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Out in Front: Act Now to Protect GPS Signal

March 1, 2011  - By
Image: GPS World

This guest editorial addresses a subject of paramount importance to the GNSS industry, to the U.S. national infrastructure, and to the global GNSS community. I urge you to take immediate action by contacting U.S. government representatives, indicated at the end of this article.

— Alan Cameron, editor-in-chief


Guest Editorial by Joe Paiva

GPS has become a key component of the U.S. national infrastructure, the driver of a significant part of the civilian economies of the world, and the enabler of millions of professional precision uses and consumer benefits.The viability of the GPS signal is now threatened — ironically by what appears to be a misguided attempt to increase accessibility to broadband by creating a needless zero-sum result for customers who want both services.

The threat is real and immediate. The U.S. Federal Communications Commission (FCC) has issued a conditional waiver to LightSquared, a company engaged in developing 4G-LTE (long-term evolution) cellular networks for wholesale-only basis commerce with its business partners.

LightSquared Scheme. LightSquared acquired a company providing a combined space-based and ancillary land-based service using the L-band radiofrequency. The FCC conditional waiver, granted to LightSquared on January 26 of this year, allows it to broadcast a new terrestrial broadband service from 1,500-watt terrestrial transmitters — 40,000 of which will eventually be installed by LightSquared — in the portion of L Band (1525 MHz–1559 MHz) immediately adjacent to the 1559–1610 MHz band used by GPS.

Instead of offering dual-mode handsets exclusively as required by their FCC license, retailers purchasing this combined service can choose to offer terrestrial mobile phones only, which was the change in license terms that LightSquared was seeking via waiver. This change amounts to a de facto reallocation of Lightsquared’s spectrum use from space to terrestrial wireless. In fact, the new broadband service is planned to operate in urban areas, and the space service will operate outside these areas.

The LightSquared terrestrial broadband signal is about 1 billion times the received power of the GPS signal on Earth. Members of the GPS industry have been conducting experiments and analyses, and these figures come from those very early studies. Soon, we may experience GPS interference — jamming — on an almost unimaginable scale and to a geographical extent that could create widespread havoc.

Threats. The GPS system works so well that we often forget the complexity behind it and take for granted the service we use daily. One reason GPS works so well and is seldom defeated is that the signals broadcast by the satellites can be received under a wide variety of conditions on Earth. Historically, the FCC and the International Telecommunications Union, understanding potential interference issues, intentionally planned uses of adjacent swaths of the L-band so that satellite-based transmissions, relatively low-power, would be natural neighbors, so as to cause as little disturbance as possible to radio-navigation uses. This dedicated purposing of the bands and the resulting environment of negligible interference is one reason that GPS has become reliable and its use ubiquitous.

Long-time observers of the GPS scene will remember how civilians, and especially potential international users, initially had uncertainty about the U.S. Department of Defense’s statements that the service would be free and not subject to any restrictions in one’s ability to receive and use the broadcast signals. This uncertainty was due primarily to the implementation of Selective Availability (SA), which intentionally degraded the available accuracy of the GPS signal. SA was permanently removed in 2000 by President Clinton’s 1996 Presidential Decision Directive.

Many factors have enabled users and potential users to see GPS as a reliable, consistent technology that provides significant increases in productivity, efficiency, precision, continuing innovation, and many other benefits. These factors include the reliability of the overall GPS technology, improvements in receivers and in successive next-generation satellites, advances in differential and relative positioning, dynamic applications, and real-time kinematic solutions. And, just as importantly: stable, predictable U.S. policy.

Investments. Now, by virtue of this unusual FCC action, uncertainty has been thrown into the viability of the hundreds of millions of GPS receivers in use today. Much research and development work is being done on improving receiver performance and taking advantage of improvements planned for the satellites. The most dollars go towards devising new applications, products, and services that improve the quality life of millions of Americans, create new companies, markets, and jobs. These dollars are also being spent by government agencies, not just the Department of Defense, but very visibly by Agriculture, Commerce, Interior, Energy, Homeland Security and Transportation. More than likely, the remaining departments either have active programs that are using or considering using GPS or are positively affected by others’ use of GPS.

That’s just the executive branch. Other parts of the federal government, as well as state and local governments, do research on GPS technology and applications and actively use GPS to improve the lives of citizens, increasing work and recreation, efficiency, and safety. In many local government settings, there is active cooperation to improve delivery of services by having governmental and non-governmental organizations collaborate around the simple fact of accurate position being available through GPS, with significant cost savings in current lean budgets.

It is inexplicable that another part of the government would be so cavalier in rapidly and uncharacteristically granting a waiver that clearly endangers the whole system. And only after granting the waiver, which must act at least as a yellow light for LightSquared’s mobilization plans, comes the requirement for a study — to be headed by LightSquared — to determine impacts and mitigation of interference with the GPS signals.

Why Fast Track? The FCC grant of a reallocation of spectrum use from space to terrestrial on a fast-track waiver did not follow the standard FCC rule-making process for reallocation of spectrum use. The standard regulatory approach allows sufficient time for robust public comment by all potentially affected parties, including the conduct of interference studies and the introduction of comments on interference results in the public record. Instead, the FCC order granting the waiver to LightSquared has mandated what appears to be fast-track GPS interference research.

Currently, the proposed LightSquared terrestrial broadband service does not have an installed user base. In contrast, the installed GPS user base represents a broad and diverse range of use representing hundreds of millions of users established over 30 years.

The final Working Group report is due to the FCC on June 15, 2011. The FCC order requires the GPS community to participate “in good faith” in this study effort. In response, the U.S. GPS Industry Council and others are working on this interference study to protect GPS operations under these extraordinary regulatory conditions.

A further problem created by the FCC conditional waiver is that LightSquared is able to move ahead with its infrastructure development, assuming that viable solutions to the jamming issue will be found. For many GPS users, theoretical fixes are not likely to prove viable.

Negative Impacts. Preliminary research done by member companies of the USGIC already has been reported in GPS World. The research indicates that LightSquared’s 1,500-watt terrest
rial transmitters will result in a signal 90 dB stronger than GPS over the coverage area; this amounts to signal strength 1 billion times stronger than GPS. There is more to the research, all done with GPS simulators and signal generators (see for test results).

Clearly the jamming level will vary with geography. We don’t yet know LightSquared’s broadcast-tower siting plan. But it is clear that if LightSquared is allowed to broadcast terrestrially on the mobile satellite system (MSS) band, dedicated until now to signals compatible with satellite transmissions, there is a substantial danger that millions of GPS receivers will be adversely affected.

Some obvious impacts are loss of operational viability of businesses involved in aviation, surveying, agriculture, engineering and construction, vehicle navigation, mariners, transportation, public safety and homeland security, disaster management, utilities, mapping, and scientific research. Several of these involve safety-of-life issues, which are at risk of being jammed.

Keep in mind that GPS was envisioned as a system for space and time. Its longest life as a useful contributor to society has been as a time standard. Countless networks, whether for computing, broadcasting, power generation — even, ironically, cell phones — are synchronized using the most precise signal practically available. Fixed GPS receiving stations for time reference may be able to be designed to withstand some interference from high-power broadcasting on adjacent frequencies, but nobody has tried so far.

Any hypothetical fixes for GPS beg a more fundamental question: Why should Lightsquared, a new entrant with no existing business, be allowed to shift the burden of mitigating interference created by its operations to millions of consumers, government agencies, and businesses who have invested in GPS over the last 30 years?

Keep in mind that other users of the MSS band will also be affected. Many commercial and governmental uses of the very band that LightSquared will occupy with its terrestrial transmitters may also be jeopardized.

We must also remember that the FCC has its own agenda, to implement its National Broadband Plan. What is truly difficult to comprehend is that broadband and GPS will serve the same mobile user.

Action Needed. Please act now.

  • Write to your representatives in Congress, and to your professional and trade associations.
  • If you are an expert on radio or spectrum or GPS or whatever else is pertinent, make your comments, do your research if possible, and publish your results with all due speed.
  • Petition the FCC to turn the yellow light to red, while other paths to achieving LightSquared’s and the FCC’s goals are investigated.
  • Do not forget the Administration: the National Telecommunications Information Administration (NTIA) represents the president and the Administration as official co-regulator with the FCC of the spectrum where GPS operates. In the recent FCC Order, NTIA must review the report on results of the FCC-mandated interference study.
  • Specifically, ask Congress to demand that the FCC include specific language to protect GPS use in the final FCC Order to LightSquared after the interference study is completed.
  • Ask the Secretary of Commerce and the White House Office of Science and Technology Policy (OSTP) to inform the NTIA Administrator to urge the FCC chairman to take this same action to protect GPS in the final FCC Order.
  • Contact the FCC chairman directly and urge this same action.
  • Finally, help develop user and beneficiary awareness of the grave danger being posed to GPS and make your elected and congressional representatives aware of the impact that interference with GPS would have on your work.

The large-scale disruption of the GPS service mustn’t be on our hands due to inaction.

Points of Contact

Send messages to FCC chairman, commissioners, and NTIA:

  • Edward.Lazarus at (Chairman Genachowski’s office
  • John.Giusti at (Comm. Copps’ office)
  • Angela.Giancarlo at (Comm. McDowell’s office)
  • Louis.Peraertz at (Comm. Clyburn’s office)
  • Charles.Mathias at (Comm. Baker’s office)
  • lstrickling at (asst. secretary for communications and information, NTIA)

International readers may contact the U.S. State Department, clorere at For further contacts, see

Joseph Paiva is a consultant to the geomatics industry, with background in private engineering, surveying and mapping consulting, and as developer and general manager for two geomatics products corporations.


High-Precision Users

High-performance L1 receivers (sub-meter) have a wide-bandwidth RF front-end to improve performance, about 20 MHz, compared to a consumer receiver that typically has a front-end bandwidth of 2 MHz. GPS World contributing editor for survey and GIS Eric Gakstatter discusses this aspect of the issue in his recent e-mail newsletter column at

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