National Academies Press: OpenBook
Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

The Global Positioning System: A Shared National Asset

Recommendations for Technical Improvements and Enhancements

Committee on the Future of the Global Positioning System

Commission on Engineering and Technical Systems

National Research Council


NATIONAL ACADEMY PRESS
Washington, D.C.
1995

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the committee responsible for the report were chosen for their special competencies and with regard for appropriate balance.

This report has been reviewed by a group other than the authors according to procedures approved by a Report Review Committee consisting of members of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine.

The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences.

The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. Robert M. White is president of the National Academy of Engineering.

The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine.

The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. Robert M. White are chairman and vice-chairman, respectively, of the National Research Council.

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Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

COMMITTEE ON THE FUTURE OF THE GLOBAL POSITIONING SYSTEM

Laurence J. Adams, Chair,

Martin Marietta Corporation (Ret.), Consultant, Potomac, Maryland

Penina Axelrad,

Colorado Center for Astrodynamics Research, University of Colorado, Boulder, Colorado

John D. Bossler,

Center for Mapping, Ohio State University, Columbus, Ohio

Ronald Braff,

Center for Advanced Aviation, System Development, MITRE Corporation, McLean, Virginia

A. Ray Chamberlain,

American Trucking Association, Inc., Alexandria, Virginia

Ruth M. Davis,

Pymatuning Group, Inc., Alexandria, Virginia

John V. Evans,

COMSAT Laboratories, COMSAT Corporation, Clarksburg, Maryland

John S. Foster,

TRW Inc. (Retired), Redondo Beach, California

Emanuel J. Fthenakis,

Fairchild Industries (Ret.), Potomac, Maryland

J. Freeman Gilbert,

Institute of Geophysics and Planetary Physics, University of California, San Diego, La Jolla, California

Ralph H. Jacobson,

The Charles Stark Draper Laboratory, Inc., Cambridge, Massachusetts

Keith D. McDonald,

Sat Tech Systems, Arlington, Virginia

Irene C. Peden,

University of Washington, (Retired) Seattle, Washington

James W. Sennott,

Department of Electrical and Computer Engineering and Technology, Bradley University, Peoria, Illinois

Joseph W. Spalding,

U.S. Coast Guard Research and Development Center, Groton, Connecticut

Lawrence E. Young,

Jet Propulsion Laboratory, Pasadena, California

Staff

Archie Wood, Executive Director,

Commission on Engineering and Technical Systems

JoAnn C. Clayton, Director,

Aeronautics and Space Engineering Board

Allison C. Sandlin, Study Director

David A. Turner, Study Consultant

Cristellyn Banks, Project Assistant

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

COMMISSION ON ENGINEERING AND TECHNICAL SYSTEMS

Albert R. C.

Westwood, Research and Exploratory Technology, Sandia National Laboratories, Albuquerque, New Mexico,

Chair

Naomi F. Collins,

NAFSA: Association of International Educators, Washington D.C.

Nancy R. Connery,

Woolwich, Maine

Richard A. Conway,

Union Carbide Corporation, South Charleston, West Virginia

Samuel C. Florman,

Kreisler Borg Florman Construction Company, Scarsdale New York

Trevor O. Jones,

Libbey-Owens-Ford Company, Cleveland, Ohio

Nancy G. Leveson,

Department of Computer Science and Engineering, University of Washington, Seattle, Washington

Alton D. Slay,

Slay Enterprises, Inc., Warrenton, Virginia

James J. Solberg,

Purdue University, West Lafayette, Indiana

Barry M. Trost,

Chemistry Department, Stanford University, Stanford, California

George L. Turin,

Berkeley, California

William C. Webster,

College of Engineering, Berkeley, California

Deborah A. Whitehurst,

Arizona Community Foundation, Phoenix Arizona

Robert V. Whitman,

Lexington, Massachusetts

Staff

Archie Wood, Executive Director,

Commission on Engineering and Technical Systems

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

Acknowledgements

The National Research Council's Committee on the Future of the Global Positioning System would like to thank all the individuals who participated in this study, especially Mr. Jules McNeff, Major Lee Carrick, Major Matthew Brennen, Lieutenant Brian Knitt, Captain Earl Pilloud, Captain Christopher Shank, Lieutenant Colonel Donald Latterman, Major Al Mason, Mr. John Clark, Mr. Scott Feairheller, Mr. Terry McGurn, Mr. Jim Graf, Mr. John Hrinkevich, and Mr. Jon Schnabel who arranged briefings and responded to committee requests throughout the study. In addition, Mr. Peter Serini and Mr. George Wiggers served as the committee's liaisons with the Department of Transportation and also were helpful in obtaining relevant information and arranging briefings. The NRC committee also benefited from the work of numerous previous study groups, and considered their recommendations. In addition to the many informative briefings, the committee requested a large number of written responses from receiver manufacturers and many others concerning various issues. The NRC committee wishes to thank all of the contributors for their cooperation in providing existing information and in researching some of the issues that arose. The committee also would like to acknowledge Mr. Michael Dyment of BoozAllen & Hamilton, who conducted an analysis of the economic impact of the removal of Selective Availability on the differential GPS market; Mr. Melvin Barmat of Jansky/Barmat Telecommunications, Inc., who performed an analysis of L-band frequency availability; and Dr. Young Lee of the MITRE Corporation, who conducted an analysis of the effect of improved accuracy on Receiver Autonomous Integrity Monitoring. A complete list of study participants is given in Appendix A.

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
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Preface

The Global Positioning System (GPS) was originally designed primarily to provide highly accurate radionavigation capability to U.S. military forces, while also providing an unencrypted signal of degraded accuracy to civilian users. As the system developed, civil usage expanded rapidly and the number of civilian users now greatly exceeds the number of military users. The timing, velocity, and positioning information provided by GPS is being used for a growing number of new, innovative applications that could not have been foreseen by the original system designers. Because of its widespread use by both the military and civilians, GPS has truly emerged as a dual-use system.

Recognizing that the continued existence of GPS as a dual-use system clearly requires some trade-offs between civilian utility and national security, Congress requested a joint study by the National Academy of Sciences and the National Academy of Public Administration (NAPA) on the Department of Defense's Global Positioning System (GPS). The National Academy of Sciences was asked to recommend technical improvements and augmentations that could enhance military, civilian, and commercial use of the system. The National Academy of Public Administration was asked to address GPS management and funding issues, including commercialization, governance, and international participation. To conduct its part of the study, the National Academy of Sciences established an expert committee through the National Research Council (NRC), the operating arm of the National Academy of Sciences and the National Academy of Engineering.

This report provides the results of the technical portion of the study conducted by the National Research Council's Committee on the Future of the Global Positioning System. Portions of this report (for example, Chapters 3, 4, and some of the appendices) also are included in the joint NRC/NAPA report, The Global Positioning System—Charting the Future, which contains the complete results of the NAPA portion of the study.

In examining future enhancements to the GPS system, the NRC committee endeavored to balance the features that would enhance civil applications against the clear requirement to maintain the military integrity of the system. The recommendations in the report were intended to meet this criterion.

LAURENCE J. ADAMS, CHAIR

COMMITTEE ON THE FUTURE OF

THE GLOBAL POSITIONING SYSTEM

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Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
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Challenges to Full Utilization of GPS,

 

35

   

Findings,

 

37

   

Land Transportation Applications,

 

38

   

Current and Future Applications and Requirements,

 

38

   

Challenges to Full GPS Utilization,

 

41

   

Findings,

 

42

   

Mapping, Geodesy, and Surveying Applications,

 

43

   

Current and Future Applications and Requirements,

 

43

   

Challenges to Full GPS Utilization,

 

45

   

Findings,

 

46

   

GPS Earth Science Applications,

 

46

   

Current and Future Applications and Requirements,

 

47

   

Challenges to Full GPS Utilization,

 

50

   

Findings,

 

51

   

GPS Timing and Telecommunications Applications,

 

52

   

Current and Future Applications and Requirements,

 

52

   

Challenges to Full GPS Utilization,

 

55

   

Findings,

 

56

   

Spacecraft Uses of GPS,

 

56

   

Current and Future Applications and Requirements,

 

57

   

Challenges to Full Utilization,

 

60

   

Findings,

 

61

   

Summary,

 

61

3.

 

Performance Improvements to the Existing GPS Configuration

 

67

   

Introduction,

 

67

   

Current GPS Performance,

 

68

   

Accuracy,

 

68

   

Integrity and Availability,

 

70

   

Selective Availability and Anti-Spoofing,

 

70

   

Selective Availability,

 

71

   

Findings and Recommendations,

 

82

   

Anti-Spoofing,

 

84

   

Findings and Recommendations,

 

85

   

Signal Structure Modifications to Reduce Atmospheric Delay Error,

 

86

   

Guidelines and Technical Considerations,

 

87

   

New Signal Structure Options,

 

88

   

Improvements Anticipated from Adding L4,

 

90

   

Reduction of Receiver Noise and Multipath Errors,

 

91

   

Findings and Recommendations,

 

97

   

Performance Improvements to the GPS Operational Control Segment and Satellite Constellation,

 

98

   

Current Status of the Operational Control Segment and Planned Upgrades,

 

98

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×
   

Recommended Upgrades to the Operational Control Segment,

 

98

   

Planned Block IIR Operation,

 

108

   

Suggested Improvements Using the Autonomous Ranging and Crosslink Communication Capability,

 

109

   

Performance Improvements to Enhance the Military Use of GPS,

 

111

   

Recommended Technical Improvements to Military User Equipment,

 

111

   

Possible Interim Operational Procedures,

 

116

   

Improvement Implementation Strategy,

 

117

4.

 

Technical Enhancements for Future Consideration

 

123

   

GPS Improvements to Improve Overall Performance,

 

123

   

Use of a 24-Satellite Ensemble Clock,

 

123

   

Reduced Satellite Clock Errors Through Use of Improved Clocks,

 

124

   

Satellite-Based Integrity Monitoring,

 

125

   

Increased L2 Signal Strength,

 

126

   

Military Enhancements,

 

128

   

Block IIF Signal Structure Military Enhancements,

 

128

   

Spot Beams,

 

132

   

Enhancements for High-Precision Users,

 

133

   

GPS Transmit Antenna Calibration,

 

133

   

Knowledge of Spacecraft Characteristics,

 

134

   

Improved L1 Signal Reception at Angles Below the Earth's Horizon,

 

134

Appendix A:

 

Study Participants

 

135

Appendix B:

 

Abbreviated Committee Biographies

 

139

Appendix C:

 

Overview of the Global Positioning System and Current or Planned Augmentations

 

145

Appendix D:

 

Accuracy Definitions and Mathematical Relationships

 

177

Appendix E:

 

Report From Mr. Michael Dyment, Booz·Allen & Hamilton

 

179

Appendix F:

 

Report From Dr. Young Lee, The MITRE Corporation

 

201

Appendix G:

 

Increased Bandwidth Performance Analysis

 

213

Appendix H:

 

Signal Structure Options

 

215

Appendix I:

 

Report from Mr. Melvin Barmat, Jansky/Barmat Telecommunications, Inc.

 

221

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
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Page xiii Cite
Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
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List of Figures

Figure 1

 

Current plan for satellite replacement. (Courtesy of the GPS Joint Program Office)

 

11

Figure 3-1

 

DGPS coverage provided by commercially available systems, including Skyfix and Sercel. (Courtesy of the National Air Intelligence Center)

 

73

Figure 3-2

 

DGPS coverage provided by the planned FAA WAAS (Wide-Area Augmentation System). Source: Innovative Solutions International, Inc. presentation at the National Technical Meeting of the Institute of Navigation Meeting, Anaheim, California, January 1995.

 

74

Figure 3-3

 

Position estimates from GPS and GLONASS obtained from measurement snapshots taken 1 minute apart over an entire day. Position from (a) GPS with SA off, (b) GPS with SA on, (c) GLONASS, and (d) GPS + GLONASS. (Courtesy of MIT Lincoln Laboratory)

 

75

Figure 3-4

 

Horizontal scatter plot of 42 meters CEP (100 meters, 2 drms) with SA at its current level and horizontal scatter plot of approximately 10 meters CEP (24 meters, 2 drms) without SA. (Figure Courtesy of Mr. Jules McNeff, Office of the Assistant Secretary of Defense, C3I)

 

77

Figure 3-5

 

Approximate stand-alone horizontal SPS accuracy, 2 drms resulting from recommended improvements and enhancements.

 

103

Figure 3-6

 

Current plan for satellite replacement. (Courtesy of the GPS Joint Program Office)

 

118

Figure 4-1

 

Wide-band GPS with a 100-watt jammer.

 

129

Figure 4-2

 

Wide-band GPS with a 10-kilowatt jammer.

 

130

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

List of Tables

Table 2-1

 

Military Aviation and Precision-Guided Munitions Applications and Requirements

 

23

Table 2-2

 

Naval Applications and Requirements

 

24

Table 2-3

 

Military Land Applications and Requirements

 

25

Table 2-4

 

GPS Performance Requirements for Aviation Applications

 

29

Table 2-5

 

Requirements for Maritime Applications

 

35

Table 2-6

 

Land Transportation Requirements

 

40

Table 2-7

 

Current and Future GPS Requirements for GIS, Mapping, Surveying, and Geodesy

 

45

Table 2-8

 

GPS Earth Science Requirements

 

50

Table 2-9

 

Timing and Telecommunications Requirements

 

54

Table 2-10

 

Requirements for GPS Spacecraft Applications

 

59

Table 2-11

 

Summary of Military Applications with Accuracy Requirements Unmet by the GPS PPS as Currently Specified

 

62

Table 2-12

 

Summary of Civilian Applications with Accuracy Requirements of 100 Meters or Greater (currently achievable with the basic GPS SPS)

 

62

Table 2-13

 

Summary of Civilian Accuracy Requirements Between 25 and 100 Meters

 

63

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
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Table 2-14

 

Summary of Civilian Accuracy Requirements Between 10 and 25 Meters

 

63

Table 2-15

 

Summary of Civilian Accuracy Requirements Between 1 and 10 Meters

 

64

Table 2-16

 

Summary of Submeter Civilian Accuracy Requirements

 

65

Table 3-1

 

Observed GPS Positioning Errors with Typical SPS and PPS Receivers

 

68

Table 3-2

 

SA Errors from DOD/DOT Signal Specification Issues Technical Group

 

71

Table 3-3

 

The Effect of Eliminating SA on GPS SPS Stand-Alone Horizontal Accuracy

 

80

Table 3-4

 

Effect of SA Removal on RAIM Availability for Aviation Applications

 

81

Table 3-5

 

Elimination of Ionospheric Error by the Addition of Another Frequency

 

93

Table 3-6

 

Effect of Reduced Ionospheric Error by the Addition of Another Frequency and Additional Improvements Obtained with Using a More Advanced SPS Receiver

 

94

Table 3-7

 

Effect of Using a More Advanced PPS Receiver on Stand-Alone Accuracy

 

95

Table 3-8

 

Effect of SA Removal and Dual-Frequency Capability on RAIM Availability for Aviation Applications

 

96

Table 3-9

 

Reduction of Combined Clock and Ephemeris Errors

 

102

Table 3-10

 

Impact of Reduced Clock and Ephemeris Error on SPS Stand-Alone Accuracy

 

104

Table 3-11

 

Impact of Reduced Clock and Ephemeris Error on PPS Stand-Alone Accuracy

 

105

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

Table 3-12

 

Effect of SA Removal, Dual-Frequency Capability and Reduced Clock and Ephemeris Errors on RAIM Availability for Aviation Applications

 

105

Table 3-13

 

Space Segment Enhancements

 

119

Table 3-14

 

Operational Control Segment Enhancements

 

120

Table 4-1

 

GPS Wide-Band Signal Augmentation Performance with a 100-Watt Jammer

 

131

Table 4-2

 

GPS Wide-Band Signal Augmentation Performance with a 10-Kilowatt Jammer

 

132

Page xvii Cite
Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

Acronyms and Abbreviations


ADS

Automatic dependant surveillance

ANSI

American National Standards Institute

A-S

Anti-Spoofing

ASIC

Application Specific Integrated Circuit

ATM

Air Traffic Management

AVI

Automatic Vehicle Identification

AVL

Automatic Vehicle Location


BIPM

Bureau International des Poids et Measures


C/A

Coarse/Acquisition code

CDMA

Code Division Multiple Access

CEP

Circular Error Probable

CGS

Civil GPS Service

CGSIC

Civil GPS Service Interface Committee

CORS

Continuously Operating Reference Station

CRPA

Controlled Radiation (Reception) Patterned Antenna


dB

decibel

DGPS

Differential GPS

DMA

Defense Mapping Agency

DOD

Department of Defense

DOP

Dilution of Precision

DOT

Department of Transportation

drms

distance root mean square

DRVID

Differential Ranging Versus Integrated Doppler


ECDIS

Electronic Chart Display Information System


FAA

Federal Aviation Administration (part of DOT)

FDMA

Frequency Division Multiple Access

FHWA

Federal Highway Administration

FM

Frequency Modulation

FRA

Federal Railroad Administration


GIS

Geographic Information Systems

GHz

Gigahertz

GLONASS

Global Navigation Satellite System

Page xviii Cite
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GNSS

Global Navigation Satellite System

GPS

Global Positioning System


HDOP

Horizontal Dilution of Precision

Hz

Hertz (cycles per second)


IALA

International Association of Lighthouse Authorities

ICAO

International Civil Aviation Organization

IF

Intermediate Frequency

IGS

International GPS Service for Geodynamics

ILS

Instrument Landing System

IMO

International Maritime Organization

Inmarsat

International Maritime Satellite Organization

INS

Inertial Navigation System

ITS

Intelligent Transportation System

IVHS

Intelligent Vehicle Highway Systems


JCS

Joint Chiefs of Staff

JPO

Joint Program Office

J/S

Jammer-to-signal ratio


KHz

Kilohertz


L1

GPS L-band signal 1 (1575.42 MHz)

L2

GPS L-band signal 2 (1227.6 MHz)

L4

Proposed GPS L-band signal

L-band

L-band frequency (about 1-2 GHz)

LADGPS

Local Area Differential GPS

LORAN-C

Long-Range Navigation, Version C


MBS

Mobile Broadcast Service

MCS

GPS Master Control Station

MHz

Megahertz

ms

Millisecond

MOA

Memorandum of Agreement


NAPA

National Academy of Public Administration

NASA

National Aeronautics and Space Administration

NCA

National Command Authority

NDB

Nondirectional Beacon

NGS

National Geodetic Survey

NIST

National Institute of Standards and Technology

NOAA

National Oceanic and Atmospheric Administration

NRC

National Research Council

ns

nanosecond

NSA

National Security Agency

NTIA

National Telecommunications and Information Administration


OCS

Operational Control Segment


P-code

Precision code

PHE

Probability of Hazardous Error

PLGR

Precision Lightweight GPS Receiver

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
×

PMD

Probability of Missed Detection

P3I

Preplanned Product Improvement

PPS

Precise Positioning Service

PRN

Pseudorandom Noise


RAIM

Receiver Autonomous Integrity Monitoring

RDS

Radio Data System

RF

Radio Frequency

RFP

Request for Proposal

RISC

Reduced Instruction Set Computing

RNP

Required Navigation Performance

ROD

Relative Operating Distance

RTCA

Ratio Technical Commission for Aeronautics

RTCM

Radio Technical Commission for Maritime Services


SA

Selective Availability

SAIM

Satellite Autonomous Integrity Monitoring

S-band

Microwave frequency band, about 2-4 GHz

SEP

Spherical Error Probable

sigma

standard deviation (symbol: a)

SNR

Signal-to-Noise Ratio

SONET

Synchronized Optical Network

SPS

Standard Positioning Service


TACAN

Tactical Air Navigation

TAI

International Atomic Time

TCAS

Traffic Alert/Collision Avoidance System

TDMA

Time Division Multiple Access

TEC

Total Electron Content

TOD

Time of day


UERE

User Equivelent Range Error

UHF

Ultra High Frequency

USAF

United States Air Force

USCG

United States Coast Guard

USNO

United States Naval Observatory

UTC

Coordinated Universal Time


VDOP

Vertical Dilution of Precision

VHF

Very High Frequency

VLBI

Very Long Baseline Interferometry

VOR

VHF Omnidirectional Range

VOR/DME

VOR with Distance Measuring Equipment

VORTAC

combined VOR and TACAN

VTS

Vessel Traffic Services


WAAS

Wide Area Augmentation System

WADGPS

Wide Area Differential GPS

WGS

World Geodetic System


Y-code

Encrypted P-code

Suggested Citation:"Front Matter." National Research Council. 1995. The Global Positioning System: A Shared National Asset. Washington, DC: The National Academies Press. doi: 10.17226/4920.
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The Global Positioning System (GPS) is a satellite-based navigation system that was originally designed for the U.S. military. However, the number of civilian GPS users now exceeds the military users, and many commercial markets have emerged. This book identifies technical improvements that would enhance military, civilian, and commercial use of the GPS. Several technical improvements are recommended that could be made to enhance the overall system performance.

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