Showing papers on "GNSS augmentation published in 2005"

Land mobile GNSS availability and multipath evaluation tool

Abstract: Applications of global navigation satellite system (GNSS) in land transportation systems are already extensively deployed and will certainly continue to grow especially in the framework of intelligent transport systems. However, one of the best-known drawbacks of such a system is the lack of satellite visibility in dense urban areas as well as in some specific embedded railway environments. This restricts considerably GNSS use for extended safety related applications. In this paper, a new tool is proposed to predict the availability of a satellite constellation from the point of view of the land transportation user. Knowing the trajectory of a land vehicle, the tool predicts the number of satellites that will be received and produces a safety criterion able to qualify the GNSS localization result. A first version of the tool, already in operation, merges an image processing approach providing the knowledge of the land environment, and the output of a satellite tracking program predicting satellite positions in the sky. This allows us to determine, using a simple optical approach, the number of satellites received in line-of-sight or blocked, with regard to the nearby environment of the receiving antenna. Results obtained in railway as well as in road environments show that satellite signals received by multipath are often used by GNSS receivers in the localization process. Thus, propagation characteristics of the satellite signals in an urban canyon configuration were characterized to determine when a signal received by reflected ray is used by the receiver or not. A criterion related to the satellite elevation is defined to improve the overall performance of the predictive tool. Comparisons with real measurements are commented on. Both simulations and measurements are very similar.

6DoF SLAM aided GNSS/INS Navigation in GNSS Denied and Unknown Environments

Abstract: This paper presents the results of augmenting 6DoF Simultaneous Localisation and Mapping (SLAM) with GNSS/INS navigation system. SLAM algorithm is a feature based terrain aided navigation system that has the capability for online map building, and simultaneously utilising the generated map to constrain the errors in the on-board Inertial Navigation System (INS). In this paper, indirect SLAM is developed based on error analysis and then is integrated to GNSS/INS fusion filter. If GNSS information is available, the system performs feature- based mapping using the GNSS/INS solution. If GNSS is not available, the previously and/or newly generated map is now used to estimate the INS errors. Simulation results will be presented which shows that the system can provide reliable and accurate navigation solutions in GNSS denied environments for an extended period of time.

Ubiquitous Positioning Technologies for Modern Intelligent Navigation Systems

Abstract: Recently new location technologies have emerged that can be employed in modern advanced navigation systems. They can be employed to augment Global Navigation Satellite System (GNSS) positioning techniques and dead reckoning as they offer different levels of positioning accuracies and performance. An integration of other technologies is especially required in indoor and outdoor-to-indoor environments. The paper gives an overview of the newly developed ubiquitous positioning technologies and their integration in navigation systems. Furthermore two case studies are presented, i.e., the improvement of land vehicle safety using Augmented Reality (AR) technologies and pedestrian navigation services for the guidance of users to certain University offices. In the first case study the integration of map matching into a Kalman filter approach is performed (referred to as “Intelligent Vehicle Navigation”) and its principle is briefly described. This approach can also be adapted for the pedestrian navigation service described in the second case study.

Method and system for providing GNSS navigation position solution with guaranteed integrity in non-controlled environments

Abstract: The invention relates to a method and to a system for providing a Global Navigation Satellite System (GNSS) navigation position solution with guaranteed integrity in non-controlled environments, said guaranteed integrity based on protection levels; the method comprises: - processing a Global Navigation Satellite System (GNSS) signal to obtain carrier phase and pseudoranges measurements, - carrying out a pre-processing of said measurements in order to detect and characterize local errors in said measurements, said characterization including providing error bounds, and providing a set of measurements rejections when said characterization is not possible; - using said error bounds, together with those already provided by the signal itself about satellite and ionospheric errors, in a weighted Receiver Autonomous Integrity Monitoring (RAIM) algorithm in order to compute position coordinates and associated protection levels.

Multi-modal navigation system and method

Abstract: A multi-modal navigation system is presented. The navigation system is multi-modal as it provides navigation information (including routes, maps, directions, and navigation instructions) for a plurality of transportation modes including, but not limited to, automobiles, pedestrian walking, trains, subways, and the like. The multi-modal navigation system may be embodied in integrated navigation devices, as stand-alone navigation systems on a variety of computing devices, as a navigation service on a computing device or as a Web service, and the like. The multi-modal navigation system includes route data for a plurality of transportation modes. Route data for the plurality of transportation modes may be integrated, may be separately available, or any combination thereof.

The ionospheric impact of the October 2003 storm event on Wide Area Augmentation System

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

CN/sub 0/ estimation and near-far mitigation for GNSS indoor receivers

Abstract: This paper covers two key points in indoor and dense-urban positioning using Global Navigation Satellite Systems: CN/sub 0/ estimation, and near-far estimation problem. For the former, a novel CN/sub 0/ estimator adequate to deal with the low signal levels encountered in indoor and dense-urban environments is described. For the latter, the results of a novel near-far problem mitigation technique are presented. Both simulations and live data have been used to illustrate the advantages of the proposed algorithms.

Method and apparatus for providing integrity information for users of a global navigation system

Abstract: The invention relates to a method for providing integrity information for users of a global navigation system, which comprises several space vehicles like satellites transmitting information to a device for position detection, wherein the transmitted information comprises a first information from the global navigation system about the accuracy of a signal in space error SISE of a faulty space vehicle and a second information whether the global navigation system assesses the faulty space vehicle as faulty or not. In contrast to known methods for providing integrity information in a global navigation system like Galileo which are based on the assumption that faults can be always detected, the invention is based on the assumption how exact a fault can be detected. Thus, the performance the global navigation system can be increased. Also, no unfounded assumption is used which improves the quality of service.

Global navigation satellite system (GNSS) receivers based on satellite signal channel impulse response

Abstract: A Global Navigation Satellite System (GNSS) receiver and associated method for the reception and processing of GNSS signals. The GNSS receiver includes an antenna and an analog front-end to intercept the incoming radio-frequency signal and to convert it to an appropriate intermediate frequency for digital sampling. A baseband signal processor is organized into functionally identical channels, each dynamically assigned to a different satellite visible. The baseband signal processor processes the signal samples to generate the satellite signal channel impulse response for a number of Doppler frequency shifts. This results in a two-dimensional delay-Doppler map of satellite signal responses from which the baseband signal processor extracts the code time and carrier phase and frequency parameters as well as navigation data for timing, positioning, and environment mapping in the data processor.

A Method of Over Bounding Ground Based Augmentation System (GBAS) Heavy Tail Error Distributions

Abstract: The purpose of this paper is to describe a statistical method for modelling and accounting for the heavy tail fault-free error distributions that have been encountered in the Local Area Augmentation System (LAAS), the FAA's version of a ground-based augmentation system (GBAS) for GPS. The method uses the Normal Inverse Gaussian (NIG) family of distributions to describe a heaviest tail distribution, and to select a suitable NIG family member as a model distribution based upon a statistical observability criterion applied to the FAA's LAAS prototype error data. Since the independent sample size of the data is limited to several thousand and the tail probability of interest is of the order of 10−9, there is a chance of mismodelling. A position domain monitor (PDM) is shown to provide significant mitigation of mismodelling, even for the heaviest tail that could be encountered, if it can meet certain stringent accuracy and threshold requirements. Aside from its application to GBAS, this paper should be of general interest because it describes a different approach to navigation error modelling and introduces the application of the NIG distribution to navigation error analysis.

Fixed Wing UAV Navigation and Control Through Integrated GNSS and Vision

Abstract: With the rapid deployment of Unmanned Airborne Vehicles (UAVs) into new applications, the pressure to extend the capabilities of current platforms is increasing. Increased capabilities, however, should preferably not come at the cost of increased aircraft size. In order to strive towards a more capable platform, the UAV must become increasingly aware of its current state (control, navigation and health) and surroundings (location of other aircraft, airspace boundaries, weather and terrain). This paper reports on the results of research into providing a new level of situational awareness to the UAV that is low in cost and complexity. In particular the paper investigates the unique benefits that can be obtained from the integration of a GNSS sensor and a forward-looking vision sensor. The motivation for this investigation is the belief that both GNSS and vision will be integral features of future UAV avionics architectures: GNSS to provide basic aircraft navigation; and vision to provide for obstacle, and aircraft collision avoidance. This paper will present results showing that when single-antenna GNSS measurements are combined with information derived from optical flow techniques, a number of unique synergies emerge. Sensor accuracies and simulated flight control results are presented based on a comprehensive Matlab® Simulink® model which creates an optical flow stream based on the simulated flight of an aircraft. The paper establishes the promise of this novel integrated GNSS/Vision Sensor Suite approach for use as a complete UAV sensor package, or as a backup sensor for an inertial navigation system.

Estimation of satellite-based augmentation system grid size at low latitudes in the indian zone

Abstract: The Total Electron Content (TEC) measured from a station situated near the northern crest of the equatorial anomaly is compared with that obtained from models such as the Parameterized Ionospheric Model (PIM 1.6) and International Reference Ionosphere (IRI-95) for well over one solar cycle (1977–1990). The limitations of conversion from vertical to slant TEC and vice versa as required for GPS ionospheric corrections in the equatorial region are discussed. It is found that the correspondence among the vertical TEC at the ionospheric pierce point, geometrically (sec χ) converted slant TEC, and slant TEC along a GPS signal propagation path becomes poor for elevation angles of less than 80 deg. Based on this finding, an optimum grid size for reliable operation of the Satellite-Based Augmentation System (SBAS) in the Indian subcontinent (GAGAN, or GPS and Geo Augmented Navigation) is estimated. The suggested grid size is much smaller than the standard 5 × 5 deg.

Extreme ionospheric storms and their impact on WAAS

Abstract: Satellite-based augmentation systems (SBAS) in the absence of selective availability, the ionosphere represents the largest source of positioning error for single-frequency users of the Global Positioning System (GPS).

Reat-time WaveSmooth™ error mitigation for Global Navigation Satellite Systems

Abstract: WaveSmooth™ is a technique to mitigate inherent measurement error for GNSS signals. The WaveSmooth™ technique can be applied for single-frequency or multi-frequency GNSS users. For single-frequency GNSS users, WaveSmooth™ enables smoothing of GNSS measurements, in real-time using wavelets without introducing significant ionosphere divergence. For multi-frequency GNSS users, the WaveSmooth™ technique effectively mitigates multipath error in a real-time fashion. The WaveSmooth™ techniques utilizes wavelet aided methods and operate on the GNSS Code minus Carrier (CmC) signal to mitigate inherent GNSS measurement errors in a real-time fashion to improve the performance of these GNSSs. The WaveSmooth™ error mitigated pseudorange measurement can be used, along with the original carrier phase measurement for a high performance user solution.

Ionospheric scintillation and impact on GNSS users in Northern Europe: Results of a 3 year study

Abstract: The IESSG, at the University of Nottingham, first initiated studies on the effects of ionospheric scintillation and Total Electron Content (TEC) gradients on GNSS users late in 2000. A network of four state-of-the-art GPS Ionospheric Scintillation Monitor receivers was set up in June 2001 to collect GPS phase and amplitude scintillation parameters, as well as TEC data, forming a Northern European monitoring network. Investigations were then carried out involving in particular the analysis of standalone GPS, DGPS, EGNOS aided DGPS and carrier phase user errors, which have been correlated with observed scintillation levels and with geomagnetic indices. A comprehensive statistical analysis was carried out, aiming to characterise ionospheric scintillation over Northern Europe. Amongst many results from our study, which mostly covered our 2002 data archive, analyses of occurrence of high levels of scintillation disturbing simultaneously a number of satellites showed that, on a day of enhanced geomagnetic activity, for up to nearly 2p of the time, two satellites may be concurrently affected. If it can be shown that scintillation levels over a certain threshold will lead to receiver loss of lock on satellites, then in addition to constellation geometry degradation, this may prove crucial during periods when only 4 or 5 satellites are in view. This scenario, of simultaneous failure of a number of satellites, is the consequential situation most likely to impact on the user community in Northern Europe, especially those involved in safety-critical applications. Also, SBAS (Satellite Based Augmentation Systems) reference stations may be adversely affected during these periods of time as they rely on both GPS carriers (L1 and L2) to compute ionospheric delay corrections for dissemination to users. This paper focuses on our latest results and includes further analyses involving isolated geomagnetically active periods as well as statistical analyses covering a larger part of our data archive (2002-2003), which have recently been carried out aiming to better establish the implications of ionospheric scintillation for GNSS users during the high of the solar cycle.

Support infrastructures based on high altitude platforms for navigation satellite systems

Abstract: In this article the use of an augmentation system based on high altitude platforms (HAPs) for supporting global navigation satellite systems is discussed. In fact, HAP-based systems are being studied and designed for several communication applications, but they can also be considered added value infrastructure if integrated with navigation systems, providing aiding services based on terrestrial stations or geostationary satellites. The article investigates the results of a feasibility study for the design of a stratospheric pseudo-satellite to provide additional ranging signal to improve the accuracy and availability of the overall navigation system, and an effective integrity service, strengthening the reliability of the positioning procedures. The work here presented discusses issues that have arisen in the design, and provides simulation performance of the proposed architecture.

Determining usability of a navigation augmentation system

Abstract: In one aspect, the invention is the system for assessing a navigation augmentation environment. The system includes a reference station for receiving messages from a satellite. The reference station has a known position. The system also includes a simulator for simulating an augmentation system by determining corrections based on the messages received and the known position of the reference station. The system further includes a monitoring system to render the corrections to a user in a form enabling determination of the usability of the augmentation system in the navigation augmentation environment.

Development of Navigation Algorithm to Improve Position Accuracy by Using Multi-DGPS Reference Stations’ PRC Information

Abstract: In this paper, the linearly interpolated PRC (Pseudorange Correction) regenerating algorithm was applied to improve the DGPS positioning accuracy at user's position by using the various PRC information obtained from multi-DGPS reference stations. The unknown user's position can be calculated from the regenerated PRC which can be expressed as the linear combination of multi-DGPS reference station's known position and PRC values of common satellite from multi- DGPS reference stations. Two sets of 3 DGPS reference stations were selected to compare the performance of the linearly interpolated PRC regenerating algorithm. To test the performance, linearly interpolated PRC regenerating algorithm adopted multi-channel DGPS receiver was developed. The results show that the DGPS positioning accuracy is improved by about 40% and with the modification of the navigation solution software of GBAS receiver, GBAS positioning accuracy improvement is expected without any modification of GBAS reference station's equipment.

Vehicular remote tolling services using EGNOS

Abstract: Future Global Navigation Satellite Systems (GNSS) will significantly improve the performance of current navigation systems, providing new and enhanced capabilities. This will enable the implementation of innovative and advanced services and applications closer to the user's needs. In this framework, the road sector is one of the major potential markets for GNSS applications and, therefore, it is very promising for future EGNOS and GALILEO related applications. Satellite navigation receivers are now commonly installed in cars as a key tool for proving new services to people on the move such as electronic charging, real-time traffic information, emergency calls, route guidance, fleet management, or advance driving assistance systems. Specifically, a very important commercial opportunity is represented by the tolling-related applications. This paper describes the Vehicular Remote Tolling (VeRT) Project sponsored by Galileo Joint Undertaking (GJU) and performed in the frame of the first GJU Call under the EC VI Framework Programme. The overall design of the service provision architecture is also presented in this paper, together with the main topics related to the following activities focused on the service prototype demonstrator development.

Precision approach guidance using global navigation satellite system (GNSS) and ultra-wideband (UWB) technology

Abstract: Improved precision navigation systems and methods are provided. In one embodiment, a navigation system is provided. The system comprises a global navigation satellite system receiver adapted to output information representing the location of a vehicle based on one or more signals from one or more satellites; an ultra-wideband ranging system adapted to output information representing the location of the vehicle based on one or more ultra-wideband signals; and a vehicle guidance system coupled to receive the location output from the global navigation satellite system receiver and the location output from the ultra-wideband ranging system. The vehicle guidance system is adapted to maneuver the vehicle based on the information from at least one of the global navigation satellite system receiver and the ultra-wideband ranging system based on a distance of the vehicle from a target object.

Next Generation Satellite Based Augmentation System (SBAS) Signal Specification

Abstract: The Satellite Based Augmentation Systems (SBASs) use satellites (geostationary satellites - GEOs) to broadcast Global Navigation Satellite System (GNSS) integrity and correction data to GNSS users, and to provide ranging signals that augment the GNSS. The current SBASs (WAAS, EGNOS and MSAS) broadcast on the GPS L1 frequency to the users, although they also broadcast at another frequency (C-band or Ku-band) to aid signal phase and frequency control. A number of next generation SBASs will broadcast at the GPS L1 and L5 frequencies, in which case the second frequency will also be available to users for signal redundancy as well as providing ionospheric corrections for GEO ranging. This paper describes details of these new SBAS signals. It also describes new receiver design requirements for tracking these new signals. Although it does not describe new (or old) data messages (still in the process of being defined), some new data requirements are discussed. These new data requirements justify the possibility of increasing the signal data rates, providing flexibility for broadcast data required for various regions covered by the future GEOs, commensurate with the capabilities of those future GEOs.

Satellite Propagation Analysis in a Masking Environment for GNSS Applications

Abstract: Most of the applications for localization and navigation in the field of transport use satellite systems (such as GPS, GLONASS, or the future European GALILEO system). With the launch of the European Galileo constellation, a new generation of satellite navigation system is envisaged. The key challenges for the development of new applications concern accuracy, availability and integrity of the positioning service that are not always guaranteed in transport environments. The PREDISSAT tool, developed at INRETS in order to predict satellite availability in a known environment, is presented. Both PREDISSAT and the ray-tracing tool ERGOSPACE have been used to produce different results: availability study along a railway line, propagation channel modeling, analysis of the positioning performance in a modeled environment. From this environment knowledge, new rules able to increase the navigation performance based on satellite only may be derived. The goal is to enhance as much as possible the use of GNSS alone for new and enlarge localization or localized based services for buses in a first step. This new technique will be extended to other transport modes. For the covering abstract please see ITRD E135207.

Tightly Coupled GNSS and Vision Navigation for Unmanned Air Vehicle Applications

Abstract: This paper explores the unique benefits that can be obtained from a tight integration of a GNSS sensor and a forward-looking vision sensor The motivation of this research is the belief that both GNSS and vision will be integral features of future UAV avionics architectures, GNSS for basic aircraft navigation and vision for obstacle-aircraft collision avoidance The paper will show that utilising basic single-antenna GNSS measurements and observables, along with aircraft information derived from optical flow techniques creates unique synergies Results of the accuracy of attitude estimates will be presented, based a comprehensive Matlab® Simulink® model which re-creates an optical flow stream based on the flight of an aircraft This paper establishes the viability of this novel integrated GNSS/Vision approach for use as the complete UAV sensor package, or as a backup sensor for an inertial navigation system

Navigating towards the future: transitioning from terrestrial radio navigation to satellite navigation and airborne surveillance

Abstract: This paper presents a proposal for transitioning from terrestrial based navigation aids to implementing satellite and airborne surveillance as the primary navigation means. The transition occurs through several steps. First the installation and use of modern navigation and surveillance equipment is mandated by the regulatory organizations. The installations should take place in a sequenced fashion to allow time for companies to absorb the initial cost. Next the existing network of terrestrial navigation aids is down sized leaving only the areas of heaviest use in service. At this point, the Global Positioning System (GPS) is deemed the primary method of terrestrial and oceanic travel. Finally, terrestrial navigation stations are available around airports and the remaining stations are put in a standby condition for use the in the event of a national emergency. This paper also discusses the security benefits and examples of cost savings through implementation of these steps.

Extending Wide Area and Virtual Reference Station Networks Far Into the Sea With GPS Buoys

Abstract: Oscar L. Colombo, GEST/NASA Goddard Manuel Hernandez-Pajares, Miguel Juan, and Jaume Sanz, Universitat Politecnica de Catalunya, Barcelona BIOGRAPHY Dr. Oscar L. Colombo works on applications of space geodesy, including gravity field mapping, spacecraft orbit determination, and precise positioning by space techniques. He develops and tests techniques for precise very long baseline differential and point-positioning kinematic and static GPS, in collaboration with groups in the USA and abroad. Dr. Manuel Hernandez-Pajares is associate professor of the Technical University of Catalonia (UPC), from 1993. He started working on GPS in 1989, for cartographic applications. His focus is in the area of GNSS ionospheric determination and GPS Modernized and Galileo real-time positioning techniques. Dr. J. Miguel Juan Zornoza is an associate professor of the UPC. His current research interest is in the area of GPS ionospheric tomography, and precise radionavigation. Dr. Jaume Sanz Subirana is an associate professor of the UPC. His current research interest is in the area of GPS and Galileo precise navigation, and of Space Based Augmentation Systems (SBAS) processing algorithms. ABSTRACT We have studied the potential of using buoys with GPS receivers as floating network stations, to extend, far into the sea, the navigation services offered by land-based WAAS/EGNOS and Virtual Reference Station networks. In particular, we have investigated the feasibility of real-time resolution of carrier phase ambiguities with a roving receiver hundreds of kilometers away from shore. Central to that resolution, is the modeling of the ionosphere using data from both land- and buoy-based GPS receivers in the network, particularly in the presence of Traveling Ionospheric Disturbances (TID) and other perturbations, and of occasional interruptions in buoy receiver operation, with complete loss of lock lasting several minutes. Establishing precise kinematic location of the buoy quickly at start-up, and recovering it soon after an interruption in GPS reception, are essential to the use of buoys as effective aids to precise navigation. Ways of speeding up the real-time convergence of the buoy’s estimated position in such cases are discussed in this paper. In our preliminary tests, we have used 5-second GPS data from widely spaced NGS CORS stations, from days with low and quite high ionospheric activity. One of them, situated eastwards from all the others, was used in lieu of a buoy, and positioned kinematically relative to the “fixed” sites, while contributing data to precise, Virtual Reference Station ionospheric differential corrections, and to WAAS-type ionospheric models. Other receivers were kept in reserve, to be treated as user “rovers”, also positioned kinematically. We then considered the quality of the ionospheric corrections, from the point of view of fixing the “rover” ambiguities relative to the “master” station. The estimated rates of successful ambiguity resolution attempts are comparable to those for conventional, land based Virtual Reference Station and DGPS networks of smaller size. The quality of the corrections of the ionosphere derived from models obtained by computed tomography is adequate, in particular, for WAAS/.EGNOS-assisted navigation.

Effect of a GPS Anomaly on Different GNSS Receivers

Abstract: On January 1st 2004, a GPS clock failure occurred suddenly onboard the GPS satellite PRN23 at around 18:30 UTC with the signal being transmitted for hours after that. The Unhealthy flag of its navigation message, used by the receivers to discard its measurements from the navigation position computation, was raised a few hours after the occurrence of this event. It was observed that the estimated user position was impacted in different manners depending on the different technology/firmware embedded in the receivers, and on the integrity monitoring information available to the receiver. Indeed, depending on the technology/ firmware used to track the signals and produce the raw measurements from the received GPS signal, the measurements and thus the position is affected differently. The integrity monitoring mechanism, depending on whether the receiver is GPS only, RAIM or SBAS for example also has an influence. For SBAS receivers, the reaction with WAAS and ESTB (the EGNOS demonstrator) was analyzed. The behavior of GPS only and RAIM receivers was also studied thanks to real data and was replayed using a signal generation tool. Following our investigation of these different observations, and using the information given on the onboard failure, this type of event was characterized and a simulation scenario using a GPS signal generator has been defined. This scenario will be used to reproduce both satellite effect and receiver behavior in order to test the reaction of other different receiver technology in front of the same event. The resulting behaviors of the receivers are in line with the actual observations made by three receivers on Jan 1st, and the failure has been tested successfully using a Septentrio receiver. So this simulation can be used as a benchmark for receiver validation or prediction of its behavior. This paper starts with the presentation of the actual observations made with GPS only, SBAS and RAIM receivers. Then, we show results of the investigation carried out to understand the effect of the failure on different receivers and more particularly on Novatel OEM3 and OEM4. Next, we present the simulation results obtained for the same two types of receivers. Then, we present the results obtained with an other type of receivers. Following this, we discuss the work that now can be done on EGNOS system behavior. Finally, we propose a conclusion on the reuse of the simulation scenario.

GPS modernisation and GNSS development

Abstract: Satellite navigation has enabled a large number of new applications among many groups of users, but a number of limitations have been observed, especially with respect to reliability and integrity of satellite navigation signals. The article deals with global navigation satellite systems (GNSS), analyzes benefits of satellite based systems, as well as problems with positioning accuracy, signal availability and system integrity. The current GPS signal structure was developed some 30 years ago, and the planned further modernization of the system meets the future requirements, improve positioning accuracy, signal availability, and system integrity. The new European Galileo system is a more efficient and reliable alternative to the GPS system. Galileo system offers superior and constant accuracy, reliability, and the very high level of continuity

Inmarsat-4 First L1/L5 Satellite: Preparing for SBAS L5 Services

Abstract: The new Inmarsat-4 GEO satellites carry dedicated navigation transponders which have been designed to provide Satellite Based Augmentation System (SBAS) Signals-In-Space, at both GPS L1 (1575.42 MHz) and L5 (1176.45 MHz) frequencies. The launch of the first of those satellites (Inmarsat-4F1) in March 2005 and subsequent in orbit test marked an important milestone for satellite navigation: for the first time a navigation signal at L5 frequency is broadcast from the space, paving the way for the introduction of the second civil frequency for SBAS systems. As for the previous Inmarsat satellite generation, the socalled Inmarsat-3s, which are used in both EGNOS (European Geostationary Navigation Overly System) and WAAS (Wide Area Augmentation System) systems, the Inmarsat-4 navigation transponders undergo a comprehensive series of tests aiming at verifying their suitability for the mission they have been conceived for. Each transponder has been subjected to pre-flight (ground) tests and are further tested once the satellites are in orbit (in-orbit tests) to ensure compliance with specifications. Data collected from these tests is useful not only for the verification of the transponder, but to predict the ability of the overall system to provide high quality user ranging and timing signals. The European Space Agency (ESA) is currently considering the use (preliminary use) of Inmarsat-4F1 satellite, which will be located at Inmarsat’s designated Indian Ocean Region (IOR), to test the potential extension of EGNOS in Africa, and to investigate the potentialities provided by the availability of an SBAS L5 signal. The uplink of signals will be based on the experimental NLES Uplink Station proposed by Telespazio and Inmarsat to be based at Fucino. This paper reports on the test results and observations for the Inmarsat-4F1 navigation transponder and the ESA proposed experimentation strategy for L5, including support to SBAS L5 standardization activities. EGNOS long-term modernization plans, in terms of coverage extension and SBAS L5 service provision, will also be described.

GridGNSS-a new conception of GNSS based on grid technology

Abstract: Developments of Computer Network make all the resources collected and shared with each other and the next generation of IP address,IPv6,will be enough to meet the need of global resources's address on the earthWith the development of mobile communication technology,the mobile user can be collected with the internet and access the resources on lineSo as to the GNSS user,internet can also be used to transmit the GNSS data and the correction dataWebService is the main topic of the next generation of internet,which is used as a platform to distribute the informationAs described,WebService can collecte global GNSS resources and share the information world-wideGrid,the third generation of the internet,provides a good solution to mass computing,which is the main work of global GNSS data processIn this paper,the new conception of GNSS and GridGNSS is explained,the basic function and main topic of GridGNSS are given in detail,and the realization of GridGNSS and also its application are also shown