June 12, 2011
LightSquared’s Network Could Jam GPS Systems
A proposed high-speed wireless broadband network being launched by LightSquared is under scrutiny by the US government due to its potential to jam GPS systems used for aviation, public safety, and military operations, among other things.
The results released this week from the Federal Communications Commission (FCC) come after increasing concerns that the new network could cripple GPS systems that are a major part of the country's infrastructure. The results also raise questions about whether the government will allow LightSquared to turn its network on as scheduled next year.
But other government agencies and GPS equipment manufacturers have raised concerns that LightSquared's network would use airwaves right next to those already set aside for GPS. They are warning that sensitive satellite receivers designed to pick up relatively weak signals could be overwhelmed when the new network goes live sending signals from as many as 40,000 transmitters on the ground.
"LightSquared's network could cause devastating interference to all different kinds of GPS receivers," Jim Kirkland, vice president and general counsel of Trimble Navigation Ltd., which makes GPS systems, told the Associated Press (AP).
Based on the level of concerns, the FCC made clear that LightSquared cannot launch its network until interference problems are resolved. It is ordering the company to participate in a technical working group with GPS makers and users to study the issue. The group conducted GPS interference tests using LightSquared equipment in Las Vegas last month and will release a report to the FCC next week.
Once it reviews the results, the FCC will seek public comments on the issue. The FCC said in a statement on Friday that it "will not allow LightSquared's commercial service to proceed if that would cause widespread harmful interference with GPS."
In another round of tests, a working group of the National Executive Committee for Space-Based Positioning, Navigation, and Timing discovered potential for widespread GPS interference. Those tests showed that LightSquared wireless signals interfered with GPS receivers used by the Coast Guard and NASA, and also caused Federal Aviation Administration GPS receivers to stop functioning.
The tests -- which were mainly conducted by federal agencies at Holloman Air Force Base and White Sands Missile Range in New Mexico in April -- also caused GPS receivers used by New Mexico state police and by fire and ambulance crews to lose reception. The interference also disrupted General Motors' OnStar navigation systems.
Nonprofit group RTCA also released its own interference test results last week, finding that LightSquared's use of airwaves closest to the GPS spectrum would cause a "complete loss of GPS receiver function" in large metropolitan areas.
The FCC insists the test results do not satisfy the interference questions and concerns. "Some of the tests to date may have relied on different assumptions, metrics and mitigation assumptions, and so may not accurately reflect the potential for interference as a result of how the network may be operated," the agency said.
LightSquared executive vice president Jeffrey Carlisle told AP that he remains confident that the company's new network and GPS systems can co-exist. After all, the findings of interference do not come as a surprise, he noted. What matters is what can be done about the interference, he added.
One solution to the problem would be modifying LightSquared's antenna patterns and reducing the power levels of its base stations. Another solution might be limiting the slices of airwaves that the company can use or moving the company to a different part of the spectrum. A third solution would be to install better filters on GPS receivers to filter out LightSquared's signals.
GPS makers do not agree with the final option for a solution since they say it would take years, and cost billions of dollars, to upgrade all of the GPS receivers in use.
On the Net:
- National Executive Committee for Space-Based Positioning, Navigation, and Timing