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Volpe Center Highlights - January/February 2006

Focus

Letter from the Director | Focus | Safety | Mobility | Environmental Stewardship | Security
New Directors | Published and Presented

The Global Positioning System (GPS) consists of a minimum of 24 satellites, providing 24-hour, worldwide coverage. GPS can facilitate enhanced safety, improved service levels, heightened security, and greater efficiency. However, the complexities of ensuring its reliability necessitate innovative yet practical approaches to developing and implementing policy, regulations and standards, and technology. The Volpe Center, with expertise in all of these arenas, can help ensure that GPS fulfills its promise for improving almost every mode of transportation.

Volpe Center Provides Leading Edge GPS Expertise for Transportation

The Global Positioning System (GPS)—which provides extremely accurate and continuous three-dimensional positioning, navigation, and timing information to users worldwide—is proving to be an indispensable tool across the transportation enterprise. Deployed and operated by the U.S. Department of Defense (DoD), this satellite-based radionavigation system has become critical for both military and civilian applications. DOT works closely with DoD in coordinating the civil capabilities of GPS. The Volpe Center has been involved in GPS activities since the mid-1980s, playing important roles—in supporting policy development, including the critical task of determining the reliability and vulnerability of GPS; in developing GPS applications for all modes of transportation; and in supporting international standardization efforts, as well as working with other agencies to support the modernization of GPS, particularly for civil use. This rich legacy of experience in the GPS arena enables the Center to take a leadership role in determining the future of navigation systems.

GPS Policy—the Center's Research and Coordination Role

Federal Radionavigation Plan
The Volpe Center develops the Federal Radionavigation Plan (FRP) under the sponsorship of DoD, DOT, and the Department of Homeland Security (DHS). The recently published 2005 edition focuses on a transition to GPS-based services, recognizing the need to maintain backup navigation aids and provide redundant systems. The plan is the official source of radionavigation policy and planning for the federal government and covers common-use, federally operated radionavigation systems—systems used by both civil and military sectors. The plan contains the current policy on the mix of radionavigation systems, and presents the federal interagency approach to the implementation and operation of radionavigation systems. It also addresses the needs of civil users beyond aviation and marine areas, and discusses GPS applications for land vehicles, surveying and mapping, weather research, space applications, and many other uses. (Systems used exclusively by the military are covered in the Master Positioning, Navigation, and Timing Plan published by the Joint Chiefs of Staff.)

Vulnerability of Transportation Infrastructure Relying on Global Positioning System
In the mid-1990s, GPS was planned to be the sole source of radionavigation for aircraft guidance systems by 2010. However, the Presidential Commission on Critical Infrastructure Protection recognized that using GPS alone would create the potential for a single source of failure. There was a broad realization that when GPS is used in a safety-of-life application, vulnerability issues must be addressed. As a result, DOT, in consultation with DoD, undertook a thorough evaluation of the national transportation infrastructure that relies on GPS to address the vulnerability of the system and to ensure that civil transportation systems are not entirely dependent on any one technology. In a highly regarded and influential study, the Volpe Center assessed the vulnerability of civil-transportation GPS applications and recommended appropriate mitigation techniques in critical applications wherever possible. The results of the study were published in a 2001 report titled Vulnerability Assessment of the Transportation Infrastructure Relying on the Global Positioning System.

GPS Action Plan
"The action plan... will ensure that the vulnerabilities identified in the (Volpe) report do not affect the safety and security of our transportation system as we work to ensure that GPS fulfills its potential."

— DOT Secretary
Norman Y. Mineta

Volpe Center GPS Reports
Available at www.navcen.uscg.gov/

• 2005 Federal Radionavigation Plan
• Vulnerability Assessment of the Transportation Infrastructure Relying on the Global Positioning System

This report identified transportation operations that employ GPS, methods for GPS disruption, possible impacts to transportation safety, and mitigation approaches to ensure service reliability. All modes of transportation are increasingly reliant on GPS and, according to the report, GPS is susceptible to various forms of intentional and unintentional interference. Unintentional disruption can result from such causes as atmospheric effects, signal blockage from buildings, and interference from communications equipment. Because of the pervasive use of GPS, intentional disruption can range from terrorist attacks to people simply trying to avoid road tolls to libertarian resistance to the perception that citizens' movements can be tracked.

A number of recommendations to address the possibility of disruption and ensure the safety of the national transportation infrastructure were presented in the report. The DOT operating administrations, having conducted a thorough review of the Volpe Center study, declared that they concur with all of the report recommendations. As announced in March 2002, DOT is implementing a GPS Action Plan that includes the following initiatives for maintaining the viability of the nation's transportation infrastructure:

• Ensure that adequate GPS backup systems are maintained
• Maintain the partnership with DoD to continue modernizing GPS with the implementation of new civil signals
• Facilitate transfer of appropriate GPS anti-jam technology from the military for civil use
• Conduct industry outreach to develop GPS receiver performance standards
• Emphasize and promote education programs with state and local departments of transportation that advise users about GPS vulnerabilities
• Assess radionavigation capabilities across all the modes of transportation to identify the most appropriate mix of systems, from both a capabilities and cost perspective, for the next 10 years and beyond. This will include completing the evaluation of the long-term need for the continuation of Loran-C.

GPS Modernization—RITA's Role

The next-generation of GPS, known as GPS III, is being designed to meet military and civilian needs through at least 2030. The goals of the GPS modernization program are to protect the service for U.S. and allied forces and prevent adversary exploitation, and to preserve civil use and provide enhancements. GPS III will eliminate some system shortcomings and vulnerabilities. The new system is currently in the development-definition phase, where system architecture is designed and requirements are identified and documented.

The Volpe Center works closely with the Civil Applications Program Manager at the GPS Joint Program Office to help capture the needs of the civil community for GPS III. One current effort is particularly significant— developing and maintaining an integrated database of requirements and establishing the relationships and traceability of requirements within the GPS system. This effort will equip the civil GPS community with the information necessary for informed decisionmaking. GPS III will enhance U.S. leadership in space navigation and help to meet the presidential goal of establishing GPS as a world standard.

Development of a National Positioning, Navigation, and Timing (PNT) Architecture — RITA's Role

The new National Security Policy Directive (NSPD-39) reaffirms the open use of GPS civil signals and unrestricted access to the technical information that is needed to manufacture equipment using those signals. DoD will maintain the primary responsibility for developing and modernizing GPS. However, identifying, specifying, and funding new civil capabilities will be the primary responsibility of DOT.

The National Space-based Position, Navigation, and Timing (PNT) Executive Committee (NPEC), co-chaired by the secretaries of defense and transportation, will develop a Five-Year National Space-based PNT plan, which will include architecture specifications. On behalf of DOT, the Research and Innovative Technology Administration (RITA, the Volpe Center's parent agency), will lead the national PNT architecture effort and will provide input on the requirements and perspectives of the civil community.

The approach for the National PNT Architecture effort is to help guide future PNT system-of-systems investment and implementation decisions. The objective is to provide more effective and efficient PNT capabilities in the post-2025 timeframe and an evolutionary path for government-provided PNT systems and services. This effort will document the current national PNT architecture and evaluate alternative future mixes of global (space and non space-based) and regional PNT solutions, PNT augmentations, and autonomous PNT capabilities to address priorities identified by both the civil and military communities.

For the Saint Lawrence Seaway, the Volpe Center established the first fully operational Automatic Identification System (AIS) network in North America.
Leveraging existing tracking technology developed to improve safety and efficiency in the Panama Canal and Saint Lawrence Seaway, the Volpe Center designed, tested, and deployed the Vessel Identification and Positioning System (VIPS) to improve maritime security and asset protection. U.S. security, operations, and force protection units can track all VIPS-equipped vessels in real time on a geographic display.

Volpe Center's GPS Work Across the Transportation Modes

Aviation—Predicting the Availability of Navigation Service with Integrity Monitoring
For many reasons, no single navigation system is reliable all of the time. It is, therefore, important that users have a means to be informed of system failures. The integrity of a system is defined by its ability to provide a timely warning when it fails to meet its stated accuracy and should no longer be used. GPS itself cannot provide integrity monitoring that satisfies aviation requirements. Receiver Autonomous Integrity Monitoring (RAIM) currently provides integrity monitoring within certified aviation receivers. RAIM is a method that examines the internal consistency of a set of redundant measurements within the GPS receiver to detect, and perhaps remove, a faulty measurement. In the case of GPS, this amounts to detecting, and perhaps excluding, a faulty satellite from the set used for navigation. When GPS is used as a supplemental navigation system, fault detection is all that is required. When GPS is used as a primary means of navigation, both fault detection and fault exclusion are required. The Volpe Center has supported the Federal Aviation Administration (FAA) in developing integrity algorithms as well as studying coverage and availability of RAIM and Fault Detection and Exclusion for all phases of flight, from oceanic through nonprecision approach.

The Center's recent work in this area also includes contributing to FAA's Wide Area Augmentation System (WAAS). Because GPS alone does not meet FAA's navigation requirements for accuracy, integrity, and availability, WAAS was developed for use in en route applications through approach with vertical guidance. WAAS uses a series of ground reference stations to correct for GPS signal errors caused by ionospheric disturbances, satellite timing, and orbit errors, and it provides integrity information on each GPS satellite. The Volpe Center has supported augmentations to WAAS, and has also evaluated integrity and continuity for FAA's Local Area Augmentation System (LAAS), an augmentation to GPS for service in airport areas (approximately a 20-30 mile radius).

DOT and the DoD are also engaged in a project to identify specific potential failures that would compromise GPS integrity. In support of the Integrity Failure Modes and Effects Analysis Project, the Volpe Center analyzes integrity anomalies that are caused by hardware and software failures in the GPS satellites and/or operational control segment.

Marine Navigation—Central America and the Saint Lawrence Seaway
When large cargo ships traverse narrow waterways, the careful management and navigation of their passage is critical to maximizing efficiency, safety, and security. The Volpe Center has developed several systems that improve vessel tracking in shipping channels using GPS and other technologies. Between 1996 and 2000, the Center installed a state-of-the-art navigation system in the Panama Canal. Subsequently, smaller-scale systems were installed in Central American ports to restore navigation capabilities that were destroyed by hurricanes. In 2002, the Center designed and implemented a comprehensive vessel communications and tracking network that identifies and tracks commercial vessels on the Saint Lawrence Seaway.

Intelligent Railroad Systems using GPS could increase safety at highway-rail intersections. Processor-based control systems and digital communications could enable reliable and timely communication between rail and highway systems, and to passenger vehicles near crossings.

The network, based on Automatic Identification System (AIS) technology, provides signal coverage from Montreal to eastern Lake Erie. Developed by the Volpe Center, AIS integrates global positioning technology with communications data links to provide vital and precise information on ship identification, position, speed, and heading to a vessel traffic control center as well as to other AIS-equipped ships. It also provides data on weather, wind, current, and water and ice levels. Volpe also installed an AIS system for the Columbia River Pilots Association.

AIS offers a range of benefits: system administrators can schedule inspections and services in a more timely manner, effect better speed control, and schedule lockages and vessel tie-ups more efficiently; as transit times are reduced, shippers improve fleet management and save on fuel; and in a time of heightened security, law enforcement officials can respond more quickly and effectively to emergencies.

Rail—Improving Safety and Mobility with Positive Train Control
Over the next decade, global positioning and navigation services will become increasingly important to railroad operations. The Federal Railroad Administration (FRA) is encouraging and facilitating the accelerated adoption of sensors, computers, and digital communications to collect, process, and disseminate information to improve the safety, security, and operational effectiveness of railroads. Elements of this approach require accurate, real-time information about the location of railroad equipment.

The use of GPS is part of a larger effort within the railroad industry seeking to develop an integrated command, control, communications, and information system for controlling train movements with safety, security, precision, and efficiency. Positive Train Control (PTC) systems being planned, or currently under pilot-project study, will improve railroad safety by virtually eliminating the risk of: collisions between trains, casualties to roadway workers, damage to equipment, and over-speed accidents. With extensive experience working with GPS applications in air and marine navigation, the Volpe Center has the technical expertise to support this effort, and has demonstrated this capability by developing a mobile tracking system that uses a GPS-based position-reporting system to provide accurate location information for off-track vehicles at the FRA's Transportation Technology Center in Pueblo, Colorado.

FRA, along with other government agencies, is performing research to assess the feasibility of improving the accuracy of the Nationwide Differential Global Positioning System (NDGPS), within the confines of the existing infrastructure, for civilian land applications. NDGPS uses ground reference stations to determine the differential between the GPS location and the true location. Enabling high-accuracy NDGPS options will require additional data rate capabilities. The Volpe Center has been actively working with FRA to investigate error-mitigation techniques for atmospheric errors (troposphere and ionosphere), multipath, and clock and orbital errors to achieve the desired accuracy of 20-40 cm from the high-accuracy DGPS architecture. Some of these techniques are similar to those under development by the FAA, such as the LAAS, and the WAAS (described above in the Aviation section). Research also is needed to achieve other performance parameters for these systems, such as integrity, availability, and continuity.

Transit—Advanced Vehicle Location Systems
Many transit systems across the country now use Advanced Vehicle Location (AVL) systems that depend on GPS to track buses and ensure accurate schedule performance, increase overall operating efficiency, and assist in fleet management. The Volpe Center's established role as an impartial evaluator of new methods and technologies, together with its understanding of those technologies, enabled a Center team to develop a set of Advanced Public Transit Systems Evaluation Guidelines that provide a common framework and methodology for evaluating individual operational tests.

International GPS Efforts
The Volpe Center is working with the International Civil Aviation Organization to better integrate operation of the global positioning satellite navigation system. These efforts have not only increased recognition of the Center's GPS capabilities, but have offered opportunities for other countries to capitalize on advances in GPS transportation applications and thus to increase safety and efficiency and facilitate trade. The Center is examining the potential improvements to aviation that the introduction of the Russian Global Navigation Satellite System (GLONASS) and the European GALILEO system could bring in conjunction with the use of GPS.

In addition, the Center supports individual countries in the introduction and operation of GPS systems. Examples of the Center's work in this area include support to:

• The Canadian Civil Air Navigation Services (NAV CANADA) in the integration of a WAAS service volume model with the Canadian Notice to Airmen (NOTAM) system for predicting and reporting outages
• Air Service Australia's Automatic Dependent Surveillance Broadcast (ADS-B) GPS RAIM Prediction System, which provides the capability to distribute GPS outage information
• Brazil's Department of Air Space Control (DECEA) in developing and deploying the first real-time GNSS performance monitoring capability for operational use. The system will be able to monitor the operational status of a GNSS system in real time, as well as predict its future performance.

Volpe Center study of integrated Loran/ GPS. This figure shows how blockage of navigation signals in New York City's Wall Street area "urban canyon" produces various estimates of the same vehicle's position (depicted by circles). All fixes but one are too inaccurate at the instant shown to locate the vehicle correctly. The one exception is the Dead Reckoning solution—the green dot—but Dead Reckoning also degrades unacceptably after further exposure to this environment.

Complementary Navigation Systems—Integrating Loran and GPS

The Volpe Center is working with FAA to validate whether the complementary positioning and timing features of Loran (LOng RAnge Navigation) and GPS can meld into a tracking system that maintains radionavigation performance standards in the urban and maritime environments. Specifically, a recent Volpe Center study assessed the extension of technologies that the Center has applied in aviation and marine navigation for land applications in urban areas, using positioning and timing information provided by an integrated GPS/Loran system. The original Loran-C is nearing completion of a significant upgrade and enhancement effort funded by FAA. Enhanced Loran complements the GPS system well. Loran is a navigation system that uses the time interval between radio signals received from two or more radio transmitters to determine the position of a ship or aircraft. It was originally developed to provide radionavigation service for U.S. coastal waters and was later expanded to include complete coverage of the continental United States as well as most of Alaska. Its signals are much less susceptible to the interference that can impair GPS, and its broadcast frequency has minimal line-of-sight issues. Loran has recently been shown to be an adequate backup system to GPS for many applications.

The Volpe Center's work examines how well the integrated GPS/Loran system can supplement GPS when the GPS signal is not usable. As part of this effort, Volpe staff conducted performance evaluations in the Boston and New York City areas, and under GPS-band jamming in New Mexico. Preliminary conclusions are that Loran can be a valuable surveillance supplement to GPS in some urban applications.

Because GPS is used to synchronize network timing, its disruption can potentially impact wide-ranging infrastructures such as finance and banking. In general, it is thought that Loran can be used to augment GPS because it provides the necessary timing backup. However, as Loran is not an international system, it does not provide a global solution.

GPS and the Future of Transportation

The uses of GPS in the transportation arena are already numerous, and future applications are wide-ranging. In aviation GPS already supports oceanic, enroute, terminal, and vertical guidance and may be used in the future for airport surface management. Maritime, land, and aviation applications will be enhanced by improvements to the accuracy and integrity of GPS. Highway applications today are focused on assisting travelers in determining their routes and in fleet management. Near-term research is underway to examine the ability to provide warnings to drivers of potential critical situations, such as a stop sign violation or to avoid crashes. In the trucking industry GPS can be used to monitor compliance with hours-of-service regulations. Applications in the transit industry include expanding fleet-tracking capabilities. GPS-based position determination is also used to determine passenger-vehicle position for emergency response; this use will increase. In summary, GPS can facilitate enhanced safety, improved service levels, heightened security, and greater efficiency. However, the complexities of ensuring its reliability necessitate innovative, yet practical approaches, to developing and implementing policy, regulations and standards, and technology. The Volpe Center offers expertise in all of these arenas and can help ensure that the use of GPS fulfills its promise.

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