The FCC must decide who will suffer the consequences of inferior GPS receivers.

In the ongoing dispute between LightSquared Inc. and the GPS industry, LightSquared has requested an FCC ruling that GPS users are not entitled to protection from LightSquared’s interference. And the FCC’s International Bureau, in turn, has asked for the public’s input on LightSquared’s request.

Back in January, 2011, the FCC gave LightSquared a waiver authorizing it to provide terrestrial, tower-based mobile data service on frequencies once set aside exclusively for mobile satellite communications. The waiver was (and remains) subject to some conditions – one of which requires LightSquared to satisfy a formal “Interference-Resolution Process” to address concerns about potential interference to GPS receivers. Meeting that condition has been a problem for LightSquared.

Because LightSquared’s frequencies are just below those coming down from the GPS satellites, GPS users feared interference. So the FCC set up a working group to run tests. 

The working group, which includes people from both LightSquared and the GPS industry, subsequently filed a report that found that LightSquared’s operations resulted in “potentially significant interference” into various GPS devices in the upper 10 MHz portion of LightSquared’s band (i.e., the portion that closely abuts the GPS frequencies). The report also identified interference issues in the lower 10 MHz portion of the band, which is farther from GPS. One chilling example: “LightSquared deployment plan[s] are incompatible with aviation GPS operations absent significant mitigation, and would result in a complete loss of GPS operations below 2000 feet above ground level (AGL) over a large radius from the metro deployment center.”

In response, LightSquared offered to avoid the upper 10 MHz for now, and to operate in the lower 10 MHz at lower power than originally planned. The FCC asked for certain additional testing. But neither LightSquared’s proposals nor the additional tests – which LightSquared alleged were biased – alleviated the interference concerns.

Then, last December, the skilled electrical engineers who make up the U.S. Congress intervened, forbidding the FCC from authorizing LightSquared until the FCC has “resolved concerns of potential widespread harmful interference” into GPS equipment.

Here in Washington, if you can’t solve a problem quickly, the automatic next step is to blame the problem on somebody else. Predictably, the finger-pointing has begun. The GPS people moved first: back in June, they asked the FCC to rule that the GPS community is not required to share any responsibility for protecting GPS receivers from LightSquared.

Now LightSquared has countered with its own request for an FCC ruling: that commercially available GPS devices have no protection from LightSquared’s interference.

A question there in the back? Ten MHz is a lot of spectrum, you say, equal to half of the entire FM band. So if LightSquared stays at least 10 MHz away from GPS frequencies, how can it still cause interference to GPS?

Good question. The answer lies in receiver design. It is possible to build a receiver that picks up just the frequencies it is meant to, and is relatively insensitive to other frequencies nearby. LightSquared has submitted evidence that such interference-resistant GPS receivers are feasible. But for consumer gear, where price competition is steep, manufacturers opt for less expensive designs that, unfortunately, respond to a range of frequencies around the ones they are meant to receive. An inexpensive consumer GPS receiver, such as those used in cars and cell phones, thus can experience interference from a strong signal even several MHz away. (To limit this kind of problem, the FCC once considered setting minimum standards for receivers, but after four years of struggle gave up on the idea.)

GPS units for critical applications, such as those used for landing commercial aircraft, are relatively better at ignoring unwanted signals. We all want the pilot of our plane to receive a strong, clear GPS signal, not somebody’s streaming of a silly cat video. But even as to these units, considering the possibly catastrophic downside of interference, the GPS industry remains wary of LightSquared.

The arguments on both sides have merit. In LightSquared’s favor is a long history of regulation that requires a potential interferor only to stay within its own frequency band and power limits, nothing more. We can’t recall another case that penalized Party A for Party B’s poor receivers. But the GPS industry can also point to long-standing principles of spectrum management: a newcomer must deal with the spectrum as he finds it; and everybody has an obligation to protect safety-of-life applications.

Both sides, moreover, have political clout. You might say politics has no place in a primarily technical controversy; but again, this is Washington. LightSquared can cite the importance of fostering U.S. technological innovation, and of delivering high-speed broadband to where it is needed – issues the FCC Chairman has publicly espoused. Behind the GPS industry, on the other hand, are the public’s fears that our in-car gadgets will stop working, and more urgently, that aviation and military GPS applications may be compromised.

One key party has not yet made its views public: the small, inconspicuous outfit called the U.S. federal government. It has a considerable stake in the outcome. For one thing, the federal government launches, owns, and operates the GPS satellites. For another, its military and aviation departments, among others, have strong interests in making sure GPS operations stay reliable. The government spectrum users, including those who rely on GPS, have a back channel to the FCC that can bypass the public record. If they have not yet conveyed their views to the FCC, they doubtless will. And unless the government is satisfied that LightSquared is harmless to its GPS operations, we very much doubt that LightSquared will get the nod it wants from the FCC.

In the meantime, the FCC is accepting input from the rest of us on LightSquared’s request to deny interference protection to GPS.  Comments are due on February 27, and reply comments on March 13.