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Journal of Global Positioning Systems Vol. 6, No. 2, 2007 |
| Cover |
| Journal of Global Positioning Systems |
| JGPS Team Structure, Copyright and Table of Contents |
JGPS Team Structure, Copyright See PDF file Table of Contents |
Editorial: The Pseudolite Special Issue |
| Jinling Wang In Global Navigation Satellite Systems (GNSS), such as GPS, Glonass, and the forthcoming European Galileo system as well as Chinese Compass system, four visible satellites are the minimum requirement for three-dimensional positioning. However, in some situations, such as in downtown urban canyons, engineering construction sites, and in deep open-cut pits and mines, the number of visible satellites may not be sufficient. In the worst situations, such as in underground tunnels and inside buildings, the satellite signals may be completely absent. Such problems with existing GNSS systems can be addressed by the inclusion of additional ranging signals transmitted from ground-based "pseudo-satellites" (pseudolites). To promote the applications of pseudolite in engineering geodesy, a working group on pseduolite applications was set up in 2001 within the International Association of Geodesy (IAG) Special Commission SC4 (Application of Geodesy to Engineering 1999-2003). In 2003, the IAG established Study Group 4.1 (2003-2007) on “Pseudolite Applications in Positioning and Navigation” within the IAG Commission 4 Positioning and Applications. The objectives of the research activities within this Group were to study: (a) Pseudolite augmentation of GNSS; (b) Pseudolite-only positioning scenarios; (c) Integration of pseudolites with other sensors, such as Inertial Navigation Systems (INS). The website of the SG4.1 can be accessed at http://www.gmat.unsw.edu.au/pseudolite/ which has listed pseudolite bibliography and some internet links to the pseudolite research groups and manufacturers. As part of the efforts of the IAG Study Group 4.1, this pseudolite special issue has invited papers focusing on a range of research issues in this field. Martin et al., discuss the interference and regulatory issues in GNSS pseudolite applications; Heinrichs et al. present the first outdoor experiment results with real Galileo signals on the ground. Chen et al. describe the development of the pseudolite system designed for the European Geostationary Navigation Overlay Service (EGNOS), which is a European Satellite Based Augmentation System (SBAS). In Japan , a new concept of augmenting the GPS system is to use a set of Quasi Zenith satellites. A test facility of such an augmentation concept is under way using the pseudolite approach (see Tsujii et al.). As the Galileo signal structure is significantly different from that of GPS, Abt et al. propose novel pulsing schemes for use in Galileo pseudolites. For terrestrial and airborne applications, the pseudlite signals travel only through the troposphere, which may cause a significant delay for ranging signals. As reported by Wang et al., such a delay can be compensated through an adaptive modelling method. Schlötzer et al. describe the developments of an array of self-calibrating transceivers towards autonomous navigation. Some pseudolite designs have used the frequencies in the ISM band to avoid the concerns of using officially defined GNSS frequencies. A time-synchronized pseudolite transceiver developed by Locata Corporation has a significant advantage for many applications in that a precise single point positioning scenario, without the use of any reference station, becomes a reality. Barnes et al. discuss the use of Locata technology in structural monitoring applications whilst Montillet et al. demonstrate the centimetre accuracy of positioning operations with Locata in Urban canyons. Some researchers have classified such new pseudoites transmitting non-GNSS signals into terrestrial-based RF positioning technologies, while there is a general trend in the literature that the term of pseudolite is used to broadly describe radio-ranging signal transmitters and/or transceivers for positioning and navigation applications, which may include for example, RFID and UWB based positioning systems. Pseudolites are an exciting technology that can be used for a wide range of positioning, navigation and timing applications as an augmentation tool, an integral part of multi-sensor navigation systems, or even as an independent system. Some remaining challenging issues in pseudolite research and applications have been discussed in the Final Report of the IAG Study Group 4.1, which is available at the group website. |
1. Interference and Regulatory Aspects of GNSS Pseudolites |
S. Martin, H. Kuhlen, T. Abt |
2. First Outdoor Positioning Results with Real Galileo Signals by Using the German Galileo Test and Development Environment - GATE |
G. Heinrichs, E. Loehnert, E. Wittmann, R. Kaniuth Under the leadership of IFEN GmbH, the Galileo Test and Development Environment GATE is being built up in southern Germany by a consortium of several German companies and institutes on behalf of the German Aerospace Center (DLR) with funding by the German Federal Ministry of Education and Research. The performance tests regarding the user positioning perform-ance will cover various test scenarios for static and dy-namic cases. The tests will be performed in all available GATE operation modes with GATE signals only and in combination with GPS. Preliminary test during system testing phase showed already impressive positioning per-formance with dedicated signals and services. The paper gives an overview on the variant test scenarios and setups and illustrates the detailed hardware setup. An introduc-tion in the GATE Backend Receiver Software, which computes the position solution, is presented. It describes the test procedures and shows the test results. Finally an evaluation on the different GATE services with respect to the positioning performance is presented. |
3. Development of the EGNOS Pseudolite System |
R. Chen, A. Hyttinen, Y. Chen In order to access the Satellite Based Augmentation System (SBAS) service, the end user needs to have a direct line of sight to at least one of the Geostationary Earth Orbit (GEO) satellites transmitting the augmentation messages. This requirement is critical for users in environments such as city canyons, valleys and fjords since high buildings and mountains in the vicinity of the end user can easily block the lines of sight to the GEO satellites. The situation becomes worse at high latitudes because of the low elevation angles to the GEO satellites. Even a very low obstacle can block the lines of sight to the GEO satellites. This limitation reduces SBAS Signal in Space (SIS) availability significantly at high latitude especially for land applications. This paper presents a solution of transmitting the European Geostationary Navigation Overlay Service (EGNOS) SIS using a pseudolite. The EGNOS pseudolite functions in a similar way as a GEO satellite. It will provide not only a terrestrial-based solution for transmitting the EGNOS SIS, but also a ranging measurement for the navigation solution. The EGNOS pseudolite system mainly consists of a Master Control Station, an EGNOS Data Server, EGNOS pseudolites and the user terminal. A preliminary test on a surveyed site has been carried out to verify the functionalities of the system. The data set collected from the test has been processed with two scenarios: one with four GPS satellites, while the other with three GPS satellites plus an EGNOS pseudolite. Both data processing scenarios have similar satellite geometries. The test result shows that the positioning accuracies are similar for both scenarios. |
4. Development of a Pseudo Quasi Zenith Satellite and Multipath Analysis Using an Airborne platform |
T. Tsujii, H. Tomita, Y. Okuno, S. Kogure, M. Kishimoto Japan has been developing a new satellite based positioning system called Quasi-Zenith Satellite System (QZSS). Since improvement of positioning availability in urban area is one of the most important advantages of the QZSS, multipath mitigation is a key factor for the QZSS positioning system. Therefore, Japan Aerospace Exploration Agency (JAXA) and GNSS Inc. develped a pseudolite, which transmits the next-generation signal such as BOC(1,1), in order to evaluate the effect of multipath on the new signal. Flight experiments using a pseudo quasi-zenith satellite, a helicopter on which the pseudolite was installed, were conducted, and multipath mitigation by the BOC signal was demonstrated. |
5. Optimal Pulsing Schemes for Galileo Pseudolite Signals |
T. L. Abt, F. Soualle, S. Martin Galileo, the European Satellite Navigation System, is currently under development. Even before first satellites of the constellation will be launched, Galileo signals will be provided through ground based Navigation Signal Generators for the investigation of signal performance and characteristics. Currently various projects are ongoing to develop these Galileo pseudolites (pseudo satellites). Since pseudolites are part of the Galileo system architecture namely as "Local Elements" it is expected that they will be used together with GNSS for position determination. The main characteristic of pseudolite navigation is the relatively small distance between the signal source and the receiver compared to the GNSS satellites. This distance causes the so-called "Near-Far-Problem". Different attempts have been made in the past to overcome the near-far problem. A possible solution is pulsing of the pseudolite transmitter signal which has been proposed by many authors and the success of pulsing has also been demonstrated. Basically these studies have been focused on GPS in the past and the proposed pulsing schemes are optimised for GPS signals (RTCM, RTCA). Due to major differences in the signal structure between GPS and Galileo these pulsing schemes cannot directly be adopted. Thus new pulsing schemes and patterns have to be found and investigated. This paper summarises and assesses the existing GPS pulse patterns and pulsing techniques. The parameters which characterise a pulsing scheme are discussed and implemented. Simulations based on the Galileo signal structure (codes, chipping rates, cross correlation properties) have been performed and the results will be presented. These simulations form the basis for the proposal of a new optimised pulsing scheme for Galileo pseudolites w.r.t. pulse length, duty cycles and pulse patterns. |
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6. Adaptive Tropospheric Delay Modelling in GPS/INS/Pseudolite Integration for Airborne Surveying |
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J.G. Wang and J. Wang Integrated GPS/INS systems have been used for geo-referencing airborne surveying and mapping platforms. However, due to the limited constellation of GPS satellites and their geometric distribution, the accuracy of such integraed systems cannot meet the requirements of precise airborne surveying. This problem can be addressed by including additional GPS-like ranging signals transmitted from the ground-based pseudolites (PLs). As GPS measurement geometry can be strengthened dramatically by the PL augmentation, systems accuracy and reliability can be improved, especially in the vertical component. Nevertheless, some challenges exist for PLs augmentation. As PLs are relatively close to the receivers, the unit vectors from a PL to reference and rover receivers can be significantly different. PL tropospheric delay modelling errors cannot be effectively mitigated in differencing procedure. Furthermore, PL signals propagate through the lower troposphere, where it is very difficult to accurately model the signal delay due to temporal and spatial variations of meteorological parameters. An adaptive PL tropospheric delay modelling method is developed to reduce modelling error by estimating meteorological parameters in a model. The performance of this method is evaluated with field test data. The testing has shown that the PL tropospheric delay modelling error can be effectively mitigated by the proposed method. |
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7. Autonomous Navigation Environment with Self-Calibrating Transceivers |
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S. Schlötzer, S. Martin, M. v. Voithenberg An operable navigation system which demonstrates successful self-calibration and precise local navigation has been developed by EADS Astrium. This paper presents the architecture of the autonomous navigation environment with the ability to calibrate itself as well as the results of field tests. The Self-calibrating autonomous Navigation Environment (SekaN) can be used as stand-alone navigation system for applications where satellite signals are not available or where autonomy and high precision is required. Cargo drop, navigation in canyons and open pit mines, indoor navigation and extraterrestrial navigation are only some possible applications. The self-calibrating feature of SekaN is of special interest in conflict areas where a temporary autonomous navigation environment has to be installed quickly and where it is not possible to calibrate the locations of the pseudolites a priori. Furthermore, the system can be operated as augmentation system to classical satellite navigation systems. Therefore a mixed mode has been introduced which allows for simultaneous tracking of both satellite signals and pseudolite signals. Referencing of the local coordinate system to e.g. WGS84 becomes possible. The SekaN system comprises the following HW units developed by EADS Astrium: at least 4 Transceivers (TCs), a Rover receiver (ROV) and a Master Control Station (MCS). A WLAN data link is used between the units. Each TC comprises a GNSS signal generator NSG 5100 which supports both GPS and Galileo signals and an Astrium-specific GPS/PSL receiver. The number of TCs in the network is scalable and dependent on the specific application of SekaN. Various TC-array sizes are supported as the output power of the pseudolites can be varied in a wide range. The rover receiver positioning takes place at the MCS. However, several numbers of receivers may be registered at the MCS. The TCs are operated unsynchronized and differential concepts are applied to eliminate the clock errors. Presently pulsed signals with pseudolite spreading codes at GPS L1 and dummy navigation messages are used as navigation signals. As soon as low-cost Galileo receivers are available the system can be switched to any Galileo frequency band. In a batch process the exact locations of the TC TX-antennas are determined without any a priori knowledge of the geometric array configuration. The general idea behind the self-calibration algorithms is based on the solution algorithm for self-calibrating pseudolite arrays presented in [2]. However, several modifications were necessary to adapt the algorithms to the SekaN system requirements. The rover which is used for data collection during the self-calibration process is designed as a Receiver-only module instead of a TC module. This makes the rover hardware less complex, smaller and lighter, but also complicates the self-calibration process. Self-differencing between the stationary TCs and the rover TC can no longer be applied. The ranges between the rover RX and the TCs are therefore not directly observable. The self-calibration and navigation algorithms developed for SekaN work for both 2-D and 3-D scenarios. Although multipath effects, non-linearities and the near-far-effect are inherent in these kind of ground-based navigation systems, precise user positioning at the sub-meter level becomes possible even with low-cost receivers within the self-calibrated navigation environment. |
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8. Achieving Centimetre-level Positioning Accuracy in Urban Canyons with Locata Technology |
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J.-P. Montillet, X. Meng, G. W. Roberts, A. Taha, C. Hancock, O. Ogundipe In 2005 The UK Department for Trade and Industry (DTI) commenced funding a project called Visualising Integrated Information on Buried Assets to Reduce Streetworks (VISTA). The project aims to precisely map buried assets (gas pipes, telecom cables, etc) and increase the efficiency of the process in challenging environments such as in urban canyons, where GPS fails to work or is not reliable enough to get a precise position. In this context the Institute of Engineering Surveying and Space Geodesy (IESSG) at the University of Nottingham purchased, at the beginning of 2007, a terrestrial network positioning system called Locata technology. This technology is developed by Locata Corporation Pty Ltd from Australia. Over the last five months researchers have carried out experiments with this new technology on the main campus of the University of Nottingham. The preliminary results show that LocataLites are a suitable technology to solve the positioning problems for the VISTA project. The overall accuracy is at the centimetre level for all points surveyed. Moreover, we underline in this paper the reliability and the flexibility of this new technology. |
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9. The Potential of Locata Technology for Structural Monitoring Applications |
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J Barnes C. Rizos, A. Pahwa, N. Politie Locata technology is becoming part of Leica Geosystems solution for the structural monitoring applications such as bridges and dams. This paper assesses the performance of the Locata technology using a test Locata network (LocataNet) established at the University of New South Wales. Using this network a long term static tests and a simulated deformation movement test, with GPS as a comparison, were conducted. This paper described the LocataNet established at UNSW and presents the results and analysis of the tests conducted. Overall the paper demonstrates the suitability of Locata for structural deformation monitoring type applications (such as bridges and dams) where there is reduced or unavailable satellite coverage. |
Corporate Members of CPGPS |
Corporate Members of CPGPS |
Instructions to Authors |
Instructions to Authors |
CPGPS Team Structure |
CPGPS Management Team (2007)
Structure |
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