Proposed 4G network threatens vital GPS services, Congress told
- By William Jackson
- Sep 09, 2011
A proposed broadband network that would pump billions of dollars into the struggling U.S. economy also would interfere with the Global Positioning System, which is vital to the nation’s security and public safety, a House committee was told Sept. 8.
LightSquared, a mobile satellite communications company, has received conditional approval from the Federal Communications Commission to build a nationwide 4G wireless network, provided it can be done without interfering with adjacent GPS signals. But government and industry tests this summer demonstrated the proposed system created harmful interference.
This could not only interfere with thousands of consumer applications for GPS but also hamper federal science and research programs, threaten management of satellites and set the GPS-based Next Generation Air Traffic Control System back a decade at a cost of more than $70 billion, the House Science, Space and Technology Committee was told.
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“LightSquared’s intended deployment of their high-power terrestrial broadband system should not be allowed to commence commercial operations until the identified problems are resolved,” said Anthony Russo, director of the federal National Coordination Office for Space-Based Positioning, Navigation and Timing.
LightSquared said the problem is created by improperly designed GPS receivers, rather than its equipment, and has offered to reduce the power and limit the radio frequency spectrum in which its network would operate to mitigate the problem.
“It is a receiver-side issue that was never raised in 2001 to 2005,” when the FCC was considering the company’s proposal, said Jeffrey Carlisle, LightSquared’s executive vice president for regulatory affairs and public policy.
Russo called the LightSquared offer a “serious and constructive proposal” but said there is no conclusive evidence yet that it would solve the interference problem. “The government recommends further testing before the proposal is accepted,” he said.
The conclusion puts legislators and regulators squarely between competing priorities: The need to stimulate economic development and expand nationwide access to competitive broadband communications services on the one hand, and the need to protect what committee chairman Rep. Ralph M. Hall (R-Texas) called a “vital national interest” on the other. Hall cited estimates that GPS contributes more than $3 trillion in direct and indirect economic activity and has created more than 3 million jobs.
“Any potential disruption to GPS, and the science activities that it supports, is of utmost concern to this committee,” Hall said.
GPS provides more than economic stimulus. The precise timing services provided by the Defense Department satellite system and the geographic locational services it enables underlie the operation of high-speed data networks and transportation networks. GPS also enables measurements used by agencies including the U.S. Geological Survey and the National Oceanic and Atmospheric Administration to forecast severe weather, floods, earthquakes and volcanic eruptions.
NASA uses GPS to operate earth-based observation systems and to navigate satellites, and the Federal Aviation Administration is trying to transition the outdated air traffic control system from radar to GPS.
The Transportation Department has estimated that accommodating the LightSquared network interference — if it could be done — could cost $72 billion in replacing and redeveloping systems, and delay the program by 10 years.
Carlisle said his company has played by the rules set out by that FCC in developing its network plans and operates within the limits set, and that the GPS industry now wants to change the rules.
“This is an issue of responsible receiver design,” he said. “We are going to make a major investment in infrastructure,” of $14 billion over eight years, “but will do nothing to degrade GPS.”
Government and industry officials, however, say that it is the LightSquared network that is changing the rules. GPS and satellite communications have coexisted for years because they both used low-powered signals that are easy to filter. The GPS industry has relied on FCC assurances that the satellite bands would remain “quiet” channels, said Scott Pace, director of George Washington University’s Space Policy Institute. This allows high-precision GPS receivers to use data correction signals from commercial carriers that are transmitted in the satellite communications band.
But that has changed with the proposed LightSquared network, which would use the satellite spectrum for a wholesale broadband terrestrial network. LightSquared would sell access to commercial carriers offering 4G communications services.
This creates a problem because terrestrial network signals are much stronger than satellite communications signals, including GPS. Russo said that at a distance of one-half mile from a base station, the LightSquared signal is 5 billion times more powerful than a GPS signal; that is equivalent to the difference between a teaspoon of water and Niagara Falls, he said.
This power difference could make filtering signals a difficult task, even if it were possible. And if accomplished, it would be years or decades before installed hardware and software, including satellites now in orbit, could be replaced or upgraded. This makes additional testing on the LightSquared proposal to limit spectrum use and reduce power essential, officials said.