Journal of Global Positioning Systems

Vol. 8, No. 1, 2009

Journal of Global Positioning Systems
Vol. 8, No. 1, 2009
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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The booming location-based services business requires more accuracy and availability from positioning technologies. While several proprietary location and positioning protocols have been developing in the market, scalable and cost-effective solutions can only be realized using standardized solutions.

Currently the positioning protocol standardization is concentrated in the 3GPP and 3GPP2 that define Control Plane (CP) positioning technologies for Radio Access Networks’ native use. The limitations of the control plane in terms of architecture and bearer protocols are necessarily reflected in the CP positioning protocols and limit the feature sets offered. In addition to 3GPP/2 positioning technologies are also defined in WiMAX Forum and in IEEE for WLAN networks.

Location protocols in IP-networks, such as OMA SUPL (Open Mobile Alliance Secure User Plane Location protocol), encapsulate the CP positioning protocols. Thus the limitations of the CP protocols have also been copied to the User Plane, although the bearer there would be much more capable.

Due to the shortcomings in the CP positioning protocols, standardization activity for a new bearer-independent positioning protocol is proposed in order to fulfil the needs of the future location-based services. This paper discusses the current solutions, trends in the location technologies and outlines requirements for the future location technology protocol in terms of protocol features and data content.

The development of a generic positioning technology protocol is seen as an important development towards a convergence in the location protocols and the capability to provide location-based services irrespective of the bearer network. This has a major impact on the service development as well as user experience.

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This paper presents research undertaken to develop sensor level autonomous integrity monitoring and quality control to support centimetre level positioning in all conditions and environments as conceived under the SPACE (Seamless Positioning in All Conditions and Environments) project. The basic philosophy for integrity monitoring and quality control is early detection of anomalies which requires monitoring of the entire processing chain.

A number of novel concepts and algorithms are developed including algorithms to deal with special issues associated with carrier phase based integrity monitoring (including integration with INS), a new “difference test” integrity monitoring algorithm for detection of slowly growing errors, and a new group separation concept for simultaneous multiple failure exclusion.

Both real and simulated data are used to test the new algorithms. The results show that the new algorithms, when used together with selected existing ones, provide effective integrity monitoring and quality control for centimetre level seamless positioning in all conditions and environments.

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This paper describes the technical aspects of the Redblade III, Miami University's third generation autonomous lawnmower. The Redblade III was created for entrance in the Institute of Navigation's 4th Annual Autonomous Lawnmower Competition by a team of undergraduate students majoring in electrical, computer, and mechanical engineering at Miami University. This paper details the five major subsystems of the lawnmower, including (1) the sensing system, (2) the control system, (3) the mechanical chassis system, (4) the safety system, and (5) the base monitoring and testing system. The paper discusses each aforementioned system in detail, along with providing cost analysis and conclusions.

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The diversification of Global Navigation Satellite Systems (e.g. the current and modernized GPS, the revitalized GLONASS, the planned Galileo and Compass), is an opportunity for engineers, surveyors and geodesists because of expected improvements in positioning accuracy, operational flexibility, redundancy, and quality assurance. Recent research activities include new algorithms for multiple frequency ambiguity resolution, software-based receivers for re-configurability, network-wide corrections for utilising redundancy, reversed real-time kinematic schemes for quality/accuracy improvement, and a wide range of rover-side applications. This paper discusses the integration of these “pieces” of work into a new framework and facilitates information and communication technologies in order to derive benefits from network infrastructure such as continuously operating reference stations and local/regional GPS networks. Operational models are proposed for precise point positioning and real-time kinematic services including “near real-time” applications, which require an optimal design to balance the computational overhead with data communication latency. The proposed framework is designed to be a comprehensive, server-based, and thin-client platform. It provides end-users with “out-of-the-box” services. End-users should be able to obtain extensive GNSS capabilities and high productivity without conventional constraints such as an expensive set of receivers, proprietary data formats, user-installed carrier phase processing software, incomplete interoperability, limited communication links, etc. The framework also adopts up-to-date database technologies and web technologies that enable servers to perform data management and spatial analysis, while end-users are able to syndicate data and create their own business models. The framework has been applied to Sydney Network (SydNET), a network of continuously operating reference stations located in Sydney, Australia. It is expected that the new framework will be versatile enough to cope with a diverse range of user performance requirements and the operational requirements for communications and positioning computations.

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When processing times series of global positioning data, one is led to introduce "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. For example, the latter occur when some satellites appear or disappear. 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. The structure is well suited to recursive QR factorization. The corresponding techniques prove to be very efficient for GNSS data processing and quality control in real-time kinematics. The main objective of this paper is to show how the QR implementation of GNSS centralized approaches combines the advantages of all the methods developed hitherto in this field. The study is conducted by considering the simple case of continuous observations with a local-scale single baseline. The extension to networks is simply outlined.

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The GPS errors can be separated into a frequency-dependent or dispersive component (e.g. the ionospheric delay) and a non-dispersive component (e.g. the tropospheric delay and orbit biases). Dispersive and non-dispersive errors have different dynamic effects on the GPS network corrections. The former exhibits rapid changes with high variations due to the effect of free electrons in the ionosphere, whilst the latter change slowly and smoothly over time due to the characteristic behaviour of the tropospheric delay and the nature of orbit biases. It is found that the non-dispersive correction can be used to obtain better ionosphere-free measurements, and therefore helpful in resolving the long-range integer ambiguity of the GPS carrier-phase measurements. A running average is proposed in this paper to provide a stable network correction for the non-dispersive term. Once the integer ambiguities have been resolved, both dispersive and non-dispersive corrections can be applied to the fixed carrier-phase measurements for positioning step so as to improve the accuracy of the estimated coordinates. Instantaneous positioning i.e. single-epoch positioning, has been tested for two regional networks: SydNET, Sydney, and SIMRSN, Singapore. The test results have shown that the proposed strategy performs well in generating the network corrections, fixing ambiguities and computing a user’s position.

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This paper describes a GNSS software receiver architecture and the associated benefits in terms of algorithm flexibility and processing efficiency. For the latter, different signal processing algorithms and implementations are considered including processing with a Graphics Processing Unit (GPU); a novel implementation in the GNSS community. The massively parallel processing capability of the GPU is demonstrated relative to other processing optimizations. Sample results of GPS processing are presented including centimetre level positioning. Results obtained with some of the Galileo and GLONASS signals are also included to demonstrate the flexibility of the receiver.

Technical Note

Technical Notes is a new column in this Journal, featuring reviews of technical or theoretical tools for topics of positioning systems and their applications. Specialists in various fields are welcome to contribute a normal article to outline the issues of interest as systematic possible. In general, the manuscripts may aim to fill the gaps between the textbooks and scientific papers published for the specific topic. In this issue, Dr Jianguo Wang, York University, will review testing statistics in the context of Kalman filter, providing useful tools for design and use of a Kalman filter in navigation and positioning applications.

The column of this issue is coordinated by Dr Jianguo Wang, who appreciates your contribution to this column, along with your comments or ideas for topics for future issues (jgwang@yorku.ca).

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The integration of Global Positioning System (GPS) with an inertial measurement unit (IMU) has been widely used in many applications of positioning and orientation. The performance of a GPS-aided inertial integrated navigation system is mainly characterized by the ability of the IMU to bridge GPS outages. This basically depends on the inertial sensor errors that cause a rapid degradation in the integrated navigation solution during periods of GPS outages. The inertial sensor errors comprise systematic and random components. In general, systematic errors (deterministic) can be estimated by calibration and therefore they can be removed from the raw observations. Random errors can be studied by linear or high order nonlinear stochastic processes. These stochastic models can be utilized by a navigation filter such as, Kalman filter, to provide optimized estimation of navigation parameters. Traditionally, random constant (RC), random walk (RW), Gauss-Markov (GM), and autoregressive (AR) processes have been used to develop the stochastic model in the navigation filters.

In this technical note, the inertial sensor errors are introduced and discussed. Subsequently, a six-position laboratory calibration test is described. Then, mathematical models for RC, RW, GM, and AR stochastic models with associated variances for gyros and accelerometer random errors are presented along with a discussion regarding ongoing research in this field. Also, the implementation of a stochastic model in a loosely coupled INS/GPS navigation filter is explained.

Corporate Members of CPGPS

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Instructions to Authors

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CPGPS Management Team (2008) Structure

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