Showing papers on "GNSS augmentation published in 2007"

Principles of GNSS, Inertial, and Multi-Sensor Integrated Navigation Systems

Abstract: Navigation systems engineering is a red-hot area. More and more technical professionals are entering the field and looking for practical, up-to-date engineering know-how. This single-source reference answers the call, providing both an introduction to overall systems operation and an in-depth treatment of architecture, design, and component integration. This book explains how satellite, on-board, and other navigation technologies operate, and it gives practitioners insight into performance issues such as processing chains and error sources. Providing solutions to systems designers and engineers, the book describes and compares different integration architectures, and explains how to diagnose errors. Moreover, this hands-on book includes appendices filled with terminology and equations for quick referencing.

High-Integrity IMM-EKF-Based Road Vehicle Navigation With Low-Cost GPS/SBAS/INS

Abstract: User requirements for the performance of Global Navigation Satellite System (GNSS)-based road applications have been significantly increasing in recent years. Safety systems based on vehicle localization, electronic fee-collection systems, and traveler information services are just a few examples of interesting applications requiring onboard equipment (OBE) capable of offering a high available accurate position, even in unfriendly environments with low satellite visibility such as built-up areas or tunnels and at low cost. In addition to that, users and service providers demand from the OBEs not only accurate continuous positioning but integrity information of the reliability of this position as well. Specifically, in life-critical applications, high-integrity monitored positioning is absolutely required. This paper presents a solution based on the fusion of GNSS and inertial sensors (a Global Positioning System/satellite-based augmentation system/inertial navigation system integrated system) running an extended Kalman filter combined with an interactive multimodel method (IMM-EKF). The solution developed in this paper supplies continuous positioning in marketable conditions and a meaningful trust level of the given solution. A set of tests performed in controlled and real scenarios proves the suitability of the proposed IMM-EKF implementation as compared with low-cost GNSS-based solutions, dead reckoning systems, single-model EKF, and other filtering approaches of the current literature.

Navigation system and methods for route navigation

Abstract: Embodiments of the present invention include systems and methods for improved navigation using the global positioning system (GPS). A method of improved navigation includes transmitting a destination to a navigation server through a wireless communication channel. The method further includes transmitting position information from a GPS-enabled device to the navigation server through the wireless communication channel automatically at a time interval. The method further includes generating navigation information by the navigation server. The navigation information is based on the position information and the destination. The method further includes receiving navigation information on the GPS-enabled device from the navigation server through the wireless communication channel.

Real-time high accuracy position and orientation system

Abstract: A real-time high accuracy position and orientation system (RT-HAPOS) system for a vehicle, such as an aircraft, comprises a global navigation satellite system (GNSS) receiver disposed on the vehicle and an integrated inertial navigation (IIN) module disposed on the vehicle. The GNSS receiver generates GNSS position data indicating approximate positions of the vehicle during a data acquisition period in which the vehicle is moving. The IIN module executes a real-time kinematic (RTK) algorithm during the data acquisition period to generate output position data indicating positions of the vehicle at a greater precision than the GNSS position data, based on the GNSS position data, inertial measurement data acquired on the vehicle during the data acquisition period, and a set of virtual reference station (VRS) observables received during the data acquisition period from a remote source external to the vehicle, where the VRS observables are based on the GNSS position data.

Fast decimeter-level GNSS positioning

Abstract: Methods and apparatus for processing of data from GNSS receivers are presented. A post-processing engine and a post-processed accuracy predictor are described. The post-processing engine provides high accuracy GNSS (GPS) position determination with short occupation time for GIS applications. The post-processed accuracy predictor calculates during data collection an estimate of the accuracy likely to be achieved after post-processing. This helps to optimize productivity when collecting GNSS data for which post-processed accuracy is important. The predictor examines the quality of carrier measurements and estimates how well the post-processed float solution will converge in the time since carrier lock was obtained.

Ephemeris extension method for GNSS applications

Abstract: Systems, methods and devices for improving the performance of Global Navigation Satellite System (GNSS) receivers are disclosed. In particular, the improvement of the ability to calculate a satellite position or a receiver position where a receiver has degraded ability to receive broadcast ephemeris data directly from a GNSS satellite is disclosed. Correction terms can be applied to an approximate long-term satellite position model such as the broadcast almanac.

Mapping and Survey of Plasma Bubbles over Brazilian Territory

Abstract: Ionospheric plasma irregularities or bubbles, that are regions with depleted density, are generated at the magnetic equator after sunset due to plasma instabilities, and as they move upward they map along the magnetic field lines to low latitudes. To analyse the temporal and spatial evolution of the bubbles over Brazilian territory, the mapping of ionospheric plasma bubbles for the night of 17/18 March 2002 was generated using data collected from one GPS receiver array, and applying interpolation techniques. The impact on the performance of Global Navigation Satellites System (GNSS) and on the Space Based Augmentation System (SBAS) in the tropical regions of the GPS signal losses of lock and of the signal amplitude fades during ionospheric irregularities is presented.

Navigation server, navigation apparatus, and navigation system

Abstract: Provided is a navigation system capable of matching map information used by a navigation apparatus and a navigation server with an appropriate frequency and at an appropriate timing. When there is differential information between the navigation map information and the support map information, index information for identifying the differential information is transmitted from the navigation server to the navigation apparatus and the navigation apparatus outputs preliminary information indicating a brief summary of the differential information generated according to the index information. When a request signal based on a request operation by a user in the navigation apparatus is transmitted from the navigation apparatus to the navigation server, the differential information is transmitted form the navigation server to the navigation apparatus, so that the navigation map information is updated in accordance with the differential information.

Performance Comparison of a Low- Cost Mapping Grade Global Positioning Systems (GPS) Receiver and Consumer Grade GPS Receiver under Dense Forest Canopy

Abstract: corrections to collected data (Leick 2004). The locations of GPS base stations are established using very accurate measurements and base stations continually compare their known locations to positions generated by satellite signals. Any difference between the known and satellite-derived location of the base station is regarded as a positional error and can be used to estimate a correction factor for field-collected GPS data. Through differential correction techniques, survey grade GPS receivers are capable of generating location measurements that are within 1 cm of true position, provided that satellite signal geometry is consistently strong and available over periods of time. However, forest environments feature canopy cover, vegetation, and topography that often preclude the efficient use of survey grade GPS receivers (Wing and Kellogg 2004). Operator skill also is necessary for both hardware and software applications of survey grade GPS receivers and forest conditions often are not suitable for the delicate nature of the equipment. In addition, many measurement applications do not require accuracies that are within 1 cm of true position. Mapping grade GPS receivers represent the middle ground between survey and consumer grade receivers, although prices still may be prohibitive to potential consumers. Costs of mapping grade GPS receivers vary from $2,000 to $12,000 depending on the manufacturer and model. Previous studies have found mapping grade GPS receivers to be capable of acceptable measurement accuracies when working under forest canopies. Bolstad et al. (2005) tested several mapping grade GPS receivers below hardwood canopies in Minnesota and found average errors between 3.0 and 4.8 m for uncorrected measurements, 2.9 m for real-time differentially corrected measurements, and average errors between 2.5 and 4.0 m for postprocessed differentially corrected data. Johnson and Barton (2004) reported nondifferentially corrected mapping grade errors of 20–30 m under a partial hardwood forest canopy in New Hampshire. Naesset and Jonmeister (2002) found positional errors between 2.2 (20-minute observation time) and 5.6 m (2minute observation time) in dense spruce forests in Norway for differentially corrected GPS measurements. Liu (2002) determined an average positional error of 4.0 m under thick hardwood canopies using uncorrected mapping grade GPS data but did not report a study location. The 4.0-m average was based on 17 observations with the average of 180 readings being used to create a location for each observation. Sigrist et al. (1999) determined a differentially corrected root mean square error of 5.1 m under a white pine (Pinus strobus) canopy in north central Indiana based on a 3-hour acquisition time for a single point. Consumer grade GPS receivers are available for several hundred dollars or less and have been found to collect measurements with accuracies that are acceptable for many forestry applications. Wing et al. (2005) found that consumer grade GPS receivers were capable of accuracies within 10 m under closed canopies and 7 m under young forest canopies in western Oregon. Bolstad et al. (2005) tested a consumer GPS receiver under heavy forest canopy (more than 70% sky obstruction) in Minnesota and found average errors of 6.5 and 7.1 m. Karsky at al. (2001) reported average errors of 3–24 m under medium canopy in Montana. Although consumer grade GPS receivers are affordable for many users, they are limited in a number of characteristics. Limitations typical of consumer grade GPS receivers include not being able to set minimum standards for satellite geometry for data collection, a data storage limitation of 500 coordinate pairs, and an inability to differentially correct data after field data collection without third-party software. Differential correction allows errors caused by atmospheric conditions to be addressed and reduced; atmospheric interference is expected to increase in future years. In addition, many consumer grade GPS receivers do not allow users to automatically conduct point averaging and the software that accompanies most consumer GPS is limited in scope. A mapping grade GPS receiver called the SXBlue (GENEQ, Montreal, Quebec, Canada) has become available for about $2,000 and makes use of Bluetooth wireless technology to communicate with a digital data logger. The SXBlue is intended to take advantage of Space-Based Augmentation Systems (SBAS) that are capable of providing conventional real-time differential corrections to GPS receivers as they collect data. Conventional real-time differential uses the more accessible coarse/acquisition satellite signals rather than phase code signals. Although phase code signals have a greater potential for more accurate GPS measurements, continuous and uninterrupted satellite signals are required, conditions which often are not attainable under forest canopy. A SBAS derives separate measurement correction factors (rather than a single factor) for several potential sources of GPS error including atmospheric interference of signals, timing intervals used to estimate satellite signal range (distance), and the tracking of satellite orbital patterns. In the United Sates, there is currently one operational SBAS. This is the US Federal Aviation administration’s Wide Area Augmentation System (WAAS), which featured two operational WAAS satellites during the study period. The satellites operate in geosynchronous orbits with equatorial locations over the Pacific Ocean and northern Brazil. A line of sight between a GPS receiver and a WAAS satellite is necessary for satellite signal reception. Forest canopy, structures, and landforms can effectively block signal reception. In addition, GPS measurement reliability decreases as distance between a GPS receiver and the WAAS satellites increases. Only a single WAAS satellite signal is necessary for a GPS receiver to apply real-time correction factors but reception from two WAAS satellite signals is preferred because a second provides a backup should reception from one satellite become unavailable. In the United States, only western states had the potential to receive signals from both operational WAAS satellites during the study period. Two additional WAAS satellites are anticipated in 2006. Other SBAS include the European Geostationary Navigation Overlay System and the Japanese Multi-Functional Transport Satellite-based Augmentation System. The SXBlue GPS receiver configuration is intended to be compatible with these international SBAS in addition to WAAS. The SXBlue GPS receiver also features a navigation system (COAST Technology) that is designed to allow accurate GPS measurements during times when satellite reception becomes degraded or lost, such as what might occur if data are being collected under a dense forest canopy. The navigation system uses algorithms that are intended to continue applying differential corrections even if real-time connectivity to WAAS is lost. More specifically, errors that would be expected from atmospheric, satellite, and ephemeris conditions are predicted and removed from recorded measurements. For the navigation feature to work, successful reception of differentially corrected satellite signals (WAAS) for up to 5 minutes must occur first. After successful reception, the 10 Journal of Forestry • January/February 2007 GPS receiver is supposed to allow up to 30–40 minutes of data collection before additional signal reception is necessary. Our objectives were to compare the accuracy and reliability of a relatively low-cost mapping grade GPS receiver operating in two different data collection modes with a consumer GPS receiver collecting measurements under a dense forest canopy. The mapping grade GPS receiver measurements were collected in autonomous mode and also through real-time differential corrections as supplied by WAAS for comparison. We synchronized measurement times for both GPS receivers and used a point averaging benchmark (the average of 60 points collected at one-second intervals) that should present field-collection efficiencies for those who collect measurements under canopy cover. In addition, we were interested in determining whether the SXBlue’s navigation system capabilities would enable us to collect accurate GPS measurements when satellite signal reception was not initially available.

Pedestrian navigation with high sensitivity GPS receivers and MEMS

Abstract: Following a brief introduction to pedestrian navigation and dead-reckoning methods, the characteristics of the current global navigation satellite system (GNSS), namely the US global positioning system (GPS), and its suitability for pedestrian navigation are reviewed. Error sources affecting system performance under both line-of-sight and attenuated signal conditions are described. Attenuated signals can now be acquired and tracked under certain indoor environments, but accuracy and other performance measures are degraded. Pedestrian navigation examples under the forestry canopy and indoor are used to show not only performance but also performance variability as a function of the environment. The use of micro-electro-mechanical systems (MEMS) to aid GPS is introduced. Their advantages and limitations are described through the use of an urban canyon test in a city core, a very harsh RF environment due to signal multipath. It is found that although MEMS aiding substantially improve performance, test conditions have a major impact on actual performance. As a consequence, enough test results are not available at this time to fully characterize performance as a function of the environment due to the high variability of the latter. Accuracy, for instance, varied between 15 and 150 m in the few tests deported herein. Finally, a few predictions are made regarding potential future improvements.

Ionospheric studies for the implementation of GAGAN

Abstract: Satellite Based Augmentation System (SBAS), being developed by Indian Space Research Organization (ISRO) in collaboration with Airports Authority of India (AAI) is known as “GPS Aided GEO Augmented Navigation” (GAGAN). It is expected to offer better accuracy and integrity of navigation service than with GPS alone by providing correction terms to the GPS signals. This is achieved by modelling a Near Real Time Grid Based Ionospheric Delay Model for correcting propagation delay at 1575.42 MHz (L1) using measurements at 1575.42 and 1227.6 MHz (L2). Existing algorithms are replaced by Kriging based model to meet the requirement of correction with 0.5 m maximum residue over Indian region. Details of the data collection and pre-processing, including estimation of the Total Electron Content (TEC), which is a measure of ionospheric delay, has been described. Kriging algorithm and some preliminary results of studies are also presented in this paper. This includes the spatial decorrelation of the stochastic random field over the deterministic variation of ionospheric TEC. Its variation with time and locations are investigated and a temporal dependence found to exist. Large scale ionospheric irregularities and depletions that cause severe amplitude and phase scintillations are also studied. Their impacts on GAGAN are also shown. Some major scientific studies required to be carried out over Indian region to improve the GAGAN performance is discussed.

GPS satellite and receiver instrumental biases estimation using least squares method for accurate ionosphere modelling

Abstract: The positional accuracy of the Global Positioning System (GPS) is limited due to several error sources. The major error is ionosphere. By augmenting the GPS, the Category I (CAT I) Precision Approach (PA) requirements can be achieved. The Space-Based Augmentation System (SBAS) in India is known as GPS Aided Geo Augmented Navigation (GAGAN). One of the prominent errors in GAGAN that limits the positional accuracy is instrumental biases. Calibration of these biases is particularly important in achieving the CAT I PA landings. In this paper, a new algorithm is proposed to estimate the instrumental biases by modelling the TEC using 4th order polynomial. The algorithm uses values corresponding to a single station for one month period and the results confirm the validity of the algorithm. The experimental results indicate that the estimation precision of the satellite-plus-receiver instrumental bias is of the order of ±0.17 nsec. The observed mean bias error is of the order −3.638 nsec and −4.71 nsec for satellite 1 and 31 respectively. It is found that results are consistent over the period.

Mitigating the Effect of Multiple Outliers on GNSS Navigation with M-Estimation Schemes

Abstract: As GNSS has been increasingly used in a wide range of applications, including safety-of-life and liability critical operations, it is essential to guarantee the reliability of the GNSS navigation solutions. Although a number of GNSS Receiver Autonomous Integrity Monitoring (RAIM) algorithms have been developed, a reliable procedure to mitigate the effects of multiple outliers on the navigation solutions is still lacking. In this paper, a robust Least Squares estimation scheme (called M-estimation) is investigated to demonstrate its potential in improving the reliability of the GNSS navigation solutions. We have analysed the theoretical background for M-estimation procedures, which include 1) Huber scheme and 2) IGGIII scheme. Then, some detail simulations and analyses with integrated GPS/Galileo constellation have been carried out to evaluate the performances of the M-estimation schemes in the case of multiple outliers. In the simulated scenario with 14 satellites, the effects of up to 4 outliers can be successfully mitigated with the M-estimation procedures, whilst the classic least-squares solutions are significantly biased. These results from the initial studies are encouraging and indicating the potentially promising strategy to address the multiple outlier issues within multi-constellation GNSS navigation systems.

Ephemeris expansion system and utilization method in gnss

Abstract: PROBLEM TO BE SOLVED: To provide a system, a method, and a device for improving the performance of the receiver of a Global Navigation Satellite System (GNSS), and especially for improving the capacity for calculating the position of a satellite or that of a receiver, when the capacity of the receiver for direct reception of the ephemeris data broadcasted from the GNSS satellite has deteriorated. SOLUTION: A correction term is applied to a generally long-term satellite position model, such as an almanac that is being broadcasted. COPYRIGHT: (C)2008,JPO&INPIT

Space Weather influence on satellite based navigation and precise positioning

Abstract: Global Navigation Satellite Systems (GNSS) are widely used to measure positions with accuracies ranging from a few mm to about 20 m. The effect of the Earth ionosphere on GNSS signal propagation is one of the main error sources which limits the accuracy and the reliability of GNSS applications. In particular, disturbed Space Weather conditions can be the origin of strong variability in the ionosphere Total Electron Content (TEC) which itself degrades the accuracy of GNSS applications. Space Weather effects on GNSS depend very much on the type of application. In this paper, we discuss the effects of Space Weather conditions on differential positioning with the Differential GPS (DGPS) technique and on relative positioning with the Real Time Kinematic (RTK) technique. We show that DGPS is affected by medium to large-scale gradients in TEC mainly observed at solar maximum when RTK will be degraded by smaller-scale ionospheric variability due to scintillations, TEC noise-like behaviour and Travelling Ionospheric Disturbances

The "System of Systems" Receiver: an Australian Opportunity?

Abstract: In the near future, there could be as many as four global navigation satellite systems (GNSS) and three regional navigation satellite systems (RNSS). This paper examines the visibility of these systems, identifying Australia as a good location to view all of them. The impacts on receiver design are also examined at sub-system level, revealing that a “system of systems” receiver would be far more sophisticated than a basic GPS L1 receiver.

An overview of GBAS integrity monitoring with a focus on ionospheric spatial anomalies

Abstract: The Local Area Augmentation System (LAAS) or, more generally, the Ground Based Augmentation System (GBAS), has been developed over the past decade to meet the accuracy, integrity, continuity and availability needs of civil aviation users. The GBAS utilizes a single reference station (with multiple GNSS receivers and antennas) within an airport and provides differential corrections via VHF data broadcast (VDB) within a 50-km region around that airport. This paper provides an overview of GBAS integrity verification, explaining how integrity risk is allocated to various potential safety threats and how monitors are used to meet these allocations. In order to illustrate GBAS integrity monitoring in detail, this paper examines the potential threat of ionospheric spatial anomalies (e.g., during ionospheric “storms”) to GBAS and how GBAS protects users against this threat. In practice, the need to mitigate potential ionospheric anomalies is what dictates CAT I GBAS availability.

Exploiting GNSS signal structure to enhance observability

Abstract: There are a number of different error sources, such as multipath and thermal noise, which corrupt satellite navigation waveforms from their theoretical structure. However, even under ideal conditions the broadcast signals have some degree of deformation as a result of the practical individual hardware implementation. For the most demanding users of satellite navigation, such as aircraft navigation and landing systems, it is important to characterize the nominal signal structure in order to detect minimal variations resulting from hardware-based errors. Thus far such precorrelation Global Navigation Satellite System (GNSS) signal quality monitoring has been performed through high gain antennas, which allow for raising the GNSS spectrum above the thermal noise floor and observing the structure of the signal directly at the front end output. This paper describes a new approach to achieve such observability based on signal processing techniques, such as dithering and averaging, which leverage the repetitive nature of the GNSS signal. The paper presents how these techniques can drastically improve the signal-to-noise ratio (SNR) in postprocessing, allowing for the direct analysis of GNSS signals using traditional front end designs and conventional antennas. Results are predicted using the appropriate theory and validated using data collected from the Global Positioning System (GPS).

Ajax GIS application for GNSS availability simulation

Abstract: This paper describes an Ajax (Asynchronous JavaScript and XML) GIS (geographic information system) application for the simulation of GNSS (Global Navigation Satellite System) availability in dense urban areas. In the forthcoming GNSS environment, satellite visibility will be greatly increased owing to the integration of multiple GNSSs such as the American GPS (Global Positioning System), the Russian GLONASS (Global Navigation Satellite System), the European Union’s GALILEO, and the Japanese QZSS (Quasi-Zenith Satellite System). However, in dense urban areas, the improvements of position accuracy may be limited because obstruction of the signal by high buildings results in bad geometries and multipath effects. To evaluate the spatiotemporally varying availability of GNSS positioning, we built an estimation model that computes the number of visible satellites, the values of DOP (dilution of position), and the amount of multipath errors, according to the location and time of a user. Then, the GNSS availability components were visualized in an Ajax-based Web application that provides a desktop-like interactiveness through the asynchronous data transfer between client and server. This Web simulation shows when and where the navigation services by integrated GNSS are available or appropriate in urban canyons. As a feasibility test, we demonstrated an experimental simulation for the Shinjuku ward of Tokyo filled with skyscrapers.

Sbas correction information in ms based agps system

Abstract: A method for providing a mobile station, being connected to a wireless communication system, with GPS assistance data, comprises obtaining (210) of correction data of a satellite based augmentation system. The method further comprises obtaining (220) of assistance data of an assisted global positioning system. Modified values of standard parameters of either assistance data of the assisted global positioning system or correction data of differential global positioning system, or both, are determined (230) from the correction data of the satellite based augmentation system in dependence on the assistance data of the assisted global positioning system. The modified values of the standard parameters are transmitted (240) from the core network to the mobile station. A node implementing the method and a system comprising such a node are also presented.

Method and device for mojnitoringthe integrity of information provided by a hybrid ins/gnss system

Abstract: The invention relates to the monitoring of the integrity of position and speed information resulting from a hybridisation between an inertial unit and a satellite positioning receiver. The invention more precisely relates to navigation equipment known in the art as a closed-loop hybrid INS/GNSS system (from 'Inertial Navigation System' and 'Global Navigation Satellite System').

GNSS markets and applications

Abstract: Introduction. Brief History of Today's GNSS. Future GNSS and SBAS. GNSS Business and Markets. Government Policies for GNSS. Future GNSS Markets. Air and Space Applications. Maritime Applications. Land Applications. Mapping and GIS. Military Applications. GNSS Industry and Financial Results. Appendices.

Wide Area Augmentation System (WAAS) - Program Status

Abstract: The FAA, the International Civil Aviation Organization (ICAO), RTCA, Inc., and other members of the civilian aviation community have agreed to use Global Navigation Satellite System (GNSS) technology as a key means of next generation radio navigation for aviation. GPS provides a practical starting point for the GNSS. However, GPS cannot satisfy all civil aviation requirements for navigation and landing without augmentation to improve its accuracy, integrity, continuity, and availability. Satellite Based Augmentation System (SBAS) and Ground Based Augmentation System (GBAS) are two augmentation methods to GNSS that are actively pursued by the international community. WAAS, the US version of the ICAO GNSS SBAS, increases the accuracy, continuity, availability, and integrity of GPS data, with concomitant improvements to air traffic system capacity and safety. WAAS also provides aviation service far exceeding that of currently fielded navigational aids. The FAA restated its commitment to WAAS in the Navigation and Landing Transition Strategy released in September 2002. It reinforced WAAS as the cornerstone Area Navigation (RNAV) system for the foreseeable future that can be used for all phases of flight including terminal-area navigation (e.g., departure procedures and standard terminal arrival procedures), en route flight, and instrument approach procedures (approaches with and without vertical guidance). In 2006, the FAA Navigation Directorate developed the FAA Navigation Roadmap. This roadmap identifies WAAS as a key component to achieve optimum runway capacity. WAAS is capable of providing service equivalent to Category I (CAT I) precision approach capability at airports with appropriate infrastructure, and vertically guided approaches to runways without existing instrument procedures. WAAS provides an en-route navigation and approach landing capability (lateral and vertical guidance) that: 1. Improves safety by reducing the likelihood of controlled flight into terrain on approach, 2. Increases the number of runway ends that are eligible for approach procedures, and 3. Provides increased RNAV capability compared to unaugmented GPS. This paper discusses WAAS operational performance requirements along with status of all phases of WAAS program (from 2003 – 2028).

L5 Satellite Based Augmentation Systems Protection Level Equations

Abstract: The current L1 Space Based Augmentation System (SBAS) protection level equations were agreed upon nearly a decade ago. These equations are provided for L1-only users and are based upon covariance propagation of zero-mean gaussian errors. While this description is reasonably accurate for some nominal error sources, it is not always a good model for actual error characteristics. When departures from the zero-mean gaussian model are significant, the broadcast confidence terms must be inflated in order to provide protection for all user geometries. This leads to a loss of availability even for users who do not observe the satellite with the problematic errors. Since these equations were first adopted, a significant amount of work has gone into accurate characterization of the error sources and the treatment of non-zero and non-gaussian errors. New SBAS signals planned for the L5frequency offer an opportunity to revisit these decisions and make changes to improve integrity and availability.

Technical Limitations of GNSS Receivers in Indoor Positioning

Abstract: This paper presents an overview of aspects that have to be taken into account in use of GNSS receivers for positioning in the difficult environment, for example indoors. The performing position determination and navigation tasks in such environments come nowadays more and more in the focus of the GNSS community. The GNSS signal indoor reception is affected by strong attenuation and due to the nature of the environment by strong multipath. The paper discusses both of them and their possible impact to the navigation tasks. The effect of the user movement is discussed and the experimental measurements are presented. The measurements were realized with use of experimental GNSS software receiver, described in the paper as well.

Recursive Detection, Identification and Adaptation of Model Errors for Reliable High-Precision GNSS Positioning and Attitude Determination

Abstract: High precision applications of Global Navigation Satellite Systems (i.e., GPS, GLONASS and GALILEO) are based on resolution of the carrier phase ambiguities. Only if these ambiguities can be reliably resolved, secure position and/or attitude information can be guaranteed. Hence it is very important that the GNSS data are cleaned for possible model errors, such as outliers and/or slips. This paper describes a rigorous procedure for the real-time statistical testing and quality control of both GNSS observations and the integer phase ambiguities. The performance of the procedure will be demonstrated using kinematic GPS data.

Design of an aircraft landing system using dual-frequency GNSS

Abstract: In the civil aviation community, there is a strong demand for new all-weather navigation aids to support aircraft precision approach and landing. The Local Area Augmentation System (LAAS) developed by the U.S. Federal Aviation Administration (FAA) is one such navigation aid that uses the Global Positioning System (GPS) as a means to estimate aircraft locations. As a safety-of-life system, LAAS is required to provide very high levels of accuracy, integrity, continuity, and availability. In particular, the integrity requirement of one undetected navigation failure in a billion approaches has been the most critical challenge for realizing and certifying this system. Tremendous efforts have been devoted to develop methods to guarantee integrity in the presence of various potential anomalies that might threaten LAAS-aided landing. Currently, almost all these risks are sufficiently mitigated by existing integrity methods. One issue that remains is the risk due to ionosphere anomalies. The central focus of this research is to create and evaluate a method that fully mitigates the safety risk due to ionosphere anomalies. To defend against ionosphere anomalies, this dissertation introduces novel integrity algorithms that take advantage of GPS modernization. Currently, GPS is undergoing major changes to enhance civil and military user capabilities, and these improvements include adding new GPS civil signals. The frequency diversity obtained from these additional signals makes possible multiple-frequency techniques, among which this research focuses on two types of dual-frequency carrier-smoothing methods: Divergence-Free Smoothing, and Ionosphere-Free Smoothing. Using combinations of these two smoothing methods, this research designs integrity algorithms for ionosphere v anomalies that satisfy the integrity requirements for Category II and III precision approach. The first algorithm introduced in this dissertation is based on Ionosphere-Free Smoothing. Simulations show that this algorithm can only obtain 96% to 99.9% availability at best over a broad region of Conterminous United States (CONUS). However, a key benefit of this algorithm is that the resulting availability is not a function of the ionosphere condition. The second algorithm, in contrast, is based on DivergenceFree Smoothing. Simulations show that this algorithm will achieve more than 99.9% availability over more than 70% of CONUS under nominal ionosphere conditions. However, it has the potential to lose availability under severe ionosphere conditions. Taking advantage of these two algorithms, this research introduces a LAAS system architecture that implements both Ionosphere-Free Smoothing and Divergence-Free Smoothing and switches between them based on the best estimate of the current ionosphere state obtained by an ionosphere monitor that is also designed in this research. With this “hybrid” architecture, Category III LAAS can achieve more than 99.9% availability over more than 70% of CONUS under nominal ionosphere conditions and more than 96% availability over 100% of CONUS under severe ionosphere conditions while meeting all integrity requirements.

Airport Surface Movement - Performance Requirements, Architecture Considerations & Integrity Algorithms

Abstract: Satellite Navigation has become increasingly important in the optimisation of efficiency and safety within the aviation industry. ANASTASIA (Airborne New and Advanced Satellite techniques and Technologies in A System Integrated Approach) is a European Commission project within the Sixth Framework Program, with the basic objectives to define and implement future (beyond 2010) communication and navigation avionics based on satellite services. The objectives are to be achieved by exploiting the multi-constellation and multi-frequency architectures in combination with multiple onboard sensors, to provide a worldwide gate-to-gate service. Included in the objectives is a study of the most stringent navigation system performance requirements for a surface movement functionality under zero visibility conditions. This paper reviews existing navigation system performance requirements and compares them with those derived in this paper based on operational requirements, for each airport category. The stringency of the performance requirements suggests that the code-based GBAS architecture currently under development for CAT III landings may not be able to meet all the requirements of surface movement, and that carrier-phase based techniques may be required. In order to address the very stringent integrity requirements of surface movement, this paper uses a novel carrier-phase RAIM (C-RAIM) algorithm developed at Imperial College London, based upon a multiple set separation method with a multiple failure detection and exclusion capability [1]. The C-RAIM algorithm performance is dependent upon the range measurement uncertainties. For relative or differential measurements (e.g. GNSS augmented by GBAS), uncertainties in the measurements by the reference station and the user, as well as the error decorrelation between these measurements contribute to the overall measurement uncertainty at user level. The principal sources of uncertainty are noise, multipath, the troposphere and the ionosphere, the latter being of particular concern for surface movement. In order to accurately determine the ionosphere error residuals in real-time, and hence mitigate integrity risks and optimise availability, this paper develops a ground-based monitoring architecture, which we have called Extended GBAS (E-GBAS), based upon a modified GBAS CAT III architecture. The performance of the C-RAIM algorithm is analysed, using as input the ionosphere uncertainty provided by the E-GBAS, taking into account the specificities of the airport environment. Initial results suggest that the CRAIM algorithm, in combination with the E-GBAS architecture, will be able to meet the surface movement performance requirements. A value added outcome is that when used in combination with a state-of-the-art codebased architecture, the E-GBAS monitoring architecture has the potential to meet the navigation system performance requirements for CAT III landings.

Communications and GNSS based Navigation: A Comparison of Current and Future Trends

Abstract: This paper gives an overview on communications system based and global navigation satellite system (GNSS) based navigation. Starting from the physical layer model of a mobile communications or navigation receiver, we highlight similarities and differences between the two receivers. We explain navigation principles for timing measurements and present the possible navigation accuracies of different communications systems and GNSSs. Finally, we examine synergies of combined receivers and systems.