The organizing committee of ICG-3: International Committee on GNSS, third meeting. International GNSS Service Central Bureau Director Ruth Neilan (first row, far left) organized the Pasadena event. Next to Neilan is meeting chair Ken Hodgkins, director of the State Department’s Office of Space and Advanced Technology. Mike Shaw (first row, fourth from right) directs the National Coordination Office for Space-Based Positioning, Navigation, and Timing (PNT). OOSA program officer Sharafat Gadimova (third from right) serves as executive secretariat for the ICG.
ICG-3: Friendly Persuasion
Clashing trajectories pressure GNSS providers . . . but growing commercial markets inspire a search for compatibility at the third plenary meeting of the International Committee on GNSS.
Sidebar: Program Updates
Representatives from the world’s GNSS and augmentation providers spent a sun-laden week in Pasadena, California, advancing aspirations for their separate enterprises while refining the basis for compatibility and interoperability among them.
The occasion was the third meeting of the International Committee on GNSS (ICG-3), a voluntary United Nations–backed association that brings together GNSS and augmentation providers — including the United States, Russia, European Union, China, India, and Japan —associate members representing key user communities.
After its formal launch in 2006, the ICG sketched out a bold vision of cooperation and shared principles in joint statements of the committee and a Providers Forum during the group’s second meeting in Bangalore, India, in September 2007.
The third meeting in Pasadena, however, reflected a more cautious approach by most members as they began collectively translating general principles into work plans that could lay the foundation for technically and operationally aligned systems — without undercutting separate and frequently divergent goals for individual GNSSes.
As one American delegate observed in an aside comparing the India and U.S. meetings: “Four steps forward and one step backward.”
Hosted by the United States, the meeting was chaired by Ken Hodgkins, director of the U.S. State Department’s Office of Space & Advanced Technology, with local arrangements taken care of by the Jet Propulsion Laboratory (JPL), California Institute of Technology, and the offices of the International GNSS Service (IGS) Central Bureau located at JPL.
The UN Office for Outer Space Affairs (OOSA) represented by Sharafat Gadimova, an OOSA program officer, serves as executive secretariat for the ICG.
Is “Interchangeability” Possible?
This concept, which allow use of “any four [GNSS satellites] anytime,” requires a closer alignment of GNSS system time and coordinate reference systems than currently proposed, Parkinson said.
Parkinson, who is vice-chair of the advisory committee to the U.S Space-Based Positioning, Navigation, and Timing (PNT) Executive Committee, also called for high-level support of earlier delivery of GPS III satellites, currently scheduled for 2014, and a more robust constellation of 30 space vehicles (SVs) in 30 orbital slots, plus spares.
His comments echoed a growing concern at the possibility of “GPS brownouts” if a substantial number of GPS spacecraft failed at the same time, creating holes in the coverage until new generations of satellites can be brought online.
Global Market Pressures vs. National Priorities
GNSS providers are acutely aware that GNSS represent critical infrastructures that can reinforce a nation’s political leadership at the global level. At the same time, however, GNSS supports commercial industries and markets that continue to grow steadily even in the current economically challenged conditions.
Participating in those markets requires an essential compatibility with a common technical standard — now represented in an ad hoc way by GPS, but likely to expand into a more generic form as the other systems are completed.
The presence of user communities and industry representatives at ICG-3, many as invited speakers, underscored the pressures that government officials are feeling to ensure that individual GNSSes remain part of the mix incorporated into manufacturers’ designs.
Divergent tendencies also reflect different priorities currently existing among the GNSS programs, which might be summarized as follows:
The United States: maintaining its lead as the first and only fully operational GNSS while ensuring open civil standards and a “level playing field” in international trade in GNSS products and services; providing a multilateral forum where representatives can discuss scientific and technology matters that national policy prevents them from addressing bilaterally (i.e., with China).
European Union: fostering the growth of European high-tech expertise while preserving its options for managing the system and still maintaining momentum to implement Galileo as globally competitive GNSS; convincing China to move off of portions of radio spectrum where Galileo’s security-oriented public regulated service (PR) will operate (not necessarily in that order).
Russia: Increasing the appeal of GLONASS to consumer manufacturers and markets and establishing ground monitoring facilities outside the Russian territory; developing its industrial base to produce domestically designed equipment for military and commercial applications.
China: Bringing its system online quickly for national security and commercially competitive reasons, capturing global mass markets for Chinese-built goods, and establishing Compass as the world’s preeminent GNSS system.
Compatible & Interoperable
The process was probably more revealing than the results, which can be viewed in the official report issued following the meeting. A copy of the report can be downloaded as a PDF here.
The nuances reflected underlying issues between individual GNSS providers, including some under discussion in bilateral talks and others have yet to be raised. These issues China’s plan to transmit Compass signals on the same frequencies as Galileo’s Public Regulated Service (PRS) and GLONASS’s possible selection of a BOC (2,2) design for its CDMA signal at L1.
As an example of the tendency toward divergence, consider the various approaches to defining compatibility and interoperability taken up by Working Group A charged with drafting appropriate language on the subject for the ICG workplan.
Spectral Separation and Other Barriers
Ultimately, the group agreed on the following language: “Compatibility should also respect spectral separation between each system’s authorized service signals and other systems’ signals. Recognizing that some signal overlap may be unavoidable, discussions among providers concerned will establish the framework for determining a mutually acceptable solution.”
Interoperability posed an even more complex challenge for reconciliation. Although European and Indian delegations remained satisfied with the language worked out in Bangalore, the intervening months appear to have brought second thoughts and diverging analyses by other providers.
In a U.S. effort to flesh out the concept, Harrington presented a lengthy set of technical characteristics that he suggested underlie interoperability. These included common time and reference frames or broadcast of the offsets between systems, common carrier frequencies, similar spreading modulation spectra, common minimum and maximum power levels, common spreading code lengths and common code family, and common data message structure and encoding.
Professor Grigory Stupak of the Russian Institute for Space Device Engineering (RISDE) introduced a formula in which interoperability could be quantified using other criteria for cost (price, size, weight, power consumption) and performance (accuracy, availability, reliability, responsiveness).
China first proposed that interoperability simply “allows navigation with signals from different systems with minimal additional receiver cost or complexity.”
Eventually, the working group agreed that, in addition to the Chinese description, for purposes of interoperability, “Geodetic reference frames realization and system time steerage standards should adhere to existing international standards to the maximum extent practical.”
The ICG-3 language also acknowledged the benefits of multiple constellation in providing improved accuracy and availability of PNT services.
In the preface to the revised document, delegates added, “For many applications, common carrier frequencies are essential to interoperability, and commonality of other signal characteristics is desirable. In some cases, carrier frequency diversity may be preferable to improve performance.”
The workplan also included language that providers should develop “proposals to widely monitor the performance of their open signals and provide timely updates to users” with a “focus on potential cooperation in the development of the necessary ground infrastructure to monitor signal and service performance for open services. . . .”
Narrow Role of the ITU
However, the ITU is essentially limited to addressing a narrow definition of compatibility, based on frequency allocations and attempts to limit cumulative increases in the RF noise floor within radio bands as a result of new systems and signals. Adding signals can eventually create interference to existing services within a frequency allocation.
China appears inclined to rely more heavily upon the ITU process, while others are less sanguine about the organization’s capability for reconciling broader differences among programs.
Among these differences is the matter of spectral separation of military or authorized services, such as the GPS M-code and Galileo PRS, which have been the subject of a series of bilateral talks — thus far inconclusive — between China and the United States and the European Union in recent years.
GPS as a “Legacy System”
Reportedly, China has posed a long list of requirements to EU negotiators, including some unrelated to GNSS, as conditions for abandoning or reducing their frequency plans for Compass.
The ICG itself has yet to demonstrate whether it will tangibly and practically improve the prospects for creating a global GNSS system of systems with true compatibility and interoperability among separate GNSSes. Or whether it is merely a debating society or paper tiger, as some have suggested.
But for the time being, the ICG appears to offer the only alternative to continuing rounds of bilateral negotiations that may achieve individual agreements but may have less success in coordinating uniformity among GNSS providers. If nothing else, the ICG offers a more open forum in which moral suasion compels a semblance of cooperation.
ICG-4 in St. Petersburg
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