Journal of Global Positioning Systems

Vol. 12, No. 1 & 2, 2013

Journal of Global Positioning Systems
Vol. 12, No. 1, 2013
ISSN 1446-3156 (Print Version)
ISSN 1446-3164 (CD Version)

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JGPS Team Structure, Copyright

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Table of Contents

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Oliver Montenbruck and Peter Steigenberger
DLR, German Space Operations Center, 82234 Weßling, Germany

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The article provides an overview of the BeiDou navigation message contents and highlights its specific communalities and differences with respect to other GNSS constellations. Making use of data collected by multi-GNSS monitoring stations of the MGEX and CONGO networks, the quality of BeiDou broadcast ephemerides is assessed through the analysis of satellite laser ranging measurements, comparison with post-processed orbit and clock products as well as positioning tests. Specific attention is given to signal-specific group delays and their proper consideration in the positioning.

Henri Nurminen, Jukka Talvitie, Simo Ali-Löytty, Philipp Müller, Elena-Simona Lohan, Robert Piché and Markku Renfors
Tampere University of Technology, Finland

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A Bayesian method for dynamical offline estimation of the position and the path loss model parameters of a wireless network's communication node is presented. Two versions of three different online positioning methods are tested using data collected from cellular networks and WLAN networks in outdoor and from WLAN networks in indoor environments. The tests show that the methods that use the estimated path loss parameter distributions with finite precisions outperform the methods that only use point estimates for the path loss parameters. They also outperform the coverage area based positioning method and path loss model method with generic path loss parameters, and are comparable in accuracy with the k-nearest neighbour fingerprinting method. Taking the uncertainties into account is computationally demanding, but the Gauss-Newton optimization methods is shown to provide a good approximation with computational load that is reasonable for many real-time solutions.

Ahmed El-Mowafy
Department of Spatial Sciences, Curtin University, Australia

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An advanced Receiver Autonomous Integrity Monitoring (ARAIM) approach is investigated when augmenting GPS satellites with the current regional BeiDou constellation. A procedure for integrity monitoring, including checking its availability, fault detection and exclusion, and integrity testing is presented. Fault modes and their probabilities using GPS and GPS+BeiDou are discussed. Testing of ARAIM for vertical guidance using real data in eight sites distributed globally (Australia, China, Netherlands, eastern Canada and Peru) show that the addition of the BeiDou constellation, despite the decreased preliminary confidence placed in its performance compared with GPS, results in a substantial improvement to ARAIM availability performance and a higher level of integrity, in particular at sites observing all of its current constellation (Australia and China). The improvement was less in sites that can only observe some or no GEO and IGSO satellites (Netherlands, Canada and Peru). However, the benefit of adding BeiDou to GPS at these sites is expected to substantially improve with full deployment of MEO satellites.

Keyvan Ansari and Yanming Feng
Science and Engineering Faculty, Queensland University of Technology

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In this paper, an integrated inter-vehicles wireless communications and positioning system supporting alternate positioning techniques is proposed to meet the requirements of safety applications of Cooperative Intelligent Transportation Systems (C-ITS). Recent advances have repeatedly demonstrated that road safety problems can be to a large extent addressed via a range of technologies including wireless communications and positioning in vehicular environments. The novel communication stack utilizing a dedicated frequency spectrum (e.g. at 5.9 GHz band), known as Dedicated Short-Range Communications (DSRC), has been particularly designed for Wireless Access in Vehicular Environments (WAVE) to support safety applications in highly dynamic environments. Global Navigation Satellite Systems (GNSS) is another essential enabler to support safety on rail and roads. Although current vehicle navigation systems such as single frequency Global Positioning System (GPS) receivers can provide route guidance with 5-10 meters (road-level) position accuracy, positioning systems utilized in C-ITS must provide position solutions with lane-level and even in-lane-level accuracies based on the requirements of safety applications. This article reviews the issues and technical approaches that are involved in designing a vehicular safety communications and positioning architecture; it also provides technological solutions to further improve vehicular safety by integrating the DSRC and GNSS-based positioning technologies.

Peiyuan Zhou and Jinling Wang
School of Civil and Environmental Engineering, University of New South Wales, Sydney, NSW 2052, Australia

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In Global Navigation Satellite System (GNSS) positioning, ranging signals are delayed when travelling through the ionosphere, the layer of the atmosphere ranging in altitude from about 50 to 1000 km consisting largely of ionized particles. This delay can vary from 1 meter to over 100 meters, and is still one of the most significant error sources in GNSS positioning. In precise GNSS positioning applications, ionospheric errors must be accounted for. One way to do so is to treat unknown ionosphere delay as stochastic parameter, which can account for the ionospheric errors in the GNSS measurements as well as keeping the full original information. The idea is adding ionospheric delay from external sources as pseudo-observables. In this paper, the performance of ionosphere-weighted model is evaluated using real data sets, and the correctness of priori ionosphere variance is also validated.

Dongju Peng(1), KefeiZhang(1), Suqin Wu(1), Jizhang Sang(2) and Bin Wu(3)
(1) Satellite Positioning for Atmosphere, Climate and Environment (SPACE) Research Centre, RMIT University, Melbourne, Australia
(2) EOS Space Systems Pty Ltd, EOS House, Mt Stromlo Observatory, Cotter Road, Weston Creek, ACT 2611, Australia
(3) Shanghai Astronomical Observatory ,Chinese Academy of Sciences, Shanghai, China

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Dynamic orbit determination is the conventional technique that has been commonly used for precise orbit determination (POD) of satellites at various orbital altitudes. The performance of this technique is mainly limited by inaccurate modelling of force perturbations acting on satellites. The perturbations include the Earth's gravity field, atmospheric drag, solar radiation pressure etc. Due to the fact that low Earth orbit (LEO) satellites are highly sensitive to the Earth's gravity field, the accuracy of the gravity field model used in the dynamic POD technique directly affects the accuracy of POD of LEO satellites. Therefore, selection of an accurate gravity field model for improving the POD accuracy plays a significant role in meeting the stringent requirements of space applications such as radio occultation, remote sensing and altimetry. Nowadays, with the successful launches of the CHAMP,GRACE and GOCE gravity missions, various high accuracy gravity field models have been developed and made publicly available at the International Centre for Global Earth Models (ICGEM).

In this study, the performance of13 selected gravity models applied in the dynamic POD was assessed using space-borne dual-frequency GPS measurements from the twin GRACE satellites during the period from 1st to 31st March 2008, and the effects of time-varying low-degree spherical-harmonic coefficients , and on POD for the twin GRACE satellites were also analysed. The results of tracking data residuals, orbital overlap, external orbit comparison and independent satellite laser ranging (SLR) validation demonstrated that the highest POD accuracies of GRACE-A and -B are about 2.1 cm and 2.7 cm with respect to SLR measurements respectively and this is achieved using those combined models ,i.e. EIGEN-51C, GO_CONS_GCF _2_DIR_R3, andGOCO03S.In addition, a comparison of the orbits generated with and without the time-varying gravity field indicates that orbit variability caused by the time-varying component of EIGEN-GL04S1 was at a few mm level, suggesting that the time-varying low-degree spherical-harmonic coefficients do not lead to a notable variability in orbit quality

Lei Wang, Yanming Feng and Charles Wang
Queensland University of Technology, Brisbane, Australia

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Stochastic modelling is critical in GNSS data processing. Currently, GNSS data processing commonly relies on the empirical stochastic model which may not reflect the actual data quality or noise characteristics. This paper examines the real-time GNSS observation noise estimation methods enabling to determine the observation variance from single receiver data stream. The methods involve three steps: forming linear combination, handling the ionosphere and ambiguity bias and variance estimation. Two distinguished ways are applied to overcome the ionosphere and ambiguity biases, known as the time differenced method and polynomial prediction method respectively. The real time variance estimation methods are compared with the zero-baseline and short-baseline methods. The proposed method only requires single receiver observation, thus applicable to both differenced and un-differenced data processing modes. However, the methods may be subject to the normal ionosphere conditions and low autocorrelation GNSS receivers. Experimental results also indicate the proposed method can result on more realistic parameter precision.

Corporate Members of CPGPS

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Instructions to Authors

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CPGPS Management Team (2013) Structure

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