U.S. defends crowded spectrum

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,

called Galileo.

* 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

industry organizations.

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.