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Journal of Global Positioning Systems Vol. 8, No. 1, 2009 |
Cover |
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Journal of Global Positioning Systems
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JGPS Team Structure, Copyright and Table of Contents |
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JGPS Team Structure, Copyright
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1. Evaluation of EPOS-RT for Real-time Deformation Monitoring |
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Junping Chen, Maorong Ge, Jan Dousa and Gerd Gendt
With the development of the EPOS-RT software system at GFZ, various tests have been performed to target some high precision applications such as real-time network deformation monitoring and that of based on real-time PPP (Precise Point Positioning). The paper provides an overview of the main features of the EPOS-RT software and focuses on the software performance assessment. The case studies of real-time detection of the well controlled station motion, using a network with stations separated by distances between 123 Km and 482 Km, show kinematic position accuracy at 7 mm in horizontal components and better than 2.5 cm in vertical component. Results from analysing real earthquake dynamics have demonstrated some unique features of the system and its capability of attaining mm accuracy in real time.
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2. Horizontal Strain Rate Distribution on an Active Ice Shelf Rift from in-situ GPS Data |
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Volker Janssen
Mass loss from the Antarctic ice sheet predominantly occurs at the fringing ice shelves via iceberg calving, which is controlled by the initiation and propagation of large rifts that precede iceberg detachment and can lead to ice shelf break-up. This paper reports on the analysis of Global Positioning System (GPS) data collected at an active rift system on the Amery Ice Shelf, East Antarctica, over two field seasons. Horizontal strain rates are determined for a network of 11 sites observed over three weeks during the 2004/05 Antarctic summer period, and the results are combined with, and compared to, strain rates obtained in the 2002/03 season. Maximum principal strain rates across the network vary between 6 and 32 [x 10-3/yr], while minimum principal strain rates are generally about 1-17 [x 10-3/yr]. Changes evident in the strain distribution can mostly be attributed to existing fractures passing through the GPS network and the episodic movement of the rift tip. It is confirmed that rift propagation in 2005/06 was slowing down. Opening rates are inferred from baselines situated normal to the rift. Analysis of the network using a cumulative sum approach is found to be an effective method to detect small baseline length changes associated with rift propagation.
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3. Developing Regional Precise Positioning Services Using the Legacy and Future GNSS Receivers |
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Yanming Feng, Chris Rizos, Matt Higgins, Samsung Lim and Maolin Tang
This paper presents an overview of technical developments within the CRCSI-funded research on "Delivering Precise Positioning Services in Regional Areas" undertaken by the authors since mid-2007. The research aims to address the technical and business issues that currently constrain GPS-based local area RTK precise positioning services so as to operate in future across larger regional areas, and therefore support services in agriculture, mining, utilities, surveying, construction, and others. Selected research findings to be presented in this paper cover the following aspects. (1) An overall technical framework has been proposed to transition the current RTK services to future larger scale coverage. The framework enables mixed use of different reference GNSS receiver types, dual- or triple-frequency, single or multiple systems, to provide RTK correction services to users equipped with any type of GNSS receivers. (2) Research on data processing algorithms appropriate for triple-frequency GNSS signals has demonstrated some key performance benefits of using triple carrier signals for reliable RTK positioning over long distances. (3) A server-based RTK software platform is being developed to allow for user positioning computations at server nodes instead of on the user's device. (4) An optimal deployment scheme for reference stations across a larger-scale network has been suggested, given restrictions such as inter-station distances, candidates for reference locations, and operational modes. For instance, inter-station distances between triple-frequency receivers can be extended to 150km, doubling the distances between dual-frequency receivers in existing RTK network designs.
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4. Detecting Multiple failures in GPS/INS integrated system: A Novel architecture for Integrity Monitoring |
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Umar Iqbal Bhatti and Washington Y. Ochieng
GPS is a widely used satellite navigation system. By design, there is no provision for real time integrity information within the Standard Positioning Service (SPS) which is available to the civilian community. However, in safety critical sectors like aviation, stringent integrity performance requirements must be met. This can be achieved using the GIC (GPS Integrity Channel) or RAIM (Receiver Autonomous Integrity Monitoring) or both. RAIM, the most cost effective method relies on data consistency, and therefore requires redundant measurements for its operation. An external aid to provide this redundancy can be in the form of an Inertial Navigation system (INS). This should enable continued performance even during RAIM holes. RAIM algorithms have traditionally been designed for the situation when only one failure occurs at a time. However, due to tighter alert limits and usage of GPS in urban environments there is now a focus on extending the RAIM concept to include multiple failures. Furthermore, in aviation, detection of simultaneous multiple slowly growing errors (SGE) is very challenging particularly in the case of integrated GPS/INS systems. This paper provides a detailed survey of RAIM approaches used to detect multiple failures proposed by navigation and geodesy communities. Furthermore the paper extends a previous algorithm proposed by the authors for the detection of a single SGE to the simultaneous multiple failure case for stand-alone GPS and integrated GPS/INS systems. Simulated and real data results attest to the effectiveness of the approach proposed. The developed algorithm is successful in the detection of multiple failures in GPS as well as in the INS. Furthermore isolation of the faulty sensor (GPS or INS) is possible with the same parallel filter structure. Hence, this approach will enhance the integrity of a GPS/INS integrated system installed on an aircraft.
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5. Simplified Algorithms of Variance Component Estimation for Static and Kinematic GPS Single Point Positioning |
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Jian-Guo Wang, Nilesh Gopaul and Bruno Scherzinger
This paper adapts Helmert's simplified variance component estimation (VCE) algorithm for static and kinematic GPS single point positioning (SPP). First, the VCE algorithm for a static GPS SPP is formulated. Second, the concept of redundancy contribution of observations is developed in Kalman filtering so that the VCE algorithm is further delivered in Kalman filtering. The proposed VCE approach in Kalman filtering allows the variance components for individual measurement noises and individual independent process noises to be estimated. Some VCE numerical results from static and kinematic GPS datasets are presented and discussed.
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6. GNSS Networks in Algebraic Graph Theory |
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A. Lannes and S. Gratton
A new approach to the GNSS network is presented. Here, this approach is restricted to the case where the user handles the network data for his own objectives: the satellite-clock biases are not estimated. To deal with the general case where some data are missing, the corresponding theoretical framework appeals to some elementary notions of algebraic graph theory. As clarified in the paper, the notion of closure delay (CD) then generalizes that of double difference (DD). The body of the paper is devoted to the implications of this apporach in GNSS data processing. One is then led to define local variables, which depend on the successive epochs of the time series, and a global variable which remains the same all over these epochs, with however possible state transitions from time to time. In the period defined by two successive transitions, the problem to be solved in the least-square sense is governed by a linear equation in which the key matrix has an angular block structure. This structure is well suited to recursive QR factorization. The state transitions included by the variations of the GNSS graph are then handled in an optimal manner. Solving the integer-ambiguity problem via LLL decorrelation techniques is also made easier. At last but not the least, is centralized mode, this approach particularly well suited to quality control.
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7. Implementation of a Complete GPS Receiver on the C6713 DSP through Simulink |
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Gihan Gomah Hamza, Abdelhaliem A. Zekry, and Mohamed N. Moustafa
In the past, the implementation of a complete GPS receiver was divided into two parts. The first part is implemented on ASIC or FPGA. This part includes the acquisition and tracking phases, where the algorithms of the both are written by the HDL programming language. The second part is the navigation solution part that is implemented on DSP by writing its algorithm by C/C++, FORTRAN, or assembly. This means that we have to deal with three environments to implement a complete GPS receiver. The three environments are the Simulation, FPGA, and DSP environments. Moreover, using a text programming languages in writing such long and complicated algorithms makes the process exhaustive and difficult to debug, modify, and learn. This article introduces the simulation and implementation of a complete GPS receiver on a DSP through a graphical programming language, which is SIMULINK. This makes every part in the receiver architecture very clear and easier to understand, follow, modify and debug. This can be considered a step added on the route of an open source GPS receiver. Using the same environment in both the simulation and implementation stages makes the designer's mind dedicated most of the time in developing and enhancing the algorithm through rapid prototyping and experimentation and less time on the coding. In general, this article can be considered as introducing a new look for designing, simulating, and implementing the most complicated parts of a typical GPS receiver using a graphical programming language, which is SIMULINK.
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8. Details of an Imaging System Based on Reflected GPS Signals and Utilizing SAR Techniques |
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M.Usman, D. W. Armitage
This research endeavor reveals a method for utilizing reflected Global Positioning System (GPS) signals to form an image of targets within a region of interest. The principle is based upon a type of bistatic synthetic aperture radar (SAR) in which a matched filter technique is employed to perform the image reconstruction. A major challenge was the appalling signal to noise ratio associated with the received reflected GPS signals. Moreover, the reconstruction method resulted in an undesirable point spread function (PSF) which degraded the reconstructed image. The entire GPS signal generation and image reconstruction process was simulated as faithfully as possible and it has been demonstrated that a spatial resolution of the order of the GPS L1 frequency (wavelength of 19 cm) is possible. The smeared image obtained due to poor quality PSF was improved by means of a Wiener filter based deconvolution method. An imaging system based on a stationary receiver has been practically demonstrated with the successful identification of a 0.5 m2 spherical target.
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9. Reliability Analysis in Kalman Filteirng |
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Jian-Guo Wang
This manuscript centers on the reliability theory and its applications in Kalman filtering. Especially, it delivers a distinct derivation of the redundancy contribution - the key element of reliability theory for the Kalman filter algorithm that has not been comprehensively discussed in literature at present. A distinction is made between the system innovation vector and the measurement (or pseudo measurement) residual vector. This allows to directly analyse the observation vector and the process noise vector. Particular attention is paid not only to the theoretical fundamentals of the reliability, and also to the introduction of some practical applications about the use of the redundancy contribution in Kalman filtering. The manuscript aims at assisting readers in a comprehensive understanding of reliability analysis in Kalman filtering.
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10. A User Needs Analysis for Precise Positioning Services in Australia |
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Robert Lorimer
The Cooperative Research Centre for Spatial Information (CRCSI) has developed an analysis of user needs for Precise Positioning Services in the Australian states of New South Wales and Queensland. The analysis was undertaken by the author as part of the CRCSI's Project 1.04 on "Delivering Precise Positioning Services in Regional Areas". The executive summary of the report is presented below and the full report is available from the CRCSI web site [1].
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Corporate Members of CPGPS |
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Corporate Members of CPGPS
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Instructions to Authors |
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Instructions to Authors
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CPGPS Team Structure |
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CPGPS Management Team (2009) Structure
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