BROADCASTING GPS INTEGRITY INFORMATION USING LORAN-C 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 Sherman Chih Lo July 2002 Ó Copyright 2002 Sherman C. Lo, All Rights Reserved ii I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality as a dissertation for the degree of Doctor of Philosophy. _______________________________________ Professor Per K. Enge (Principal Advisor) I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality as a dissertation for the degree of Doctor of Philosophy. _______________________________________ Professor Stephen M. Rock I certify that I have read this thesis and that in my opinion it is fully adequate, in scope and in quality as a dissertation for the degree of Doctor of Philosophy. _______________________________________ Dr. Todd F. Walter Approved for the University Committee on Graduate Studies: _______________________________________ iii ABSTRACT The United States Federal Aviation Administration (FAA) will adopt the Global Positioning System (GPS) as its primary navigation systems for aviation as stated by the Federal Radionavigation Plans (FRP) of 1996 and 1999. The FRP also proposes the reduction or termination of some existing radionavigation system in favor of GPS and satellite navigation. It may be beneficial to retain some of these existing terrestrial navigation systems if they can provide increased safety and redundancy to the GPS based architecture. One manner in which this can be done is by using or creating a data link on these existing radionavigation systems. These systems thus can provide both navigation and an additional broadcast of GPS integrity information. This thesis examines the use of terrestrial data links to provide Wide Area Augmentation System (WAAS) based GPS integrity information for aviation. The thesis focuses on using Loran-C to broadcast WAAS data. Analysis and experimental results demonstrating the capabilities of these designs are also discussed. Using Loran for this purpose requires increasing its data capacity. Many Loran modulation schemes are developed and analyzed. The data rates developed significantly increased the Loran data capacity. However, retaining compatibility with Loran legacy users resulted in data rates below the WAAS data rate of 250 bps. As a result, this thesis also examines means of reducing the data requirements for WAAS information. While higher data rates offer improved performance and compatibility with WAAS, this thesis demonstrates that iv higher rates incur greater interference. Therefore, this work develops and considers a 108 bps and 167 bps Loran GPS integrity channel (LOGIC) design. The performance of the two designs illustrates some of the advantages and disadvantages of using a higher data rate. Analysis demonstrated means of maintaining integrity with these low data rate systems and determined the theoretical capabilities of the systems. The system was tested empirically by developing software that generated the LOGIC message and applied these messages to a GPS user. The resulting 108 bps and 167 bps systems demonstrated capability to provide lateral navigation/vertical navigation (LNAV/VNAV) and approach with vertical guidance (APV) respectively. v ACKNOWLEDGEMENTS While Ph.D. theses are supposed to be individual efforts, I have to say that there are many people without whose help, guidance and support, this thesis would not have been possible. First, I would like to thank my advisor, Professor Per Enge. His support and encouragement of my work has been tremendous and I cannot imagine completing my work for any one else. I have learned much under his tutelage and he has given me many opportunities to expand my talents and knowledge base. Professor Enge is a friend, fellow researcher, mentor, teacher, supporter, and role model for me. I would also like to express my gratitude to the other members of my reading and defense committee, Professor Stephen Rock, Dr. Todd Walter and Professor Chris Gerdes. I am grateful for the time and insights of Professor Rock both on this thesis and in his classes. Dr. Todd Walter is the first person I see whenever I have a WAAS question. His door is always open and he is always willing to help out. I’d like to thank him for his keen advice. In addition, I'd like to thank Dr. Changdon Kee. He advised me in my first research project at Stanford. He has always enthusiastically encouraged my work and given me great advice about research and life. It was he that insisted that I join the GPS laboratory. I appreciate all that he has done for me. I would like to thank the Federal Aviation Adminstration for their support of research in WAAS and Loran which made this work possible. In particular, I'd like to thank Mitch vi Narins of the FAA and Jim Nagle formerly of Booz Allen Hamilton. In addition, I am grateful to Dr. Ben Peterson, Captain, USCG retired. It is a real pleasure to work and learn from him. I am privileged to have worked with Lt. Jay Boyer, Lt. Kevin Carroll, and Lt. Cmdr. Charles Schue (retired) of the USCG Loran Support Unit. I am grateful to the Office of Naval Research (ONR) for supporting me during my first three years at Stanford. Of course, it goes without saying that we have some of the best people in our laboratory and department. Their help, collaboration, and comments have been invaluable. I wish to thank, in no particular order, Dr. Dennis Akos, Dr. Sam Pullen, Dr. Rich Fuller, Dr. Eric Phelts, Dr. Demoz Gebre-Egziahber, Dr. Andrew Hansen, Dr. Donghai Dai, Shau Shiun Jan, Per-Ludvig Normark, Dr. Sharon Houck, Lee Boyce, Chad Jennings, Juan Blanch, Aubrey Chen, Dr. Gabriel Elkaim, Doug Archdeacon, Dana Clarke, Guttorm Opshaug. I am honored have them as colleagues and friends. I’d like to also thank fellow graduate students and friends Brian Engberg, Jonathan Stone, Jonathan Fay and Jonathan Chow. I’d like especially to thank Brian for being my friend and house mate for the past 6 years. I want to also acknowledge the Department of Aeronautics and Astronautics, in particular the office staff, without whom the hurdles of bureaucracy may have never been cleared. Sally Gressens, in addition to her help as office manager, has been a friend and confidant. I greatly appreciated her advice. Thanks to Meg Alduino, for helping me through the final steps. I would also like to thank the Yasmeen Husain, Susie Madsen, Katherine Montoya, Ralph Eschenbach, Dianne Le and Diana Bell. My gratitude goes out to Sherann Ellsworth and Dana Parga who made sure that we didn't get lost in the bureaucratic paperwork. Last but not least, I'd like to thank my family. First, my parents, Barbara and Ging Show Lo, who have always encouraged me and given me all the love and support anyone could ever want. I dedicate this thesis to them. I'd also like to thank Jimmy, for, well, being my brother and putting up with me. I'd like to thank my grandparents for helping to raise me and, for spoiling me a bit! Thanks goes to my uncles, Wei Shiong and Wei Yan Tsai, for their advice about education and school. I'd like to thank Olivia Tsai for always lending me her ear and support. vii TABLE OF CONTENTS Broadcasting GPS Integrity Information Using Loran-C ................................................................................ i Abstract ......................................................................................................................................................... iv Acknowledgements ....................................................................................................................................... vi Table of Contents ........................................................................................................................................ viii List of Figures ............................................................................................................................................. xiii List of Tables.............................................................................................................................................. xvii List of Acronyms......................................................................................................................................... xix Chapter 1 Introduction.................................................................................................................................... 1 1.1 Background.......................................................................................................................................... 1 1.2 Phases of Flight and Typical Flight Operations ................................................................................... 2 1.2.1 Approaches with No Vertical Guidance........................................................................................ 5 1.2.2 Aproaches with Vertical Guidance................................................................................................ 6 1.3 Aircraft Navigation Requirements ....................................................................................................... 8 1.4 Terrestrial Navigation Systems & Radio Links ................................................................................. 10 1.5 Data Requirements for GPS Integrity Signals...................................................................................