PNT Advisory Board Hears Air Force CNAV Plan

March 12, 2014  - By


The U.S. National Space-Based Positioning, Navigation, and Timing (PNT) Advisory Board has published the minutes of its December 4–5, 2013, meeting, opening with a quote from Albert Einstein, “We cannot solve our problems with the same thinking we used when we created them,” courtesy of Board Chair Dr. James Schlesinger. Among many other topics addressed, the Board heard a report from Major General Martin Whelan, Director of Requirements, Air Force Space Command, on the road ahead for implementation of the GPS Civil Navigation (CNAV) message on L2C and L5. The subject has stirred some controversy of late, particularly between the U.S. Departments of Transportation (DoT) and Defense (DoD), and DoT is currently seeking public comments on the plan.

The meeting minutes relay the gist of General Whelan’s CNAV remarks as follows:

“While sequestration is having various impacts on DoD budgets, thus far GPS quality, service and refresher plans are unaffected. The FY15 budget is under development.

“CNAV has been under discussion for a considerable time. Currently, L2C and L5 signals are being transmitted, but without a navigation message. AFSPC is working hard to activate these messages as soon as possible. One of the reasons for the delay is that additional time was needed to complete testing prior to activation. Testing began in late summer 2013 and, based on initial test results, a “way ahead” has been plotted. Gen William Shelton, AFSPC commander, wished to assure the Advisory Board of his unwavering commitment to providing full-time broadcast CNAV messaging capability on L2C and L5 as soon as possible.

“The CNAV capability will add diversity and robustness for dual frequency users. Gen Shelton intends to provide details plans to the NCO and a report to the next EXCOM meeting. Current plans are to begin initial broadcasting in the spring of 2014. CNAV uploads will occur twice weekly. The signal will meet GPS Standard Positioning System (SPS) standards, but may not achieve current accuracy levels until full implementation in late 2014.

“CNAV live sky testing occurred in June and was conducted in cooperation with civil, industry, and international partners. The two-week test series included independent assessment and verification. The tests identified four errors that required action. The first, which was addressed in real time, related to implementation of the test series. The second required improvement to the tools suite, which should be totally integrated into the ground segment by December 2014. The third and fourth errors required patches to satellite software. All four issues are now regarded as closed.”

The meeting minutes report this further discussion of CNAV.

“Dr. Schlesinger raised the topic of sequestration and how, based on his early career in budgeting, no budget item is sacrosanct. GPS has enjoyed protection from Deputy Secretary of Defense Ashton Carter, but he is now stepping down and his replacement not yet known. This could provide an opportunity for “the men with the green eyeshades” to come forward to eliminate things.

“Gen Whelan said he agreed that with sequestration, everything – including GPS – is on the table. However, AFSPC continues to strive to avoid any degradation in service. He also welcomed the continued support of the Advisory Board.

“Dr. Schlesinger quoted from a 2006 document: “Our position is to continue to provide the best space-based positioning, navigation and timing service in the world.” The Chinese are now “moving up” on GPS. How is GPS going to stay ahead?

“Gen Whelan said AFSPC is aware of China’s steps in capacity and signal diversity. This, however, does not alter his confidence that GPS remains the “Gold Standard” of world GNSS systems. AFSPC is committed to maintain GPS leadership. However, because of sequestration and budget cuts, this position could not be the position of some people outside of the Air Force.”

A subsequent presentation from the Department of Transportation given by Karen Van Dyke, Director for PNT, DOT Research & Innovative Technology Administration (RITA), did not directly mention CNAV, according to the meeting minutes, but did include this update on civil signal monitoring, taken from the meeting minutes.

“DOT is responsible for performance monitoring of GPS civil signals. She called attention to the International Committee on GNSS’s (ICG’s) transparency principle that “Every GNSS provider should publish documentation that describes the signal and system information, the policies of provision, and the minimum levels of performance offered for its open service.” Currently, this is only done on GPS L1 C/A signals. Performance standards for L2C and L5 have not yet been established. The crucial function of signal/service monitoring is to verify that commitments to GNSS performance are being met. Additionally, monitoring improves the situational awareness for GNSS operators, and provides assurance that any civil service failure is detected and resolved promptly. All these factors support the GPS performance history that has made it the world’s Gold Standard.

“The DOT “GPS Civil Monitoring Performance Specifications” (CMPS) document defines the measurements required to show if performance standards for monitoring GPS’ signals/service are met. The document’s first version was developed in 2005 and listed 193 requirements, covering performance monitoring, signal monitoring, non-broadcast data requirements, and reporting and archiving requirements. The document was later updated to align with the 2008 GPS SPS Performance Standard. The most current CMPS was completed in April 2009 and is available at Since 1999, DOT has published quarterly reports providing analysis of SPS performance for the Federal Aviation Administration (FAA).”

Further Topics

Other reports delivered to the Advisory Board, and available in the the full meeting minutes, available here,  include the following. In addition, many PDFs of the individual reports  are available through the meetings Agenda page.

Global Differential GPS System as a Civil Monitoring Utility
Dr. Yoaz Bar-Sever, Manager, Global Differential GPS System, NASA Net Propulsion Laboratory

Automated Driving & Safety Considerations (collision avoidance warning, vehicle-to-vehicle communications, and driverless automobiles)
Russell Shields, PNT Board Member, founder of Ygomi LLC

GPS Disruptions: Efforts to Assess Risks to Critical Infrastructure
The Government Accountability Office’s (GAO) Report on Enhancing Interagency Actions
Eli Albagli, senior analyst, GAO

2013 National Infrastructure Protection Plan (NIPP)
Department of Homeland Security Implementation
Robert Kolasky, Director Strategy and Policy, DHS Office of Infrastructure Protection

Economic Impacts of GPS on Key Sectors in the U. S. Economy
Dr. Nam D. Pham, economist/managing partner, NDP Consulting Group

GNSS Signal Capability – Multi-Constellation Management
Cross-Correlation of Existing & Evolving C/A System Signals
Dr. A. J. Van Dierendonck, AJ Systems

How Far to Take GNSS Interoperability/Interchangeability?
Ken Hodgkins, Office of Space & Advanced Technology, Department of State.


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