GPS interference tests were conducted in 2010 by a technical working group, commissioned by the National Telecommunications and Information Administration (NTIA). The group included RTCA GPS experts and LightSquared representatives. It concluded that LightSquared's high-powered ATCs indeed could pose a threat to GPS. Further research would be needed to quantify the problem.

In January 2012, the National Executive Committee for Space-Based Positioning, Navigation and Timing (PNT), wrote a letter to the FCC and NTIA stating that the nine federal departments and agencies it represents had reached a “unanimous conclusion” that LightSquared's original and subsequently scaled-back plans for ATCs “would cause harmful interference to many GPS receivers.” Moreover, the letter also stated that the FAA concluded that the ATCs would interfere with GPS-based TAWS boxes as well as GPS navigation systems.

With no “practical solutions or mitigations” available, PNT said that “no additional testing is warranted at this time.” It also added that PNT fully supports the White House's plan to open up 500 MHz of spectrum for wireless broadband. The letter was signed by deputy secretaries of Defense and Transportation Ashton Carter and John Porcari, respectively, who are executive committee co-chairmen.

LightSquared immediately complained that the GPS interference tests were rigged to put its proposed system at a disadvantage. But the firm now isn't just battling Trimble, Garmin, Deere and other GPS manufacturers. It's going up against the federal government.

If the FCC and NTIA disapprove LightSquared's plan, the company financially plunges into very hot water. Billions have been invested in the technology by Harbinger Capital Partners and time is running out before marketing partners lose patience and possibly back out of agreements. Sprint, for instance, set a Jan. 31, 2012, deadline for LightSquared to gain necessary approvals to proceed with network development.

With so much at stake on both sides, the outcome of the battle between LightSquared and the GPS community is uncertain. The FCC and the White House want to make broadband as universally available to homes in the 21st century as electricity became available in the 20th century during the FDR administration.

“Politically, there's a high degree of design to put Internet into every home,” comments one GPS expert. And LightSquared stands to reap billions in profits from wholesaling wireless broadband connectivity using the L-band spectrum.

GPS users, particularly the aviation community, have staked their future on L-band satnav. The standards for aviation grade WAAS receivers have been in place for more than a decade and thousands of boxes are in service today. Aviation industry groups claim it would take 10 to 15 years to develop and certify new GPS avionics that would be immune to interference from LightSquared's ground stations. Retrofitting the fleet with new gear would cost several billion dollars.

“The FCC jumped on approving LightSquared's request before it considered the implications,” says another source. “You can't just throw away safety services and the FAA's next generation air traffic management system.”

“Effectively, the FCC is directing that a quiet-spectrum neighborhood be rezoned for concert rock bands at the threshold of pain. It is being suggested that its current neighbors should simply add more insulation and foot-thick windows to their houses,” says Bradford Parkinson, GPS pioneer and emeritus professor at Stanford University.

“Radio frequency spectrum is a limited natural resource. You can't make more of it,” adds another source. L-band is appealing for wireless broadband because it suffers less signal loss in precipitation than Ku or Ka band. The demand for L-band could make the LightSquared versus GPS battle a zero sum game. One side has to lose for the other side to win.

But the battle over GPS is just one of many frequency spectrum struggles facing the aviation community. Civil users, for instance, are quietly gaining L-band spectrum near the 1435- to 1525-MHz band used for flight-test telemetry.

The military also has plenty of history on spectrum wars. Years ago, the FCC had to sort out a frequency use battle between DirectTV and Hughes Radar Systems, developer of the APQ-181 radar aboard the B-2 bomber. Later the FCC accidentally sold off that military-use frequency band to a multinational organization, requiring the U.S. Air Force to retrofit all 20 B-2 aircraft in service with a new radar. The loss of the B-2 radar band license is emblematic of problems the military is having with holding onto spectrum it needs for new technology systems while civilian users are demanding more capacity for video-capable PDAs and other high-speed wireless broadband applications.

Modern military aircraft, operating with airborne data links such as the Joint Tactical Information Distribution System, have need for large amounts of bandwidth. JTIDS, for instance, operates on 51 channels in the 969- to 1206-MHz range in the bottom of L-band. Neighboring L-band frequency spectrum being bought by civil users has the military scrambling for additional spectrum in other bands, potentially costing the Pentagon billions of dollars for new data link systems.

There also is a threat to aviation users from bandwidth hunters looking for spectrum above the 3.7-MHz upper limit specified in the National Broadband Plan. Now the spectrum neighborhood around the 4.2- to 4.4-GHz radio altimeter band is being eyed for other uses. Precise and reliable radio altimetry is vital to the functioning of GPWS boxes. It also is used by some digital flight control systems to trigger certain changes in control laws during landing.

But potential L-band encroachment remains the main concern for civil aviation users. The next generation of civil GPS receivers will use both the L-1 channel centered at 1575.42 MHz and the L-2 channel at 1227.6 MHz to increase position fixing precision.

The dual frequency system will enable receivers to detect and correct for ionospheric signal distortion. Eventually a third GPS channel, L-5 centered at 1176.45 MHz, will become available for safety services.

Each channel will require 20 to 30 MHz bandwidth to be available to assure proper GPS receiver performance. That means there will be triple the number of L-band GPS frequencies that must be protected from encroachment from other users, particularly wireless broadband network service providers.

The message is clear. The LightSquared versus GPS battle was a harbinger of huge spectrum wars ahead. The aviation community initially was slow to respond to this latest threat to GPS operability, but it cannot afford to relax even as it, along with other GPS stakeholders, prevails on this single non-compatible frequency use issue.

Aviation users better be vigilant so that they can detect future frequency invaders in the early stages. They must mount a vigorous defense to prevent encroachment by the wireless broadband industry, among other non-aviation interests, if they are serious about building a 21st century air traffic management system. BCA