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Running Interference

Despite ultrawideband’s promise, attempts to deploy the technology face significant obstacles. The most immediate barrier is the FCC rules, which are designed to mitigate ultrawideband’s potential to interfere with virtually every existing radio frequency service. “With the rules the commission enacted, you’ll be lucky to get a signal across a room,” says Dewayne Hendricks, founder of the Fremont, CA, wireless engineering firm the Dandin Group and a technical advisor to the FCC on new wireless technologies.

Ultrawideband’s unique nature made the FCC’s approval process especially contentious. The proposed short-range applications would use very low power pulses, which ordinarily would lessen their potential to cause interference. But ultrawideband signals overlay large parts of the radio spectrum. Although many proponents say these broadband pulses look like harmless “noise” to other radios, the signals could, in theory at least, disrupt a host of wireless applications-from TV to cell phones to GPS-that have paid big money for their slices of the spectrum. And if large numbers of ultrawideband transmitters come into use, the cumulative effects might inflict even greater interference. Many of the comments to the FCC on ultrawideband constitute a “yes it does, no it doesn’t” back and forth on the interference question-even in the interpretation of data from technical studies. “As usual with studies,” says Hendricks, “you can get credible scientists on both sides of the story.”

Sprint PCS, for example, conducted tests indicating that ultrawideband signals could lead to more dropped calls and even lower the number of calls the network could handle, meaning more busy signals. Satellite radio companies Sirius and XM Radio are concerned about potential interference with their services. And tests performed by the National Telecommunications Information Administration showed that ultrawideband signals could make it more difficult for GPS receivers to lock onto satellite signals-and could also reduce their accuracy. That prospect would be especially troubling for the air traffic control system, which in coming years will rely increasingly on GPS.

The FCC’s prohibition on ultrawideband emissions at certain frequencies was designed specifically to prevent potential interference with such systems. But those limitations are not enough, say some in the affected industries. Preliminary tests by NASA’s Langley Research Center using ultrawideband emitters placed inside and outside United Airlines planes show that even at frequencies that the FCC is permitting, ultrawideband interference could compromise the instrument landing system pilots use to land in bad weather. James Miller, program manager of flight operations technology at United, says that ultrawideband noise could additionally affect voice communications between air traffic controllers and pilots, the radars air traffic controllers use to track aircraft, and the collision avoidance system designed to prevent planes from crashing in midair. Airlines and the Federal Aviation Administration adamantly oppose permitting ultrawideband to operate in any frequency used by airlines; even a single ultrawideband radio could cause problems with these critical systems. “The question is not whether there’s interference, the question is how much interference can flight crews tolerate,” says Miller-and he says the airline industry’s position is zero tolerance. “Any interference injected into the cockpit is a bad idea.”

Many ultrawideband proponents contend that improper testing exaggerates the technology’s interference effects. “A lot of the stuff put up for testing purposes with the FCC-you can’t build efficient systems that way,” says Pulse-Link’s Watkins. Others suggest that the approval process became highly politicized. “Science wasn’t really part of the debate anymore after a time-it became politics,” says the Dandin Group’s Hendricks.

Makers of ultrawideband systems hope that working commercial products will demonstrate that the radios do not cause interference. In fact, some devices under development-like ther Wire’s systems combining GPS and ultrawideband-would not work if ultrawideband caused as much interference as critics say it will. Indeed, says XtremeSpectrum’s Rofheart, avoidance of interference-caused “radio fratricide” is key to future applications that would mingle cell phone, GPS and ultrawideband radios.

Ultrawideband proponents also worry about the trouble other radio technologies might cause them. Because conventional narrowband systems, like cordless phones, operate at much higher power than ultrawideband radios, their transmissions could overwhelm nearby ultrawideband devices. Designing ultrawideband receivers so that they block certain frequencies could solve the problem-but also make the radios more complex and costly.

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