PNT Board Report: GPS Critical Infrastructure, Concern over International Signals

January 13, 2015  - By

Report on the 14th meeting of the National Space-based PNT Advisory Board in Washington, D.C., held December 10-11, 2014.

By Ron Hatch

Ron Hatch

Ron Hatch

The December meeting of the PNT Advisory Board meeting brought forth important developments and proposals for the protection of GPS as part of the U.S. critical national infrastructure. A separate presentation made by speakers from the National Telecommunications and Information Administration (NTIA) and the Federal Communications Commission (FCC), concerning possible limitations on the use of signals from other GNSS, generated some controversy, alarm, and extensive follow-on discussion by industry, users, and other concerned parties.

Critical Infrastructure. Perhaps the most important presentation was that of Brad Parkinson, the acting chair, in his recap of the recommendations to be made by the Advisory Board to the PNT EXCOM.

The first recommendation was a reiteration of the Advisory Board opinion that the GPS be designated as one of the “critical infrastructures” of the United States. This opinion was based upon the fact that 14 of the existing designated critical infrastructures involves the use of GPS. The feeling was that such a designation would enhance the attention focused upon ensuring GPS reliability.

A second recommendation was that a comprehensive threat assessment to GPS operation be generated that can be used to assess its vulnerabilities. The remaining recommendations to the EXCOM were based upon the results of studies by the two working groups that were presented next.

The two working groups of the advisory board, specifically the “Assured Availability and the “Economic Value of PNT” working groups, gave the next set of presentations. The Assured Availability working group was split into three sub-groups. The three aspects addressed were to “Protect,” “Toughen,” and “Augment.” The Protect working group recommended action to encourage the reversal of European initiatives to authorize pseudolites that broadcast within the GNSS L1 frequency band. Since such pseudolites would constitute authorized interference to standard GNSS receivers, it was recommended that our State Department encourage a reconsideration of the pseudolite proposals and that they be constrained to operate on a frequency outside the L1 frequency band.

The Toughen working group looked at a number of measures by which GNSS receivers could be improved to better withstand intentional and unintentional interference. Phased array antennas, inertial aiding and various software tracking improvements were discussed. An invited presentation by Gary McGraw of Rockwell addressed some of these issues particularly from a military perspective. An additional invited presentation upon the requirements for precise time-keeping in trading of financial transactions was presented by Andrew Bach.

The Augment working group discussed a number of ways in which the GNSS capabilities could be augmented. Prior recommendations that eLoran should be maintained as a backup was again strongly recommended. In addition, the ability to track other GNSS satellites in addition to GPS satellites was encouraged, even though it was recommended that special precautions and automated checks needed to be implemented in the light of the system failures that have been noted with the GLONASS satellites. A very interesting invited presentation by Robert Lutwak of the Defense Advanced Research Projects Agency (DARPA) described the continuing progress toward higher precision inertial sensors.

The second working group, the Economic Value of PNT, reported on firmed up plans to strengthen the existing studies of the economic value of PNT by engaging the economists resident within the various cabinet departments within the EXCOM to which the Advisory Board reports. The detailed plans were given in a presentation by Irv Leveson that outlined the plans for “A Comprehensive Quantitative Economic Assessment of GPS.”

It is not my intention to slight any of the other presentations, but I felt two of the remaining presentations were very important. Specifically, the presentation by Karen Van Dyke on Department of Transportation plans regarding “Adjacent L-Band Compatibility and GPS Signal Monitoring” was very encouraging. Among other items, it indicates that adjacent band-power limits will be carefully analyzed and tested to ensure that all existing applications of GPS will not be harmed.

FCC on International Signal Use. The second presentation that I felt was very important was by Paige Atkins of the National Telecommunications and Information Administration (NTIA) and Ronald Repasi of the Federal Communications Commission (FCC). Their presentation was titled “NTIA/FCC Spectrum Management Perspectives.” The presentation  covered the background and intent of the various authorizing legislation. There were, however, some disturbing comments made.

Specifically, the item on the slide about National Space Policy that had a major bullet: “Guidance to all departments and agencies – ‘maintain and enchance’ space-based PNT systems. To this end the U.S. shall (among other things)…” There were two sub-bullets.

The first addressed GPS protection as a critical infrastructure component. The second sub-bullet stated “Foreign PNT services ‘may be used to augment and strengthen the resiliency of GPS.’” The verbal transcript is not yet available, but it seemed to me that Ron Repasi minimized this statement by indicating that resilience was subject to interpretation.

The real alarm was in his following comments during the question-and-answer discussion, where he indicated that the use of GLONASS within U.S.-based receivers was not authorized and that, therefore, the frequency band they used was not necessarily subject to protection. In addition, it was indicated that three years ago, procedures were developed whereby one could apply for authorization to the use the GLONASS signals. To date, Ron Reposi indicated that no organization had applied for authorization to use GLONASS, and that therefore it was currently illegal to use it.

Significant discussion was generated by the above, both following the presentation and the next day in a recap. From the discussion, it appears that a March 2011 regulation outlining the requirements for authorization of receiving “Earth stations” is being interpreted by the FCC as requirements for authorization of GLONASS receivers.

[Editor’s note: The process for securing a waiver of FCC regulations requiring authorization to receive international RNSS satellite signals was identified in an FCC Public Notice released in 2011.  This process is initiated by National RNSS System providers, which have the satellite information needed to secure a waiver.  Members of the GPS Innovation Alliance (GPSIA,, formerly the U.S. GPS Industry Council) have stated that they remain fully committed to producing  multi-GNSS signal user equipment consistent with U.S. policy, and to working with the FCC and NTIA in considering these requests.]

In light of the multitude of GLONASS receivers already in use, including a number of U.S. government and agency receivers, the discussion was primarily on what should be done next. The decision taken was not to panic, but to bring the problem to the attention of the various government departments represented on the EXCOM and proceed with some caution.

The possibility was raised that NASA, in conjunction with the State Department and other interested parties, could seek a blanket authorization to use GLONASS within GPS receivers. This was discussed and presented as a possible way forward. Clearly, the issue is one that will be followed with great interest.

For all the presentations at the December meeting, see the presentation slides here.

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