Journal of Global Positioning Systems

Vol. 3, No. 1-2, 2004

Journal of Global Positioning Systems
Vol. 3, No. 1-2, 2004
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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Chris Rizos
The University of New South Wales, Australia

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I am pleased to be the guest editor for these special issues of the Journal of Global Positioning Systems to publish the selected papers from the 2004 International Symposium on GPS/GNSS (GNSS-2004), 6-8 December 2004, organised by the School of Surveying and Spatial Information Systems, University of New South Wales, Australia.
The GNSS-2004, attended by over 340 delegates from 29 countries, was the largest symposium in the Asia/Pacific region in 2004 dedicated to GNSS and wireless positioning. On the first day of the symposium the plenary session consisted of several presentations by invited speakers. The Civil GPS Service Interface Committee (CGSIC) convened a public meeting where representatives from the US Dept of Transport and US Coast Guard informed participants of recent developments in GPS policies and modernization. Presentations by several European speakers introduced the future GNSS “Galileo”, scheduled for deployment by the end of the decade. The Symposium also featured technical workshops and around 200 oral and ‘flashing poster’ presentations.
Over 130 papers presented at the symposium were submitted to the special issues of the Journal of Global Positioning Systems (JGPS). However, given the limited space pages in these special issues many high quality papers could not be selected for publication. This has been a considerable administrative challenge and I wish to thank the reviewers for their assistance in reading and selecting the papers.
The 2004 and 2005 volumes of the JGPS feature the selected papers from the symposium on various GNSS topics, as well as research and development into a variety of other positioning technologies.

Gérard Lachapelle
University of Calgary, Canada
Received: 15 November 2004 / Accepted: 3 February 2005

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This paper presents an overview of GNSS-based indoor location technologies. Current and emerging users and their potential requirements are first discussed. Signal attenuation and multipath caused under indoor environments are described. The basic method to acquire and track attenuated signals, namely longer integration of signal measurements, is summarized. The need for assisted GPS is addressed. Availability and accuracy performance currently achievable under various conditions (wooden structure building, single family residence, large sport facility) are illustrated through selected test results. The limitations of current technologies and potential enhancements are discussed. These include measurement noise, existing signal structure and future enhancements, frequency and time errors, user motion, sensor aiding such as ultra-tight integration, and solution reliability and continuity. The paper concludes with a discussion of receiver testing standards. The possibility of using a GNSS hardware simulator to create reproducible indoor environments in order to overcome the controllability issue encountered with real environments is analysed.

Glen Gibbons
GPS World, USA
Received: 15 November 2004 / Accepted: 3 February 2005

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In the next 5 to 10 years, the world will experience the emergence of a true Global Navigation Satellite System (GNSS) — a compatible and, in many respects, interoperable system of systems. The U.S. Global Positioning System, Europe’s Galileo, perhaps Russia’s Glonass system, and regional augmentations including the Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay Service (EGNOS), radiobeacon-based systems such as the U.S. Nationwide Differential GPS, and compatible commercial differential correction services will comprise this multifaceted GNSS. Common signal structures and frequency plans will enable combined user equipment that reduces the technical complexity and cost, while vastly expanding related applications. Additional satellites and signals, both more powerful and with improved designs, will increase the availability of robust signal reception outdoors and strengthen the potential of indoor positioning using only GNSS user equipment. But the path to the future is not without its risks: political, technical, economic, and cultural.

Hasanuddin Z. Abidin, H. Andreas, M. Gamal
Institute of Technology Bandung, Indonesia
M. Hendrasto, Ony K. Suganda, M.A. Purbawinata
Directorate of Vulcanology and Geological Hazard Mitigation, Indonesia
Irwan Meilano, F. Kimata
Nagoya University, Japan
Received: 15 November 2004 / Accepted: 3 February 2005

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Bromo is an active type-A volcano located inside Tengger caldera in East Java province of Indonesia. In her history, Bromo has erupted at least about 50 times since 1775. The last eruption occurred on June 2004. Monitoring of Bromo activities has been continuously done since early 1989 by using seismograph. EDM and GPS surveys have also been conducted since the last eruption in Dec. 2000. Up to now there have been four GPS surveys that have been conducted, namely on Dec. 2000, June 2002, August 2003, and June 2004, respectively. The obtained GPS and EDM results show that the deformation of Bromo volcano is typically in order of a few cm, with the inflation and deflation processes before and after the eruption. Estimated location of the pressure source is found to be beneath the active crater with depth of about 1 km below the caldera floor.

Deuk Jae Cho, Sang Jeong Lee
Chungnam National University, Korea
Chansik Park
Chungbuk National University, Korea
Received: 15 November 2004 / Accepted: 3 February 2005

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Recently, there has been increasing demands on the positioning capability in weak signal environment such as inside building and urban area. The present assisted GPS technology uses GPS L1 signals only. Meanwhile, according to the GPS modernization plan, Block IIR-M GPS satellite will be first launched in 2005, transmitting the civil code in L2 frequency as well as in L1 frequency with the updated signal structure. Since the L2 civil code has a worst-case cross correlation performance of 45 dB (over 251 times better than 21 dB cross correlation performance of the L1 C/A code), it will be much more effective in weak signal environment. This paper proposes an assisted GPS acquisition method using L2 civil signals. It will show that the acquisition success rate of the proposed assisted GPS acquisition method is better than that of the existing assisted GPS method using L1 signals in the same environment. The constellation of the next generation GPS satellites is scheduled to launch in 2005. Therefore, in order to design and test the assisted GPS acquiring the L2 civil signal, it is necessary to design a signal generator which can generate the L2 civil signal. The signal generator will be designed using the pseudo random noise (PRN) code generation method and navigation message protocol defined in GPS ICD PIRN 200C-007B. Finally, through the simulations using the designed signal transmitter, the success rate of the proposed assisted GPS acquisition method will be compared with that of the existing assisted GPS method to show the performance improvements.

Hae Don Chon, Sibum Jun, Heejae Jung, Sang Won An
Samsung Electronics Co., LTD, Korea
Received: 15 November 2004 / Accepted: 3 February 2005

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In Korea, telematics is regarded as the technology to enhance and make everyday-driving experience more comfortable and safer. An essential part of the telematics is navigation and it is mainly based on GPS as the choice of positioning technology. The accuracy of GPS, however, is approximately ten to twenty meters. Combining with map-matching technologies, most navigation systems guide drivers with a best effort manner. In addition to telematics, RFID (Radio Frequency Identification) is an old but newly emerged technology. In this paper, we incorporate RFID technology into a navigation system to improve the accuracy. The skeleton of the idea is as follows: install RFID tags on roads in a certain way, store very accurate location information along with other necessary information in the tags, add an RFID reader module to the navigation system, and use this new location information along with GPS and a gyroscope to produce highly accurate location information. With this scheme, the accuracy of positioning can be dramatically improved, especially in tunnels and in downtown areas. Preliminary results show that this idea is feasible.

Eric Lagier, Desiree Craig
46th Test Group, US
Paul Benshoof
746th Test Squadron, US
Received: 15 November 2004 / Accepted: 3 February 2005

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From May 24-28, 2004, the 746th Test Squadron, located at Holloman Air Force Base (AFB), New Mexico (NM), planned and executed an innovative Global Positioning System (GPS) jamming program at White Sands Missile Range, NM. This program, known as JAMFEST, was aimed at providing low to no cost, realistic, GPS jamming scenarios for testing GPS-based navigation systems, as well as, training personnel in unique GPS denied environments. Through sponsorship from the GPS Joint Program Office, White Sands Missile Range, and the 46th Test Group, the 746th Test Squadron was able to provide this opportunity at a significantly reduced cost to each participant. During JAMFEST, the 746th Test Squadron hosted twelve simultaneous, yet very diverse customers, including multi-service Department of Defense (DoD) organizations, several defense contractors, and civil organizations. Their objectives ranged from training personnel on the effects of GPS jamming to characterizing the performance of prototype advanced anti-jam technologies against operationally realistic threats. To accomplish these goals, participants drove, flew, or walked through 59 jamming scenarios specifically tailored to stress the systems under evaluation. These tests would have cost a total of $660,000 or more if conducted separately. However, JAMFEST achieved the same objectives for approximately $85,000 in available funds coupled with discounted or donated services totaling $175,000. This paper details overall test and participant objectives, strategies, conduct, and addresses future JAMFEST activities.

Andrew Dempster
The University of New South Wales, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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Increasingly, software radio techniques are being used in the implementation of communications receivers in general, and GNSS receivers in particular. In such a receiver, the received signal is sampled as close to the receive antenna as possible, and all subsequent processing uses digital signal processing (DSP) techniques. The sampling clock will suffer from phase noise instabilities, leading to a phenomenon known as aperture jitter. This paper examines the effects of aperture jitter for a number of “typical” software radio GNSS receivers. A jitter specification is derived which restricts the noisy effects due to jitter to 10dB below thermal noise. It transpires that regardless of the new signals that are selected to accompany it, it is the L1 signal that drives this jitter specification.

Fabio Dovis, Marco Pini, Massimiliano Spelat
Politecnico di Torino, Italy
Paolo Mulassano
Istituto Superiore Mario Boella, Italy
Received: 15 November 2004 / Accepted: 3 February 2005

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The increased interest for applications based on both navigation and communication systems, represents an important driver for the design and implementation of innovative receivers architectures. The realization of civil GPS applications, the advent of the European navigation system Galileo, and the integration of localization services in communication network make the reconfigurability an indispensable requirement for the development of innovative Global Navigation Satellite Systems (GNSS) platforms. In addition, it must be pointed out that several problem as indoor positioning and multipath recovery, are pushing the research activity in order to provide users of flexible devices able to adapt their functionalities according to the environment. Considering this complex scenario, the Software Defined Radio (SDR) approach constitutes an interesting perspective to develop modular architectures. In this paper, the implementation of a reconfigurable user terminal integrating both navigation and communication capabilities will be discussed. The work will be presented focusing the attention on software-designed functionalities and the Navigation Unit will be analyzed and tested. An example of adaptability of the receiver to the operating environment will be presented. The reconfigurable module for multipath mitigation in the tracking phase will be described with particular attention to the implementation aspect, and some simulation results will be presented.

Benjamin B. Peterson, Kenneth Dykstra
Peterson Integrated Geopositioning, LLC, US
Kevin M. Carroll, Anthony H. Hawes
U.S. Coast Guard Loran Support Unit, US
Received: 15 November 2004 / Accepted: 3 February 2005

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A multimodal group of engineers, scientists, and industry representatives, including the U.S. Coast Guard (USCG) and Federal Aviation Administration (FAA) completed a major effort to define and analyze the performance of a new Enhanced Loran system as a backup for the navigation and timing services provided by the NAVSTAR Global Positioning System (GPS) provided services. Each mode of transportation has defined requirements that the new Enhanced Loran must meet to be acceptable in the radionavigation mix of systems. The group developed a set of requirements for Loran maritime navigation in terms of availability, accuracy, integrity and continuity for the Harbor Entrance and Approach (HEA) requirements defined in the Federal Radionavigation Plan (FRP). This paper discusses the goals of the Loran Support Unit for Fiscal Year 2005 (FY05), and the program to support these goals. The factors related to achieving the objective of moving Differential Loran from the proof-of-concept stage to an operational status will be discussed. Also covered are the results of an initial survey of the Inner Harbor at Boston, MA, USA.

Frank Engel, Gernot Heiser
National ICT Australia
Peter Mumford, Kevin Parkinson, Chris Rizos
The University of New South Wales, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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In this article we present the concept of a FPGA-based GPS receiver architecture with the aim of providing a framework for investigating new receiver architectures for current and upcoming GNSS standards. This development system facilitates researchers to prove new receiver concepts using real signals, which nowadays can only be simulated using tools such as Matlab. One will be able to work with the satellites as soon as they are operational, rather than having to wait for the availability of commercial products. The system allows individual development of signal processing solutions for base-band processing. A soft-core processor implements higher layer services that provide data to the user.

Hans-Jürgen Euler, Stephan Seeger, Frank Takac
Leica Geosystems AG, Switzerland
Received: 15 November 2004 / Accepted: 3 February 2005

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Using the Master-Auxiliary concept, described in Euler et al. (2001), Euler and Zebhauser (2003) investigated the feasibility and benefits of standardized network corrections for rover applications. The analysis, focused primarily in the measurement domain, demonstrated that double difference phase errors could be significantly reduced using standardized network corrections. Extended research investigated the potential of standardized network RTK messages for rover applications in the position domain (Euler et al, 2004-I). The results of baseline processing demonstrated effective, reliable and homogeneous ambiguity resolution performance for long baselines (>50km) and short observation periods (>45 sec). In general horizontal and vertical position accuracy also improved with the use of network corrections. This paper concentrates on the impact of wrongly determined integers within the reference station network on RTK performance. A theoretical study using an idealized network of reference stations is complemented by an empirical analysis of adding incorrect L1 and L2 ambiguities to the observations of a real network. In addition, the benefits of using network RTK corrections for a small sized network in Asia during a period of high ionospheric activity is also demonstrated.

N. Castleden, G.R. Hu, W.E. Featherstone
Curtin University of Technology, Australia
D.A. Abbey, C.J. Earls
AAMHatch Pty Ltd, Australia
D. Weihing
University of Karlsruhe, Germany
O. Øvstedal
Agricultural University of Norway, Norway
Received: 15 November 2004 / Accepted: 3 February 2005

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Over the past 18 months, a team in the Western Australian Centre for Geodesy at Curtin University of Technology, Perth, has been researching the optimum configurations to achieve long-range and precise GPS-based aircraft positioning for subsequent airborne mapping projects. Three parallel strategies have been adopted to solve this problem: virtual reference stations (VRS), precise point positioning (PPP), and multiple reference stations (MRS). This paper briefly summarises the concepts behind the PPP and VRS techniques, describes the development and testing of in-house software, and presents the latest experimental results of our research. Current comparisons of the PPP and VRS techniques with an independently well-controlled aircraft trajectory and ground-based stations in Norway show that each deliver precisions of around 3 cm. However, the implementation of more sophisticated error modelling strategies in the MRS approach is expected to better deliver our project’s objectives.

Roger Fraser, Adam Mowlam, Philip Collier
The University of Melbourne, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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Low–cost GPS receivers can produce positions almost instantly, however they have a limited use and application due to the impact of random and systematic errors associated with real time autonomous positioning. To achieve higher levels of accuracy and precision, some other form of correction or augmentation information must be applied. There are various real time augmentation alternatives, such as WAAS/LAAS, integrated sensors and systems, receiver based optimal estimation algorithms, and potentially, combined GNSS. To improve the accuracy of low–cost GPS receivers, a feasible option is Differential GPS (DGPS). A popular means for transferring real time DGPS corrections is via the RTCM SC–104 protocol over radio transmission. In recent times, the Internet has been shown to be an efficient and reliable form of data communication. In this paper, the Web services architecture is examined as a viable protocol and communication alternative for disseminating DGPS augmentation information over the Internet. Preliminary results from a simple prototype indicate that Web services offers a practical, efficient and secure method for exchanging CORS network data, and augmenting GPS enabled mobile devices capable of wirelessly reaching the internet. Web services are further shown to provide advantages for disseminating other GPS related data, such as IGS satellite orbit data, carrier–phase data for location–centric augmentation, and a host of other LBS information.

Yang Gao, Kongzhe Chen
University of Calgary, Canada
Received: 15 November 2004 / Accepted: 3 February 2005

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The real-time availability of precise GPS satellite orbit and clock products has enabled the development of a novel positioning methodology known as precise point positioning (PPP). Based on the processing of un-differenced pseudorange and carrier phase observations from a single GPS receiver, positioning solutions with centimeter to decimeter accuracy can be attained globally. Such accuracy can currently be achieved only through differential processing of observations acquired simultaneously from at least two receiver stations. The potential impact of PPP on the positioning community is expected to be significant. It brings not only great flexibility to field operations but also reduces labor and equipment cost and simplifies operational logistics by eliminating the need for base stations. This paper will address issues related to precise point positioning and perform data analysis to assess the performance of different application solutions from PPP using real-time precise orbit and clock corrections. They include the discussion of an algorithm for un-differenced data processing, error source and mitigation, and critical elements related to real-time GPS orbit and clock products. Numerical results will be presented to show the positioning accuracy attained with datasets acquired from different environments using real-time precise orbit/clock products currently available. Features of a software package that has been developed at the University of Calgary for precise point positioning will also be described.

Goh Pong Chai
Nanyang Technological University, Singapore
Received: 15 November 2004 / Accepted: 3 February 2005

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Location-Based-Services (LBS) have not made any significant foray into commercial applications following the mandatory 911 requirements for emergency location initiated by US. Commercial adoption of LBS has been hampered by cost issues and technical difficulties faced by the various modes of positioning. For LBS to be really usable, positioning, irrespective of the technology, has to be a seamless and transparent process and made available under most environments and to within acceptable accuracy. Several services for positioning technologies had been researched and developed around GSM radio network, each with varying success. This paper describes a commercial application that has been developed on the Symbian platform. It allows user-friendly access to maps on a phone and incorporates a proprietary location algorithm that resides within the phone. The algorithm is a significant improvement from basic cell-id location methods.

Gabriel Bucco, Matthew Trinkle, Doug Gray, Wai-Ching Cheuk
University of Adelaide, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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The FPGA (Field-Programmable Gate Array) implementation of an adaptive filter for narrow band interference excision in Global Positioning Systems is described. The algorithm implemented is a delayed LMS (Least Mean Squares) adaptive algorithm improved by incorporating a leakage factor, rounding and constant resetting of the filter weights. This was necessary as the original adaptive algorithm had stability problems : the filter weights did not remain fixed, and tended to drift until they overflowed, causing the filter response to degrade. Each model was first tested in Simulink, implemented in VHDL (Verilog Hardware Description Language) and then downloaded to an FPGA board for final testing. Experimental measurements of anti jam margins were obtained.

Dorota A. Grejner-Brzezinska
The Ohio State University, US
Pawel Wielgosz
University of Warmia and Mazury
Israel Kashani
Israel Institute of Technology
Dru A. Smith, Paul S. J. Spencer, Douglas S. Robertson, Gerald L. Mader
National Geodetic Survey
Received: 15 November 2004 / Accepted: 3 February 2005

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The primary objective of this paper is to test several methods of modeling the ionospheric corrections derived from a reference GPS network, and to study the impact of the models’ accuracy on the user positioning results. The five ionospheric models that are discussed here are: (1) network RTK (NR) carrier phase-based model — MPGPS-NR, (2) absolute, smoothed pseudorange-based model — MPGPS-P4, (3) IGS Global Ionosphere Model — GIM, (4) absolute model based on undifferenced dual-frequency ambiguous carrier phase data — ICON, and (5) carrier phase-based data assimilation method — MAGIC. Methods 1–4 assume that the ionosphere is an infinitesimal single layer, while method (5) considers the ionosphere as a 3D medium.The test data set was collected at the Ohio Continuously Operating Reference Stations (CORS) network on August 31, 2003. A 24-hour data set, representing moderate ionospheric conditions (maximum Kp = 2o), was processed. The ionospheric reference “truth” in double-difference (DD) form was generated from the dual-frequency carrier phase data for two selected baselines, ~60 and ~100 km long, where one station was considered as a user receiver at an unknown location (simulated rover). The five ionospheric models were used to generate the DD ionospheric corrections for the rover, and were compared to the reference “truth.” The quality statistics were generated and discussed. Examples of instantaneous ambiguity resolution and RTK positioning are presented, together with the accuracy requirements for the ionospheric corrections, to assure integer ambiguity fixing.

Neil Harper, Peter Nicholson, Eric Poon
Nortel, Nortel Building , Northfields Ave, University of Wollongong, Australia
Peter Mumford
The University of New South Wales, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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This paper introduces a process for analysing and improving the quality of the acquisition assistance data produced for Assisted GPS (A-GPS) positioning in cellular networks. An experimental test bed is introduced and a series of experiments and results are provided. The experiments validate the GPS acquisition assistance data in open-sky conditions. Accuracy results for initial testing of our server location determination engine in a range of different environments are also given with results of a long-term run. Acquisition assistance data provides the GPS handset with information that allows it to detect the GPS signals more quickly and allows detection of much weaker signals. It does this by providing information to the handset about where to look for the signals. The A-GPS server is a mobile location server determining the location of devices within a cellular network. In order to measure the quality of the acquisition assistance data produced by the A-GPS server a piece of hardware has been developed called the “A-GPS Trainer”. This takes assistance data and uses it to lock on to the satellites. It then provides code phase measurements back to the server for it to do a location calculation. The trainer also reports on the amount of time it takes to lock on to the signals of the individual satellites. It can run multiple calculations over a period of time and report the results.

Ronald R. Hatch, Richard T. Sharpe
NavCom Technology, Inc., US
Received: 6 December 2004 / Accepted: 2 February 2005

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A general review of NavCom Technology’s StarFire Global DGPS system is followed by a description of a number of improvements which have been either recently introduced or are in the process of being introduced. These improvements include: (1) an improved mode switching between various differential aiding signals and between dual-frequency and single-frequency operation when the L2 signal is lost; (2) a high-rate, high-accuracy, and efficient time-difference of carrier-phase position propagation process, which is used to generate the position coordinates between the one-second epochs; (3) an improved RAIM measurement error detection process; (4) a simplified process of computing the earth tides caused by both the sun and the moon; and (5) a built-in RTK capability (referred to as RTK Extend) which can make use of the synergism between the Global and RTK correction streams to continue RTK accuracy for up to 15 minutes when the RTK corrections are lost due to obstructed line-of-site or other problems with the local RTK corrections. Each of these will be addressed at least briefly. The more significant improvements will be addressed at greater length.

Mustafa Ozgur Kanli
The University of New South Wales, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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Pseudolites (PLs) are ground-based transmitters that transmit GPS-like signals. They have been used to test GPS system elements and to enhance GPS in certain applications by providing better accuracy, integrity and availability through the use of PL signals in addition to the GPS signals. PLs are also a promising technology for providing positioning in indoor, high multipath environments where GPS signals are generally unavailable or severely attenuated and of questionable quality. In experiments to date, researchers have almost exclusively used PLs that transmit C/A code on L1/L2 in order to use existing off-the-shelf GPS receivers. This is because no hardware modifications to the GPS receiver are necessary and only minor changes to the receiver firmware are needed to track a PL’s signal. However, there are some fundamental issues that limit the effectiveness of a PL system using C/A code on L1/L2. These include the legality of transmitting on L1/L2, cross-correlation between PL and GPS signals, saturation of GPS receiver front-ends, and the limited multipath mitigation offered by C/A codes. When combined with other problems inherent to all PL systems such as near-far, multipath, and synchronization, the issues in using L1/L2 C/A code PL systems further complicates the design and deployment of such systems and places limits on its operational effectiveness. This paper presents the issues which limit PL systems that use GPS hardware and explores the impact of these issues on some common PL applications.

Jonghyuk Kim, Matthew Ridley, Salah Sukkarieh
The University of Sydney, Australia
Eric Nettleton
BAE Systems, UK
Received: 15 November 2004 / Accepted: 3 February 2005

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This paper presents the real-time results of an air-to-ground feature tracking algorithm using a passive vision camera and a low-cost GPS/INS navigation system on a UAV (Uninhabited Air Vehicle) platform. The vision payload is able to observe a number of ground features, and the GPS/INS navigation system is used in conjunction with a waypoints-based guidance and flight control module. Due to limited processing resources, the vision node employs a simple but fast method of point based feature extraction algorithm. The feature tracking performance is greatly affected by the accuracy of the on-board navigation system. Conversely though, it can be used as a performance indicator of the navigation filter by comparing it with the truth feature location and some simple geometry. This paper will present the results of targeting performance against known location of features, and hence verifying the accuracy of the real time GPS/INS system.

T.H. Diep Dao, Paul Alves and Gérard Lachapelle
University of Calgary, Canada
Received: 15 November 2004 / Accepted: 3 February 2005

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Carrier phase-based differential GPS is commonly used for high accuracy RTK positioning because it effectively reduces the effects of spatially corrected errors such as orbital and atmospheric errors. The spatially correlated error reduction is a function of the correlated errors measured by the two receivers. Carrier phase-based single reference station (SRS) positioning is capable of providing cm accuracy for static positioning and dm for kinematic positioning under normal atmospheric conditions when the inter-antenna distance is less than approximately ten kilometres. However, under highly localized atmospheric activity, and/or with a longer inter-antenna distance, the residual differential error increases and the accuracy degrades. The University of Calgary MultiRef™ multiple reference station (MRS) approach uses a network of GPS reference station to model the atmospheric conditions over a geographic region to reduce correlated measurement errors. This approach uses a conditional least-squares adjustment to predict the errors in the network area. This study focuses on an evaluation of the MultiRef™ approach relative to the single reference station (SRS) approach in the observation, position and ambiguity domains. Long-term and short-term convergence accuracy tests are used to assess the effectiveness of the approach. The network used for this assessment is located in Southern Alberta, Canada. This is a medium scale network with baseline lengths ranging from 30 to 60 km. The results show a minor to significant improvement of the MRS method in all domains.

Qingquan LI, Zhixiang FANG, Hanwu LI
Wuhan University, P.R.China
Received: 15 November 2004 / Accepted: 3 February 2005

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The applications of Global Positioning System (GPS) are increasingly widespread in China. GPS positioning is more and more popular. Especially the automotive navigation system which relies on GPS and Dead Reckoning technology is developing quickly for future huge market in China. In the paper a practical combined positioning model of GPS/DR is put forward .This model makes use of Kalman Filter to improve positioning precision and computative precision. This model designed for automotive navigation system makes use of Kalman filter to improve position and map matching veracity by means of filter the raw GPS and DR signal. In practical examples, the validity of the model is illustrated. Several experiments and their results of integrated GPS/DR positioning in automotive navigation system will show that Kalman Filter based on integrated GPS/DR position is necessary, feasible and efficient for automotive navigation application. Certainly, this combined positioning model, similar to other model, can not resolve all situation issues. In the paper, the applicable principles of the model are given and the advantages and disadvantages of this model are compared with other positioning models. Finally, suggestions are given for further improving integrated GPS/DR application, and the application respects of integrated GPS/DR technology in the automotive navigation system are summarized.

Xaiojing Li
The University of New South Wales, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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Monitoring structural response induced by severe loadings such as typhoon is an efficient way to mitigate or prevent damage. Because the measured signal can be used to activate an alarm system to evacuate people from an endangered building, or to drive a control system to suppress typhoon excited vibrations so as to protect the integrity of the structure. A 108m tall tower in Tokyo has been monitored by an integrated system combining RTK-GPS and accelerometers. Data collected by the multi-sensor system have been analysed and compared to the original finite element modeling (FEM) result for structural deformation monitoring studies. Especially, the short time Fast Fourier Transform (FFT) analysis results have shown that the time-frequency relation does give us almost instantaneous frequency response during a typhoon event. In this paper the feasibility of integrating advanced sensing technologies such as RTK-GPS with traditional accelerometer sensors, for structural vibration response and deformation monitoring under severe loading conditions, is discussed. The redundancy within the integrated system has shown robust quality assurance.

Oscar Pozzobon, Chris Wullems
Qascom, Italy
Kurt Kubik
University of Queensland, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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This paper describes a secure framework for tracking applications that use the Galileo signal authentication services. First a number of limitations that affect the trust of critical tracking applications, even in presence of authenticated GNSS signals, are detailed. Requirements for secure tracking are then introduced; detailing how the integrity characteristics of the Galileo authentication could enhance the security of active tracking applications. This paper concludes with a discussion of our existing tracking technology using a Siemens TC45 GSM/GPRS module and future development utilizing our previously proposed trusted GNSS receiver.

Günther Retscher, Michael Thienelt
Vienna University of Technology, Austria
Received: 15 November 2004 / Accepted: 3 February 2005

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In the research project NAVIO (Pedestrian Navigation Systems in Combined Indoor/Outdoor Environements) at our University we are working on the improvement of navigation services for pedestrians. Thereby we are mainly focusing on the information aspect of location-based services, i.e., on the user’s task at hand and the support of the user’s decisions by information provided by such a service. Specifications will allow us to select appropriate sensor data and to integrate data when and where needed, to propose context-dependent routes fitting to partly conflicting interests and goals as well as to select appropriate communication methods in terms of supporting the user guidance by various multimedia cartography forms. These taks are addressed in the project in three different work packages, i.e., the first on “Integrated positioning”, the second on “Pedestrian route modeling” and the third on “Multimedia route communication”. In this paper we will concentrate on the research work and findings in the first work package. For continuous positioning of a pedestrian suitable location technologies include GNSS and indoor location techniques, cellular phone positioning, dead reckoning sensors (e.g. magnetic compass, gyro and accelerometers) for measurement of heading and travelled distance as well as barometric pressure sensors for height determination. The integration of these sensors in a modern multi-sensor system can be performed using an adapted Kalman filter. To test and to demonstrate our approach, we take a use case scenario into account, i.e., the guidance of visitors to departments of the Vienna University of Techology. The results of simulation studies and practical tests could confirm that such a service can achieve a high level of performance for the guidance of a pedestrian in urban areas and mixed indoor and outdoor environments.

Craig Roberts, Chris Rizos, Linlin Ge
The University of New South Wales, Australia
Kefei Zhang
RMIT University, Australia
Allison Kealy
The University of Melbourne, Australia
Peter Ramm, Martin Hale
Dept of Sustainability and Environment, Victoria Government, Australia
Doug Kinlyside, Paul Harcombe
Department of Lands, NSW Government, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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This contribution describes a recent Australian Research Council (ARC) project funded under the ARC-Linkage Scheme. The research team comprises researchers from RMIT University, UNSW, University of Melbourne, Spatial Information Infrastructure and the Department of Lands, NSW. The aim of the project is to enhance the utility of continuously operating reference station (CORS) networks in the states of Victoria and New South Wales by developing improved atmospheric correction models to support high accuracy, real-time positioning even when the density of reference stations is insufficient for standard operational GPS techniques such as RTK (‘real-time kinematic’). Many applications of Global Navigation Satellite System (GNSS) technology, such as surveying, mapping and precise navigation, require real-time positioning accuracies to centimetre levels. To support these applications, many countries are establishing dense CORS networks with stations, positioned typically a few tens of kilometres apart. However, for Australia with its large and sparsely populated landmass, such dense networks cannot be justified economically. This ARC project will investigate enhancements of sparse networks to maintain similar levels of accuracy as dense CORS networks. It will seek a better understanding and modelling of atmospheric conditions, currently a major limitation in the use of sparse networks for high accuracy techniques. This paper will describe the status of current developments in CORS network infrastructure in Australia, namely GPSnet in Victoria and SydNet in New South Wales. The major research components of the project will be outlined and the technical and practical challenges will be discussed, including some methodologies that will be investigated.

Gethin W Roberts, Emily Cosser, Xiaolin Meng, Alan Dodson
The University of Nottingham, UK
Received: 15 November 2004 / Accepted: 3 February 2005

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The use of GPS for the deflection and deformation monitoring of structures has been under investigation for a number of years. Previous work has shown that GPS not only measures the magnitude of the deflection of the structure, but also it is able to measure the frequency of the movement. Both sets of information are useful for structural engineers when assessing the condition of the structure as well as evaluating whether Finite Element (FE) models of such structures are indeed correct. GPS has the advantage of resulting in an absolute 3-D position, with a very precise corresponding time tag. However, until recently, the maximum data rate was typically 10-20 Hz, meaning that the maximum detectable frequency was about 5-10 Hz. GPS also has the disadvantage of multipath and cycle clips, and the height component’s accuracy is typically 2 – 3 times worse than that of plan. Previous work at the IESSG has included the integration of RTK GPS, gathering data at a rate of up to 10Hz, with that of data from an accelerometer, typically gathering data at up to 200 Hz. Accelerometers tend to drift over time, and can not detect low vibration frequencies, but the acceleration data can be double integrated resulting in changes in positions. The integration of GPS and accelerometers can help to overcome each others’ shortfalls. This paper investigates the use of high rate carrier phase GPS receivers for deflection monitoring of structures. Such receivers include the Javad JNS100, capable of gathering data at up to 100 Hz. Static trials have been conducted to investigate the precision of such a receiver, as well as the potential applications of such a high data rate. Trials were carried out in a controlled environment and actual bridge monitoring, and comparisons made with a Leica SR510 receiver.

Cedric Seynat
GPSat Systems Australia, Australia
Allison Kealy
The University of Melbourne, Australia
Kefei Zhang
RMIT University, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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For an increasing number of applications, the performance characteristics of current generation Global Navigation Satellite Systems (GNSS) cannot meet full availability, accuracy, reliability, integrity and vulnerability requirements. It is anticipated however that around 2010 the next generation of GNSS will offer around one hundred satellites for positioning and navigation. This includes constellations from the US modernised Global Positioning System, the Russian Glonass, the European Galileo, the Japanese Quasi-Zenith Satellite System and the Chinese Beidou. It is predicted that the performance characteristics of GNSS will be significantly improved. To maximise the potential utility offered by this integrated infrastructure, this paper presents an approach adopted in Australia to quantify the performance improvements that will be available in the future. It presents the design of a GNSS simulation toolkit developed in Australia and the performance expectations of future GNSS for a number of important applications within the Asia Pacific region. In quantifying the improvement in performance realised by combined systems, this paper proposes a practical approach to facilitate the development of innovative applications based on future GNSS.

Donald H Sinnott
Department of Transport and Regional Services, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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In May 2000 the Australian Minister for Transport and Regional Services, advised by his Department, established a non-executive stakeholder body, the Australian GNSS Coordination Committee (AGCC), with terms of reference aimed at national coordination of GNSS application. This initiative responded principally to perceptions of potential for economies and efficiencies from national-level standardising and investment-sharing of equipment and services, especially in GNSS infrastructure and augmentation. In the event, in its first three years the AGCC was little able to exert significant influence in such market-driven areas. Rather, it successfully developed for government endorsement, in August 2002, a wide-ranging national GNSS policy and also addressed priority applications issues concerning GNSS jamming and interference, spectrum licensing, legal positioning/timing matters, and national and international connections, including with GPS and Galileo program management. Following a performance review in 2003 the AGCC’s mandate was extended to 2006, with revised terms of reference. This paper critically examines the experience of the AGCC in national-level coordination of GNSS application. As in many countries, Australia does not control sources of GNSS signals and applications are pervasive within a free-market economy. No single government agency or industry sector has general GNSS control or policy mandate. The degree to which, in this environment, a non-executive body like the AGCC can be effective in its role is discussed. The experience and future plans of the AGCC reported in this paper raise topics of relevance not only for Australia but for other countries as well that seek a degree of national coordination and efficiency in GNSS application.

S. Skone, R. Yousuf, A. Coster
University of Calgary, Canada
Received: 15 November 2004 / Accepted: 3 February 2005

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One of the greatest challenges in developing accurate and reliable satellite-based augmentation systems (SBAS) is modeling of ionospheric effects. Wide area GPS networks are generally sparse (station spacings of 500-1000 km), and ionosphere models can suffer degraded performance in regions where large spatial gradients in total electron content (TEC) exist. Of particular concern for Wide Area Augmentation System (WAAS) users is the feature called storm enhanced density, which is associated with large TEC gradients at mid-latitudes. This effect is a significant source of error in the WAAS correction models. The Canadian GPS Network for Ionosphere Monitoring (CANGIM) consists of three GPS reference stations in western Canada, augmented by two additional sites in the northern United States. In addition to measures of ionospheric activity, WAAS messages are collected continuously at these sites and decoded (post-mission) at University of Calgary. Localization schemes have been developed to compute WAAS ionosphere corrections for any location in North America. In this paper, performance of the broadcast WAAS ionosphere model is quantified through comparison with truth data from over 400 GPS reference stations in North America. WAAS ionosphere model accuracies throughout North America are evaluated for intense storm events, and compared with WAAS Grid Ionosphere Vertical Error (GIVE) bounds. Limitations in the WAAS ionosphere model are identified for enhanced ionospheric activity and, in particular, the storm enhanced density phenomenon.

Hideto (Duke) Takahashi
ITOCHU Corporation, Japan
Received: 15 November 2004 / Accepted: 3 February 2005

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Current Global Navigation Satellite Systems (GNSS) have enabled quality of life improvements and new business opportunities on an international scale. The range of applications and improvements includes a multitude of disciplines such as Agriculture, Transportation, Recreation, Public Safety and Security. Independent financial institutions have estimated the annual business market value for GNSS user equipment and related components in the billions of US dollars. The Government of Japan recognizes the importance of investing in GNSS today to establish a foundation for future quality of life improvements and business opportunities for current and future generations. The current Japanese program QZSS—Quasi Zenith Satellite System with 3 GPS-supplementary satellites—represents a bold step in the development of a Regional Navigation Satellite System (RNSS) for all of Asia. In January 2004, the Council for Science and Technology Policy (CSTP) in the Cabinet Office published a report regarding the future outlook of RNSS in Japan. This paper provides an update on QZSS progress, the real-world challenges and demands facing Japanese decision makers as reflected in the CSTP report, and a glimpse into the future options for the expansion of 3-satellite QZSS to a 7-satellite constellation system that can autonomously provide satellite-based position, velocity and time services, while preserving the reciprocity and compatibility with the GPS. In September 2004, CSTP published another report regarding space policy that states a long-term goal of the government to build the "autonomous" and "GPS-complementary" regional satellite navigation system in the future.

Todd Walter, Juan Blanch, Jason Rife
Stanford University, US
Received: 15 November 2004 / Accepted: 3 February 2005

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The original protection level equations for SBAS assumed that all actual error distributions could be easily overbounded by zero-mean gaussian distributions. However, several error sources have since been found that could lead to significant biases for specific users. The expectation is that over long periods of time and all users, the aggregate errors should have a very small mean. However, certain users, at specific times or locations, may have significant biases in their measured pseudoranges. One source of bias is signal deformations. Originally thought of as a failure mode, it is now recognized that geostationary satellites have a noticeably different signal than the GPS satellites (primarily due to their bandwidth limit). Recent results also show that the GPS satellites have measurable differences from satellite to satellite as well. The magnitude and sign of the biases depend on the user equipment and have been shown to have significant unit-to-unit variation. A biased distribution may be overbounded by a zero mean gaussian, provided the sigma value has been sufficiently increased. As the bias becomes larger, this inflation leads to a greater loss of availability than if the protection level equations had explicitly accounted for it. It is therefore important to find the smallest possible inflation to adequately bound the bias. This paper makes use of new overbounding methods to relate the required inflation to the bound.

Jeong Won Kim, Han Jin Jang, Dong-Hwan Hwang
Chungnam National University, Korea
Chansik Park
Chungbuk National University, Korea
Received: 15 November 2004 / Accepted: 3 February 2005

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Recently, several simple and cost-effective pedestrian navigation systems (PNS) have been introduced. These systems utilized accelerometers and gyros in order to determine step, stride and heading. The performance of the PNS depends on not only the accuracy of the sensors but also the measurement processing methods. In most PNS, a vertical impact is measured to detect a step. A step is counted when the measured vertical impact is larger than the given threshold. The numbers of steps are miscounted sometimes since the vertical impacts are not correctly measured due to inclination of the foot. Because the stride is not constant and changes with speed, the step length parameter must be determined continuously during the walk in order to get the accurate travelled distance. Also, to get the accurate heading, it is required to overcome drawbacks of low grade gyro and magnetic compass. This paper proposes new step, stride and heading determination methods for the pedestrian navigation system: A new reliable step determination method based on pattern recognition is proposed from the analysis of the vertical and horizontal acceleration of the foot during one step of the walking. A simple and robust stride determination method is also obtained by analysing the relationship between stride, step period and acceleration. Furthermore, a new integration method of gyroscope and magnetic compass gives a reliable heading. The walking test is preformed using the implemented system consists of a 1-axis accelerometer, a 1-axis gyroscope, a magnetic compass and 16-bit microprocessor. The results of walking test confirmed the proposed method.

K.Zhang, R. Deakin, R. Grenfell, Y. Li, J. Zhang, W.N. Cameron, D.M. Silcock
RMIT University, Melbourne, Australia
Received: 9 December 2004 / Accepted: 3 February 2005

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This paper introduces two sport-related projects conducted by the Satellite Positioning and Orientation Research Team (SPORT) at RMIT University – speed sailing world record challenge and development of a smart GPS rower tracking system. In the first project, both traditional and contemporary surveying technologies are investigated to assist the Macquarie Speed Sailing Team to reliably record and subsequently claim a world speed sailing record. In the second project, an integrated rower tracking system has been developed in collaboration with other research partners and the system has been used prior to and during the Athens Olympic Games. Three Olympic rowing medals were won by Australia. The technology, research procedures and major developments are presented.

Samsung Lim
The university of New South Wales, Australia
Binh Quoc Tran
Hanoi University of Sciences, Vietnam
Received: 15 November 2004 / Accepted: 3 February 2005

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Because of the integer-valued nature of carrier phase ambiguities, it is essential to fix the float estimates into integer values in order for high precision DGPS positioning. A decorrelation process is necessary to solve the problem since double-differenced ambiguities are highly correlated in general. In this paper, Block Decorrelation Method (BDM) is presented and tested for its convergence. BDM divides the variance-covariance matrix into four blocks and decorrelates them simultaneously. A number of randomly selected examples show that BDM is comparable to the existing decorrelation algorithm, however its speed of convergence is relatively faster due to the computations performed on small blocks.

C. Rizos, T.S. Yan
University of New South Wales, Australia
D.A. Kinlyside
Department of Lands, Australia
Received: 15 November 2004 / Accepted: 3 February 2005

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Over the past few years, there has been substantial growth in multiple-reference-station networks used to overcome the limitations of standard real-time kinematic (RTK) systems. SydNET is a project to establish a permanent real-time GPS network in the Sydney basin area providing Network-RTK support to users in the area. SydNET is being developed by NSW Department of Lands in partnership with the School of Surveying & SIS at the University of New South Wales. This paper presents recent developments of the SydNET network. Preliminary test results will be presented which will show the network’s performance, achievable accuracy. It will outline the SydNET system, its operation, current status and vision of future development as a high precision positioning service infrastructure.

Wu Chen, Congwei Hu, Zhihua Li, Yongqi Chen, Xiaoli Ding, Shan Gao, Shengyue Ji
The Hong Kong Polytechnic University, Hong Kong
Received: 15 November 2004 / Accepted: 3 February 2005

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In this paper, the basic precise point positioning model has been reviewed. A recursive least square algorithm that separates the position coordinate sand other parameters, such as ambiguities and tropospheric delays, is proposed for kinematic PPP applications. A test was carried out to test the method proposed in this paper, which made use of a GPS buoy equipped with a pressure and a tilt meter to monitor the sea level in Hong Kong. The initial results from kinematic PPP positioning compared with conventional kinematic positioning methods shows the accuracy of decimetre level positioning accuracy can be achieved by the PPP method.

Walter Blanchard
Royal Institute of Navigation, UK
Received: 15 November 2004 / Accepted: 3 February 2005

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No navigator likes to be totally dependent on only one navaid – it is an article of faith for many that there should always be a backup system. Several systems have been put forward as possible backups for a GNSS but they seem to have originated more in a generalised feeling that there ought to be one rather than a dispassionate examination of what is involved. GPS/Galileo are radical departures from any previous concepts of radio navigation aids and a full-blown GNSS is an even more radical proposal. There is a good deal more involved than simply engineering and technical matters. There are the questions of who controls them; what the customer interface is; who certifies them for use in safety-related situations; and what legal recourse there is. On the answers to these questions depends whether a backup is needed and if so what form it should take. It is found in this paper that for many non-critical users there is no need for a backup, and that others who may be involved in safety-critical situations already have a backup in the form of their current systems. It is also found that in fact it may be extremely difficult to compose a GNSS in the form it is generally given; that is, a combination of GPS, Galileo and perhaps Glonass. The problem lies not in on the engineering side, but in matters of legality and the sovereignty of individual nations. For these reasons it is concluded that the development or implementation of a new system purely to act as a backup for a GNSS is not necessary.

Tajul A. Musa, Jinling Wang, Chris Rizos, Young-Jin Lee
University of New South Wales, Australia
Azhari Mohamed
Department of Survey and Mapping, Malaysia
Received: 15 November 2004 / Accepted: 3 February 2005

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Existing apriori tropospheric models are not sufficiently accurate to remove tropospheric delay from GPS observations. Remaining effects of residual tropospheric delay need to be estimated to ensure high accuracy and reliability of GPS positioning. Other researchers have shown that implementations of network-based positioning techniques can adequately model the residual tropospheric delay as well as ionospheric delay and orbit biases. However, the effectiveness in removing residual tropospheric delay is highly dependent on the degree to which the wet component from the troposphere can be estimated or mitigated, an effect which shows strong variation with time and space. The aim of this paper is to illustrate the performance of an existing apriori tropospheric model and to discuss some issues concerning the estimation of the (total) tropospheric delay in the equatorial area. Finally, the network approach is applied to mitigate the effect of residual tropospheric delay. Some preliminary results from test experiments using GPS network data from an equatorial region, a location with the highest effect of tropospheric delay, are presented.

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