GPS PSEUDOLITES: THEORY, DESIGN, AND APPLICATIONS gps pseudolites: theory, design, and applications

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  • SUDAAR 707

    GPS PSEUDOLITES:

    THEORY, DESIGN, AND APPLICATIONS

    A DISSERTATION

    SUBMITTED TO THE DEPARTMENT OF AERONAUTICS AND ASTRONAUTICS

    AND THE COMMITTEE ON GRADUATE STUDIES

    OF STANFORD UNIVERSITY

    IN PARTIAL FULFILLMENT OF THE REQUIREMENTS

    FOR THE DEGREE OF

    DOCTOR OF PHILOSOPHY

    H. Stewart Cobb

    September 1997

  • c© Copyright 1997 by

    H. Stewart Cobb

    ii

  • I certify that I have read this dissertation and that in my

    opinion it is fully adequate, in scope and in quality, as a

    dissertation for the degree of Doctor of Philosophy.

    Bradford W. Parkinson (Principal Advisor)

    I certify that I have read this dissertation and that in my

    opinion it is fully adequate, in scope and in quality, as a

    dissertation for the degree of Doctor of Philosophy.

    J. David Powell

    I certify that I have read this dissertation and that in my

    opinion it is fully adequate, in scope and in quality, as a

    dissertation for the degree of Doctor of Philosophy.

    Per K. Enge

    Approved for the University Committee on Graduate Studies:

    Dean of Graduate Studies

    iii

  • iv

  • Abstract

    Pseudolites (ground-based pseudo-satellite transmitters) can initialize carrier-phase differ-

    ential GPS (CDGPS) navigation systems in seconds to perform real-time dynamic posi-

    tioning with 1σ errors as low as 1 cm. Previous CDGPS systems were rarely used due

    to cumbersome initialization procedures requiring up to 30 minutes; initialization of the

    carrier-phase integer ambiguities via pseudolite removes these constraints. This work de-

    scribes pseudolites optimized for this application which cost two orders of magnitude less

    than previous pseudolites.

    Synchrolites (synchronized pseudolites), which derive their timing from individual Glo-

    bal Positioning System (GPS) satellites, are also described. Synchrolites can replace the

    CDGPS reference station and datalink, while simultaneously serving to initialize CDGPS

    navigation. A cluster of well-placed synchrolites could enable CDGPS navigation even if

    only one GPS satellite signal is available.

    A prototype CDGPS system initialized by pseudolites and synchrolites was designed and

    tested. The goal of this system, known as the Integrity Beacon Landing System (IBLS),

    was to provide navigation accurate and reliable enough to land aircraft in bad weather.

    Flight test results for prototype pseudolite and synchrolite systems, including results from

    110 fully automatic landings of a Boeing 737 airliner controlled by IBLS, are presented.

    Existing pseudolite applications are described, including simulation of the GPS constel-

    lation for indoor navigation experiments. Synchrolite navigation algorithms are developed

    and analyzed. New applications for pseudolites and synchrolites are proposed. Theoretical

    and practical work on the near/far problem is presented.

    v

  • vi

  • Acknowledgements

    This research would not have been possible without the efforts of a large number of other

    people. Foremost among these is my advisor, Professor Brad Parkinson, who guided the

    original development of GPS two decades ago and arranged the funding which made this

    research possible. I have learned technology, leadership, and management from him. Pro-

    fessor David Powell equipped his own Piper Dakota (N4341M) to support this research,

    and piloted it many times for flight tests. On the ground, he taught me dynamics and

    control theory. Professor Per Enge guided me through the finer points of electrical engi-

    neering and estimation theory. Professors Jonathan How and Donald Cox heard, analyzed,

    and approved my thesis defense. Thanks to all of these for their expertise, friendship, and

    support.

    The other three members of the original IBLS team were Clark Cohen, David Lawrence,

    and Boris Pervan. Clark originated the IBLS concept, Boris created the integer initialization

    algorithm, and Dave wrote the real-time navigation algorithm and analyzed the data. As a

    team, we shared successes and setbacks, design and redesign, long discussions, long journeys,

    and long hours. In the end, teamwork triumphed over all the obstacles we faced.

    Other members of the GPS group donated their time and efforts to this research when-

    ever necessary. Andy Barrows debugged the radio datalinks, then went to Germany as the

    IBLS advance man. Gabe Elkaim proved to be an expert at both digging holes and getting

    permission to dig them. Konstantin Gromov helped build modulators, interfaces, and many

    other bits of hardware and software required in the course of this research. Renxin Xia de-

    signed the circuitry inside the programmable logic chip that was the heart of the simple

    pseudolite. Chris Shaw designed and built the weatherproof pseudolite housings and their

    mounts. Todd Walter and Changdon Kee offered design ideas and advice. Jock Christie,

    Mike O’Connor, Jennifer Evans, Y. C. Chao, and many others helped load, move, install,

    and retrieve the mountain of equipment required for each test. To all of these, many thanks.

    vii

  • Thanks also to Kurt Zimmerman, Paul Montgomery, Jonathan Stone, Carole Parker, and

    Mike Ament for suggesting improvements to this dissertation.

    The test pilots, who chose to risk their nerves and perhaps their lives advancing the state

    of the art, included Keith Biehl at the FAA, Bill Loewe of United Airlines, Manfred Dieroff of

    T. U. Braunschwieg, and the previously-mentioned David Powell. Steve Kalinowski, Mark

    Ostendorf, Lutz Seiler, and the people of Elsinore Aerospace helped install IBLS on various

    aircraft while keeping them flightworthy. Victor Wullschleger at the FAA, Gerry Aubrey of

    United, and Andreas Lipp at T. U. Braunschweig arranged for their institutions to sponsor

    our flight tests. Without the diligent efforts of all these people, the IBLS experiments never

    would have gotten off the ground.

    Flight tests cannot take place without airplanes, and airplanes cannot fly for long with-

    out mechanics. Thanks to Alberto Rossi and his co-workers at PAO, the FAA’s mechanics

    at ATC, the United maintenance crews at SFO, and the Aerodata team at BWE. Their

    hard work kept us all safe in the air.

    The GP-B office staff gave me an enormous amount of support. Denise Freeman shot

    many of the photographs which appear on these pages. Sally Tsuchihashi, Mindy Lumm,

    and Jennifer Gale-Messer brightened my days while keeping me in touch with the rest of

    the universe.

    Trimble Navigation allowed us to purchase their receivers at a discount and modify their

    receiver software to track pseudolites. The FAA funded most of this research under grant

    number 93G004. Earlier work was performed under NASA grant number 188N002.

    Finally, I’d like to thank my family. My parents, Hank and Mary Jane, nurtured a small

    spark of inquisitiveness and fanned it into a flame with toys, tools, and books. My two

    brothers, Mitchell and Tucker, helped me along with fellowship, guidance, and sympathy—

    or lack thereof—as necessary. I couldn’t have done this without their support. Thanks,

    y’all, more than I can say.

    viii

  • Contents

    Abstract v

    Acknowledgements vii

    1 Introduction 1

    1.1 Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

    1.2 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

    1.3 Previous Work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

    1.4 Contributions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

    1.5 Nomenclature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

    1.6 Outline of this Dissertation . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

    2 Pseudolite Concepts 13

    2.1 Code-phase GPS Navigation . . . . . . . . . . . . . . . . . . . . . . . . . . . 14

    2.1.1 Pseudorange Measurements . . . . . . . . . . . . . . . . . . . . . . . 14

    2.1.2 Navigation Algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . 15

    2.1.3 Direct Ranging Pseudolite . . . . . . . . . . . . . . . . . . . . . . . . 17

    2.1.4 Mobile Pseudolite . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

    2.2 Differential Code-phase GPS . . . . . . . . . . . . . . . . . . . . . . . . . . 20

    2.2.1 Digital Datalink Pseudolite . . . . . . . . . . . . . . . . . . . . . . . 20

    2.3 Carrier-phase Differential GPS Navigation . . . . . . . . . . . . . . . . . . . 21

    2.3.1 Carrier-phase Ambiguity . . . . . . . . . . . . . . . . . . . . . . . . . 22

    2.3.2 Carrier phase Ambiguity Resolution . . . . . . . . . . . . . . . . . . 24

    2.3.3 Ambiguity Resolution using Pseudolites . . . . . . . . . . . . . . . . 25

    2.4 Synchrolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

    ix

  • 2.4.1 Synchrolite Differential Measurements . . . . . . . . . . . . . . . . . 30

    2.4.2 Synchrolite Reflection Delay . . . . . . . . . . . . . . . . . . . . . . .