Mobile startup LightSquared may go from the frying pan to the fire on Wednesday when it releases a report on potential interference between its planned network and GPS.
Reports on recent tests have shown the company’s LTE (Long-Term Evolution) equipment knocked out Global Positioning System gear used for aviation, surveying, consumer navigation and other applications. The U.S. Defense Department and Transportation Department have also criticized LightSquared’s plan. LightSquared will need to persuade the Federal Communications Commission (FCC) that the interference can be prevented before the agency will allow the project to continue.
On Wednesday, the carrier is due to issue a report from a Technical Working Group it formed with vendors and other interested parties in the GPS community. The group was formed to devise tests to determine interference.
LightSquared gained access to valuable terrestrial cellular spectrum by agreeing to combine an LTE network with a satellite system, which the FCC sees as a tool to improve mobile data access in rural areas of the U.S. The carrier plans to sell its cellular and satellite services wholesale to service providers who can offer subscribers either or both services. It won’t offer any service plans of its own. Electronics retailer Best Buy and cellular carrier Leap Wireless have announced plans to resell LightSquared service.
However, part of the cellular spectrum LightSquared holds is next to frequencies used by GPS, the service that allows vehicles, airplanes, cell phones and other systems to determine their location via satellite signal. Conditions of the FCC’s approval of LightSquared’s network require the company to show GPS service would not be hurt. Over the past few months, LightSquared and its Technical Working Group have been devising and carrying out tests leading up to Wednesday’s report.
Some test results disclosed at a meeting in Washington, D.C., on June 9 indicate the LTE network might put aviation, public safety and other valued uses of GPS at risk.
A series of tests in April had serious effects on several types of GPS systems, according to the National Positioning Navigation and Timing (PNT) Systems Engineering Forum. The Forum conducts assessments for the Space-Based PNT Executive Committee, a government agency set up to coordinate efforts around GPS and similar systems.
Tests in an anechoic chamber at White Sands Missile Range in New Mexico showed a simulated LightSquared network knocked out GPS receivers used for aviation, surveying, agriculture, the U.S. Coast Guard and Garmin personal navigation devices. All the aviation units lost their GPS connections, as did all the tested high-precision receivers for scientific use by NASA.
The PNT agency also reported the results of “live sky” tests conducted using a production transmitter set up and operated by LightSquared at Holloman Air Force Base in New Mexico. Among other things, those tests showed that police cars lost their GPS reception within about 600 feet from the tower and ambulances and fire trucks lost service about 1,000 feet away. General Motors’ OnStar vehicle navigation systems also were significantly degraded, the agency said.
To mitigate the interference, the PNT group proposed shifting LightSquared service to other frequencies or adding filters to GPS receivers, a solution that the agency noted would be expensive and might affect GPS performance. Other possible solutions were changing LightSquared’s antenna patterns and cutting transmitter power.
The RTCA, a non-profit corporation that advises the Federal Aviation Administration, said its tests showed that LightSquared’s operations in one part of its spectrum band would make GPS unavailable to aircraft over a large region of the Northeastern U.S. RTCA recommended LightSquared not be able to use that band, and called for further study.
At the June 9 meeting, LightSquared said there were several possible ways to mitigate the interference, including ones involving the frequencies and transmitting power the carrier uses, and that it had not taken any options for mitigation off the table.
