MITRE Supports the Advancement of GPS Technology for Users Worldwide

December 2000

"GPS modernization is a complex project that involves high levels of technical and operational expertise. It's one of those projects where we have to balance the often competing need of military and civilian users," observes Wait Scales, a MITRE principal engineer. "In my opinion, this is an aerea where MITRE really lives up to its commitment to work in the public interest and support a solution that benefits a variety of GPS users."

Originally developed by the Department of Defense (DOD) as a military system, the Global Positioning System (GPS) now functions as an indispensable utility for both civil and military applications. A vast array of users, including pilots, motorists, hikers, boaters, and emergency personnel, have come to rely on the highly accurate navigation and timing data capabilities of GPS.

The rapid proliferation of civilian users in the last decade created a need for an expanded system with more GPS frequencies available for civilian use. In addition, recent changes in the government oversight of GPS allow civilian users access to more precise GPS signals previously reserved for the military. MITRE, in a cross-corporation effort, played an integral role in both the decision to add more GPS signal frequencies and the May 2000 decision to suspend the intentional degrading of the signals available to civilian users, which was done in the interest of national security.

In a March 1996 Presidential Decision Directive (PDD), President Clinton approved a comprehensive national policy on GPS. Specified in the PDD were the goals to: "strengthen and maintain our national security; encourage acceptance and integration of GPS into peaceful civil, commercial and scientific applications worldwide; and to encourage private sector investment in and use of US GPS technologies and services." To help achieve these goals, the Directive established an Interagency GPS Executive Board co-chaired by the Department of Defense and the Department of Transportation. The Executive Board called upon a number of Federally Funded Research and Development Centers (FFRDCs), including MITRE’s Center for Advanced Aviation System Development (CAASD) and MITRE’s DOD FFRDC, to assist them in moving GPS to expanded use by civilian and commercial users while preserving the military utility of GPS.

GPS applications include: aviation, agriculture, communications network synchronization and timing, contruction/civil engineering, environmental management, fishing and boating, mapping, mining, offshore drilling, personal naviagation, power grid interfaces, public safety, railroads, recreation, surveying, trucking and shipping.

Two initial accomplishments were agreement on new military signals and new civil signals that could co-exist with present systems. Currently, civil users of GPS have just one frequency available to them, which does not exploit all of the potential of GPS. Timing was critical since the replacement of the GPS constellation of satellites was set to begin soon. A cross-MITRE team collaborated with government to study the relative costs and performance levels of alternative solutions. MITRE conducted frequency management and interoperability analyses and evaluated the most promising candidate frequencies. MITRE CAASD performed several analyses of the compatibility of the new signals with existing systems using the GPS RFI Environment Evaluation Tool, otherwise known as GREET. After completing the analyses and evaluations, the Executive Board accepted the recommendations to implement two new civilian frequencies and new military signals.

In conjunction with the question of whether the United States should add new civilian GPS frequencies was the option of opening up more precise GPS signals to civilian and commercial users. In the past, the United States intentionally degraded certain GPS signals, a feature known as Selective Availability (SA), in order to limit their accuracy. MITRE was part of a multi-department and agency effort examining the issue of discontinuing SA, contributing to analyses on upgrading military GPS capabilities and enabling civilian users more extensive access to GPS. A significant part of the decision to discontinue SA was the enhanced ability of the military to selectively deny GPS signals on a regional basis when national security is threatened. After reviewing the recommendations of the Executive Board and a number of executive branch departments and agencies, President Clinton announced the decision to discontinue SA on May 2, 2000.

MITRE’s role in supporting the DOD and DOT is yet another example of our commitment to working in the public interest and supporting our government partnerships. MITRE’s system engineering and integration expertise has helped enable GPS to become a dual-use, dual-service system. As our military and civilian partners integrate GPS services into their operations, they rely on MITRE to support their efforts by providing thorough research and analysis. Our work on GPS issues spans the corporation; as a result, our DOD and FAA FFRDC’s have become key players in several areas including the definition of augmentations and improvement of GPS capabilities in terms of accuracy, integrity, interference immunity, resistance to exploitation, and security.

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