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Anthea Coster - One of the best experts on this subject based on the ideXlab platform.

  • The ionospheric impact of the October 2003 storm event on Wide Area Augmentation System
    GPS Solutions, 2005
    Co-Authors: Attila Komjathy, Lawrence Sparks, Anthony J. Mannucci, Anthea Coster
    Abstract:

    The United States Federal Aviation Administration’s (FAA) Wide-Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite-Based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Multi-transport Satellite-based Augmentation System (MSAS). Navigation using WAAS requires accurate calibration of ionospheric delays. To provide delay corrections for single frequency global positioning System (GPS) users, the wide-area differential GPS Systems depend upon accurate determination of ionospheric total electron content (TEC) along radio links. Dual-frequency transmissions from GPS satellites have been used for many years to measure and map ionospheric TEC on regional and global scales. The October 2003 solar-terrestrial events are significant not only for their dramatic scale, but also for their unique phasing of solar irradiance and geomagnetic events. During 28 October, the solar X-ray and EUV irradiances were exceptionally high while the geomagnetic activity was relatively normal. Conversely, 29–31 October was geomagnetically active while solar irradiances were relatively low. These events had the most severe impact in recent history on the CONUS region and therefore had a significant effect on the WAAS performance. To help better understand the event and its impact on WAAS, we examine in detail the WAAS reference site (WRS) data consisting of triple redundant dual-frequency GPS receivers at 25 different locations within the US. To provide ground-truth, we take advantage of the three co-located GPS receivers at each WAAS reference site. To generate ground-truth and calibrate GPS receiver and transmitter inter-frequency biases, we process the GPS data using the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This software allows us to compute calibrated high resolution observations of TEC. We found ionospheric range delays up to 35 m for the day-time CONUS during quiet conditions and up to 100 m during storm time conditions. For a quiet day, we obtained WAAS planar fit slant residuals less than 2 m (0.4 m root mean square (RMS)) and less than 25 m (3.4 m RMS) for the storm day. We also investigated ionospheric gradients, averaged over distances of a few hundred kilometers. The gradients were no larger than 0.5 m over 100 km for a quiet day. For the storm day, we found gradients at the 4 m level over 100 km. Similar level gradients are typically observed in the low-latitude region for quiet or storm conditions.

Per Enge - One of the best experts on this subject based on the ideXlab platform.

  • projected performance of a baseline high integrity gnss railway architecture under nominal and faulted conditions
    Proceedings of the 30th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2017), 2017
    Co-Authors: Sam Pullen, Per Enge, Juan Blanch, Alessandro Neri, Veronica Palma, Maurizio Salvitti, Cosimo Stallo
    Abstract:

    GNSS is being gradually adopted for both navigation and control of many safety critical transportation System. This paper focuses on the important area of high integrity GNSS for railway applications which is critical for safe use of GNSS. While aviation has led the development of high-integrity GNSS applications, the Railway High Integrity Navigation Overlay System (RHINOS) effort aims to apply GNSS to railways utilizing similar integrity methodologies. In particular, it seeks to provide the accuracy necessary to support the most critical railway operations while assuring a very low probability of Hazardously Misleading Information (HMI). The RHINOS efforts are studying the most appropriate architectures (e.g., combinations of GNSS Augmentations) and developing an integrity methodology suitable for the architecture that is chosen. This paper describes a reference RHINOS architecture and examines its performance under nominal and faulted conditions. The performance analysis is conducted through simulation using the Matlab Algorithm Availability Simulation Tool (MAAST). MAAST, which was developed for aviation integrity analyses, was modified to support Protection Level (PL) calculations based on a proposed RHINOS reference architecture. It calculates PLs at representative locations throughout Europe for both nominal and faulted cases. The nominal case assumes that all GNSS range measurements are bounded by faultfree error models. Error models derived from accepted Satellite Based Augmentation System (SBAS) and Ground Based Augmentation System (GBAS) models are used. The main exception is multipath, which is known to be more severe for trains than for aircraft. The fault cases examined are those where either ionosphere gradients, satellite (ephemeris or clock) errors, or multipath exceed the nominal models. The integrity monitoring should detect and exclude the fault, if it is sufficiently large or not detected it, in which case it will bound its effect. Finally, sensitivity analysis is conducted to provide insights for designing the System. Different multipath assumptions are tested and different levels of mitigation are examined what level of mitigation and monitoring should be targeted.

  • reversion from l1 l5 dual to l5 single frequency waas in the presence of rf interference
    IEEE Transactions on Aerospace and Electronic Systems, 2010
    Co-Authors: Shau Shiun Jan, Todd Walter, Per Enge
    Abstract:

    Techniques available to sustain dual-frequency ionosphere performance when a dual-frequency airborne Global Positioning System (GPS)/wide area Augmentation System (WAAS) user loses all but one GPS frequency while descending into radio frequency interference (RFI) are investigated. We are particularly interested in the case where the user transitions from L1-L5 to having L5-only since the uncertainty of the L5-only ionospheric delay estimation is larger than the case for L1-only. The goal is to provide the techniques necessary for single-frequency users to sustain a performance similar to those of dual-frequency users. The proposed techniques are 1) the code and carrier divergence technique, 2) the WAAS ionosphere threat model technique, and 3) the maximum ionospheric delay gradient model technique. The results show that all three proposed techniques provide good ionospheric delay estimation for the full duration of approach.

  • ionospheric threat parameterization for local area global positioning System based aircraft landing Systems
    Journal of Aircraft, 2010
    Co-Authors: Seebany Dattabarua, Jiyun Lee, Sam Pullen, Ming Luo, Alexandru Ene, Di Qiu, Godwin Zhang, Per Enge
    Abstract:

    Observations of extreme spatial rates of change of ionospheric electron content and the characterization strategy for mitigation applied by the U.S. local area Augmentation System are shown. During extreme ionospheric activity, the gradient suffered by a global navigation satellite System user a few kilometers away from a ground reference station may reach as high as 425 mm of delay (at the GPS L1frequency) per km of user separation. The method of data analysis that produced these results is described, and a threat space that parameterizes these possible threats to user integrity is defined. Certain configurations of user, reference station, global navigation satellite System satellite, and ionospheric storm-enhanced density may inhibit detection of the anomalous ionosphere by the reference station.

  • authenticating aviation Augmentation System broadcasts
    IEEE ION Position Location and Navigation Symposium, 2010
    Co-Authors: Per Enge
    Abstract:

    This paper studies the feasibility and means by which authentication can be overlaid upon the existing SBAS and GBAS designs. It considers how to achieve the authentication that is compatible with the current Augmentation System and its users. It also considers how to perform the security necessary to support authentication within the current NAS framework. One important issue is secure key distribution and the paper presents some options designed to be reasonable for aviation infrastructure and operations. One means is a key distribution protocol that utilizes the operation of the aircraft and air traffic to aid in key verification. This provides to distribute keys and provide some ability to validate them without significant additions to the NAS. Another issue is bandwidth. The paper presents ways of modifying protocols such as TESLA to reduce bandwidth use while maintaining an acceptable level of security. The paper uses the current L1 SBAS and GBAS as case studies. The paper presents reasonable method to provide authentication on the current SBAS using about ten percent of bandwidth. The method is compatible to current SBAS user equipment in that they will not be adversely affected. GBAS can employ similar means. As it has greater data bandwidth, a more critical issue for GBAS is key distribution to the ground stations.

  • impact and mitigation of ionospheric anomalies on ground based Augmentation of gnss
    Radio Science, 2009
    Co-Authors: Sam Pullen, Young Shin Park, Per Enge
    Abstract:

    [1] This paper describes the impact that extreme ionospheric spatial gradients occurring during severe ionospheric storms have on Global Navigation Satellite System Ground Based Augmentation Systems and how the U.S. Local Area Augmentation System (LAAS) mitigates the integrity risk due to these events. Gradients in slant ionospheric delay of as large as 425 mm/km over baselines of 40–100 km have been observed in the United States during ionospheric storms since April 2000 by both the U.S. Wide Area Augmentation System and the network of Continuously Operating Reference Stations receivers. Because ionospheric gradients affecting a LAAS site may not be observed by the LAAS Ground Facility (LGF) before users are affected, a simulation-based method has been developed to determine, in near real time, which potential LAAS user geometries would be unacceptably threatened by a hypothetical worst-case ionosphere gradient. Geometries of this type are made unavailable to LAAS users by having the LGF inflate the broadcast ionospheric-gradient sigma, which increases the Vertical Protection Level of the unacceptable geometries so that they exceed the allowed Vertical Alert Limit; thus ensuring user safety.

Attila Komjathy - One of the best experts on this subject based on the ideXlab platform.

  • The ionospheric impact of the October 2003 storm event on Wide Area Augmentation System
    GPS Solutions, 2005
    Co-Authors: Attila Komjathy, Lawrence Sparks, Anthony J. Mannucci, Anthea Coster
    Abstract:

    The United States Federal Aviation Administration’s (FAA) Wide-Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite-Based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Multi-transport Satellite-based Augmentation System (MSAS). Navigation using WAAS requires accurate calibration of ionospheric delays. To provide delay corrections for single frequency global positioning System (GPS) users, the wide-area differential GPS Systems depend upon accurate determination of ionospheric total electron content (TEC) along radio links. Dual-frequency transmissions from GPS satellites have been used for many years to measure and map ionospheric TEC on regional and global scales. The October 2003 solar-terrestrial events are significant not only for their dramatic scale, but also for their unique phasing of solar irradiance and geomagnetic events. During 28 October, the solar X-ray and EUV irradiances were exceptionally high while the geomagnetic activity was relatively normal. Conversely, 29–31 October was geomagnetically active while solar irradiances were relatively low. These events had the most severe impact in recent history on the CONUS region and therefore had a significant effect on the WAAS performance. To help better understand the event and its impact on WAAS, we examine in detail the WAAS reference site (WRS) data consisting of triple redundant dual-frequency GPS receivers at 25 different locations within the US. To provide ground-truth, we take advantage of the three co-located GPS receivers at each WAAS reference site. To generate ground-truth and calibrate GPS receiver and transmitter inter-frequency biases, we process the GPS data using the Global Ionospheric Mapping (GIM) software developed at the Jet Propulsion Laboratory. This software allows us to compute calibrated high resolution observations of TEC. We found ionospheric range delays up to 35 m for the day-time CONUS during quiet conditions and up to 100 m during storm time conditions. For a quiet day, we obtained WAAS planar fit slant residuals less than 2 m (0.4 m root mean square (RMS)) and less than 25 m (3.4 m RMS) for the storm day. We also investigated ionospheric gradients, averaged over distances of a few hundred kilometers. The gradients were no larger than 0.5 m over 100 km for a quiet day. For the storm day, we found gradients at the 4 m level over 100 km. Similar level gradients are typically observed in the low-latitude region for quiet or storm conditions.

  • the ionospheric impact of the october 2003 storm event on waas
    Proceedings of the 17th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2004), 2004
    Co-Authors: Attila Komjathy, Lawrence Sparks, Anthony J. Mannucci, A J Coster
    Abstract:

    The United States Federal Aviation Administration's (FAA) Wide Area Augmentation System (WAAS) for civil aircraft navigation is focused primarily on the Conterminous United States (CONUS). Other Satellite- Based Augmentation Systems (SBAS) include the European Geostationary Navigation Overlay Service (EGNOS) and the Japanese Global Navigation Satellite System (MSAS). Navigation using WAAS requires accurate calibration of ionospheric delays. to provide delay corrections for single frequency GPS users, the wide area differential GPS Systems depend upon accurate determination of ionospheric total electron content (TEC) along radio links. Dual frequency transmissions from GPS satellites have been used for many years to measure and map ionospheric TEX on regional and global scales.

Roberto Sabatini - One of the best experts on this subject based on the ideXlab platform.

  • global navigation satellite Systems performance analysis and Augmentation strategies in aviation
    Progress in Aerospace Sciences, 2017
    Co-Authors: Roberto Sabatini, Terry Moore, Subramanian Ramasamy
    Abstract:

    In an era of significant air traffic expansion characterized by a rising congestion of the radiofrequency spectrum and a widespread introduction of Unmanned Aircraft Systems (UAS), Global Navigation Satellite Systems (GNSS) are being exposed to a variety of threats including signal interferences, adverse propagation effects and challenging platform-satellite relative dynamics. Thus, there is a need to characterize GNSS signal degradations and assess the effects of interfering sources on the performance of avionics GNSS receivers and Augmentation Systems used for an increasing number of mission-essential and safety-critical aviation tasks (e.g., experimental flight testing, flight inspection/certification of ground-based radio navigation aids, wide area navigation and precision approach). GNSS signal deteriorations typically occur due to antenna obscuration caused by natural and man-made obstructions present in the environment (e.g., elevated terrain and tall buildings when flying at low altitude) or by the aircraft itself during manoeuvring (e.g., aircraft wings and empennage masking the on-board GNSS antenna), ionospheric scintillation, Doppler shift, multipath, jamming and spurious satellite transmissions. Anyone of these phenomena can result in partial to total loss of tracking and possible tracking errors, depending on the severity of the effect and the receiver characteristics. After designing GNSS performance threats, the various Augmentation strategies adopted in the Communication, Navigation, Surveillance/Air Traffic Management and Avionics (CNS + A) context are addressed in detail. GNSS Augmentation can take many forms but all strategies share the same fundamental principle of providing supplementary information whose objective is improving the performance and/or trustworthiness of the System. Hence it is of paramount importance to consider the synergies offered by different Augmentation strategies including Space Based Augmentation System (SBAS), Ground Based Augmentation System (GBAS), Aircraft Based Augmentation System (ABAS) and Receiver Autonomous Integrity Monitoring (RAIM). Furthermore, by employing multi-GNSS constellations and multi-sensor data fusion techniques, improvements in availability and continuity can be obtained. SBAS is designed to improve GNSS System integrity and accuracy for aircraft navigation and landing, while an alternative approach to GNSS Augmentation is to transmit integrity and differential correction messages from ground-based Augmentation Systems (GBAS). In addition to existing space and ground based Augmentation Systems, GNSS Augmentation may take the form of additional information being provided by other on-board avionics Systems, such as in ABAS. As these on-board Systems normally operate via separate principles than GNSS, they are not subject to the same sources of error or interference. Using suitable data link and data processing technologies on the ground, a certified ABAS capability could be a core element of a future GNSS Space-Ground-Aircraft Augmentation Network (SGAAN). Although current Augmentation Systems can provide significant improvement of GNSS navigation performance, a properly designed and flight-certified SGAAN could play a key role in trusted autonomous System and cyber-physical System applications such as UAS Sense-and-Avoid (SAA).

  • a novel avionics based gnss integrity Augmentation System for manned and unmanned aircraft
    2017
    Co-Authors: Roberto Sabatini
    Abstract:

    The aviation community has to implement very stringent navigation integrity requirements in a variety of manned and unmanned aircraft applications. This thesis presents the results of the research activities carried out by the Italian Air Force Research and Flight Test Centre (CSV-RSV) in collaboration with the Nottingham Geospatial Institute (NGI) and RMIT University in the area of Avionics Based Integrity Augmentation (ABIA) for mission-essential and safety-critical Global Navigation Satellite Systems (GNSS) applications in the civil/military aviation context. Space and Ground Based Augmentation Systems (SBAS/GBAS) have been developed in recent years to improve GNSS integrity, accuracy and availability for aircraft navigation and particularly for landing applications. SBAS satellites broadcast correction messages back to the earth, where suitably enabled receivers use the information to improve accuracy and integrity. The US, Europe and other nations have developed their own SBAS Systems. In the US, the Wide Area Augmentation System (WAAS) exists and is operational. In Europe, SBAS coverage is provided by the European Geostationary Navigation Overlay Service (EGNOS), in Japan by the Multi-functional Satellite Augmentation System (MSAS) and India is developing the GNSS Aided Geo Augmented Navigation (GAGAN) System. An alternative approach to GNSS Augmentation is to transmit integrity and correction messages from ground-based Systems. An example is the American Local Area Augmentation System (LAAS), which allows a suitably equipped receiver to derive enhanced accuracy and integrity information in a local area. The combination of WAAS and LAAS is targeted to provide the Required Navigation Performance (RNP) in all phases of aircraft navigation, including en-route, terminal, approach/landing and surface operations. Along with SBAS and GBAS, GNSS Augmentation may take the form of additional information being provided by other avionics Systems. In most cases, the additional avionics Systems operate via separate principles than GNSS and, therefore, are not subject to the same sources of error or interference. A System such as this is referred to as an Aircraft Based Augmentation System (ABAS). The additional sensors used in ABAS may include Inertial Navigation Systems (INS), TACAN/VOR-DME, Radar, Vision Based Sensors, etc. Unlike SBAS and GBAS technology, research on ABAS is limited and mainly concentrates on additional information being blended into the position calculation to increase accuracy and/or continuity of the integrated navigation solutions. Additionally, no significant attempts have been made of developing ABAS architectures capable of generating integrity signals suitable for safety-critical GNSS applications (e.g., aircraft precision approach and landing) and no flight certified ABAS products are available at present. During flight test activities with GNSS and Differential GNSS (DGNSS) Systems, it was observed that one or more of the following conditions was prone to cause navigation data outages or severe performance degradations: • Antenna obscuration due to aircraft manoeuvring; • Bad satellite geometries and low carrier-to-noise ratios (C/N0); • Doppler shifts caused by aircraft-satellites relative motion; • Interference, at the airborne GNSS antenna, caused by non-GNSS RF signals; • Multipath caused by GNSS signals reflected by the earth surface or the aircraft body. The last two problems can be mitigated by existing technology solutions (i.e., choosing a VHF/UHF Data Link, filtering the radio frequency signals reaching the GNSS antenna, identifying suitable locations for the GNSS antenna and providing adequate shielded of the antenna itself, either by physical devices or via dedicated software masks, etc.). However, there is little one can do in order to prevent critical events during realistic test/training manoeuvres and particular approach procedures (e.g., curved and segmented approaches) performed with high performance military aircraft. Furthermore, although in some cases a careful mission planning may significantly reduce the number of GNSS outages, the adoption of specific aircraft piloting strategies (using the information currently available in the cockpit) cannot effectively avoid the occurrence of these events. ABIA is a new concept that progressively evolved based on research with GNSS-based Time and Space Position Information (TSPI) Systems. TSPI research activities included design, integration and ground/flight testing carried out on MB-339CD, TORNADO and TYPHOON military aircraft. As soon as the validity of the TSPI-ABIA (T-ABIA) concept was established, a prototype System was developed for use in flight test applications. This System is capable of alerting the pilot when the critical conditions for GNSS signal loss are likely to occur (within a specified maximum time-to-alert). In this T-ABIA prototype, the aircraft on-board sensors provide information on the aircraft relevant flight parameters (navigation data, engine settings, etc.) to an Integrity Flag Generator (IFG), which is also connected to the on-board GNSS receiver. The IFG can be incorporated into one of the existing airborne computers or can be a dedicated processing unit. Using the available data on GNSS and the aircraft flight parameters, integrity signals are generated which are displayed on one of the cockpit displays and sent to an Aural Warning Generator. At the same time, an alternate flight path is computed taking into account the geometry and the tracking status of the available GNSS satellites, together with the current mission requirements and the information provided by the aircraft Flight Test Instrumentation (FTI) and standard on-board sensors. Based on the results of T-ABIA research a more advanced ABIA System was developed suitable for manned and unmanned aircraft applications. Detailed mathematical algorithms were developed to cope with the main causes of GNSS signal outages and degradation in flight, namely: obscuration, multipath, interference, fading due to adverse geometry and Doppler shift. Adopting these algorithms, the ABIA System is able to provide steering information to the pilot and electronic commands to the aircraft flight control System, allowing real-time avoidance of safety-critical flight conditions and fast recovery of the required navigation performance in case of GNSS data losses. This is achieved by implementing both caution (predictive) and warning (reactive) integrity flags, as well as 4-Dimensional Trajectory (4DT) optimisation models suitable for all phases of flight. The detailed design of the ABIA IFG module was completed and validation activities were performed on TORNADO-IDS, A-320 and AEROSONDE UAV simulated platforms to determine the Time-to-Alert (TTA) performances of the ABIA System in various flight phases from departure to final approach. The results of these activities were encouraging, showing that the System TTA performance is in line with current ICAO, FAA and CAA requirements for the different flight phases, with a potential synergy with SBAS and GBAS Systems to support departure, en-route and TMA operations, including CAT-I/III precision approach. Further research concentrated on the 4DT computation module and extended the scope of ABIA applications to Unmanned Aircraft Systems (UAS). In particular, an initial investigation was accomplished to identify the potential synergies of ABIA with UAS Sense-and-Avoid (SAA) architectures for mid-air collision avoidance tasks. In conclusion, although current and likely future SBAS/GBAS Augmentation Systems can provide significant improvement of GNSS navigation performance, it is shown that the novel ABIA System developed in this research can play a key role in GNSS integrity Augmentation for mission-essential and safety-critical applications such as aircraft precision approach/auto-landing and UAS sense-and-avoid. Furthermore, using suitable data link and data processing technologies, a certified ABIA System could play a key role as part of a future GNSS Space-Ground-Aircraft Augmentation Network (SGAAN).

  • a novel gnss integrity Augmentation System for civil and military aircraft
    World Academy of Science Engineering and Technology International Journal of Mechanical Aerospace Industrial Mechatronic and Manufacturing Engineering, 2013
    Co-Authors: Roberto Sabatini, Terry Moore, Chris Hill
    Abstract:

    This paper presents a novel Global Navigation Satellite System (GNSS) Avionics Based Integrity Augmentation (ABIA) System architecture suitable for civil and military air platforms, including Unmanned Aircraft Systems (UAS). Taking the move from previous research on high-accuracy Differential GNSS (DGNSS) Systems design, integration and experimental flight test activities conducted at the Italian Air Force Flight Test Centre (CSVRSV), our research focused on the development of a novel approach to the problem of GNSS ABIA for mission- and safety-critical air vehicle applications and for multi-sensor avionics architectures based on GNSS. Detailed mathematical models were developed to describe the main causes of GNSS signal outages and degradation in flight, namely: antenna obscuration, multipath, fading due to adverse geometry and Doppler shift. Adopting these models in association with suitable integrity thresholds and guidance algorithms, the ABIA System is able to generate integrity cautions (predictive flags) and warnings (reactive flags), as well as providing steering information to the pilot and electronic commands to the aircraft/UAS flight control Systems. These features allow real-time avoidance of safety-critical flight conditions and fast recovery of the required navigation performance in case of GNSS data losses. In other words, this novel ABIA System addresses all three cornerstones of GNSS integrity Augmentation in mission- and safety-critical applications: prediction (caution flags), reaction (warning flags) and correction (alternate flight path computation).

  • a new avionics based gnss integrity Augmentation System part 2 integrity flags
    Journal of Navigation, 2013
    Co-Authors: Roberto Sabatini, Terry Moore, Chris Hill
    Abstract:

    This paper presents the second part of the research activities carried out to develop a novel Global Navigation Satellite System (GNSS) Avionics-Based Integrity Augmentation (ABIA) System for manned and Unmanned Aerial Vehicle (UAV) applications. The ABIA System's architecture was developed to allow real-time avoidance of safety-critical flight conditions and fast recovery of the required navigation performance in case of GNSS data losses. In more detail, our novel ABIA System addresses all four cornerstones of GNSS integrity Augmentation in mission- and safety-critical avionics applications: prediction (caution flags), avoidance (optimal flight path guidance), reaction (warning flags) and correction (recovery flight path guidance). Part 1 (Sabatini et al., 2012) presented the ABIA concept, architecture and key mathematical models used to describe GNSS integrity issues in aircraft applications. This second part addresses the ABIA caution and warning integrity flags criteria and presents the results of a simulation case study performed on the TORNADO Interdiction and Strike (IDS) aircraft.

  • a new avionics based gnss integrity Augmentation System part 1 fundamentals
    Journal of Navigation, 2013
    Co-Authors: Roberto Sabatini, Terry Moore, Chris Hill
    Abstract:

    The aviation community has very stringent navigation integrity requirements that apply to a variety of manned and Unmanned Aerial Vehicle (UAV) operational tasks. This paper presents the results of the research activities carried out by the Italian Air Force Flight Test Centre (CSV-RSV) in collaboration with the Nottingham Geospatial Institute (NGI) and Cranfield University (CU) in the area of Avionics-Based Integrity Augmentation (ABIA) for mission- and safety-critical Global Navigation Satellite System (GNSS) applications. Based on these activities, suitable models were developed to describe the main causes of GNSS signal outage and degradation in flight, namely: antenna obscuration, multipath, fading due to adverse geometry and Doppler shift. Adopting these models in association with suitable integrity thresholds and guidance algorithms, the ABIA System delivers integrity caution (predictive) and warning (reactive) flags, as well as steering information to the pilot and electronic commands to the aircraft/UAV flight control System. These features allow real-time avoidance of safety-critical flight conditions and fast recovery of the required navigation performance in case of GNSS data losses. This paper presents the key ABIA concepts, architecture and mathematical models. A successive paper will address the ABIA integrity thresholds criteria and detailed results of a TORNADO simulation case-study.

Shau Shiun Jan - One of the best experts on this subject based on the ideXlab platform.

  • reversion from l1 l5 dual to l5 single frequency waas in the presence of rf interference
    IEEE Transactions on Aerospace and Electronic Systems, 2010
    Co-Authors: Shau Shiun Jan, Todd Walter, Per Enge
    Abstract:

    Techniques available to sustain dual-frequency ionosphere performance when a dual-frequency airborne Global Positioning System (GPS)/wide area Augmentation System (WAAS) user loses all but one GPS frequency while descending into radio frequency interference (RFI) are investigated. We are particularly interested in the case where the user transitions from L1-L5 to having L5-only since the uncertainty of the L5-only ionospheric delay estimation is larger than the case for L1-only. The goal is to provide the techniques necessary for single-frequency users to sustain a performance similar to those of dual-frequency users. The proposed techniques are 1) the code and carrier divergence technique, 2) the WAAS ionosphere threat model technique, and 3) the maximum ionospheric delay gradient model technique. The results show that all three proposed techniques provide good ionospheric delay estimation for the full duration of approach.

  • vertical guidance performance analysis of the l1 l5 dual frequency gps waas user avionics sensor
    Sensors, 2010
    Co-Authors: Shau Shiun Jan
    Abstract:

    This paper investigates the potential vertical guidance performance of global positioning System (GPS)/wide area Augmentation System (WAAS) user avionics sensor when the modernized GPS and Galileo are available. This paper will first investigate the airborne receiver code noise and multipath (CNMP) confidence (σair). The σair will be the dominant factor in the availability analysis of an L1-L5 dual-frequency GPS/WAAS user avionics sensor. This paper uses the MATLAB Algorithm Availability Simulation Tool (MAAST) to determine the required values for the σair, so that an L1-L5 dual-frequency GPS/WAAS user avionics sensor can meet the vertical guidance requirements of APproach with Vertical guidance (APV) II and CATegory (CAT) I over conterminous United States (CONUS). A modified MAAST that includes the Galileo satellite constellation is used to determine under what user configurations WAAS could be an APV II System or a CAT I System over CONUS. Furthermore, this paper examines the combinations of possible improvements in signal models and the addition of Galileo to determine if GPS/WAAS user avionics sensor could achieve 10 m Vertical Alert Limit (VAL) within the service volume. Finally, this paper presents the future vertical guidance performance of GPS user avionics sensor for the United States' WAAS, Japanese MTSAT-based satellite Augmentation System (MSAS) and European geostationary navigation overlay service (EGNOS).