GPS users hope to forestall new tech

The latest threat to the much- embattled U.S. satellite-based navigation

system may be another emerging technology that promises to revolutionize

wireless communications and radar.

The new technology, known as ultra-wideband, is awaiting approval by

the Federal Communications Commission, which is expected to release a Notice

of Proposed Rule Making this spring that would open radio spectrum for UWB

transmission systems.

However, government and industry organizations that rely on signals

from the Global Positioning System say UWB could interfere with GPS signals,

posing a hazard to navigation systems and other applications that rely on

the positioning data.

They are concerned because the growing roster of UWB companies — including

Time Domain Inc., U.S. Radar Inc., Zircon Corp., Multispectral Solutions

Inc. (MSSI) and Fantasma Networks Inc. — is looking to operate under the

FCC's Part 15 rules, which allow unlicensed devices that are not subject

to government approval.

What the GPS community wants is adequate testing of the risks of interference

from UWB, as well as possible alternatives to allowing the technology to

broadcast in restricted spectrum bands, said Sally Frodge, policy analyst

at the Transportation Department.

The question, Frodge said, is "at what point on your flight are you

comfortable with the navigation systems being interfered with?" It is already

complicated enough to fly aircraft without possible interference from new

communications technologies, she said.

DOT is sponsoring tests, begun recently at Stanford University, to verify

whether UWB systems meet the interference requirements for aviation. The

aviation industry plans to transition to satellite navigation as its primary

navigation aid.

"We have enough results to say there is the potential for interference,"

Frodge said. Now testing is needed to identify what the level of interference

is, when it occurs and which UWB forms cause it, she said.

The FCC does not plan to approve UWB for radio spectrum until the results

of various tests sponsored by DOT and industry are available, said John

Reed, senior engineer in the FCC's Office of Engineering and Technology,

which is responsible for preparing the proposed rules.

The office last year issued three companies a waiver to operate UWB

systems on an experimental basis. The proposed rules are due out very soon,

he said, and once they are released, the FCC will allow at least six months

for the test results and a comment period before making a decision.

But Reed said the FCC does not see any problem with GPS. UWB emissions

meet the safety and noise standards set by the National Telecommunications

and Information Administration, RTCA Inc. and the International Telecommunication

Union for GPS use in aviation, and in many cases UWB exceeds those standards,

he said.

A primary question that needs to be addressed is at what distance between

a UWB transmitter and GPS receiver the agency has to regulate interference,

Reed said.

One solution would be to notch out UWB transmissions so that they avoid

restricted bands. If a system is properly designed, the likelihood of ultra-wideband

signals interfering with other signals is very low, said Robert Fontana,

president of MSSI.

"The problem is [that] not every one is designed the right way," he

said. "The problem is [that] there are one or two companies in the field

that have not taken the effort to try to filter these wave forms to keep

them from interfering with existing services."

Fontana said MSSI and other companies have proposed to the FCC that

ultra-wideband technology be permitted, but outside the frequencies used

by the aviation industry.

Several industry organizations are prepared to express objections if

sufficient testing is not completed before the FCC issues its decision.

Rex Morey, a technical staff member at Lawrence Livermore National Laboratory

and pioneer in the ultra-wideband ground-penetrating radar field, said data

will be the deciding factor but it must be objective.

An independent organization, such as the National Academy of Science,

should study the effects of UWB, rather than groups that can be pinned to

particular interests, he said.

"How can [the FCC] make rules, or even suggest rules, if they don't

have any data to justify or support their rule making?" Morey said. "If

they do have some data, the question is the validity of that data. Are they

making rules based on questionable data?"

Government and GPS industry groups that have been promoting use of GPS

over other countries' existing and proposed satellite navigation systems

see FCC's support as vital to U.S. policy. Allowing other systems to intentionally

radiate energy into restricted spectrum bands sets a poor precedent for

defending exclusive use of radionavigation bands for GPS in the international

forum, according to government and industry officials.

GPS users at DOT and the Defense Department must constantly battle to

protect the portions of spectrum allocated for radionavigation systems from

infringement and interference in an already crowded spectrum.

For example, a number of companies have proposed allowing mobile satellite

communications services to broadcast in the spectrum that GPS uses to emit

its low-power signals. The issue is expected to come up again next month

at the latest World Radiocommunication Conference.

"If we don't take actions to protect and defend GPS in our own country,

it's hard to convince others to protect it," said David Stempler, president

of the Air Travelers Association. "We're not getting the support from the

FCC to protect and defend the safety spectrum that we really need to set

an example for the rest of the world."