Tests confirm concerns about GPS interference

Feb 17, 2012
by DTN

Potential interference with GPS signals was too much to overcome to make the proposed LightSquared wireless network feasible in rural areas as the Federal Communications Commission (FCC) announced last Tuesday it would not allow the project to move forward.

The LightSquared proposal has drawn a wide swath of opposition from the likes of the U.S. Department of Defense (DOD), the Federal Aviation Administration (FAA), agriculture equipment companies and the GPS industry.

Though rural areas are in need of wireless service, agriculture groups and farm equipment companies have opposed the project based on concerns that the LightSquared signal could interfere with GPSbased precision-agriculture systems.

Syracuse, NE, soybean farmer and American Soybean Association (ASA) President Steve Wellman said FCC made the right decision.

“Tuesday’s decision by the FCC is certainly a great relief for more than 600,000 soybean farmers across the country who use GPS technology to precision-apply seed and fertilizer, to test fields for fertility and to monitor yields, to reduce chemical and fuel use, and to map field boundaries, roads, irrigation systems,” Wellman said in a news release. “In short, GPS technology has enabled farmers to produce more food for a growing world population with fewer inputs.

“Farmers invest thousands of dollars in highprecision GPS equipment and applications to run more efficient, sustainable, cost-effective and productive farms. The Light- Squared network would have rendered that investment—not to mention the consumer GPS market projected to reach almost $29 billion in the U.S. by 2015— all but useless.”

Wellman said Light- Squared’s efforts “underscore the pressing need for better broadband service” in rural America.

“ASA supports the pursuit of a commercial solution that will better connect the rural communities in which agriculture thrives,” he said, “while protecting the value of precision agricultural GPS systems.”

DTN’s attempts to reach LightSquared for comment were unsuccessful.

Concerns verified

Interference concerns were verified by tests performed last year, according to a letter to the FCC from the National Telecommunications and Information Administration (NTIA).

Tests were conducted last year on 92 personal/general navigation GPS receivers compared to earlier tests on just 29 receivers, NTIA Assistant Secretary for Communications and Information Lawrence E. Strickling said in a letter to the FCC. The test found 69 of the devices were affected “by the lower 10 MHz base station signal” as proposed by LightSquared.

In addition, the letter said the company helped to develop a plan for validating the test measurements.

“Accordingly, NTIA concludes that there is no practical way at this time to mitigate the interference that LightSquared’s proposed network would cause to personal/general navigation GPS receivers,” the letter said.

The tests also verified similar concerns raised by the aviation industry and DOD, according to the letter.

“Based on the analysis, GPS receivers used for lowaltitude aviation operations such as terrain awareness navigation and surveillance would not be compatible with a LightSquared base station operating at its maximum proposed EIRP taking into account transmitter and GPS receiver antenna patterns,” according to the letter.

“Interference would occur when the GPS receiver is in the vicinity of a base station, or at lower altitudes in the presence of multiple base stations.”

The FAA and Light- Squared could not reach agreement on “certain technical issues,” the letter said.

LightSquared reportedly offered several mitigation strategies, but “Light- Squared’s proposals would require constant, individualized monitoring and adjustment to over 40,000 sites nationwide to ensure consistency with air safety requirements,” the letter said.

Interference ‘not tolerated’

FCC Spokesperson Tammy Sun said in a statement that the LightSquared proposal offered “potential to unleash new spectrum for mobile broadband and enhance competition.” In the end, however, she said there were too many questions.

“The commission clearly stated from the outset that harmful interference to GPS would not be permitted,” Sun said.

Jim Kirkland, vice president and general counsel of Trimble, a founding member of the Coalition to Save Our GPS, which represents a number of aviation, GPS, ag equipment and other industries, said NTIA’s conclusions illustrate why the group opposed the LightSquared proposal from day one.

“After a year of extensive testing, NTIA has now conclusively stated that Light- Squared’s operations will interfere with GPS and that there is no viable mitigation path for the foreseeable future. The findings of widespread interference include serious threats to safety-of-life systems, as the FAA report details,” Kirkland said.

“The coalition stands ready to work with the NTIA and the FCC to address the important policy issues relating to longerterm use of satellite spectrum and reduction of potential interference to maximize the efficient use of all satellite spectrums.”

NTIA said in the letter to FCC that federal agencies this year will work to develop new GPS spectrum interference standards that will “help inform future proposals for nonspace commercial uses in the bands adjacent to the GPS signals.”

Grassley questions

Last April, Sen. Charles Grassley, R-IA, started asking questions about FCC’s fast-tracking of the project. LightSquared officials have told DTN that the project has been in the public eye for the past decade.

“The FCC’s action seems to acknowledge the point I’ve been making since April,” Grassley said in a statement. “Prematurely granting a conditional waiver in a rushed process is not the way to get the right result. Now that the interference issue is settled, we need to find out more than ever why the FCC did what it did.

“The agency put this project on a fast track for approval with what appears to have been completely inadequate technical research. After all of this time and expense, still, no one outside of the agency knows why. That’s not the way the people’s government should work.”

Sen. Pat Roberts, R-KS, said the FCC decision was important for GPS users.

“Any Kansan with a GPS in his or her car was going to be affected by the interference this conflicting network posed,” he said in a statement. “This is a particularly big win for public safety as well as precision agriculture, aviation and other industries critical to the Kansas economy that rely on seamless GPS communication.”

Roberts said in a news release that he worked with a variety of groups, including but not limited to: GPS company Garmin, John Deere and Company, Case New Holland, FedEx, UPS, National Business Aviation Association, Aircraft Owners and Pilots Association, General Aviation Manufacturers Association, National Rural Electric Cooperatives Association, Caterpillar, Agricultural Retailers Association, and the American Association of State Highway and Transportation Officials. — Todd Neeley, DTN