Planned LightSquared cell network is incompatible with aviation GPS, group says

A new nationwide broadband cellular network planned by startup LightSquared will cause complete loss of GPS receiver functionality when operated in the upper band of the frequency allocated to the company, a Federal Aviation Administration advisory group said in the executive summary of a report sent to FAA last week.

Manufacturer Deere and Co., whose agricultural equipment uses GPS to support precision farming operations, told the Federal Communications Commission late last month that tests this April in New Mexico showed that the LightSquared network will result in "massive interference" to the system it uses to provide location information.

Last month, first responders reported that the LightSquared system knocked out GPS receivers in tests at Holloman Air Force Base in New Mexico.

LightSquared, the GPS industry and federal agencies are conducting tests to determine the extent of interference from the company's system to GPS receivers, with a final report due to FCC on June 15. FCC directed the company to work with the industry to determine the potential effect its terrestrial transmitters, which operate in the 1525-1559 MHz and 1626.5-1660.5 MHz bands, would have on GPS systems that operate in the nearby 1559-1610 MHz bands.

The Radio Technical Commission for Aeronautics told FAA that operation of the LightSquared cellular network "would be incompatible with the current aviation use of GPS, however, modifications could be made to allow the LightSquared system to coexist with aviation uses of GPS."

The upper channel of the LightSquared spectrum, the executive summary of the RTCA study said, would make GPS unavailable over an entire region of the country: "From an aviation perspective, LightSquared upper channel operation should not be allowed."

But the study also said operations of LightSquared cellular transmitters in the lower band "is compatible with aviation GPS operations." The findings have significant implications for FAA's plans to replace its ground-based air traffic system, which uses radar to track aircraft, with a new GPS based system by 2025. The aviation system, known as NextGen, is estimated to cost more than $40 billion.

When asked if the company would consider operations only in the lower band, Jeff Carlisle, executive vice president for regulatory affairs at LightSquared, said, "we are not taking any options off the table." He said that initially the company would take a "flexible" approach to its national deployment of 40,000 cell sites, but eventually wants to use all its spectrum.

In letters and reports it sent to FCC last month, Deere said tests at Holloman Air Force Base and White Sands Missile Range in New Mexico last month demonstrated that the LightSquared system caused a "complete loss" of GPS service at a distance of between 4 and 22 miles, depending on the propagation of the cell signal and "severe interference" at a distance of more than 20 miles.

Deere also operates a global satellite system called Starfire, which corrects atmospheric errors in normal GPS signals and provides accuracy within 3 feet, rather than 50 feet for uncorrected GPS signals, and said LightSquared causes "massive interference" to this system.

The company told FCC there is no "potentially effective mitigation solution" to prevent GPS interference from LightSquared. As a result, the system risks "serious harm to the U.S. agriculture industry." Deere estimated that precision farming reduces the cost of food production in the United States by as much as $3 billion a year.

Carlisle said that LightSquared did not cause interference to the Deer receivers or systems but said those receivers "see" into and pick up signals from company's transmitters operating outside GPS frequencies. He said LightSquared remains committed to helping GPS users like Deere resolve their problems.

Top officials at the Defense and Transportation departments sharply criticized FCC in April for giving LightSquared permission to build its network, and they expressed concern about its potential for interference with GPS.

FCC plans a public comment period after LightSquared and the GPS industry file their final report next week.