Session C4: INTEGRATION OF GPS & GALILEO
Paper #1

ADVANTAGES OF GPS PLUS GALILEO:
J. Spiller, R. Peckham, T. Tapsell, Astrium, UK

Since the launch of GPS, there continues to be strong growth in the development of technologies able to exploit satellite derived position and timing information for commercial and private uses. Applications include aircraft and maritime navigation, road transport fleet management, private in-car navigation, surveying, sailing and other leisure pursuits, animal tracking in wildlife conservation programmes and many more.

The planned development of the European Galileo satellite navigation system alongside GPS and its various augmentation services extends the number of satellite position and timing services that will become available in a few years. This could be particularly beneficial to critical and safety related applications such as civil aviation where total dependence upon a single navigation sensor poses considerable risk. The additional satellites also offers worthwhile improvements for many other users of the technology. This paper considers the range of applications and possible benefits that might be gained from a hybrid and complementary GPS/Galileo services.
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Session C4: INTEGRATION OF GPS & GALILEO
Paper #2

GPS AND GALILEO - COMPATIBILITY AND INTEROPERABILITY FOR KEY APPLICATIONS:
P.M. Fyfe, The Boeing Company

GPS is presently provides positioning and timing services worldwide for a wide variety of applications, and for the majority of them the present GPS performance is more than sufficient. The Galileo system currently being defined will provide a universally available service with similar performance to GPS, plus different capabilities to satisfy more demanding applications. Both systems will operate simultaneously and so it is paramount that they do not interfere with each other. Availability of the two systems also provides the opportunity to enhance and expand some applications as well as develop new ones.

This paper evaluates several major elements in signal and system design from the aspect of compatibility (do not interfere/separate systems) and interoperability (combined use of two systems). It discusses features that support compatibility and interoperability, and identifies issues that need to be worked to allow compatibility and interoperability. Elements evaluated include frequency plans, signal characteristics and structure, time and position reference frames and integrity concepts. Present international efforts will be reviewed and recommendations for further studies made.
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Session C4: INTEGRATION OF GPS & GALILEO
Paper #3

THE EFFECT OF GALILEO ON CARRIER PHASE AMBIGUITY RESOLUTION:
P. Alves, The University of Calgary, Canada

ION Sponsored Student Paper
In order to achieve the highest level of positioning accuracy using GPS, one must first determine the carrier phase integer ambiguities. This will also be true with the Global Navigation Satellite System (GNSS) proposed by the European Union, Galileo. This paper discusses the effect of the proposed satellite system, GPS, and an integrated solution of the two systems on ambiguity resolution in kinematic mode. This paper will examine the effectiveness of ambiguity resolution with the Galileo GNSS, GPS, and a combined solution.

The addition of the Galileo constellation will increase the efficiency and reliability of ambiguity resolution when combined with GPS. The addition of 30 satellites transmitting with L-Band frequencies can decrease the time required for a user to wait before determining the correct integer ambiguities and therefore achieving the best possible position accuracy.
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Session C4: INTEGRATION OF GPS & GALILEO
Paper #4

AVAILABILITY AND RELIABILITY ADVANTAGES OF GPS/GALILEO INTEGRATION:
K. O'Keefe, University of Calgary, Canada

ION Sponsored Student Paper
The performance of a Global Navigation Satellite System (GNSS) can be quantified by availability, accuracy and reliability. The deployment of Galileo by the European Union will provide double the number of navigation satellites currently available to users and offer improvements in accuracy and reliability. This paper briefly describes the design of the proposed Galileo system. Availability and accuracy are then defined and statistical reliability theory is reviewed. Worldwide availability, accuracy and reliability estimates for GPS, Galileo and the combined GPS/Galileo system are obtained by software simulation. The simulation results are presented using Horizontal Dilution of Precision (HDOP) as a measure of availability and accuracy and maximum Horizontal Position Error (HPE) due to one undetected blunder as a measure of reliability. The proposed 30 satellite, 3 orbital plane Galileo constellation shows a slight improvement over the existing GPS constellation when low elevation masks are employed. At higher mask angles GPS slightly outperforms Galileo. The use of the two systems together is shown to provide major improvements in accuracy and reliability. A local simulation comparing the availability of GPS and Galileo in an urban environment is also presented. The use of GPS and Galileo together is shown to provide the necessary satellite availability to obtain a navigation
solution in extreme masking environments.
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Session C4: INTEGRATION OF GPS & GALILEO
Paper #5

AVAILABILITY AND ACCURACY OF COMBINED GPS AND GALILEO OBSERVATIONS IN RTK APPLICATIONS:
J. Johansson, P. Jarlemark, SP Swedish National Testing and Research Institute

Global Navigation Satellite Systems (GNSS) have the potential to provide users worldwide with accurate co-ordinate results in real time. GNSS carrier phase-based methods used in real time, usually referred to as Real Time Kinematic (RTK) positioning, has the capability to provide centimetre-level results. Thus, GNSS may be a very effective tool at very low cost.

Unfortunately, the technique is very sensitive to several different error sources. Some of these are natural, such those associated with the signal path delay trough the atmosphere of the Earth. Others are tightly connected to the observation methods or the location where the observations are made. In this paper we have evaluated the possibility to use any single GNSS, or a combination of several such systems, in RTK measurements for several different locations at high latitude.

We have used computer simulations to study the RTK technique performance depending on the different local conditions. The study was initiated by the Swedish National Rail Administration and their observational condiations and accurcy requirements were used in the computer simulations. Obstructions, such as forests and rocks, near the receiving antennas may limit the performance of GNSS-based methods. Signals from the satellites may be blocked, delayed or reflected by the obstruction causing outages or serious errors.

The accuracy requirements that are to be met are 15 mm (2 sigma) both horizontally and vertically. However, currently there is an investigation regarding the possibility to lower the accuracy requirement to 25 mm (2 sigma) instead. The simulations include both these scenarios.

We have made simulations that can help to give a priori indications on the quality of RTK measurements using several different configurations under a large variety of conditions. We have compared the results obtained from using GPS only with those obtained from combined GPS and Galileo observations. We also report on the effects casued by reflection (multipath), high elevation masks, and delay caused by trees and forests.
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Session C4: INTEGRATION OF GPS & GALILEO
Paper #6

GALILEO PERFORMANCE IMPROVEMENT FOR URBAN USER:
M. Malicorne, M. Bousquet, V. Calmettes, Supaero, France

Over the past few years, many applications of satellite navigation system have been developed. Europe has initiated the Galileo program targeting the implementation of navigation system independent and interoperable with GPS and Glonass. Among the wide range of applications of such system, transportation in urban environment seems to be one of the most prominent. Hence, it is important to fully and accurately characterize the receiver performance for this application.

Investigating the receiver performance in this medium requires a model of the wave propagation. A deterministic method, based on geometrical optic, has been selected and allows to model the environment in 3D and multipath propagation to the desired level of accuracy. So, a ray launching simulation tool is used to characterize different environments and to observe the receiver errors due to multipath and the receiver performance with and without augmentation.

In order to calibrate the performance of the simulation tool, measurements of satellite visibility statistics for different types of environments have been performed and compared with the results obtained with our simulation tool. The urban environment is characterized by high masking angles and the presence of a great number of obstacles which produce multipath. We may assume that an urban user needs availability greater than 90% with an accuracy better than 10 meters. However meeting this objective is not generally an easy task since the urban medium presents quite constraining conditions which do not always enable to compute the user location at the level of accuracy required. Several types of solutions to improve the system performance are considered in this paper :
- Sensors as baro-altimeter or dead reckoning
- Differential station
- Pseudolites

In our simulations, the architecture of Galileo is based on MEO constellation of 30 satellites with 3 spares at an altitude of 23616 km, with an inclination of 56, distribute over 3 planes, and only the case of the non coherent delay lock loop is considered.
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Session C4: INTEGRATION OF GPS & GALILEO
Paper #7

AN INTEGRATED GNSS CONCEPT, GALILEO & GPS, BENEFITS IN TERMS OF ACCURACY, INTEGRITY, AVAILABILITY AND CONTINUITY:
M.M. Romay Merino, E. Herriz Monseco, A.B.M. Peir, GMV S.A., Spain

The design of the future Global Navigation Satellite Systems should be oriented to the mass market. Neither GPS nor Galileo will be able to satisfy requirements of users under stringent masking conditions (like users in urban environments) or very demanding integrity requirements without additional augmentation systems. This is a major drawback for each of the systems that will have to be overcome by using additional means and therefore increasing not only the cost of the system but also the cost of the user equipment. Another possibility will be to use simultaneously Galileo and GPS, this optionwill be investigated thoroughly in this paper. The major benefits of the integration of Galileo & GPS will be presented and supported by simulations.

A performance assessment tool has been developed. This tool allows the analysis of the performances of the Galileo and GPS constellations independently and it also covers the cases of simultaneous operations. Performances will be analysed by computing:
- Accuracy; the horizontal and vertical positioning accuracy provided by the independent and combined constellations will be computed.
- Availability; different availability concepts will be analysed for all possible cases. In particular, the classical mean availability concept will be studied as well as the service provider oriented concept of availability over a certain time period.
- Outage time; the maximum continuous time without providing the service will be analysed for each possible configuration.
- Continuity; the continuity of the service will also be analysed for each possible configuration.

A particular effort has been devoted to the analysis of performances in urban environments and RAIM (Receiver Autonomous Integrity Monitoring) algorithms.

It should be considered that most of the users are located in urban environments and buildings frequently block the visibility of satellites. Under these circumstances, it is difficult to obtain a navigation solution. To improve this, a significant number of satellites would have to be launched. A pragmatic approach will be based on the use of Galileo and GPS simultaneously. A simulation tool allowing the analysis of urban environments has been developed and the improvement achieved by combining Galileo with GPS will be shown. Different types of urban environments will be analysed to try to obtain some representative figures. It can be advanced that the benefit obtained is quite remarkable.

Current RAIM algorithms are very much oriented to GPS, where due to the number of satellites in view the performances achieved are not satisfactory for many users. When using simultaneously Galileo and GPS a user may expect to have in view around 15 satellites. This opens some new possibilities for developing some new algorithms. A new RAIM algorithm has been developed and the major results and conclusions will be shown in this paper. It can be advanced that the use of GPS and Galileo in combination with RAIM algorithms will satisfy most of the users in terms of integrity.
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Session C4: INTEGRATION OF GPS & GALILEO
Paper #8

GALILEO CONSTELLATION MEO ONLY - ADVANTAGES AND DISADVANTAGES:
J. Januszewski, Gdynia Maritime Academy, Poland

Nowadays there are two world wide satellite systems - American GPS and Russian GLONASS. A new system - Galileo will be constructed in Europe. The calculations were realized for the most possible Galileo constellation - MEO only - 30 satellites distributed in 3 planes in an altitude 23222 km and with an inclination 54 degrees. Fix position can be calculated from these satellites only, which elevation angle at moment of measurement is higher than masking elevation angle Hmin. The geometry of the visible satellites is an important factor in achieving high quality results. A measure for this geometry (which changes with time) is Geometric Dilution of Precision - GDOP.

We can ask the questions:
* if all 30 satellites are fully operational which is the distribution of the number ls of satellites visible and the distribution of GDOP coefficient value for different Hmin at different observer's latitude,
* can the user equipped with Galileo receiver obtain her position at each moment and at each point on the Earth when one or more satellites SNO (satellite non operational) of this system is out of service?
* how GDOP increases for SNO = 1, 2 and 3 for different Hmin and for different observer's latitude?

The latitude of observer 0'90O was divided into 9 zones, each 100 wide. Angle Hmin was assumed 0O, 5O, 10O and 15O. Satellite selection criterion (combination of 4 satellites) was founded on the minimization of GDOP. All calculations, based upon a reference ellipsoid WGS-84, were made with the use of author's simulating program. For 30 satellites fully operational and for each number of SNO, for each zone of latitude and for each Hmin 1000 geographic-time coordinates of the observer were generated by random-number generator with uniform distribution. For each coordinates the number ls and GDOP coefficient value were calculated. GDOP value was divided into 8 intervals.

The results are demonstrated in different tables. The number of Galileo satellites visible depends on latitude of observer and for Hmin = 0O changes between 8 and 14, for 15O between 3 and 11. The weighed mean number of these satellites has minimum for Hmin = 0O (10,95), in zone 30'40O, for Hmin = 15O (7,61) in zone 40'50O and maximum for Hmin = 0O (12,62) in zone 60'70O, for Hmin = 15O (9,29) in zone 80'90O. GDOP coefficient value is less at latitude 0'70O than at latitude 70'90O, irrespective of Hmin, considerably. If the number of satellites fully operational is less than 30, the increase of GDOP depends on the number SNO and their position on the orbit, the angle Hmin and the latitude of observer. If Hmin = 15O and SNO = 1 or 2 the position in option 3D can be obtained in each zone, if SNO=3 at latitude 70'90O only.

Comparison of Galileo constellation against GPS constellation (24 satellites) is demonstrated in this paper also. At latitude 40'70O (latitude of Europe) Galileo constellation is better for the user (GDOP coefficient is smaller) than GPS constellation considerably.
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Session C4: INTEGRATION OF GPS & GALILEO
Alternate #1

NAVIGATION RELATED COMMUNICATION SERVICES, THE CASE OF A GALILEO SERVICE OPTION:
R. Pasquali, G. Mocci, R. Capua, M. Biagini, S. Viviano, S. Carlini, Telespazio S.p.A, Italy

One of the options for GALILEO service elements are the Navigation Related communication Services (NRS): a two-way packed date communication capability bundled with GALILEO navigation services.

The proposal of the NRS option for GALILEO service definition, obliges the navigation community to think around a change in the system and service paradigmas defined (with success) by GPS.

But from the Mobile Service Providers and the Final Users point of view this GALILEO perspective is quite natural, convergent and complementary to the tendency of UMTS NAV/COM service convergence. In the next decade scenario a (low data rate but RT) communication service integrated a (highly performing) navigation service from space, could really be synergetic with the (low performance) navigation and the (high data rate, high performance) communication services expected to be supported by the next generation of mobile radio network.

NRS option for GALILEO is presented in the future evolution of navigation/location market structure and of the mobile services value chain. The comparative and competitive analysis of GALILEO NRS versus present and incumbent technologies (GPS and mobile communication networks) is here derived. The expected market associated to this service elements is therefore characterised and quantified.

GALILEO NRS service performances and system design are detailed together with the result of different (but convergent) market analysis. The business model for the NAV/COM service downstream and the Business Case for the NRS Service Operator and for the VAS Service Provider is detailed.

The capability to provide from a GNSS constellation a bundled service competitive with the future NAV/COM integrated solutions is based on a market driven system design. Service performance, terminal weight/dimension/cost, as well as satellite antenna design have been defined starting from the NRS market needs and the GALILEO mission and design constraints.

In conclusion here is shown as a system based on a 60Kg/600W bent pipe communication payload on each GALILEO satellite, can become one of the future standard platform for Personal Emergency, Fleet Management and Info-mobility. It is shown how GALILEO NRS alone can generate commercial revenues (from the European market) to largely balance the whole GALILEO (NAV and COM) operative costs. Finally in this paper it is detailed as the GALILEO NRS, costing 0.003 Euro for 100 Byte packet, could sustain a business case for a purely private financing approach to this element of GALILEO.

NRS technical and business case was studied in "PPP Case Study" for the European Space Agency, in "Euronav", "Sidereus", "GEMINUS" and "GALA" for the European Commission and in "STENAV" for the Ente Nazionale Assistenza al Volo as well as in a number of internally funded studies.
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Session C4: INTEGRATION OF GPS & GALILEO
Alternate #2

PROPAGATION DELAYS IN A GNSS2 PAYLOAD DEMONSTRATOR:
L. Lestarquit, L. Ries, J. Dantepal, C. Zanchi, L. Lapierre, F. Gizard, M. Brunet, J. Delporte, J.F. Dutrey, P. Dumon, J.L. Issler, CNES, France

The CNES ( french space agency ) engaged the predevelopment of a GNSS2 navigation payload demonstrator. The goal of this demonstrator is to study in detail the stability of the propagation times ( group delay, phase delays ) of the complete payload, as this stability is involved in the UERE budget.

This payload is constituted of a very stable clock, a C/A code signal generator, a L1 and L2 frequency synthesizer, BPSK modulators, and L1/L2 transmission channel, including filters and power amplifiers. The L1 filter is specified to be compliant with the E1 transmission chain of GALILEO, and its bandwidth is maximized in order to minimize the impact of multipath and group delay thermal variations. The payload is driven by two types of clocks : Hydrogen Maser ( as a frequency reference ) or a spaceceborne atom clock ( prototype ).

The experimentations are carried out in a thermal controlled environment, allowing to simulate an on board thermal regulation system. The navigation signals are analyzed by a prototype of GNSS2 receiver and a numerical oscilloscope provided with a high sampling rate. The group delays are computed using correlation functions at the output of each equipment of the payload, and pseudorange measurements.

The paper describes in detail the architecture of this navigation payload demonstrator and the associated test bench. It discusses also preliminary results.
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