Despite denials by LightSquared and its allies, tests by two government bodies of LightSquared's broadband data system find there is significant interference with GPS navigation systems.
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 that
there 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.
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Wayne Rash is a Senior Analyst for eWEEK Labs and runs the magazine's Washington Bureau. Prior to joining eWEEK as a Senior Writer on wireless technology, he was a Senior Contributing Editor and previously a Senior Analyst in the InfoWorld Test Center. He was also a reviewer for Federal Computer Week and Information Security Magazine. Previously, he ran the reviews and events departments at CMP's InternetWeek.
