Session F2: PRECISION LANDING APPLICATIONS
Paper #1

FLIGHT TEST OF THE JPALS LDGPS DEMONSTRATION SYSTEM:
C.J. Bett, S.A. Simon, B.J. Farnworth, Raytheon Company; R.W. Boyd, J.J. Brewer, JPALS Responsible Test Organization

The Joint Precision Approach and Landing System (JPALS) Local Area Differential Global Positioning System (LDGPS) Program for the Architecture Requirements Definition (ARD) involves the examination of available technologies to support the development of requirements for guidance quality (GQ), GPS receiver vulnerability and interoperability with civil differential GPS systems. Program efforts include test and evaluation of demonstration hardware to record raw sensor and environmental data during precision approaches in high levels of electromagnetic interference (EMI).

Raytheon Company has developed a JPALS LDGPS Demonstration System. The Demonstration System is a test platform hosting multiple antenna, antenna electronics (AE) and GPS receiver technologies integrated to provide a differential GPS precision approach capability based primarily on the civil Local Area Augmentation System (LAAS). The Demonstration System consists of a ground segment and an airborne segment. The ground segment forms carrier-smoothed pseudorange corrections and broadcasts LAAS Type 1, 2 and 4 Messages in accordance with RTCA DO-246A. The airborne segment forms a carrier-smoothed corrected pseudorange solution and indicates course deviations to the pilot. The Demonstration System is configured to collect data from all integrated sensor electronics, the differential correction processor, and the navigation processor.

The Demonstration System was implemented to perform approximately 90 hours of precision approaches at Holloman AFB, NM using the USAF 746th Test Group C-12J test aircraft. Collected data is used to develop and refine simulations, models and analyses for the purposes of assessing GQ in the presence of high levels of EMI. Substantiated critical performance parameters will be useful for the JPALS LDGPS Program Management Office (PMO) to shape the JPALS LDGPS Engineering and Manufacturing Development (EMD) program and/or will identify the technology roadmap to meet the JPALS LDGPS objectives.

This paper will describe the JPALS LDGPS Demonstration System design and capabilities, ARD flight test activities, and supporting data processing capabilities used to generate the performance assessment. Results of the performance assessment will be presented, including a comparative assessment of system level performance in high EMI environments when the system employs different antenna/AE/receiver front-ends.

The significance of the results presented is traced directly to the diversity of approach data collected simultaneously by multiple GPS sensor technologies in high EMI environments. To our knowledge, this has not been previously accomplished. Consequently, the reported results will be new as well.
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Session F2: PRECISION LANDING APPLICATIONS
Paper #2

CERTIFICATION AND OPERATIONAL PERFORMANCE OF GPS-BASED LANDING SYSTEMS:
D.A. Stratton, C. Douglas, R. Gollnick, Rockwell Collins Inc.; R. Cole, Federal Express, Inc.

The paper discusses the certification and early operational experiences with the world's first two Local Area Augmentation System (LAAS) certified aircraft, a Federal Express' Boeing 727-200 and a Rockwell Collins' Sabreliner 65. Both aircraft have been certified under the FAA Government Industry Partnership (GIP) program, in partnership with Honeywell (LAAS ground station provider); the Memphis, TN, and Cedar Rapids, IA airport authorities; and the Federal Aviation Administration (FAA). Both installations are based on the Rockwell Collins GNLU-930 Multi-Mode Receiver (MMR). The GNLU-930 combines GNSS-Based Landing System (GLS), Instrument Landing System (ILS), and VHF Omni-directional Radio-range (VOR) to enable the use of common procedures, interfaces, and equipment for ILS and GLS along with VOR replacement. Other MMR products can include Microwave Landing Systems (MLS), Flight Management Systems (FMS), and Marker Beacon. This year's supplemental type certification for the 727 includes dual GNLU-930 with data acquisition and recording equipment for long-term performance evaluations. These Category I (CAT I) Instrument Flight Rule (IFR) certifications were based on interim standards developed by RTCA (DO-246 and DO-253). The aircraft are operated under special operational specification approvals. On-going improvements planned for the system include migration to the final RTCA and ICAO standards for Category I, II, and III. The paper describes the goals and certification approach, the performance testing of the GNLU-930, flight test results from the certification and data acquisition program, and feedback on the operational performance of the system from test pilots and operational users.
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Session F2: PRECISION LANDING APPLICATIONS
Paper #3

INTEROPERABILITY BETWEEN CIVIL LAAS AND MILITARY JPALS PRECISION APPROACH AND LANDING SYSTEMS:
C. Bett, T. Katanik, S. Simon, Raytheon Company; B. Driscoll, D. Tsamis, Rockwell-Collins; R. Norwood, ARINC, Inc.

The Federal Aviation Administration and the Department of Defense are each developing GPS based precision approach and landing systems. These systems are known as the Local Area Augmentation System (LAAS) and the Joint Precision Approach and Landing System (JPALS), respectively. While each of these systems has unique requirements and architectural features dictated by their respective missions, a primary objective of JPALS is civil/military interoperability. This capability does not exist today due to the proliferation of legacy landing system technologies, but is essential to achieving the much more closely coupled civilian and military missions envisioned in the future. Civil LAAS equipped aircraft must be able to make all-weather landings at JPALS equipped airfields when pressed into service for transporting military troops and cargo. Military JPALS equipped aircraft must also be able to operate into civil, LAAS equipped airfields. Raytheon Company has developed prototype LAAS equipment under a Government/Industry Partnership (GIP) with the FAA, and demonstration JPALS equipment under contracts with the U.S. Air Force . This paper presents the results of the first interoperability flight testing conducted between the military JPALS ground station and a civil LAAS equipped commercial aircraft. Testing will be conducted at Holloman AFB using the Raytheon developed JPALS demonstration ground station, and a Rockwell-Collins civil Multimode Receiver (MMR) installed in a Federal Express Boeing 727-200 aircraft. Testing results will be presented, and will include both quantitative data as well as subjective pilot comments on flyability and operational use. The paper also describes the similarities and differences in requirements and implementation between JPALS and LAAS ground and airborne equipment.
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Session F2: PRECISION LANDING APPLICATIONS
Paper #4

THE LAAS VHF DATA BROADCAST SERVICE VOLUME MODELING, SITING, FLIGHT INSPECTION, AND FLIGHT TEST RESULTS:
T. Skidmore, A. Wilson, B. Foyen, Ohio University; O. Nyhus, Honeywell; M. Dickinson, Federal Aviation Administration

This paper is a comprehensive look at the key elements necessary to demonstrate the fielded performance of a given LAAS VHF Data Broadcast (VDB) subsystem. The VDB is a critical element of the Local Area Augmentation System (LAAS) as well as the corresponding Ground Based Augmentation System (GBAS) developed by the International Civil Aviation Organization (ICAO). The VDB is used to transfer GPS (and GNSS) differential corrections, integrity, and final approach segment information from the LAAS (GBAS) ground facility to aircraft conducting approaches to the LAAS (GBAS) serviced airport. The paper includes the theoretical background and simulation results of a model for determining the optimal VDB transmit antenna height and location. The model considers factors such as antenna gain pattern, single versus multi-element arrays, horizontal, vertical, and elliptical polarization effects, aircraft position, and the required LAAS service (coverage) volume. The validity of this VDB Antenna Model Program (VAMP) is then demonstrated by flight test. Results of the flight test campaign, performed at the Federal Aviation Administration's William J. Hughes Technical Center in Atlantic City, New Jersey, show that the VAMP is well suited for predicting coverage performance under a variety of operational conditions. Data is presented comparing measured field strength performance with that predicted by the VAMP for the key regions of the LAAS service volume: at a minimum vectoring altitude of 2000 feet (AGL), along a typical 3 degree approach path, and throughout the coverage region for other select LAAS operations such as terminal area guidance and surface movement, guidance, and control. Key aspects of VDB-related flight inspection are also discussed.
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Session F2: PRECISION LANDING APPLICATIONS
Paper #5

THE NEXT GENERATION INTEGRITY MONITOR TESTBED FOR GROUND SYSTEM DEVELOPMENT AND VALIDATION TESTING:
P.L. Normark, D.M. Akos, S. Pullen, G. Xie, J. Lee, M. Luo, P. Enge, Stanford University; B. Pervan, Illinois Institute of Technology

The Integrity Monitor Testbed (IMT) is a prototype of the Local Area Augmentation System (LAAS) Ground Facility (LGF). It is used to evaluate whether the LGF can meet the integrity and continuity requirements that apply to Category I precision approach. With support from the U.S. Federal Aviation Administration (FAA), Stanford University has developed IMT algorithms and has implemented them in real-time software with special emphasis on automated fault diagnosis and recovery. To validate the underlying LGF Specification requirements and to verify that IMT meets these requirements, Stanford has conducted extensive nominal and failure testing of the IMT. The first generation IMT hardware platform consists of choke-ring antennas, long cables, GPS-card receivers, and a computer platform formerly used for flight testing. It was designed in the mid-1990s, and since then, computer power and receiver technology has evolved dramatically. Our dated processing platform and RF hardware limits further progress. Therefore, we chose to transition to a new and improved system to further continue development and testing for Category I precision approach and to use as a starting point for Category III LGF development.

This paper describes the design goals and motivation behind the second-generation IMT system, or IMT2. The IMT2 is a real time prototype and it is not intended to be a fully-certified LGF system. This allows for flexibility in the choice of computer hardware and operating system and allows us to focus on providing a effective development environment. The hardware upgrade involves new L1 and L2-capable antennas, low-loss antenna cables, new L1 and L2-upgradeable GPS receivers, and a new computer platform. Considerable effort was placed on the computer platform to provided additional flexibility, incorporated new GPS hardware, and enhance the development environment. One key element of the upgrade has been the development of new software to communicate with the receivers. This function, known as Signal-in-Space Receive and Decode 2 (SISRAD2), is now a modular means of integrating different receiver types, providing synchronization of receiver measurement packets, and fitting the measurement packets into a single IMT2 data format. This enhancement allows us to position reference receivers far apart (e.g., in different buildings on the Stanford campus) and provide their measurements to the IMT2 processor via the Stanford data network. This modular interface also provides the capability to integrate our separate Signal Quality Monitoring (SQM) prototype that detects C/A code signal deformation. In addition, a new Graphical User Interface has also been developed to provide visualization of the current state and recent history of IMT2 processing.

With these modifications, the new IMT2 is able to support more extensive and efficient nominal and failure testing. Now that the upgrade has been completed, the original set of IMT2 tests is being repeated to verify its proper functioning, and new failure tests will soon be run to simulate unusual multipath (which affects the mean and standard deviation of the LGF receiver pseudorange errors), low GPS signal power (or sudden loss of power), and satellite ephemeris errors that are smaller than the 5000 - 7000 meter errors tested with the previous IMT. Our goal is to verify the previous partial validation conducted with the old IMT and extend the validation to cover as-yet-untested LAAS failure modes.
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Session F2: PRECISION LANDING APPLICATIONS
Paper #6

CALIBRATION OF LAAS REFERENCE ANTENNAS:
A.R. Lopez, BAE SYSTEMS Advanced Systems

The Differential GPS, DGPS, Local Area Augmentation System, LAAS, utilizes reference antennas to measure the time of arrival of GPS signals at precisely surveyed points. These measurements are then used to broadcast differential corrections to approaching aircraft. A common misconception is to relate the antenna phase center to the surveyed point. The variation of the antenna phase center over the antenna coverage region is used to calibrate DGPS reference antennas. The antenna phase center is a well defined concept: "The location of a point associated with an antenna such that, if it is taken as the center of a sphere whose radius extents into the far-field, the phase of a given field component over the surface of the radiation sphere is essentially constant, at least over that portion of the surface where the radiation is significant," (IEEE definition). The antenna phase center is defined at one frequency. For DGPS a new antenna concept, the antenna "group-delay center," should be defined. The IEEE definition of phase center can be used to define group-delay center by replacing the words, "the phase of a given field component," by "the group delay of a given field component." The antenna phase and group-delay centers are not necessarily the same point.

For DGPS the parameters (observables) of interest are the code phase delay and the carrier phase delay. The code phase delay is equal to the signal modulation or group delay. The code phase delay time is equal to the rate of change of phase with respect to angular frequency (d*/d*). The carrier phase delay time is defined at the carrier frequency, and is equal to the total phase divided by the angular frequency (*/*). For LAAS calibration purposes, measurement (or determination) of the variation, over the antenna coverage region, of the group and phase delays is a requirement.

This paper reviews the concepts of group and phase delays as related to the calibration of LAAS reference antennas. It describes the characteristics of one candidate type of reference antenna for LAAS. It discusses the results of some recent field measurements of antenna code-phase minus carrier-phase. It also discusses antenna-range measurements of code and carrier phase delays.
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Session F2: PRECISION LANDING APPLICATIONS
Paper #7

THE EFFECTS OF CRPA BASED A/J ADAPTIVE ANTENNA SYSTEMS ON PSEUDO-RANGE AND CARRIER PHASE TRACKING WITH KCPT SOLUTIONS:
G. Colby, Navair PAX River; P. McIlroy, G. Myers, Raytheon Systems Limited, UK

As part of a research and investigative study in support of the Naval Air Systems Command Research and Engineering Group, Patuxent River, MD, Raytheon Systems Limited (UK) has been looking at issues relating to the use of Kinematic Carrier Phase Tracking (KCPT) for military precision approach and landing systems.

The candidate system makes use of a closed loop power minimisation algorithm for spatial nulling with a CRPA. The paper describes a theoretical study on both pseudorange and carrier phase performance. This is followed by simulation results and finally by test with both civil and military GPS receivers and Raytheon GAS-1 antenna electronics anti-jamming system.

The paper will also identify the effects of Group delay on carrier phase tracking and pseudorange measurements in such systems with particular attention to the future M-Code implementation.
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Session F2: PRECISION LANDING APPLICATIONS
Paper #8

SYSTEM CONCEPTS FOR CYCLE AMBIGUITY RESOLUTION AND VERIFICATION FOR AIRCRAFT CARRIER LANDINGS:
B. Pervan, F.C. Chan, Illinois Institute of Technology; S. Pullen, D. Gebre-Egziabher, M. Koenig, P. Enge, Stanford University

The Shipboard-Relative GPS (SRGPS) variant of the Join Precision Approach and Landing System (JPALS) is being developed with the ultimate goal of providing a navigation system to support automatic aircraft carrier landings in zero-visibility conditions. At present, the required navigation system vertical accuracy is envisioned to be on the order of 0.3 m, and the vertical protection level is 1.1 m with an associated integrity risk of approximately 10^-9. Because of the stringent requirements, it is evident that any viable GPS-based solution will use differential carrier phase. In turn, it is understood that the use of differential carrier phase for precise navigation is contingent upon the successful estimation or resolution of cycle ambiguities. In this regard, this paper quantifies the potential cycle resolution performance (integrity, availability, and continuity) of alternative system architecture concepts for SRGPS implementation.

The full availability of both the L1 and L2 GPS signals for this military application is tempered by the simultaneous need to provide redundancy in the event of hostile jamming or interference. In this respect, although dual-frequency architectures may be acceptable, a single-frequency carrier phase solution is preferable. Pseudolites have been used in similar single-frequency aircraft landing applications to provide geometric observability for cycle ambiguity estimation. However, pseudolites have the undesired effect of adding a signal-with origin at the aircraft carrier-which may potentially be used by a hostile force to identify the location of the ship. For this reason pseudolites are undesirable for SRGPS; however, their use has not been explicitly ruled out. An advantageous feature of SRGPS is the large service volume (200 nmi) in which broadcast reference carrier phase measurements are available to the airborne user. The large service volume can potentially provide the time for GPS satellite motion to improve cycle ambiguity observability. It is clear, however, that the spatial decorrelation of carrier phase measurement errors over such long baselines must be carefully handled. A second advantage provided by SRGPS is the relative freedom available for coupling GPS with existing inertial instruments aboard the aircraft and ship. The potential benefits of inertial coupling are numerous, ranging from improved detection of GPS carrier cycle slips to the possibility of increased cycle ambiguity observability afforded by the redundant relative position trajectory from the inertial system. In this paper, the cycle ambiguity resolution performance derived from these various candidate architecture elements is assessed relative to system integrity, availability, and continuity requirements with the ultimate goal of defining options suitable for SDRGPS.
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Session F2: PRECISION LANDING APPLICATIONS
Alternate #1

WIDEBAND AIRPORT PSEUDOLITE FOR THE LOCAL AREA AUGMENTATION SYSTEM:
S. Kiran, C. Bartone, Ohio University

This paper details the development of a Wideband Airport Pseudolite (APL), and its integration into the Local Area Augmentation System (LAAS) for CAT II/III precision approach and landing operations. This development has been sponsored by the Federal Aviation Administration, Satellite Navigation Division, LAAS Program Office. The paper will present data from the real-time inclusion of a differentially corrected WBAPL into a LAAS position solution. Issues relating to robust direct WB-code acquisition will be discussed, along with comparison of the performances obtained using several APL RF pulsing duty cycles. Flight test data (obtained using the Ohio University DC-3 aircraft) showing the pseudorange and position errors resulting from the integration of the WBAPL into LAAS will be presented. Kinematic position solution using an Ashtech Z-12 receiver will be used as the truth reference. B-value data, used for integrity verification of the differential broadcast correction, will be presented as well.
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Session F2: PRECISION LANDING APPLICATIONS
Alternate #2

PSEUDOLITE SIGNAL CREEPING ON CONDUCTING SURFACES:
R.J. Biberger, G.W. Hein, B. Eissfeller, T. Schuler, Institute of Geodesy and Navigation, University FAF Munich, Germany

The "GNSS Based Precision Approach Local Area Augmentation System" (LAAS) involves a number of novel architectural elements. Pseudolites (APL) have been introduced to accomplish the stringent performance requirements imposed on the system. Analysis of pseudolites have been performed by the institute using an experimental airport pseudolite.

Although the ideal view of an APL is a "satellite-on-the-ground", there are many effects that have to be considered and modeled in a different way than for GPS signals. Among those are signal creeping, signal interference and multipath on conducting materials.

The paper presents the creeping effect of pseudolite signals when incident upon conducting surfaces. A two-dimensional model based on the Maxwell equations is developed and verified by experimental tests. Interference and special multipath problems will be discussed. By using this theoretical model a reduction of the pseudorange and/or carrier phase measurement errors can be achieved.
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Session F2: PRECISION LANDING APPLICATIONS
Alternate #3

A FEDERATED APPROACH TO INTRODUCING CIVIL GPS AIR TRAFFIC MANAGEMENT ON MILITARY AIRCRAFT:
D.A. Stratton, M. Surathu, Rockwell Collins Inc.

Military aircraft navigation systems must balance tactical requirements with civil airspace compatibility. Parallel introduction of new satellite navigation technology in the military and civil arenas presents logistical, technical and operational challenges. This includes compatibility of military aircraft with the new Communication, Navigation, Surveillance and Air Traffic Management (CNS/ATM). Rockwell Collins is in development of GPS Air Traffic Management (GATM) upgrade to the U.S. Air Force KC-135 aircraft. This includes the integration of Rockwell Collins GNLU-955 Multi-Mode Receivers with existing and non-civil-approved military navigation equipment. The GNLU-955 combines a Global Navigation Satellite System (GNSS), Instrument Landing System (ILS), Microwave Landing Systems (MLS), and Marker Beacon receivers in a single Line Replaceable Unit. The goals of the KC-135 GATM upgrade include compatibility with the civil RNP requirements of RTCA DO-236 and DO-229 Receiver Autonomous Integrity Monitoring/Fault Detection and Exclusion (RAIM/FDE).

This paper analyzes methods for introducing civil- and non-civil-approved navigation equipment to meet civil accuracy, integrity, continuity, and availability requirements. Achievement of the accuracy and integrity requires methods for evaluating Actual Navigation Performance (ANP) and, in particular, its Estimated Position Uncertainty (EPU) component. The paper evaluates the utility of DO-229-compliant RAIM/FDE to meet the integrity requirement. The continuity and availability of the EPU estimate depends on the RAIM/FDE capabilities and the available satellite performance. The paper includes analysis of the availability of integrity for an example federated civil- and non-civil-approved navigation system. The influences of satellite User Range Accuracy (URA), Selective Availability, barometric altitude aiding, satellite outage and mask angle assumptions are evaluated. The results indicate the relative merits of the integration approaches and give insight into the operational characteristics of integrated civil-military CNS/ATM systems.
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