1,721,008 research outputs found
Guidance, Navigation, and Separation Assurance for Local-Area UAV Networks: Putting the Pieces Together
No full textVertical Position Error Bounding for Integrated Sensors to Support Unmanned Aerial Vehicles (UAV)
No full textEnhancements of Long Term Ionospheric Anomaly Monitoring for the Ground-Based Augmentation System
No full textExtremely large ionospheric gradients can pose a potential integrity threat to the users of ground-based augmentation systems (GBAS). A better understanding of the ionospheric behavior (not limited to that during extreme ionospheric activity) is important in the design and operation of GBAS to meet its integrity and availability requirements. A tool for long-term ionosphere monitoring was developed to build an ionosphere threat model, evaluate its validity over the system operation, monitor ionospheric behavior continuously, and update it when necessary. This paper presents the enhanced algorithms of long-term ionospheric anomaly monitoring and evaluates its performance using data from a ionospheric storm day, 20 November 2003, and a nominal day, 9 November 2004. The automation of data processing enables us to more accurately categorize ionospheric behavior under both nominal and anomalous conditions. This paper also demonstrates that the automated procedure of enhanced long-term ionosphere monitoring not only identifies gradients large enough to threaten GBAS users but periodically generates reliable statistics of ionospheric gradients under all conditions
Sigma Overbounding using a Position Domain Method for the Local Area Augmentaion of GPS
No full textThe local area augmentation system (LAAS) is a differential GPS navigation system being developed to support aircraft precision approach and landing navigation with guaranteed integrity and availability. While the system promises to support Category I operations, significant technical challenges are encountered in supporting Category 11 and III operations. The primary concern has been the need to guarantee compliance with stringent requirements for navigation availability. This paper describes how a position domain method (PDM) may be used to improve system availability by reducing the inflation factor for standard deviations of pseudo-range correction errors. Used in combination with the current range domain method (RDM), a 30% reduction in the inflation factor is achieved with the same safety standard. LAAS prototype testing verifies the utility of the PDM to enhance Category IVIII user availability.
Assessment and mitigation of equatorial plasma bubble impacts on category I GBAS operations in the Brazilian region
No full textPrior to initiating GBAS service in equatorial regions, it is vital to evaluate potential integrity threats posed by equatorial plasma bubble (EPB)-induced ionospheric gradients and assess availability when implementing ionospheric threat mitigation methods. Earlier work developed a preliminary EPB model with a gradient bound larger than twice that for mid-latitude ionospheric storms. Position-domain geometry screening (PDGS) with this higher gradient bound decreases availability to 58.3% at the Galeao International Airport, Brazil, during nighttime. A new mitigation method using Monte Carlo simulation randomizes ionospheric scenarios using randomly generated parameter combinations within the threat model and assesses the ensemble impacts. By taking credit for a prior probability of an extreme EPB, this algorithm determines the inflated integrity parameters to meet the safety requirement in the probabilistic definition. This paper shows that with this method, the system availability for category I precision approaches dramatically improved to 89.6% when a data-driven prior probability of 10-5 was applied.
High-Integrity Local-Area Differential GNSS Architectures Optimized to Support Unmanned Aerial Vehicles (UAVs)
No full textSigma-mean monitoring for the local area augmentation of GPS
No full textThe local area augmentation system (LAAS) is a ground-based differential GPS system being developed to support aircraft precision approach and landing navigation with guaranteed integrity. To quantitatively appraise navigation integrity.. an aircraft computes vertical and lateral protection levels using the standard deviation of pseudo-range correction errors. sigma(pr_gnd), broadcast by the LAAS ground facility (LGF). Thus, one significant integrity risk is that the true standard deviation (sigma) of the pseudo-range correction error distribution may grow to exceed the broadcast correction error sigma or that the true mean of the correction error distribution becomes excessive during LAAS operation. This event may occur due to unexpected anomalies of GPS measurements. To insure that the true error distribution is bounded by a zero-mean Gaussian distribution with the broadcast sigma value, real-time sigma and mean monitoring is necessary. Both direct estimation and cumulative sum (CUSUM) methods are useful to detect violations with acceptable residual integrity. risk. For sigma monitoring, the estimation method more rapidly detects small violations of sigma(pr_gnd), but the fast initial response (FIR) CUSUM variant more promptly detects significant violations that would pose a larger threat to user integrity. For the purposes of mean monitoring. the FIR CUSUM variant is superior to the estimation method in detecting any mean violations. The results demonstrate that real-time protection is achievable against all sizes of sigma/mean failures that can threaten navigation integrity.The constructive comments and advice regarding this work provided by many other people in the Stanford GPS research group are greatly appreciated
Networked UAV Detection and Alerting of Ionospheric Anomalies within LADGNSS Navigation Framework
No full textLocal Area Differential GNSS (LADGNSS) is a simplification of the Ground-based Augmentation System (GBAS) architecture to provide navigation and guidance for nearby UAVs. Recent research has evaluated the impacts of severe ionospheric anomalies on Dual-Frequency, Multiple-Constellation (DFDC) LADGNSS and its monitors. To protect against all possible ionospheric anomalies, the system assumes that the worst-case undetected ionosphere-induced differential errors might affect users. The hypothetical impact of ionospheric anomalies can be lowered by improving monitoring capability, and one possible improvement not studied previously is to utilize two-way transmissions from the multiple networked UAVs supported by LADGNSS at any given time. Two-way datalinks are already part of the LADGNSS architecture to support UAV status reports and cooperative guidance, and they can be exploited to allow all UAVs connected to LADGNSS ground stations to share the threat information collected by any of them. This paper examines the benefit of networked UAVs for LADGNSS under anomalous ionospheric conditions by proposing a monitor strategy that leverages observations from networked UAVs to enhance ionospheric monitor capability. The strategy utilizes UAVs within the network which have superior ionospheric gradient monitor (IGM) detection capability to reduce the maximum undetected gradient of a specific user UAV, leading to reduced maximum undetected ionosphere-induced differential errors (MIEV) at that user. Simulation results show a significant reduction in the worst ionosphere-induced differential error by utilizing multiple monitor capability of networked UAVs, where the benefit increases with a larger number of UAVs that are more widely distributed
SS-RAIM-Based Integrity Architecture for CDGNSSs Against Satellite Measurement Faults
No full textCarrier-phase differential global navigation satellite systems (CDGNSSs) present an attractive option for autonomous vehicles that require accurate and safe navi-gation. The key to high precision in a CDGNSS is resolving integer ambiguities. However, the discrete nature of ambiguities complicates the analysis of posi-tion errors in relation to satellite measurement faults, which poses challenges in protection level (PL) calculation. This paper presents an integrity architecture based on solution separation receiver autonomous integrity monitoring. The test statistic for this monitor is defined in the position domain, directly captur-ing position errors due to faults. This approach facilitates easier and less conser-vative evaluations of PLs. This paper provides detailed derivations of PLs and monitor thresholds starting from a common definition of integrity and continu-ity risk. Additionally, this work presents a method for ensuring that PLs reliably bound actual position errors using a measurement overbounding technique. Simulation results show that the monitor detects most faults and that the PLs bound the position errors from undetected faults.
Automated Front Speed Computation of Ionospheric Anomalies for Ground-Based Augmentation Systems
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