A method is presented for real-time validation of GNSS measurements of a single receiver, where data from each satellite are independently processed. A geometry-free observation model is used with a reparameterized form of the unknowns to overcome rank deficiency of the model. The ionosphere error and non-constant biases such as multipath are assumed changing relatively smoothly as a function of time. Data validation and detection of errors are based on statistical testing of the observation residuals using the detection---identification---adaptation approach. The method is applicable to any GNSS with any number of frequencies. The performance of validation method was evaluated using multi-frequency data from three GNSS (GPS, GLONASS, and Galileo) that span 3 days in a test site at Curtin University, Australia. Performance of the method in detection and identification of outliers in code observations, and detection of cycle slips in phase data were examined. Results show that the success rate vary according to precision of observations and their number as well as size of the errors. The method capability is demonstrated when processing four IOV Galileo satellites in a single-point-positioning mode and in another test by comparing its performance with Bernese software in detection of cycle slips in precise point-positioning processing using GPS data.

/pdf/gnss-multi-frequency-receiver-single-satellite-measurement-1vy21z3drz.pdf

GNSS multi-frequency receiver single-satellite measurement validation method

The single receiver single satellite validation method is a technique that screens data from each satellite independently to detect and identify faulty observations. A new method for estimation of the stochastic properties of multi-constellation GNSS observation is presented utilising parameters of this validation method. Agreement of the characteristics of the validation statistics with theory is used as the criterion to select the best precision of the observations, spectral density and correlation time of the unknowns. A curve fitting approach in an iterative scheme is employed. The method is applicable to any GNSS with any arbitrary number of frequencies. Demonstration of the method results and performance is given using multiple-frequency data from GPS, GLONASS and Galileo in static and kinematic modes.

/pdf/estimation-of-multi-constellation-gnss-observation-4uwn71hfn3.pdf

Estimation of multi-constellation GNSS observation stochastic properties using single receiver single satellite data validation method

Satellite navigation is quickly becoming a multidimensional complex challenge, with four Global Navigation Satellite Systems (GNSS) fully or partially deployed, more than 90 GNSS satellites currently in the sky, and 12 open-service GNSS signal types available to the end-user. Research papers about GNSS performance typically focus on single or dual GNSS solutions, and there are still very few papers addressing jointly the four existing GNSS together. It is the goal of our paper to present a unified, fast, modular, and simple-to-program theoretical analysis of the four GNSS, focusing on performance limits in terms of spectral characteristics, tracking, multipath robustness, and positioning accuracy. A unified new compact approach for dealing with all the modulations employed in GNSS is also included.We show a unified generic framework for analyzing the multi-GNSS signals in a fast and simple-to-implement manner, without the need of simulating constellations or gathering measurement data. Our approach is also validated with Spectracom-based constellation data. Our analysis can be used as the starting point in further design process or system analysis.

Accuracy limits in multi-GNSS

Prediction and analysis of GBAS integrity monitoring is important, especially at the airports where a GBAS station it to be installed. Based on existing standard documents and published research, we present a software tool for GBAS availability prediction. Simulations have been conducted that include single point, single approach path, and multiple repetitions of a same approach path in order to analyze the availability of GNSS signal integrity monitoring with a GBAS at LinZhi airport. The results show that the long-term 24-h service availability figure at two typical single points along the approach path for GBAS Approach Service Type C (GAST C) is above 99.999 % for each point, and for GBAS Approach Service Type D (GAST D) at three typical single points, it is lower than 99.8 % for each point. The unavailability percentage over a 24-h period is 0.76 and 2.40 % for GAST C and GAST D, respectively. The results of sensitivity tests show that the impact of the mask angle and the latitude on the GBAS availability at LinZhi airport are more important than that of the constellation. Our conclusions could also be of interest for the implementation of GBAS stations at other plateau airports.

https://hal-enac.archives-ouvertes.fr/hal-00937606/document

Prediction and analysis of GBAS integrity monitoring availability at LinZhi airport

A new type of service has been proposed for Ground Based Augmentation Systems (GBAS) that is intended to support approach and landing operations down to the lowest minimums (i.e., CAT IIIb). Proposed standards for this new service type have been drafted and are currently being validated. This so called GBAS Approach Service Type D (GAST D) includes new low level requirements for monitoring as well as a requirement for additional geometry screening in order to protect the user from failures of several types. This paper discusses how the proposed requirements can be interpreted in order to develop a fault model that describes the magnitude and dynamics of malfunction induced navigation systems errors for malfunctions that are undetected, or prior to their detection. Such a fault model can be used to demonstrate acceptable airplane system level responses to malfunctions as part of airworthiness approvals. The paper includes a review of the types of malfunctions that are anticipated and the monitoring requirements that limit the impact of those malfunctions. Then a dynamic error model is proposed and the parameters of that model are presented for each type of failure. The relationship between the largest undetected errors and the user defined geometry screening is explored for each type of malfunction. Some discussion of how this model is anticipated to be used in the context of airworthiness demonstrations is included. This work represents an important step towards development of airworthiness requirements needed in order for GBAS to support CAT III operations in the future. Copyright © 2012 Institute of Navigation.

/pdf/fault-modeling-for-gbas-airworthiness-assessments-4vmgousuev.pdf

Fault Modeling for GBAS Airworthiness Assessments

A method for guiding an aircraft during its final approach to a landing runway, whereby the aircraft is guided during its approach by aircraft position information obtained from an GNSS satellite navigation system, wherein: prior to the start of the final approach a first time t FAF is determined corresponding with the start of said final approach and a second time t TD corresponding with the landing of the aircraft on said runway, then a set of satellites is determined of the satellite navigation system for excluding from the calculation of said aircraft position information during at least a part of the time interval comprised between said first and second times; and during the final approach, the aircraft position information is determined while excluding the information corresponding with all the satellites of said set of satellites and the aircraft is guided along its final approach path by said position information.

Method and system for determining the position of an aircraft during its approach to a landing runway

Since many years, civil aviation has identified GNSS as an attractive mean to provide navigation services for every phase of flight due to its wide coverage area. However, GPS standalone cannot meet ICAO requirements in terms of accuracy, integrity, availability and continuity, particularly in the case of precision approaches. To achieve improved level of performance, different augmentation systems have been developed aiming at enhancing and monitoring the quality of the Signal-In-Space (SIS). In particular GBAS, for Ground Based Augmentation System, allows guarantying a very high level of performance in a given coverage area surrounding an airport for example.

GBAS NSE model for CAT II/III autoland simulations

Since many years, civil aviation has identified GNSS as an attractive mean to provide navigation services for every phase of flight due to its wide coverage area. However, to do so, GNSS has to meet relevant requirements in terms of accuracy, integrity, availability and continuity. To achieve this performance, augmentation systems have been developed to correct the GNSS signals and to monitor the quality of the received Signal-In-Space (SIS). We can distinguish GBAS (Ground Based Augmentation Systems), ABAS (Airborne Based Augmentation Systems) SBAS (Satellite Based Augmentation Systems). In this context, the aim of this study is to characterize and evaluate the GNSS position error of various positioning solutions which may fulfil applicable civil aviation requirements for GNSS approaches. In particular, this study focuses on two particular solutions which are: • Combined GPS/GALILEO receivers augmented by RAIM where RAIM is a type of ABAS augmentation. This solution is a candidate to provide a mean to conduct approaches with vertical guidance (APV I, APV II and LPV 200). • GPS L1 C/A receivers augmented by GBAS. This solution should allow to conduct precision approaches down to CAT II/III, thus providing an alternative to classical radio navigation solutions such as ILS. This study deals with the characterization of the statistics of the position error at the output of these GNSS receivers. It is organised as following. First a review of civil aviation requirements is presented. Then, the different GNSS signals structure and the associated signal processing selected are described. We only considered GPS and GALILEO constellations and concentrated on signals suitable for civil aviation receivers. The next section details the GNSS measurement models used to model the measurements made by civil aviation receivers using the previous GNSS signals. The following chapter presents the GPS/GALILEO and RAIM combination model developed as well as our conclusions on the statistics of the resulting position error. The last part depicts the GBAS NSE (Navigation System Error) model proposed in this report as well as the rationales for this model.

Use of GNSS signals and their augmentations for Civil Aviation navigation during Approaches with Vertical Guidance and Precision Approaches

For many years, civil aviation has identified GNSS as an attractive means to provide navigation services for every phase of flight due to its wide coverage area. However, to do so, GNSS must meet stringent requirements in terms of accuracy, integrity, availability and continuity. To achieve this performance, augmentation systems have been developed to correct the GPS L1 C/A and to monitor the quality of the received Signal-In-Space (SIS). Different solutions exist depending on where and how the augmentation is implemented. We can distinguish ABAS (Aircraft Based Augmentation Systems), SBAS (Satellite Based Augmentation System) and GBAS (Ground Based Augmentation System). ABAS systems are very interesting as they are autonomous, meaning that no signal external to the aircraft is needed to monitor the SIS thereby reducing the dependency on a ground navaids network. It uses redundant information within GNSS constellation to provide integrity monitoring. It is important to note that unlike other augmentation systems, ABAS does not improve position accuracy. Two types of ABAS systems can be distinguished: Receiver Autonomous Integrity Monitoring (RAIM) where only GNSS information is used, Aircraft Autonomous Integrity Monitoring (AAIM) where information from other on-board sensors is also used. This paper will study the RAIM temporal behavior. Today RAIM and/or AAIM are commonly used to provide integrity monitoring for phases of flight down to Non Precision Approaches using GPS L1 C/A measurements. However, current performance associated with GPS L1 and GPS constellation is not sufficient to meet civil aviation requirements for more stringent phases of flight and in particular, the associated vertical requirements of APV and LPV200. The introduction of new signals and constellations - such as GPS L5 and GALILEO for example - will significantly increase the number of available signals and satellites, the quality of the measurements as well as the quality of constellation geometries. Thus, RAIM may provide a simple means to monitor the quality of the SIS and to reach more stringent phases of flight such as approaches with vertical guidance like APV or LPV200 operations. This possibility has been investigated by the civil aviation community during recent years and RAIM is now foreseen as an interesting candidate to provide integrity monitoring for LPV200. Different algorithms have been studied and their performance, in terms of availability, has been published. It results that RAIM alone does not appear to provide sufficient protection for LPV200 approaches. New possibilities to extend RAIM to APV and LPV200 are under study and it can be reasonably assumed that RAIM using GPS and GALILEO constellations could be used in the near future (Advanced RAIM). Therefore, it appears necessary to address the specific phenomena that will result from the combination of two different constellations in one positioning solution. The aim of this paper is to present a microscopic analysis of the temporal behavior of GPS and GALILEO Navigation System Error (NSE) and RAIM, under various constellations and signal configurations for LPV200 types of operation. Indeed, the use of different types of satellites, the constellation changes, the potential loss of frequencies may imply unexpected behavior of NSE. Thus, the impact of the introduction of this new positioning solution must be investigated so as to limit unwanted effects for aircraft flight control systems which use the GNSS computed position. To enable this study to take place, a GPS/GALILEO + RAIM receiver model has been developed. The first section is a presentation of the receiver model used for the simulations which is composed of the following different modules: an aircraft trajectory generator, the measurement error models, the receiver model, the Position Velocity Time (PVT) module and the integrity monitoring (only RAIM will be used in this study). The receiver model is based on a correlator outputs generator able to model different receiver configurations for several signals and constellations. The error models used as well as the inputs and outputs of the simulator are described. The Least Square Residuals (LSR) RAIM algorithm is also detailed. The second section describes the study case defined for our simulations including various configurations of constellations, signals and approaches as well as the spatial and temporal grid used to evaluate the behavior of NSE. The following section provides a microscopic study of the position error time behavior when using GPS and GALILEO dual frequency, and in the presence of constellation changes. Aircraft maneuvers along the approach will be considered so as to observe their impact on the error. For example, a sharp turn can result in the loss of a satellite due to the antenna pattern. The next section discusses the benefits of using special configurations with respect to the additional complexity and errors introduced. The typical example to study is the resulting benefits from using single frequency on one constellation and dual frequency on the other. On the one hand, additional satellites provide a better geometry but on the other hand single frequency measurements are far less accurate than dual frequency measurements and will therefore introduce additional errors in the positioning solution. This section also investigates the impact of unbalanced numbers of satellites in the two different constellations. Finally, the last section of this paper studies the possibility of using methods such as constellation prediction to prevent unwanted NSE behaviors.

Study of the Temporal Behavior of GPS/GALILEO NSE and RAIM for LPV200

Since many years, civil aviation has identified GNSS as an attractive mean to provide navigation services for every phase of flight due to its wide coverage area. However, GPS standalone cannot meet ICAO requirements in terms of accuracy, integrity, availability and continuity, particularly in the case of precision approaches. To achieve improved level of performance, different augmentation systems have been developed aiming at enhancing and monitoring the quality of the Signal-In-Space (SIS). In particular, GBAS for Ground Based Augmentation System allows guarantying a very high level of performance in a given coverage area surrounding an airport for example. Currently, GBAS is foreseen as an important source of innovation for civil aviation since it has already been certified for CAT I precision approaches and may allow reaching ICAO requirements down to CAT II/III minima, then providing an alternative to ILS. This possibility is actively investigated and ICAO and Industry standardization bodies are currently deriving requirements for GBAS CAT II/III. Autoland simulations for CAT II/III certification require numerous simulations to assess statistically the aircraft capability to autoland. Therefore, it is necessary to identify the GBAS GLS behavior with sufficient fidelity, taking into account physical phenomenon affecting accuracy, continuity and integrity, but still, with adequate limited representativity, assuming that it will feed an autoland simulator dedicated to airworthiness demonstration of aircraft guidance laws. A model has been proposed in the past but the evolution of CAT II/III requirements and the lack of information on the validation methods used make it necessary to investigate further this subject. The goal of this paper is to provide the first steps to the development of a model of GBAS L1 C/A depicting the behavior of the outputs of the system with sufficient fidelity for CAT II/III autoland simulations. Our study is based on the previously proposed model. We focused here on the nominal error model which so far appears to be an adequate representation of GBAS behavior for autoland simulations. However, we propose some improvements to update this model so as to reflect the evolution of the requirements and enhance its representativeness while meeting its primary objective to serve airworthiness demonstration. Moreover, additional simulations have been run to extend this model to Cat III airports all over the world since it has been first developed only for North America.

http://telecom.recherche.enac.fr/data/doc.ltst/2009/Study%20of%20GBAS%20Model%20for%20CAT%20II_III%20Simulations.pdf

Pierre Neri

Papers

Method and system for determining the position of an aircraft during its approach to a landing runway

GBAS NSE model for CAT II/III autoland simulations

Use of GNSS signals and their augmentations for Civil Aviation navigation during Approaches with Vertical Guidance and Precision Approaches

Study of the Temporal Behavior of GPS/GALILEO NSE and RAIM for LPV200

Study of a GBAS Model for CAT II/III Simulations