Two government bodies have now reported their findings confirming that LightSquared's satellite-based LTE broadband data system interferes with the global GPS system run by the U.S. government.
The short answer is that the interference ranges from significant to completely blanking out GPS signals required for navigation and many other uses. When this issue first emerged, LightSquared said thatthere would be no interference.
I looked at the specs, and I looked at the frequencies, and I relied on my tests of GPS receivers performed over the years for eWEEK, The Washington Post, Plane & Pilot magazine and others. During those tests it was clear that strong signals from nearby transmitters would desensitize GPS receivers. The amount of desensitization depended on how close in frequency the offending transmitter was, how strong the signal was and how well-designed the GPS receiver was.
In May the National Space-Based PNT (Positioning Navigation and Timing) National Executive Committee and the Federal Aviation Administration in concert with contractor RTCA tested the LightSquared system's interference with GPS. Both agencies revealed in a panel discussion in June that the interference was significant.
In some tests, all receivers including those used by the U.S. Coast Guard completely lost the ability to navigate. GPS systems used by NASA for scientific use were seriously impacted. The FAA had similar results in its tests, concluding that aviation GPS receivers would be rendered useless at altitudes below 2,000 feet in urban area. You'll note that aircraft frequently fly below 2,000 feet in urban areas because that's where the airports they most frequently use for landings are, and GPS plays a significant role in approach navigation.
What this means is that in spite of LightSquared's claims to the contrary, its LTE system, which operates on frequencies adjacent to the GPS frequency bands, would effectively kill most GPS uses. There has been a great deal written about this issue, with many, especially those supporting LightSquared, suggesting that this is all the fault of poor GPS receiver design. Apparently the GPS manufacturers should have anticipated that a high-powered broadband Internet service would decide to locate next door.
But the fact is that millions of GPS receivers were built long before LightSquared was a gleam in anyone's eye, and long before the Federal Communications Commission gave approval for operations. The result now is that if the FCC continues to authorize it, GPS will effectively be compromised.