A WIDEBAND AIRPORT PSEUDOLITE ARCHITECTURE FOR THE LOCAL AREA AUGMENTATION SYSTEM A dissertation presented to the faculty of the Fritz J. and Dolores H. Russ College of Engineering and Technology of Ohio University In partial fulfillment of the requirements for the degree Doctor of Philosophy Sai Kiran November 2003 This dissertation entitled A WIDEBAND AIRPORT PSEUDOLITE ARCHITECTURE FOR THE LOCAL AREA AUGMENTATION SYSTEM by Sai Kiran has been approved for the School of Electrical Engineering and Computer Science and the Russ College of Engineering and Technology Chris G. Bartone Assistant Professor of Electrical Engineering R. Dennis Irwin Dean, Russ College of Engineering and Technology ABSTRACT KIRAN, SAI. Ph.D. November 2003. Electrical Engineering A Wideband Airport Pseudolite Architecture for the Local Area Augmentation System (168 pp.) Director of Dissertation: Chris G. Bartone This dissertation documents the design, development, and field and flight testing of a WBAPL for integration into a prototype LAAS. One major area of risk in the LAAS CAT II/III program is the unresolved issue of sufficient system availability. One feasible, low-cost, means of augmenting the GPS constellation for LAAS to enhance availability is by the incorporation of APLs. Critical issues that seek consideration in APL design are a low-cost solution to the near-far problem, effective mitigation of APL multipath at the LGF reception sites, and a solution to the issue of measurement errors as a function of peak received signal power level. This dissertation details the development of a prototype WBAPL within the framework of LAAS requirements, with the intent of resolving the aforementioned issues. The architecture includes a simple and novel method to facilitate rapid direct-WB signal acquisition, and details a cost-effective resolution to the power- bias problem. Results from laboratory tests to verify and characterize the power-induced measurement errors are described in the dissertation. Independent solutions to the power- bias problem at the ground and airborne segments were incorporated into the prototype WBAPL architecture. The solution on the ground involves the employment of RF power- control techniques. With the aim of low-cost implementation, the solution adopted for the airborne segment relies on carrier-phase measurements as the aircraft approaches the WBAPL transmission antenna. A time-differenced carrier-phase positioning algorithm that does not require real-time resolution of the unknown carrier-phase integer ambiguities is adopted. This differential CP approach is launched from a carrier- smoothed code based solution that is maintained from the beginning of the approach until the phase handover-point. A modification to the WBAPL single difference geometry matrix is incorporated into the TDCP algorithm. The proposed architecture was successfully flight-tested to demonstrate the feasibility of its incorporation into LAAS, the results of which are presented in the dissertation. The performance of the prototype WBAPL-inclusive LAAS is gauged in terms of the accuracy of the differential positioning solution. The integration of the WBAPL into the prototype LAAS provided an additional ranging measurement, and increased system availability. Approved: Chris G. Bartone Assistant Professor of Electrical Engineering ACKNOWLEDGEMENTS The research documented in this dissertation was funded by the Federal Aviation Administration (FAA) under the Aviation Research Cooperative Agreement 98-G-002. First and foremost, the author would like to thank Dr. Chris Bartone, the director of this dissertation, for his thoughtful guidance, unceasing support, and friendship over the years. The author has tremendously benefited from his collaboration with Dr. Bartone, and for that he expresses his utmost gratitude. Dr. Frank van Graas is thanked for his contribution to this research effort, and also for serving on the dissertation committee. The author is indebted to Dr. van Graas for providing the initial opportunity that introduced him to world of avionics research. Dr. van Graas’ dedication to the scientific method, work ethic, and positive attitude continue to serve as an inspiration to the author, and he considers himself fortunate to have come across such a role model early on in his career. Dr. Michael Braasch and Dr. Jeff Dill of the School of Electrical Engineering and Computer Science, and Dr. James Fales of the Department of Industrial Technology are thanked for serving on the dissertation committee, and for their valuable suggestions toward improving this dissertation. The author would like to thank Tom Arthur, Jeff Dickman, Lukas Marti, Sidharth Nair, and Ranjeet Shetty for their assistance in the flight test efforts. The author has benefited from his numerous discussions with Dr. Maarten Uijt de Haag, Dr. Andrey Soloviev, and Lukas Marti, for which he is thankful. Jeff Dickman provided the antenna gain and D/U plots that appear in Chapter 4, and Sanjeev Gunawardena developed the software to generate the APL pulsing sequence used for this research. The author thanks the enthusiastic flight-crew of Dr. Richard McFarland and Bryan Branham for the several hours of excellent piloting, and extends a special thanks to Jay Clark, the Chief of Airborne and Mobile Laboratories at the Avionics Engineering Center, for his industrious support of the flight-test efforts. Finally, the author expresses his heartfelt gratitude to his family and friends for making the journey such a gratifying one. vii TABLE OF CONTENTS LIST OF FIGURES ........................................................................................................... ix LIST OF TABLES............................................................................................................ xii ABBREVIATIONS .........................................................................................................xiii 1. INTRODUCTION ............................................................................................. 16 2. BACKGROUND ............................................................................................... 21 2.1 The Global Positioning System ......................................................................... 21 2.1.1 The Concept of Multilateration.............................................................. 21 2.1.2 Errors in GPS Positioning...................................................................... 23 2.1.3 Ranging Errors, Their Sources and Effects............................................ 25 2.1.4 The Influence of Geometry.................................................................... 29 2.2 Overview of LAAS............................................................................................ 33 2.2.1 Precision Approach, Profile and Requirements..................................... 33 2.2.2 The Basic Principle of LAAS Operation ............................................... 37 2.3 A Historical Perspective on the Development of PLs for Civil Aviation Applications ....................................................................................................... 39 2.4 Scope of the Dissertation ................................................................................... 48 3. APL DESIGN CONSIDERATIONS................................................................. 50 3.1 LAAS Availability Considerations.................................................................... 50 3.2 Design Constraints for APLs within LAAS....................................................... 53 3.2.1 The Near-Far Problem ........................................................................... 55 3.2.2 Multipath at the Ground Station ............................................................ 60 3.2.3 High-Power Induced Measurement Errors ............................................ 61 3.2.4 Airframe Multipath and APL Line-of-Sight Issues ............................... 62 4. THE OHIO UNIVERSITY PROTOTYPE WBAPL ARCHITECTURE ......... 64 4.1 The Prototype Ground Subsystem ..................................................................... 64 4.1.1 Ground Reception Antennas.................................................................. 66 4.1.2 APL Transmission Antenna................................................................... 73 4.1.3 LGF Equipment ..................................................................................... 79 4.1.3.1 APL Signal Generation.......................................................................... 80 4.1.3.2 Pulse Blanking and Gain Control .......................................................... 82 4.1.4 LAAS Ground Processing......................................................................84 4.1.4.1 Determination of the WBAPL Transmitter Clock Offset...................... 88 4.2 The Prototype Airborne Subsystem................................................................... 90 4.2.1 LAAS Airborne Processing................................................................... 91 4.2.1.1 CSC Solution......................................................................................... 92 4.2.1.2 Position Propagation Using a Time-Differenced Differential CP (TDCP) Approach................................................................................................ 92 viii 4.2.1.3 SD Geometry Correction for the APL ................................................... 95 4.2.1.4 Differential Tropospheric Correction for the WBAPL.......................... 98 5. LABORATORY