U.S. defends crowded spectrum
- By Paula Shaki Trimble
- Jul 17, 2000
The United States has successfully blocked mobile satellite communications
companies from laying claim to part of the radio spectrum allocated to the
Global Positioning System, but the government now faces a threat from a
new communications technology.
At this spring's World Radiocommunication Conference 2000 in Istanbul,
Turkey — where the International Telecommunication Union met from May through
June — a U.S. delegation led by Ambassador Gail Schoettler ended a 3-year-old
proposal for allowing mobile satellite communications services to share
portions of the spectrum allocated for GPS.
GPS, a system of at least 24 satellites operated by the Defense Department,
provides accurate positioning and timing information to users on the ground,
in the air or in space. GPS is used to navigate and land aircraft, guide
missiles and time cellular telephone transfers, all of which require high
levels of accuracy.
"Of all the many complicated issues we had, the one we did best on was GPS,"
Schoettler said recently, crediting industry for its efforts to gain support
from other countries, each of which get one vote at WRC 2000.
The U.S. gained protection for GPS in three major areas:
* The ITU approved 1,164 MHz to 1,215 MHz for a third civilian GPS signal
to be developed based on requirements for aviation.
The new signal, called L5, will be centered on 1,176.45. The allocation
also provides 24 MHz of spectrum for Europe's satellite navigation system,
* Protection for the GPS satellite signal broadcast from one space asset
to another space asset was granted in all three GPS spectrum bands — 1,176.45
MHz, 1,227.6 MHz and 1,575 MHz.
* The ITU suppressed a resolution to allow mobile satellite services to
share the GPS spectrum, which means the proposal is dead for the time being.
Still, Schoettler said the issue of sharing the GPS spectrum could be
raised again. "Even though the U.S. won big on GPS at WRC, I don't think
you can count on being safe," she said.
And the United States now faces a threat to GPS signals by a new radar
and wireless communications technology called ultra-wideband.
Studies to measure the effects of ultra-wideband on GPS signals are
being conducted by the Transportation Department at Stanford University,
by the National Telecommunications and Information Administration, and by
The Federal Communications Commission has issued a notice of proposed
rule-making on whether to allow ultra-wideband technology to operate in
the radio spectrum, and it plans to use the results of interference studies
to make a decision in the fall.
Witnesses at a June 29 House Transportation and Infrastructure Committee
hearing on the Federal Aviation Administration's GPS-based Wide-Area Augmentation
System and other spectrum issues stressed the need for adequate time to
analyze the impact of ultra-wideband on GPS and the importance of interference-free
GPS bands when pilots are using the system to land passenger airplanes.