A novel solution-technique applied to a novel WAAS architecture

Three years ago, FAA started on an ambitious program to perform research, development and implementation of satellite navigation based on the approval and use of the DoD's Global Positioning System (GPS). One of the research and development (R&D) projects was to determine the capabilities and requirements for a GPS Wide-Area Augmentation System (WAAS), a ground-based GPS augmentation. The FAA's WAAS will consist of up to about 30 ground reference stations that will combine data to estimate separate corrections for clock and ephemeris for each monitored satellite, and also generate a correction term for ionospheric delays at lattice points on a grid formed by the intersection of lines of constant latitude and longitude. The corrections are relayed through geostationary satellites in order to reach all users in a wide geographic area. Since WAAS is expected to support Category I (CAT I) precision approaches, stringent integrity monitoring requirements will have to be satisfied. Existing single location navigation sources, such as ILSs, are monitored at a single location, whereas WAAS must be monitored at many locations and the information combined to produce a single integrity broadcast message suitable for a wide geographic area. In addition, the WAAS message includes separate differential correction components that can be individually monitored, but the integrity information must be correlated with an aircraft position error. The authors develop integrity monitoring requirements, starting with the instrument landing system (ILS), and extrapolating them for WAAS.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

This paper addresses topics concerning the development of future Unmanned Aerial Vehicles (UAV) so that they can operate safely within the community of the Federal Aviation Administration (FAA) and the International Civil Aviation Organization (ICAO). Studies by the Defense Science Board; the Office of Science and Technology; Government Accountability Office; and the Congressional Research Service: Library of Congress; have all emphasized that soon there will be a significant number of UAVs operating sideby- side with manned civil aircraft in the FAA’s National Airspace System (NAS). It is anticipated that future UAVs will start to perform many of the dull, dirty, and dangerous civilian missions. In 2006, about 600 UAVs are expected to be manufactured in the US alone. Therefore, there is an urgent need for developers of UAVs to understand safety certification for operations in the NAS, and that safety certification starts with the safety requirements; safety design; safe development process; safety verification; and safe operating procedures in the planned operational environment. This paper presents and discusses the experiences and lessons gained by the authors on the development of end-toend aviation safety; from the safety requirements to their final safety certification in the planned operational environment. The authors’ previous and ongoing works include the Global Navigation Satellite Systems (GNSS) systems such as the GPS; WAAS; LAAS; MSAS; GPS III; and different operational environments at different airports such as Incheon International Airport. The FAA started with the two traditional safety certifications processes: airborne system certification and ground system certification; governed mostly by Federal Aviation Regulations (FAR) and FAA’s Acquisition Management System (AMS), respectively. However, when FAA started to implement GNSS, the lines between airborne and ground systems became blurred, and as a result many current Communications, Navigation, Surveillance, and Air Traffic Management (CNS/ATM) systems have to follow both processes. We will also discuss the current Safety Management Systems being developed by both FAA and ICAO as an integrated, systematic, and harmonized approach and process to sort out the differing safety requirements from FAA, SAE-ARP, MIL-STD, RTCA, ASTM, ICAO, etc. to provide the eventual safe operations within the NAS. The discussion will then focus on the real world of institutional, operational, and technical issues for safety certification worldwide. Despite the numerous standards and guidance documents, many past safety analyses and studies were guided by best practices that had been used successfully in the past to streamline the process of providing all the required documentations and verifications. One such area is in the use of the “Integrity Panel of Experts” that had been used successful in the implementation of safety for the FAA’s Wide Area Augmentation System (WAAS) and Local Area Augmentation System (LAAS) programs. In many areas of the world, safety certification from a technical point of view is only the first step to achieving safety certification to fly in their national and sovereign airspace. Finally, we will show the first steps that UAV manufactures need to consider if they want their UAVs to be approved to fly safely in different national civilian airspace.

The Federal Aviation Administration (FAA) is investigating the feasibility of using the Global Positioning System (GPS), together with local augmentation as the primary navigation system for the Category II and III precision approach of aircraft. This augmented system would be known as a local area augmentation system (LAAS) because it would place subsystems on the ground at or near an airport to greatly enhance the performance of airborne GPS receivers approaching that airport. The LAAS would complement space-based augmentations of GPS, such as the wide area augmentation system. When complete, the integrated system will meet stringent requirements on accuracy, integrity, continuity, and availability. Indeed, the LAAS will improve the airborne accuracy from approximately 100 m for stand-alone GPS to better than 1 m. This high accuracy is required so that LAAS can guarantee the integrity and continuity of the aircraft guidance during the approach phase of flight. Integrity requires the LAAS to detect any situations which threaten the safety of the landing, and notify the aircraft within 2 s of such a threat. Continuity is a competing consideration-it requires that the total number of alarms, true plus false, sent to the aircraft is very small. High continuity guarantees that the total number of aborted approaches is manageably small. Finally, availability is the fraction of the time during which LAAS is operational-providing position fixes with the specified accuracy, integrity and continuity. This paper describes the LAAS which has been proposed by the FAA. It discusses the fundamental operation of the LAAS.

The MITRE Corporation developed a computer-based tool that estimates the Height Above Touchdown (HAT) and visibility minima for Global Positioning System (GPS) instrument approaches using electronic databases of terrain and obstacles. The model uses criteria from the U.S. Federal Aviation Administration (FAA) Terminal Instrument Procedures (TERPS) developed for GPS approaches, but can be modified to use different criteria. The design of the model allows the evaluation of a large number of runways, with subsequent analysis of the benefits of a particular approach procedure. The development of wide area systems to augment the GPS has long promised the capability of providing or improving the instrument approach capability at many airports. In particular, one of the objectives of the Wide Area Augmentation System (WAAS) is to provide, where possible, straight-in instrument approaches with vertical guidance to all instrument capable runways in the USA. There are over 5000 airports in CONUS that have at least one runway over 3000 ft long. At present, the minima for approaches with vertical guidance that would result from the development of WAAS are known for only a few runways. Using the present FAA approach design apparatus to estimate the minima for Copyright © 2001 The MITRE Corporation. Published by the American Institute of Aeronautics and Astronautics, Inc. with permission. This paper is based on system analysis studies performed by the Center for Advanced Aviation System Development (CAASD), the MITRE Corporation for the FAA Satellite Program Office (AND-730). This paper reflects the views of the authors, who are responsible for the accuracy of the facts, analyses and suggestions presented herein, and does not reflect the official views or policy of the FAA. all the possible runways would be an impossibly long task. Application of the MITRE Corporation computer model enables a timely high-level evaluation of HAT estimates for a large number of runway ends, and will eventually include considerations for airport infrastructure. This paper provides a statistical summary of preliminary results showing HAT and visibility benefits for approaches to a large number of airports in the USA, and also provides a comparison of approach minima between different classes of augmented GPS approaches. The intent of the analysis is to assist in the final design criteria for GPS approaches in the USA.

An experiment to measure equatorial amplitude scintillations on the geostationary Wide Area Augmentation System (WAAS) Satellite Based Augmentation System (SBAS) signal was conducted in Cachoeira Paulista (22.70°S, 45.01°W geographic coordinates; −17.74°N, 21.74°E geomagnetic coordinates), Brazil from December 2003 through February 2004. The purpose of this paper is to estimate the scattering height of the irregularities using the WAAS signal scintillations as compared to nearby Global Positioning System (GPS) signal scintillations. Estimating the scattering height is important because the calculated zonal drift velocity of the irregularities using the measured scintillation pattern velocity on the ground is height dependent. Accurate height estimation is also required if one wishes to develop phase screen scintillation models. The difference in the pattern velocities is due to the different signal puncture point velocities with respect to the ionospheric drift. Two east‐west receivers are used to measure the scintillation pattern drift velocity and to compare the results of the geostationary WAAS satellite signal to that of a GPS satellite signal, which has a nonzero ionospheric signal puncture point velocity. By varying the assumed scattering height for the measurements from the nearby GPS signal, the zonal velocity measurements from the GPS scintillations can be matched to those of the WAAS scintillations, and a scattering height estimate can be made. When the puncture points have minimal separation, the inferred ionospheric irregularity zonal velocities should be equal. On the two nights for which data are available, scattering height estimates of 669 ± 209 km for the first night and 388 ± 139 km for the second night were obtained. On the second night, the reported mean hmF2 as calculated using a collocated Digisonde was 385 ± 17 km over the same period as the GPS/WAAS scattering height estimate. The geometry of this experiment was not optimal, but analysis demonstrates that future experiments could be substantially more accurate.

The Federal Aviation Administration (FAA) is implementing an aircraft navigation scheme for the United States using the Global Positioning System (GPS) L1 signal (1575.42 MHz). To achieve position accuracies of a few meters, sufficient to allow precision airfield approaches, it will be necessary to broadcast corrections to the direct GPS signal. A significant component of these corrections is the delay in the GPS signal introduced by its propagation through the ionosphere. Ionospheric delay corrections will be derived using a ground network of at least 24 dual‐frequency GPS receivers distributed across the continental United States. This network is part of the FAA's wide area augmentation system (WAAS) and will provide real‐time total electron content (TEC) measurements. We present a technique for converting these TECs into gridded vertical delay corrections at the GPS L1 frequency, which will be broadcast to users every 5 min via geosynchronous satellite. Users will convert these delays to slant corrections for their own particular lines of sight to GPS satellites. To preserve user safety, estimates of the error in the user delay corrections will also be broadcast. However, the error algorithm must not resort to excessive safety margins as this reduces the expected accuracy, and thus utility, of the navigation system. Here we describe an error algorithm and its dependence on various factors, such as user location with respect to the WAAS ground network and ionospheric conditions.

Some deficiencies of the system of exciting satellite navigation augmentation are analyzed in the application of civil aviation. Since there is no local monitoring in Wide Area Augmentation System (WAAS), the protect level is increased, and the availability is reduced, so it could not satisfy the requirement of the precise approach. Moreover, because the Local Area Augmentation System (LAAS) could not solve the problem brought by ionosphere storms, the LAAS certification becomes complex and expensive. The basic principle of the new satellite navigation augmentation system named Local Airport Monitor (LAM) proposed by Federal Aviation Administration (FAA) is introduced. And the error distribution characteristic of LAM is discussed by sorting three conditions. Moreover, the expressions of LAM protection level and availability are studied. Some conclusions are obtained by simulations. In normal condition, the position accuracy of LAM is better than the one of WAAS and similar to LAAS and the availability of LAM is better than the one of WAAS and worse than LAAS. When there are ionosphere storms, the position precision and availability of LAM and WAAS reduce a little, but the position precision and availability of LAAS reduce 20.5% and 19.3% respectively. Furthermore, the availability of LAM is analyzed and simulated. And some conclusions are obtained: airborne user should first choose satellites whose elevation is lower than 10 degree and bigger than 70 degree. Reference station and airborne should use GAD-A and AAD-B receiver respectively, thus, the availability of LAM could bigger than 99.99%

Radio frequency signal compatibility is the basis of interoperability of the Satellite e-Based Augmentation System (SBAS). SBAS should abide by relative international radio regulations of International Telecommunication Union (ITU) and meet the compatibility requirements of radio frequency signal between the Global Navigation Satellite System (GNSS)/SBAS, in order to avoid negative mutual interference. According to ITU Proposal and related reference and assumptions, the paper made simulation of signal receiving maximum power in the BeiDou Satellite-Based Augmentation System (BDSBAS) global signal coverage. And then, interference of BDSBAS to Global Positioning System (GPS)/WAAS (Wide Area Augmentation System) on L1/L5 bands were calculated and analyzed, with equivalent carrier-to-noise ratio as the evaluation parameter. The result shows that the carrier-to-noise ratio decrease of GPS/WAAS caused by BDSBAS B1C and B2a signals are extremely lower than inter-system interference of GPS/WAAS, and thus can be ignored in practical applications. Therefore, BDSBAS will not cause the service performance degradation of GPS and WAAS.

Concerns over accuracy, availability, integrity, and continuity have limited the integration of Global Positioning System (GPS) and Global Navigation Satellite System (GLONASS) for safety-critical applications. More recent augmentation systems, such as the European Geostationary Navigation Overlay Service (EGNOS) and the North American Wide Area Augmentation System (WAAS) have begun to address these concerns. Augmentation architectures build on the existing GPS/GLONASS infrastructures to support location based services in Safety of Life (SoL) applications. Much of the technical development has been directed by air traffic management requirements, in anticipation of the more extensive support to be offered by GPS III and Galileo. WAAS has already been approved to provide vertical guidance for aviation applications. During the next twelve months, the full certification of EGNOS for SoL applications is expected. This paper discusses similarities and differences between the safety assessment techniques used in Europe and North America.

This paper considers what the SNS (Satellite Navigation Systems), such as Global Positioning System (GPS), GLONASS, Galileo, and Compass; and SBAS (Satellite Based Navigation Systems) such as European Geostationary Navigation Overlay System (EGNOS), Wide Area Augmentation System (WAAS), Multi-functional Transport Satellite Based Augmentation System (MSAS) and GPS and Geo Augmented Navigation (GAGAN) services, might look like 10 years from now. All these systems, called GNSS (Global Satellite Navigation System), are undergoing construction or modernization (new satellites, new frequencies, new signals, new monitoring stations, etc.) and continuous improvement to increase accuracy, availability, integrity, and resistance to interference. The most significant events in SNS and SBAS over the last 10 years are presented. In addition, three possible scenarios for SNS in the years 2016 and 2021 (most probable, optimistic, and pessimistic), including the number of satellites, are presented.

ABSTRACT: Aircraft precision approach guidance systems require accurate positioning relative to the runway with a high level of integrity. Most precision approach guidance systems in use today require ground-based electronic navigation components with at least one installation at each airport, and in many cases multiple installations to service approaches to all qualifying runway ends. A terrain-referenced approach guidance system is envisioned to provide precision guidance to an aircraft without the use of ground-based electronic navigation components installed at the airport. An Airborne Laser Scanner (ALS), when integrated with an Inertial Measurement Unit (IMU) and a Digital Elevation Model (DEM) with approximately a 1 m horizontal resolution and elevation accuracy on the order of 30 cm RMS, can provide navigation and guidance information in support of aircraft precision approach and landing operations. The proof-of-concept terrain-referenced navigation system provides horizontal and vertical position estimates with accuracies on the order of one meter RMS and capitalizes on the position and integrity benefits provided by the Global Positioning System (GPS) Wide Area Augmentation System (WAAS) to reduce the terrain navigator's initial position search space size and to reduce the required size of the high accuracy/high resolution database. This paper describes the proof-of-concept aircraft approach system and presents results from flight tests where the approach system is used to provide real-time guidance cues to the pilot.

Two Wide Area Augmentation System (WAAS) satellites are now transmitting the standard L1 and L5 carriers and codes of the Global Positioning System (GPS), though with a five times higher data-bit rate. Since these are geostationary satellites, it is possible to aim a parabolic dish at one and obtain high-gain, low-multipath interference signals without interruption. Such high-gain dishes, along with appropriate GPS receivers, were set up at three timing laboratories in North America: the National Institute of Standards and Technology (NIST) in Boulder, Colorado, U.S.A., the United States Naval Observatory (USNO) in Washington D.C., U.S.A., and the National Research Council (NRC) in Ottawa, Ontario, Canada. We report the results of this experiment over a 104 d period: January 1 to April 14, 2008, though with several significant outages, and other clock/data problems.

The Federal Aviation Administration (FAA) and general aviation (GA) industry are working collaboratively to publish lower minimum en route altitudes (MEAs) for Global Positioning System (GPS)-equipped aircraft operating at low altitudes, and more direct transition routes through Class B airspace based on area navigation (RNAV) (commonly achieved in GA aircraft with GPS). These efforts are intended to improve access to airspace, safety of flight, and seamless RNAV operations in the NAS - in accordance with the FAA's roadmap to performance-based navigation published in July 2003. The roadmap initiatives were developed jointly by FAA and industry under the sponsorship of the Performance-Based Operations Aviation Rulemaking Committee (PARC). The GA representation on that committee was provided by Aircraft Owner's and Pilot's Association (AOPA), who was spearheading the movement toward achieving benefits with GPS and spurring a growth rate in aircraft equipage. This paper presents the concepts of use for lower MEAs based on GPS and RNAV transition routes through Class B airspace. The paper also provides a description of the benefits and an outline of the implementation strategy.

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