from iBiquity.

Off to a wrong start
Digital AM and FM is not new. Since the mid-1990s, many broadcasters in Europe, Canada, Asia and Australia have struggled to implement their own versions of digital radio, using a common standard called Eureka 147. This transmits CD-quality audio along with extra data to provide the performer's name and song title, or weather and traffic reports. However, Eureka 147 is rooted in an outmoded compression technology. It also requires radio broadcasters to transmit their digital signals over an entirely separate swathe of frequencies to their analogue signals.

In America, that part of the spectrum is simply not available, having long since been allocated to the armed forces. How about tweaking Eureka 147 to transmit elsewhere on the spectrum? Unfortunately, that is not a realistic option. It would still require broadcasters to pay for two licences—one for analogue and another for digital. That is what makes IBOC so attractive. It lets broadcasters use their existing part of the spectrum for both digital and analogue transmissions.

For that, America's radio broadcasters can thank some extra precautions taken by the FCC. When the regulator apportioned spectrum to radio stations, it added a tiny 200 kilohertz buffer to each slice of assigned frequency—like saddle-bags on a horse (see illustration above). An FM station that was assigned the 93.5 megahertz broadcasting frequency actually got an allocation that spanned from 93.3 to 93.7 megahertz. The FCC's intention was to prevent interference from one station affecting others broadcasting on adjacent frequencies. What engineers at iBiquity found was that they could squeeze a compressed digital signal into that buffer and still have 100 kilohertz left over to prevent their signal from interfering with a neighbouring station's.

The company has designed a chipset that can not only process the old analogue signal, but also combine it with two new digital streams. Moreover, the digital broadcast was found to consume very little bandwidth, leaving plenty of room for the fat analogue signal to spread its wings. In fact, enough space was found in the saddle-bags to carry additional data. So, apart from hearing local AM and FM with pin- sharp digital reception, listeners can also get stock quotes, news headlines, weather forecasts, or movie times on a display fitted in their car's dashboard. And if digital reception is somehow obstructed, the IBOC chip can switch back to analogue, which tolerates weak or reflected signals.

Field trials of the IBOC hardware in Las Vegas, Washington, DC, and San Francisco have been overwhelmingly successful. The National Radio Systems Committee, a standards body, wrote of one test that “the digital signal remains robust and unimpaired [when] analogue reception is severely compromised.”

To station owners, the advantage of IBOC is that it does not require new transmitters or additional licences. Mr Struble estimates that stations can make the switch in three days. The average cost to upgrade a station's broadcasting equipment is a modest $75,000. He argues that, with all other entertainment media having joined the digital bandwagon, it is time for terrestrial radio to climb aboard.