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



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--> 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

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--> 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. Library of Congress Catalog Card Number 95-69627 International Standard Book Number: 0-309-05283-1 Available in limited supply from: The Aeronautics and Space Engineering Board 2101 Constitution Avenue, N.W. Washington, D.C. 20418 (202) 334-2855 Additional copies available for sale from: National Academy Press 2101 Constitution Avenue, N.W., Box 285 Washington, D.C. 20055 1-800-624-6242 or (202) 334-3313 Copyright 1995 by the National Academy of Sciences. All rights reserved. Printed in the United States of America Copies of The Global Positioning System - Charting the Future are available for sale from: National Academy of Public Administration Publications Desk 1120 G Street, NW Suite 850 Washington, D.C. 20005-3801 (202) 347-3190 First Printing, May 1995 Second Printing, August 1995 Third Printing, February 1997

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--> 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

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--> 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

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--> 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 Booz•Allen & 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.

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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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--> Table of Contents     Acknowledgements   v     Preface   vii     List of Figures   xiii     List of Tables   xiv     Acronyms and Abbreviations   xvii     Executive Summary   1 1.   Introduction   13     The Task,   13     Joint Study Approach,   14     National Research Council Study Approach,   15     Major Issues and Considerations,   15     Report Organization,   16     GPS Program Overview,   16     GPS Technical Overview,   17 2.   GPS Applications and Requirements   19     Introduction,   19     GPS Military Applications,   20     Current and Future Applications and Requirements,   21     Challenges to Full GPS Utilization,   22     Findings,   26     GPS Aviation Applications,   26     Current and Future Applications and Requirements,   27     Challenges to Full Utilization of GPS,   30     Findings,   32     Maritime Use of GPS,   32     Current and Future Applications and Requirements,   33

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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

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-->     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

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--> Appendix J:   Selective Denial of Civilian GPS Signals by the Military   249 Appendix K:   Direct Y-Code Acquisition   253 Appendix L:   Enhanced Signal Structures for the Military   255 Appendix M:   Accuracy of a 14-Satellite Ensemble Versus a 24-Satellite Ensemble   263

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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

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--> 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

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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

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--> 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

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--> 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

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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

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--> 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

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