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Interference events, both intentional and unintentional, are significant threats to global navigation satellite system (GNSS) service continuity. In the presence of interference, it can be difficult for GNSS receivers to maintain continuous tracking of carrier phase and frequency. To address this issue, in place of a traditional phase-locked loop (PLL), we develop and validate a new estimation-based approach to allow GNSS receivers to correctly estimate carrier phase and frequency under conditions of low carrier-to-noise power. An adaptive Kalman filter forms the core of the estimator, with a multiple-model algorithm to account for discrete navigation data bit transitions. The performance of the estimator in the presence of wideband interference is validated through simulation and experiment, showing performance markedly superior to that of a PLL. [ABSTRACT FROM AUTHOR]

Advanced receiver autonomous integrity monitoring (ARAIM) is under development to support both lateral and vertical guidance. A key component of ARAIM is the integrity support message (ISM), which contains validated input parameters including the probabilities of satellite and constellation failure. A service commitment for the former is provided in the global positioning system (GPS) performance standards, whereas further commitments from GLONASS, Galileo, and Beidou are expected to follow. However, air navigation service providers may demand some flexibility in setting the ISM. This article presents a procedure for setting ISM parameters employing a means to determine the a priori probabilities using the Bayesian inference of a Poisson process model given in the literature. This method and a novel way to accumulate the service history are used to analyze the effects of satellite block and age. Results show that while the type and age of satellite are clearly drivers in the likelihood of a fault; such effects may be accounted for without significant impact on the broadcast values. This article also addresses the probability of unscheduled satellite outages using the new method. Finally, this article gives a high-level scheme of how the validity of the ISM parameters may be assured. [ABSTRACT FROM AUTHOR]

In this work, a new time‐sequential positioning and fault detection method is developed for dual‐frequency, multi‐constellation Advanced Receiver Autonomous Integrity Monitoring (ARAIM). Unlike conventional "snapshot" ARAIM, sequential ARAIM exploits changes in satellite geometry at the cost of slightly higher computation and memory loads. From the perspective of users on Earth, the motion of any given GNSS satellite is small over short time intervals. But the accumulated geometry variations of redundant satellites from multiple GNSS can be substantial. This paper quantifies performance benefits brought by satellite motion to ARAIM. It specifically addresses the following challenges: (a) defining raw GNSS code and carrier error models over time, (b) designing estimators and fault detectors exploiting geometric diversity for positioning, cycle ambiguity estimation, and integrity evaluation, and (c) formulating these algorithms in a computationally efficient implementation. Performance improvements provided by sequential ARAIM over snapshot ARAIM are evaluated by worldwide availability analysis for aircraft approach navigation. [ABSTRACT FROM AUTHOR]

In this article, we describe a new method for detecting global navigation satellite system (GNSS) spoofing using an inertial navigation system. We specifically address the most difficult-to-detect scenario, in which a spoofer replicates the authentic GNSS signal with only additive errors due to the spoofer’s uncertainty in knowledge of the target’s position. We derive an optimal monitor to detect the anomalous temporal structure of the spoofed measurements caused by the spoofer’s target tracking errors. This new monitor uses accumulated Kalman filter innovations projected into the position state domain. We demonstrate how the monitor window length can be set to achieve any required missed detection probability, and we evaluate the performance of the monitor for both white and colored tracking error. Finally, we present a complementary solution separation monitoring concept to detect rapid-onset spoofing and to achieve protection levels in real time. [ABSTRACT FROM AUTHOR]

Highlights from the article: FLIGHT RESULTS OF GPS-BASED ATTITUDE DETERMINATION FOR THE MICROSATELLITE FLYING-LAPTOP presents attitude determination results obtained with the "GPS Enhanced Navigation system for the University of Stuttgart micro satellite" (GENIUS) onboard "Flying Laptop". ROBUST TRANSFORM DOMAIN SIGNAL PROCESSING FOR GNSS Robust signal processing techniques are effective mitigation approaches that can enable Global Navigation Satellite System (GNSS) receiver operations even in the presence of strong interference. PERFORMANCE ASSESSMENT OF 3D-MAPPING-AIDED GNSS PART 1: ALGORITHMS, USER EQUIPMENT AND REVIEW a full performance assessment of 3D-mapping-aided (3DMA) GNSS in dense urban areas is presented. PERFORMANCE ASSESSMENT OF 3D-MAPPING-AIDED GNSS PART 2: ENVIRONMENT AND MAPPING a full performance assessment of 3D-mapping-aided (3DMA) GNSS in dense urban areas is presented.

In this paper, a new safety risk evaluation method is developed, simulated, and tested for laser-based navigation algorithms using feature extraction (FE) and data association (DA). First, at FE, we establish a probabilistic measure of separation between features to quantify the sensor's ability to distinguish landmarks. Then, an innovation-based DA process is designed to evaluate the impact on integrity risk of incorrect associations, while considering all potential measurement permutations. The algorithm is analyzed and tested in a structured environment. [ABSTRACT FROM AUTHOR]

We propose a novel GPS phase-lock loop (PLL) performance metric based on the standard deviation of tracking error (defined as the discriminator's estimate of the true phase error), and explain its advantages over the popular phase jitter metric using theory, numerical simulation, and experimental results. We derive an augmented GPS phase-lock loop (PLL) linear model, which includes the effect of coherent averaging, to be used in conjunction with this proposed metric. The augmented linear model allows more accurate calculation of tracking error standard deviation in the presence of additive white Gaussian noise (AWGN) as compared to traditional linear models. The standard deviation of tracking error, with a threshold corresponding to half of the arctangent discriminator pull-in region, is shown to be a more reliable/robust measure of PLL performance under interference conditions than the phase jitter metric. In addition, the augmented linear model is shown to be valid up until this threshold, which facilitates efficient performance prediction, so that time-consuming direct simulations and costly experimental testing can be reserved for PLL designs that are much more likely to be successful. The effect of varying receiver reference oscillator quality on the tracking error metric is also considered. [ABSTRACT FROM AUTHOR]

This paper provides new integrity and continuity risk evaluation methods for fault detection and exclusion (FDE) using receiver autonomous integrity monitoring (RAIM). These methods are developed for both solution separation (SS) and Chi-squared RAIM: they capture the fact that exclusion enables continuity risk reduction in exchange for a higher integrity risk. The two approaches are implemented in an example advanced RAIM (ARAIM) application for worldwide vertical guidance of aircraft using multiconstellation Global Navigation Satellite Systems (GNSS). [ABSTRACT FROM PUBLISHER]

A dynamic state realization for tightly coupling Global Positioning System (GPS) measurements with an Inertial Navigation System (INS) is described. The realization, based on the direct fusion of GPS and INS systems through Kalman filter state dynamics, explicitly accounts for temporal and spatial decorrelation of GPS measurement errors (such as tropospheric, ionospheric, and multipath errors) through state augmentation, thereby ensuring Kalman filter integrity under fault-free error conditions. Predicted system performance for a Local Area Augmentation System (LAAS) aircraft precision approach application is evaluated using covariance analysis and validated with flight data.Built-in fault detection mechanisms based on the Kalman filter innovations are also evaluated to help provide integrity under certain fault conditions. It is shown that an algorithm based on the integral of Kalman filter innovations outperforms other existing GPS fault detection methods in the detection of slowly developing ranging errors, such as those caused by ionospheric and tropospheric anomalies. [ABSTRACT FROM PUBLISHER]

A new theoretical approach is described to quantify position-domain integrity risk for cycle ambiguity resolution problems in satellite-based navigation systems. It is typically conservatively assumed that all incorrectly fixed cycle ambiguities cause hazardously large position errors. While simple and practical, this conservative assumption can unnecessarily limit navigation availability for applications with stringent requirements for accuracy and integrity. In response, a new method for calculating the integrity risk for carrier phase navigation algorithms is developed. In this method we evaluate the impact of incorrect fixes in the position domain and define tight upper bounds on the resulting navigation integrity risk. Furthermore, a mechanism to implement this method with partially-fixed cycle ambiguity vectors is also derived. The improvement in navigation availability using the new method is quantified through covariance analysis performed over a range of error model parameters. [ABSTRACT FROM AUTHOR]

Carrier phase differential GPS (DGPS) navigation architectures and algorithms for automatic shipboard landing of aircraft are described. Processing methodologies are defined to provide high integrity carrier phase cycle estimation and positioning by optimally exploiting the complementary benefits of measurement filtering and satellite geometric redundancy for the terminal navigation problem. Navigation performance sensitivity to the standard deviations of raw carrier and code phase measurement errors, measurement error correlation times, and the filtering duration is quantified. Necessary conditions to ensure acceptable terminal navigation availability are specifically defined. [ABSTRACT FROM AUTHOR]

Methodologies sufficient to monitor GPS satellite orbit ephemeris for Category I aircraft precision approach navigation are described. In the absence of a satellite maneuver, it is shown that a monitor based on the projection of previously validated ephemeris parameters is adequate to meet navigation integrity and availability requirements. After scheduled station keeping maneuvers, no previously validated ephemerides are available, so a measurement-based method is required. The feasibility of such a monitor is also established. [ABSTRACT FROM AUTHOR]

Focuses on a study which examined the sensitivity of integrity risk to statistical uncertainties in the knowledge reference receiver error standard deviation and error correlation across the multiple reference receivers to be used in the Local Area Augmentation System (LAAS) ground segment. Basic function of the LAAS ground facility integrity; Σ sensitivity analysis; Correlation sensitivity analysis.

Presents corrections to the paper, Robust modeling of GNSS tropospheric delay dynamics (E. Gallon, M. Joerger, and B. Pervan), IEEE Trans. Aerosp. Electron. Syst., vol. 57, no. 5, pp. 2992–3003, Oct. 2021, doi: 10.1109/TAES.2021.3068441. [ABSTRACT FROM AUTHOR]

Examines the limits of high-integrity and high-continuity satellite-based navigation performance using carrier phase measurements and parity space techniques. Description of the Global Positioning System (GPS) developed by the United States Department of Defense; Validation of fault detection and removal algorithm performance; Presentation of a linear observation equation for differential GPS positioning.

This paper investigates how global navigation satellite systems (GNSSs) and inertial navigation systems (INSs), when appropriately augmented by ranging from local landmarks, can safely navigate vehicles through a real-world urban environment. We begin by considering safety requirements for driverless vehicles under fault-free assumptions and developing measurement models for multi-sensor integrated navigation systems using an extended Kalman filter. The critical elements of urban navigation are then discussed, including individual INS noise parameter specifications, vehicle speed, and the effect of velocity updates. Covariance analyses performed along a 9-km-long urban transect in downtown Chicago show that velocity updates measured by wheel speed sensors, vehicle kinematic constraints, and zero-velocity updates can extend navigation continuity by bridging intermittent GNSS signal availability. However, position reference updates at intervals between 15 and 35 m, based on light detection and ranging data from local landmarks in our case, are needed to achieve full navigation availability through the transect. [ABSTRACT FROM AUTHOR]

In this article, we develop new stochastic tropospheric error models for positioning, fault detection, and integrity monitoring over time. We first perform time-domain and frequency-domain analyses of residual tropospheric delays observed over 12 months at multiple globally distributed locations. We then derive bounding error models for time-sequential safety-critical navigation systems including global navigation satellite systems integrated with inertial navigation systems and Kalman filter implementations of advanced receiver autonomous integrity monitoring. [ABSTRACT FROM AUTHOR]

In this article, we develop a ground monitor capable of detecting anomalous signal-in-space spatial gradients for rising, newly acquired, and reacquired satellites in the ground-based augmentation system using either single or dual frequency. These gradients can be caused by satellite orbit ephemeris faults and ionospheric fronts. The monitor utilizes differential code and carrier phase measurements across multiple reference receiver antennas as the basis for detection. We show that the new monitor significantly improves performance over existing detection algorithms and is capable of meeting Category III precision approach and landing requirements. [ABSTRACT FROM AUTHOR]

This paper investigates the impact of the autocorrelations of monitor test statistics on navigation integrity and continuity. General analytical methods are rigorously developed to evaluate the actual integrity risk and false alert probability over the exposure interval. Prior to this work, the probabilities computed based on one-sample test have been widely applied in aviation navigation. However, it will be shown that using the one-sample probability may lead to overly optimistic results, because the actual risk can be significantly higher, especially for false alert. The new methods are applied to an example problem of advanced receiver autonomous integrity monitoring. To quantify integrity, a simple but conservative upper bound is derived. As for continuity, both analytical and experimental results show that the actual false alert probability is two orders of magnitude higher than previously thought, due to the time-correlation effects. A feasible solution to mitigate this impact is provided, without degrading navigation availability. [ABSTRACT FROM AUTHOR]

This paper analyzes the effect of error correlation on the SISRE bounding for GPS and Galileo satellites. For a given period of data collection, it computes the effective number of independent samples contained in a dataset applying an estimation variance analyses. Results show that the time between effective independent samples is highly dependent on the constellation and onboard clock type. On one hand, GPS satellites equipped with Rubidium clocks exhibit significantly longer error correlation than those with onboard Cesium clocks. On the other hand, Galileo satellites show substantially shorter correlation time among samples with less variability on a monthly basis. This paper also introduces a methodology to compute SISRE bounding accounting for the limited number of independent samples. Using a Bayesian approach, it computes the so‐called uncertainty factor by which the Gaussian distribution needs to be inflated in order to account for the observation data independence. [ABSTRACT FROM AUTHOR]

This paper comprehensively investigates the fault exclusion problem in multi-constellation Global Navigation Satellite Systems (GNSS). In future GNSS, the heightened likelihood of fault detection events will cause more interruptions in the continuity of the navigation operation. The main contribution of this paper is to establish the theoretical basis to quantify the contributions of fault events on continuity risk, therefore allowing us to assess the desired exclusion function performance based on specific continuity requirements. Accordingly, a new real-time exclusion algorithm is developed, for which the upper bounds on integrity risks are rigorously derived. Using the new method, performance is comprehensively investigated for two important civil aircraft navigation operations using various numbers of constellations. We show that high service availability can be achieved for both operations. [ABSTRACT FROM AUTHOR]

Differential carrier phase applications that utilize cycle resolution need the probability density function of the baseline estimate to quantify its region of concentration. For the integer bootstrap estimator, the density function has an analytical definition that enables probability calculations given perfect statistical knowledge of measurement and process noise. This paper derives a method to upper bound the tail probability of the integer bootstrapped GNSS baseline when the measurement and process noise correlation functions are unknown, but can be upper and lower bounded. The tail probability is shown to be a non-convex function of a vector of conditional variances, whose feasible region is a convex polytope. We show how to solve the non-convex optimization problem globally by discretizing the polytope into small hyper-rectangular elements, and demonstrate the method for a static baseline estimation problem. [ABSTRACT FROM AUTHOR]

For a growing number of aviation applications of the Global Positioning System (GPS) and of other Global Navigation Satellite Systems (GNSS), it is essential to establish a rigorous bound on measurement error. Most existing bounding methods rely on representing the actual measurement error distribution with a conservative, continuous model (e.g., a Gaussian "overbound"). We propose a conservative, discrete model as a practical alternative. A key limitation of continuous error models is validation, particularly in the distribution tails where comparatively little statistical data is available. With a discrete model, it is easy 1) to define a minimally conservative core region, where data are plentiful, and 2) to introduce a highly conservative tail region, where data are sparse. The trade-off is increased computational complexity, as no closed-form expression exists for convolution of non-Gaussian error distributions. We propose a particular form of a discrete error distribution, which we call the NavDEN model. Through application to a heavy-tail GPS data set, we demonstrate that the NavDEN model compares favorably to Gaussian models, both in providing more margin for tail uncertainty and, at the same time, in providing generally tighter protection levels (PLs) when multiple distributions are convolved. [ABSTRACT FROM PUBLISHER]

In this paper, a methodology is developed to evaluate differential carrier phase navigation architectures subject to reference receiver faults. Carrier phase measurements can be used to provide high accuracy estimates of a user's position. But in applications that involve safety-of-life, such as in precision approach for autonomous shipboard landing, integrity also plays a critical role. One source of integrity risk is the potential for GPS reference receiver failure. Integrity risk in these situations is typically mitigated by equipping the reference station with redundant receivers. However, various approaches to utilize redundant carrier phase measurements from multiple reference receivers are possible. In this paper, we describe two new methods: an averaging approach where different position solutions are averaged in the position domain, and a coupled estimation approach where the measurements from all reference receivers are coupled in the range domain and used to estimate a unified position solution. Furthermore, we investigate the impact of using these methods on accuracy and integrity from several perspectives, including availability performance, cycle resolution capabilities, implementation complexity, and computational efficiency. [ABSTRACT FROM AUTHOR]

This paper introduces a navigation system based on combined global positioning system (GPS) and laser-scanner measurements for outdoor ground vehicles. Using carrier-phase differential GPS, centimeter-level positioning is achievable when cycle ambiguities are resolved. However, GPS signals are easily attenuated or blocked, so their use is generally restricted to open-sky areas. In response, in this work we augment GPS with two-dimensional laser-scanner measurements. The latter is available when GPS is not and further enables obstacle detection. The two sensors are integrated in the range domain for optimal navigation performance. Nonlinear laser observations and time-correlated code and carrier-phase GPS signals are processed in a unified and compact measurement-differencing extended Kalman filter. The resulting algorithm performs real-time carrier-phase cycle ambiguity estimation and provides absolute vehicle positioning throughout GPS outages, without a priori knowledge of the surrounding landmark locations. Covariance analysis, Monte Carlo simulations, and experimental testing in the streets of Chicago demonstrate that the performance of the range-domain integrated system far exceeds that of a simpler position-domain implementation, in that it not only achieves meter-level precision over extended GPS-obstructed areas, but also improves the robustness of laser-based simultaneous localization and mapping. [ABSTRACT FROM AUTHOR]

Autonomous airborne refueling requires that the position of the receiving aircraft relative to the tanker be known very accurately and in real time. To meet this need, highly precise carrier-phase differential global positioning system solutions are being considered as the basis for navigation. However, the tanker introduces severe sky blockage into the autonomous airborne refueling mission, which reduces the number of visible global positioning system satellites and hence degrades the positioning accuracy. In this paper, we analyze the autonomous airborne refueling navigation problem in detail, define an optimal navigation architecture, and quantify navigation system availability. As part of this work, a high-fidelity dynamic sky-blockage model is developed and used to plan autonomous airborne refueling flight tests. The flight tests were conducted to obtain time-tagged global positioning system and attitude data that were processed offline to validate the blockage model. [ABSTRACT FROM AUTHOR]

This paper is the second part of a two-part research effort to find the optimal detector and estimator that minimise the integrity risk in Receiver Autonomous Integrity Monitoring (RAIM). Part 1 shows that for realistic navigation requirements, the solution separation RAIM method can approach the optimal detection region when using a least-squares estimator. This paper constitutes Part 2. It presents new methods to design Non-Least-Squares (NLS) estimators, which, in exchange for a slight increase in nominal positioning error, can substantially lower the integrity risk. A first method is formulated as a multi-dimensional minimisation problem, which directly minimises integrity risk, but can only be solved using a time-consuming iterative process. Parity space representations are then exploited to develop a computationally-efficient, near-optimal NLS-estimator-design method. Performance analyses for an example multi-constellation Advanced RAIM (ARAIM) application show that this new method enables significant integrity risk reduction in real-time implementations where computational resources are limited. [ABSTRACT FROM AUTHOR]

ABSTRACT Future multi-constellation Global Navigation Satellite Systems (GNSS) will offer the possibility to fulfill stringent navigation integrity requirements using Receiver Autonomous Integrity Monitoring (RAIM). This paper presents a detailed comparison of residual-based (RB) and solution separation (SS) RAIM. A complete step-by-step derivation of the two methods, which is currently missing in the literature, is given for the detection of single and multi-measurement faults, starting from common definitions of the integrity and continuity risks. In addition, a parity-space representation of SS RAIM is developed. It is shown that the integrity monitoring performance of SS RAIM can be superior to RB RAIM because SS test statistics are tailored to the fault hypotheses, and to the state of interest. However, for practical reasons of computational efficiency in conventional SS implementations, which are fully detailed in the paper, RB RAIM ultimately provides tighter bounds on integrity risk. Copyright © 2014 Institute of Navigation. [ABSTRACT FROM AUTHOR]

The Global Positioning System (GPS) was designed as a passive radio navigation system to provide positioning capability without the need for receiver clock synchronization to GPS time. In theory, a GPS receiver equipped with a high-quality receiver clock can provide better system performance. More importantly for integrity-driven navigation applications, the additional redundancy provided by a clock dynamic model can increase fault detection performance and availability for receiver autonomous integrity monitoring (RAIM). In the work presented here, a stochastic model is used to rigorously account for the time correlation of random errors in high-quality GPS receiver clocks. A batch estimator (BE) is then developed to use GPS measurements collected over time to estimate current user position. The BE incorporates the stochastic clock model to ensure that position errors are properly quantified and, therefore, that navigation integrity is ensured. The resulting improvement in positioning performance is demonstrated using covariance analysis. [ABSTRACT FROM AUTHOR]

The concept of Relative Receiver Autonomous Integrity Monitoring (RRAIM) using time differential carrier phase measurements is investigated in this paper. The precision of carrier phase measurements allows for mitigation of integrity hazards by implementing RRAIM monitors with tight thresholds without significantly affecting continuity. In order to avoid the need for cycle ambiguity resolution, time differences in carrier phase measurements are used as the basis for detection. In this work, we examine RRAIM within the context of the GNSS Evolutionary Architecture Study (GEAS), which explores potential architectures for aircraft navigation utilizing the satellite signals available in the mid-term future with GPS III. The objectives of the GEAS are focused on system implementations providing worldwide coverage to satisfy LPV-200 operations, and potentially beyond. In this work, we study two different GEAS implementations of RRAIM. General formulas are derived for positioning, fault detection, and protection level generation to meet a given set of integrity and continuity requirements. [ABSTRACT FROM AUTHOR]

This paper describes a method to determine global navigation satellite systems (GNSS) satellite orbits and clocks for advanced receiver autonomous integrity monitoring (ARAIM). The orbit and clock estimates will be used as a reference truth to monitor signal-in-space integrity parameters of the ARAIM integrity support message (ISM). Unlike publicly available orbit and clock products, which aim to maximise estimation accuracy, a straightforward and transparent approach is employed to facilitate integrity evaluation. The proposed monitor is comprised of a worldwide network of sparsely distributed reference stations and will employ parametric satellite orbit models. Two separate analyses, covariance analysis and model fidelity evaluation, are carried out to assess the impact of measurement errors and orbit model uncertainty on the estimated orbits and clocks, respectively. The results indicate that a standard deviation of 30 cm can be achieved for the estimated orbit/clock error, which is adequate for ISM validation. [ABSTRACT FROM AUTHOR]

Two critical parameters for advanced receiver autonomous integrity monitoring are the probability of satellite fault and the probability of constellation fault. This paper provides specific definitions for each of these fault types. We describe how these faults are evaluated and how to estimate their probability occurrence. Providing a precise definition of what constitutes a fault is essential so that all observers are able to agree on whether or not one has occurred. [ABSTRACT FROM AUTHOR]

In this paper, we develop new methods to assess safety risks of an integrated GNSS/LiDAR navigation system for highly automated vehicle (HAV) applications. LiDAR navigation requires feature extraction (FE) and data association (DA). In prior work, we established an FE and DA risk prediction algorithm assuming that the set of extracted features matched the set of mapped landmarks. This paper addresses these limiting assumptions by incorporating a Kalman filter innovation-based test to detect unwanted object (UO). UO include unmapped, moving, and wrongly excluded landmarks. An integrity risk bound is derived to account for the risk of not detecting UO. Direct simulations and preliminary testing help quantify the impact on integrity and continuity of UO monitoring in an example GNSS/LiDAR implementation. [ABSTRACT FROM AUTHOR]

In this paper, we describe and evaluate a new monitor that uses inertial navigation system (INS) measurements to detect spoofing attacks on global navigation satellite system (GNSS) receivers. Spoofing detection is accomplished by monitoring the Kalman filter innovations in a tightly coupled INS/GNSS mechanization. Monitor performance is evaluated against worst case spoofing attacks, including spoofers capable of tracking vehicle position. There are two main contributions of this paper. The first is a mathematical framework to quantify postmonitor spoofing integrity risk. The second is an analytical expression of the worst case sequence of spoofed GNSS signals. We then apply these to an example spoofing attack on a Boeing 747 on final approach. The results show that GNSS spoofing is easily detected, with high integrity, unless the spoofer's position-tracking devices have unrealistic, near-perfect accuracy, and no delays. [ABSTRACT FROM AUTHOR]

This paper describes the first of a two-part research effort to find the optimal detector and estimator that minimise the integrity risk in Receiver Autonomous Integrity Monitoring (RAIM). In this first part, a new method is established to determine a piecewise linear approximation of the optimal detection region in parity space. The paper presents examples suggesting that the optimal detection boundary lays in between that obtained using chi-squared residual-based RAIM, and that provided by Solution Separation (SS) RAIM, as one varies the alert limit requirement. In addition, these examples indicate that for realistic navigation requirements, the SS RAIM method approaches the optimal detection region. The SS RAIM detection tests will be employed in the second part of this work, which focuses on the design of non-least-squares estimators to reduce the integrity risk in exchange for a slight increase in nominal positioning error. [ABSTRACT FROM AUTHOR]

In this paper we introduce a ground monitoring architecture to validate the Integrity Support Message (ISM) parameters to be used by aircraft for Advanced Receiver Autonomous Integrity Monitoring (ARAIM). This work focuses on two critical ISM parameters: Psat, which designates the prior probabilities of satellite faults, and bmax, which is a range domain bound on small faults that may occur at probabilities higher than Psat. We show that the choices of bmax and Psat are not independent. The paper first establishes the relationship between bmax, Psat, Time to Integrity Alert (TIA) and constellation service provider performance commitments. We then provide an example ground monitor design that detects inter-frequency bias faults and code-carrier divergence faults. We show that the performance of the monitor can be used to validate specific bmax and Psat values for ARAIM. [ABSTRACT FROM PUBLISHER]

We present a baseline multiple fault and multiconstellation advanced receiver autonomous integrity monitoring user algorithm for vertical guidance. After reviewing the navigation requirements for localizer performance with vertical guidance down to 200 feet, we describe in detail how to process the pseudorange measurements, the nominal error models, and the prior fault probabilities to obtain the protection levels and other figures of merit. In particular, we show how to determine which fault modes must be monitored and a method for performing fault exclusion. Finally, we present a list of possible algorithm improvements and simplifications. [ABSTRACT FROM AUTHOR]

The advent of multiple Global Navigation Satellite System (GNSS) constellations will result in a considerable increase in the number of satellites for positioning worldwide. This substantial improvement in measurement redundancy has the potential to radically advance receiver autonomous integrity monitoring (RAIM) performance. However, regardless of the number of satellites, the performance of existing RAIM methods is sensitive to the assumed prior probabilities of individual fault hypotheses. In this paper, a new method is developed using Bayes’ theorem to generate upper bounds on posterior probabilities of individual fault hypotheses given current user measurements. These bounds are used in a Bayesian fault-tolerant position estimator (FTE) that minimizes integrity risk. The detection test statistic is a measurement-based integrity risk bound, which is directly compared with a pre-specified risk requirement. The associated challenge of quantifying continuity risk is resolved using a bounding approach, which is also detailed in this work. The new Bayesian FTE method is shown to be more robust to uncertainty in prior probability of fault occurrence than existing RAIM methods. [ABSTRACT FROM PUBLISHER]

This paper describes the design, analysis, and evaluation of new ionospheric measurement error models for high-integrity multiconstellation navigation systems, The robustness of the newly derived models is experimentally evaluated using months of dual-frequency global positioning system (GPS) data collected at multiple locations, In parallel, an integrity analysis is devised to quantify the impact of traveling ionospheric disturbances on user position, Finally, overall carrier phase positioning performance is assessed over continental areas for various combinations of GPS and Galileo and Iridium satellites. [ABSTRACT FROM PUBLISHER]

A significant challenge in fielding space-based and ground-based augmentation systems (SBAS and GBAS) for GPS involves the validation of navigation integrity, which requires the establishment of error bounds for aircraft position. This paper introduces a new approach to validating position-domain integrity by using two-sided envelopes for each ranging source. This paired-bounding approach allows for error distributions of arbitrary form and thus improves on earlier integrity validation approaches restricted to zero-mean, symmetric, and unimodal distributions. [ABSTRACT FROM AUTHOR]

Ground-based augmentations of the global positioning system (GPS) demand the greatest safety and reliability to support aircraft precision approach and landing navigation. One troublesome failure mode for these systems is the possibility of large orbit errors; discrepancies between the locations of GPS satellites in space and the locations derived by the ephemeris data that they broadcast. To counter this possibility, several ephemeris monitor algorithms detecting orbit errors are described. The method is based on a comparison between satellite positions given by the current satellite ephemeris [today's ephemeris (TE)] and the ephemeris broadcast by the same satellite on its preceding pass [yesterday's ephemeris (YE)]. Variants of this YE-TE test are shown to provide protection against ephemeris errors and also to support minimum detectable errors as low as 1145 m, which will minimize the resulting impact on ground-based augmentation system User availability. In addition, to initialize these monitors when no earlier validated ephemerides are available, means of using raw measurements are proposed. The results show that the YF-TE and the measurement-based methods together are adequate to meet navigation integrity and availability requirements for category 1 precision approaches. [ABSTRACT FROM AUTHOR]