GPS users hope to forestall new tech
- By Paula Shaki Trimble
- Apr 10, 2000
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
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
"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,
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,
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."