机械专业外文文献翻译-外文翻译--空白频段标志着无线界

http:/www.eetasia.com/White spaces marked off as wireless arenaPosted: 16 Oct 2008When the long-awaited DTV switchover in the United States occurs next February, broadcasters will relinquish the analog channels some have held for more than half a century. Considering the prices mobile operators paid for "beachfront" spectrum above 700MHz earlier this year, these unlicensed VHF/UHF channelsknown as white spaces and scattered throughout the 54MHz to 698MHz region of the RF spectrumwould easily have pulled in billions had they been auctioned. But they weren'tand a range war is raging over how they should be used. The first squatters in the newly unlicensed channels will likely be a handful of tech giants, including Google, Hewlett-Packard, Microsoft and Motorola, which have joined with public-interest groups and media companies to create the Wireless Innovation Alliance (WIA). Several RF companies with links to WIA members are testing prototype products known as white-spaces devices (WSDs) with the U.S. Federal Communications Commission (FCC). Superior UHF propagationTransmissions from these WSDs would enjoy UHF propagation characteristics far superior to those of the now overcrowded 2.4GHz band. Applications range from a data network that Google's Larry Page has described as "Wi-Fi on steroids" to all sorts of video, to networks of humble household objects like washing machines, toasters and light bulbs, all communicating with one another. The brave new wireless world envisioned by the WIA could possibly disrupt the airwaves with interferenceand undoubtedly will upset the broadcasters' VHF/UHF monopoly. The broadcasters are livid, describing the plan as unworkable. And although neither side is saying so, it is not difficult to translate "broadband" into video and "unlicensed" into dollars. The FCC has just concluded its field testing of WSD submitted by Motorola, Philips, Adaptrum, Shared Spectrum, and Singapore's Institute for Infocomm Research. The test results will almost certainly start another round of vituperation between the techs and the broadcasters. There is quite a bit of white space out there, particularly in rural areas of the U.S., according to the New Frontiers Foundation, a member of WIA. But the contested turf is in large media markets where the broadcasters rake in most of their profits. New Frontiers, which believes the socially proactive use of white spaces can help close the digital divide, has estimated the percentage of unused spectrum varies from 18 percent in New York to more than 60 percent in less densely populated areas, such as Wichita, Kansas. These figures are contested by the broadcast lobby, led by Maximum Service TV (MSTV), which describes itself as the engineering arm of the National Association of Broadcasters. David L. Donovan, president of MSTV, argues that "you can't just add up the DTV channels" that are not licensed in a geographic area, because high-power TV signals can travel many miles beyond their licensed region. More important, he said, is the presence of low-power devices licensed to operate in the VHF/UHF bands. Wireless microphones such as those used by sportscasters who interview coaches and players on the sidelines of sporting events can be licensed to operate legally in the VHF/UHF bands (although many more operate unlicensed). Because wireless microphones are mobile and transmit at much lower power than DTV stations, they represent a tougher interference problem for WSDs. WIA is not to be deterred. Noting that maximum WSD power transmission has been limited to 100mW, WIA consultant Edmund Thomas is confident the interference problem can be solved by deploying the right set of technologies. At first glance, most RF engineers might think it unduly cautious to fear that low-power (below 100mW) use of part of an unoccupied 6MHz channel could cause problems for DTV, even with the longer range of UHF signals. RF engineers have been solving interference problems for years, notably the Wi-Fi/Bluetooth contention in the 2.4GHz band. But the WIA has set its counterinterference bar high. Two technologiesand possibly a thirdwould be employed: global positioning systems, cognitive radio and beacons. To guard against interference with wireless mikes, some WIA prototypes include beacon technology. When a broadcaster sets up at a sporting event, for example, its technical team will deploy a beacon that will broadcast at a power the white-spaces devices can easily sense. Incumbents in the VHF/UHF space, which include broadcasters and wireless-microphone interests led by U.S. manufacturer Shure Inc., have launched a spirited verbal attack on WSDs. Infection analogyMSTV and a group of stations asked the FCC why it would consider allowing "millions and millions of these interference-causing devices, like 'germs,' to spread throughout America with the ability to attack the TV receivers in people's homes, apartments, hotel