LightSquared Reports Major GPS Interference

LightSquared has formally presented a revised plan for its nationwide wireless broadband network as the final report on interference testing shows that its original deployment plan is “incompatible with aviation GPS operations.”

Without significant mitigation, the report says LightSquared’s plans to deploy 40,000 high-power terrestrial transmitters across the U.S. “would result in a complete loss of GPS operations below 2,000 ft. above ground level over a large radius” from metropolitan areas.

The final report by a technical working group formed by LightSquared and the U.S. GPS Industry Council, representing receiver manufacturers and users, was submitted to the Federal Communications Commission (FCC) on June 30.

“For the originally defined LightSquared spectrum deployment scenarios, GPS-based operations are expected to be unavailable over entire regions of the country at any normal operational aircraft altitude,” the working group’s aviation sub-team concluded.

Acknowledging the interference, LightSquared has revised its plans and now proposes beginning service using only the lower of its two 10-mhz-wide blocks of frequency spectrum. This lower block is farthest away from GPS frequencies, and tests show interference is limited.

“Analysis performed by RTCA suggests that a shift to using only a lower 5-mhz channel likely would be compatible with aviation GPS operations,” the final report says, but adds, “compatibility of aviation GPS operations with a single lower 10-mhz channel could not be determined definitively without additional study.”

LightSquared says testing “demonstrates that, while additional analysis needs to be done by the FAA with respect to its airborne receiver standards ... of the approximately 400 million GPS devices in use today [in the U.S.] well over 99% ... can be expected to experience no meaningful interference from LightSquared operations in the lower 10-mhz channel.”

Meanwhile, opponents of LightSquared’s plans have stepped up calls to move the service to a different band in the wake of the report.

As LightSquared’s original deployment plan was to use both of its frequency blocks, “that’s what the [FCC-mandated] working group studied,” says Jim Kirkland, vice president and general counsel of receiver manufacturer Trimble Navigation, founding member of the Save Our GPS coalition. “Testing of transmissions in the lower block of frequencies only “was a very late addition, but the limited tests results in the low band still show significant interference.”

LightSquared believes filters could be developed that prevent GPS receivers being overloaded by its transmissions, but did not produce any for testing, Kirkland says. “There are no actual test results relative to mitigation because no filters are available. There is no retrofit option because there is nothing to retrofit receivers with,” he says.

LightSquared says its proposed solution has already cost it “over $100 million to shift the timing of its access to portions of the frequency bands it shares with Inmarsat” with further costs expected from delays in using its full set of frequencies at full power.

The GPS industry’s position “that LightSquared should simply ‘go away’ is both ironic and troubling,” the company says, arguing the industry “has built an entire business based on a large subsidy from taxpayers — estimated to be worth $18 billion — in the form of free access to the government’s GPS satellite infrastructure and frequencies.”