Dude, Where’s My Spectrum: LightSquared vs. GPS

Since late last year, ACI-NA has been tracking the potential for global positioning system (GPS) signals to be disrupted by wireless broadband network proposed by LightSquared.  This past week, the debate over these services heated up, both in Congressand within technical groupsthat are assessing the impacts of LightSquared’s network on global positioning system signals.

LightSquared is a mobile satellite service provider that uses two satellites positioned over North America to provide digital communications.  In November 2010, the company applied to the Federal Communications Commission to supplement this satellite communications network with a series of ground-based transmitters that would enable the company to provide better coverage across the U.S.  These transmitters would broadcast signals in what is known as the “L-Band”—a part of the electromagnetic spectrum that is very close to frequencies used to transmit both military and civilian GPS signals.

In late January, the FCC approved LightSquared’s application to the dismay of military and commercial GPS users—including many within the aviation community.  The concerns have arisen because preliminary tests have indicated that LightSquared’s ground based transmitters—which will operate at relatively high power levels—drown out much weaker GPS signals.  For aviation, the consequences of such disruption can be severe.  They include the inability of aircraft to utilize GPS procedures—a cornerstone of the FAA’s NextGen program—as well as the inability of navigation and communications systems that are dependent on GPS signals to operate properly.  (For a more detailed discussion of these technical issues, the website ArsTechnica has an excellentarticle.)

For airports, there are other significant consequences associated with GPS disruption.  For example, GPS-based survey equipment might not function reliably, requiring surveyors to revert to more traditional survey methods.  Ground-vehicle surface surveillance reliant on GPS signals might also be disrupted.  In addition, a host of supporting technologies that rely on GPS signals for accurate time and date information might not function reliably.

Because of these concerns, a broad-based coalition of industries and associations—The Coalition to Save Our GPS—came together earlier this year to lobby for more substantial evaluations of the LightSquared network’s impacts on GPS as well as for federal government action to halt implementation of the network until these impacts are fully understood.  Both the FAA and the Department of Defense have been working on parallel efforts within their organizations.

This spring, a working group led by LightSquared and the US GPS Industry Counsel was formed to conduct testing to determine these impacts.  The working group is due to issue a report concerning these impacts and potential mitigation options on June 15.  However, early reports from the technical group conducting these tests—the National Position, Navigation and Timing Engineering Forum indicate that LightSquared’s ground-based transmitters will result in significant GPS disruption.

ACI-NA will continue to track developments regarding LightSquared and will let you know. In the meantime, if you feel strongly that GPS signals should be protected, you may want to consider joining The Coalition to Save Our GPS.

Contact ACI-NA’s Chris Oswaldfor more information.