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Tests show wireless network could harm GPS systems

Tests show wireless network could harm GPS systems

By Associated Press | Updated: 5 June 2012 02:00 IST

Highlights

New test results show that wireless broadband network would produce significant interference with GPS systems

New test results show that a proposed nationwide wireless broadband network would produce significant interference with GPS systems used for everything from aviation to high-precision timing networks to consumer navigation devices. Changes to the proposal could reduce interference, but wouldn't eliminate it.

The findings, based on extensive equipment tests conducted in Las Vegas, increase pressure on the Federal Communications Commission to block a Virginia company called LightSquared from launching the network, which is designed to compete with super-fast systems being rolled out by AT&T and Verizon Wireless.

Although the FCC in January gave LightSquared approval to build the system, the agency said it would not let the company turn on the network until GPS interference problems are resolved.

The agency required LightSquared, GPS equipment makers and GPS users to establish a working group to study the matter.

That group filed its report with the commission on Thursday, with the two sides offering different interpretations of the test results.

LightSquared insisted that the interference problems are fixable.

But GPS equipment makers, and companies and government agencies that rely on GPS technology, warn that the planned network would jam their systems because LightSquared would use airwaves close to those already set aside for GPS.

They say that sensitive satellite receivers - designed to pick up relatively weak signals coming from space - could be overwhelmed when LightSquared starts sending high-powered signals from as many as 40,000 transmitters on the ground. GPS signals, they say, will suffer the way a radio station can get drowned out by a stronger broadcast in a nearby channel.

"The FCC needs to consider other options for the LightSquared signals where they do not run up against the laws of physics," said Charles Trimble, co-founder of Trimble Navigation Ltd., which makes GPS systems.

With the working group report complete, the FCC will now seek public comments. The FCC said it will review the report, adding that it has "a long-standing record of resolving interference disputes."

The working group's report follows the release of federal test results that also found significant interference with GPS systems used by a broad cross-section of government agencies, including the Coast Guard, the Federal Aviation Administration and NASA.

Faced with growing GPS industry resistance, LightSquared last week proposed to launch its network using a different slice of airwaves located farther away from GPS frequencies. It also proposed to transmit signals at lower power levels to ensure that its network would not interfere with most nearby GPS systems.

Most of the testing conducted by the working group was based on the company's original plan to use airwaves next to the GPS band.

The working group said that plan would produce significant, across-the-board interference. Among the findings:
- GPS systems used for aviation would be unavailable over entire regions of the country at normal aircraft altitudes.
- GPS receivers built into cellular devices could experience interference at significant distances from LightSquared's base stations - resulting in delayed or inaccurate location readings.
- Space-based GPS receivers used in NASA science missions could be disrupted.

Although the working group conducted only limited testing based on LightSquared's proposal to use different airwaves, it said the change could reduce problems for some GPS receivers, including those used in aircraft navigation and cellphones.

LightSquared, however, acknowledges that other GPS devices, particularly high-precision receivers used in construction and agriculture, would still experience significant disruption.

LightSquared maintains that the interference is largely a problem of the GPS industry's own making. That's because GPS receivers are picking up signals outside their own bands - in frequencies licensed to LightSquared.

That had never presented a conflict until the FCC provisionally approved LightSquared's wireless broadband network. Until now, that spectrum has been used primarily for satellite communications, with only limited ground-based wireless service to fill coverage gaps.
GPS receivers can easily screen that out.

LightSquared, which is based in Reston, Va., also insists the problem can be fixed by installing better filters in GPS devices to screen out its signals. Those filters, LightSquared says, cost as little as 5 cents each.

GPS manufacturers say that solution is speculative because such filters do not yet exist and were not available for testing. They add that although filters might work with some GPS receivers, such as those embedded in cellphones, they would not work in all GPS equipment and could significantly degrade performance and battery life.

Bronson Hokuf, an engineer with GPS maker Garmin Ltd., also said it would be nearly impossible retrofit hundreds of millions of existing GPS devices already in use. The working group said installing new filters in GPS equipment used for aviation, for instance, would be very expensive and could take at least 10 years.

Although the FCC has promised that it won't let the LightSquared network harm GPS systems, it is eager to see the company succeed.

The FCC views the network as one part of a broader government push to free up more airwaves for mobile broadband services to keep up with the explosive growth of online apps, mobile video and other bandwidth-hungry wireless applications.

The agency also hopes LightSquared will help it advance its goal of bringing high-speed Internet connections to all Americans. The company, which plans to wholesale network access to other companies that will rebrand the service under their own names, has pledged to reach 260 million Americans with its coverage by 2015.

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