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17-06-2010, 01:34 PM

.docx   GALILEO-GLOBAL NAVIGATION S YSTEM.docx (Size: 256 KB / Downloads: 73)

Satellite Communications

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Final ECE
Final ECE


GALILEO is the European satellite radionavigation programme. It was launched at the initiative of the European Commission and developed jointly with the European Space Agency . It will lead to the development of a new generation of universal services in sectors such as transport, telecommunications, agriculture or fisheries. So far, only the American GPS system and the Russian GLONASS system have harnessed this technology . Galileo uses satellite radio navigation which is an advanced technology. It is based on the emission from satellites of signals indicating the time extremely precisely. This enables any individual to determine his or her position or the location of any moving or stationary object to within one metre using a small cheap individual receiver. GALILEO is based on a constellation of 30 satellites and ground stations providing information concerning the positioning of users in many sectors such as transport, social services, the justice system and customs services, public works, search and rescue systems . The Galileo satellite navigation system is the European alternative to the US Global Positioning System (GPS) and the Russian GLONASS, both funded and controlled by military authorities. Devised by the EU and the European Space Agency (ESA).Due to the diverse applications we are intended to go with this paper.


The Galileo project and implimentation is being developed in four phases . They are
1) Definition phase (2000)
2) Development and validation phase (2001-2005)
3) Deployment phase (2006-2007)
4) Operating phase (from 2008)
The fully deployed Galileo system consists of 30 satellites (27 operational + 3 active spares), positioned in three circular Medium Earth Orbit (MEO) planes in 23616 km altitude above the Earth, and at and inclination of the orbital planes of 56 degrees with reference to the equatorial plane. Once this is achieved, the Galileo navigation signals will provide a good coverage even at latitudes up to 75 degrees north, which corresponds to the North Cape, and beyond. The large number of satellites together with the optimisation of the constellation, and the availability of the three active spare satellites, will ensure that the loss of one satellite has no discernible effect on the user.
A user will be able to take a position with the same receiver from any of the satellites in any combination. By offering dual frequencies as standard, however, Galileo will deliver real-time positioning accuracy down to the metre range, which is unprecedented for a publicly available system. It will guarantee availability of the service under all but the most extreme circumstances and will inform users within seconds of a failure of any satellite. This will make it suitable for applications where safety is crucial, such as running trains, guiding cars and landing aircraft.

Why Europe needs Galileo :

Satellite navigation users in Europe today have no alternative other than to take their positions from US GPS or Russian GLONASS satellites. Yet the military operators of both systems give no guarantee to maintain an uninterrupted service.
As far back as the early 1990s, the European Union saw the need for Europe to have its own global satellite navigation system. The conclusion to build one was taken in similar spirit to decisions in the 1970s to embark on other well-known European endeavours, such as the Ariane launcher and the Airbus. The European Commission and European Space Agency joined forces to build Galileo, an independent system under civilian control which will be guaranteed to operate at all times, bar the direst emergency. Galileo is now at the point of moving from definition to full-scale development.
European independence is the chief reason for taking this major step. However, other subsidiary reasons include:
By being inter-operable with GPS and GLONASS, Galileo will be a cornerstone of the Global Navigation Satellite System (GNSS). This system will be under civilian control and will allow positions to be determined accurately for most places on Earth, even in high rise cities where buildings obscure signals from satellites low on the horizon. This is because the number of satellites available from which to take a position more than double.
By placing satellites in orbits at a greater inclination to the equatorial plane than GPS, Galileo will achieve better coverage at high latitudes. This will make it particularly suitable for operation over northern Europe, an area not well covered by GPS. With Galileo, Europe will be able to exploit the opportunities provided by satellite navigation to the full extent. GNSS receiver and equipment manufacturers, application providers and service operators will benefit from novel business opportunities. Under request from the European Commission, PricewaterhouseCoopers (PwC) prepared astudy on the business plan for the Ga l i l e o p r o g r a m m e .

Infrastructure :

Space and Ground Segment The core of the Galileo system is the global constellation of 30 satellites in medium Earth orbit, three planes inclined at 56° to the equator at about 23 222 km altitude. Nine satellites will be spread evenly around each plane, with each taking about 14 hours to orbit the Earth. Each plane has one additional dormant spare, able to provide cover for any failed satellite in that plane.The satellites will use largely proven technologies.The body will rotate around its Earth- pointing (yaw) axis for its solar wings to rotate and point towards the Sun (generating peak power of 1600 W). A basic box structure will group the payload and platform elements.The launch mass is about 700 kg each.
After the initial constellation is established, further launches will replace failed satellites and replenish the system as the original satellites reach their ends of life. The baseline for creating the constellation is to carry multiple satellites on a single rocket, with a dispenser able to deliver up to six spacecraft simultaneously into medium Earth orbit. Smaller launchers will be used for the early in-orbit validation missions and for replenishments. A network of ground stations consisting of sensor stations, control centres and uplink stations will support satellite operations. A worldwide network of Galileo Sensor Stations will continuously monitor the satellites. Its precise measurements of the navigation signals will be sent to the two Galileo Control Centres, in Europe, for further processing. There, sophisticated software will determine the satellite orbits and the time synchronisation error of the satellitesâ„¢ atomic clocks with respect to the Galileo system time maintained on the ground.
The orbits and clock data will be uploaded to the satellites about every 2 hours for dissemination to the users, who will use them in their position-calculation algorithms. Such a 2frequent update rate will achieve the high level of positioning accuracy demanded of the system.The Control Centres will also compute the integrity data,which are provided as part of the Safety-of-Life service. The integrity data will be uploaded to the satellites for dissemination to the users even more frequently than the orbit and clock data. In the case of alarms (e.g.malfunctioning signals), the system will be able to alert the users with a delay of only 6-10 seconds.
Data transfer to and from the satellites will be performed through a global network of Telemetry, Telecommunications and Tracking Stations (satellite control and monitoring data) and Mission Uplink Stations (uplinking navigation data: orbits, clock errors, integrity). The integrity data computed at the Galileo Control Centres will be usable by any users worldwide because they are based on the measurements from the global network of sensor stations . However, it will also be possible for regional service providers to deploy their own networks of sensor stations to compute the integrity of the Galileo signals over their region.Those regional integrity data can be made available to the users via authorised integrity uplink channels provided in the Galileo satellites. Alternatively, those data can also be sent to the Galileo Control Centres for integration with the integrity data computed centrally. Local components will enhance the above with local data distribution via terrestrial radio links or existing communication networks, in order to provide extra accuracy, integrity or extended coverage around airports, harbours, railways and in urban areas. Local components will also be deployed to extend navigation services to indoor users.

How to build up a constellation of 30 navigation satellites:

Planners and engineers at ESA have good reasons for choosing such a structure for the Galileo constellation. With 30 satellites at such an altitude, there is a very high probability (more than 90%) that anyone anywhere in the world will always be in sight of at least four satellites and hence will be able to determine their position from the ranging signals broadcast by the satellites..From most locations, six to eight satellites will always be visible allowing positions to be determined very accurately, to within a few centimetres. Even in high rise cities, there will be a good chance that a road user will have sufficient satellites overhead for taking a position, especially as the Galileo system will be interoperable with the US system of 24 GPS satellites. So to build up such a constellation of satellites and ensure that each one is in precisely the correct position at any time will take place in stages.
First, ESA will launch an experimental satellite at the end of 2005 on board a Soyuz launcher.The experimental satellite will be placed in the first orbital plane from where it will be used to test the equipment on board and the functioning of ground stations. It will also permit the securing of the Galileo frequencies within the International Telecommunications Union. This test campaign will last two and a half years.
Next, ESA will launch the first four operational satellites using two separate launchers. The first two satellites will be placed in the first orbital plane and the second in the second orbital plane. These four satellites, plus part of the ground segment, will then be used to validate the Galileo system as a whole, using advanced system simulators. Then, the next two satellites will be launched into the third orbital plane.
Once the Galileo system has been validated, the next and final stage will be to build up the rest of the constellation quickly so that a full service can be provided to users. The remaining satellites will each be launched by a heavy rocket like Ariane 5, Europe's heavy launcher, completing the constellation on all its 3 orbital planes and Galileo will be fully operational, providing guidance to a wide variety of users throughout the world.


The operating principle is simple, the satellites in the constellation are fitted with an atomic clock measuring time very accurately. The satellites emit personalised signals indicating the precise time the signal leaves the satellite. The ground receiver, incorporated for example into a mobile phone, has in its memory the precise details of the orbits of all the satellites in the constellation. By reading the incoming signal, it can thus recognise the particular satellite, determine the time taken by the signal to arrive and calculate the distance from the satellite. Once the ground receiver receives the signals from at least four satellites simultaneously, it can calculate the exact position The position accuracy depends on the accuracy of the time measurement. Only atomic clocks provide the required accuracy, of the order of nanoseconds (10“9 s), and the necessary stability, of the order of 10 nanoseconds per day for Rubidium Atomic frequency standard and 1 nanosecond per day for hydrogen- maser atomic clocks. Such clocks are a major technology element aboard the Galileo satellites and contribute to the definition of international time standards. The time measurement is improved by including the signal from a fourth satellite, so special care is being taken in selecting the numbers of satellites and their orbits.


Commercial Service(CS): It is aimed at market applications requiring higher performance than offered by the Open Service. It provides added value services on payment of a fee. CS is based on adding two signals to the open access signals.This pair of signals is protected through commercial encryption,which is managed by the service providers and the future GOC. Access is controlled at the receiver level, using accessprotection keys.
Open Service(OS):It is defined for mass- market applications. It provides signals for timing and positioning, free of direct user charge. The Open Service will be accessible to any user equipped with a receiver. While up to three separate signal frequencies are offered within the Open Service, cheap single-frequency receivers will be used for applications requiring only reduced accuracy. In general,Open Service applications will use a combination of Galileo and GPS signals,which will improve performance in severe environments such as urban areas.. Safety-of-Life Service (SoL): will be used for most transport applications where lives could be endangered if the performance of the navigation system is degraded without real-time notice. The Safety-of-Life Service will provide the same accuracy in position and timing as the Open Service.
Public Regulated Service: will be used by groups such as the police, coastguard and customs.Civil institutions will control access to the encrypted Public Regulated Service. Access by region or user group will follow the security policy rules applicable in Europe. The PRS is operational at all times and in all circumstances, including during periods of crisis. A major PRS driver is the robustness of its signal, which protects it against jamming and spoofing. Search and Rescue Service (SAR): is Europeâ„¢s contribution to the international cooperative effort on humanitarian search and rescue. It will allow important improvements in the existing system, including: near realtime reception of distress messages from anywhere on Earth (the average waiting time is currently an hour); precise location of alerts (a few metres, instead of the currently specified 5 km);multiple satellite detection to overcome terrain blockage in severe conditions; increased availability of the space segment .


Transport :The transport applications are the user category par excellence for Galileo.The system™s services will be used in every transport domain “ aviation,maritime, road, rail and even pedestrian.. In civil aviation, Galileo can be used in the various phases of flight: enroute navigation, airport approach, landing and ground guidance. In maritime navigation, Galileo will be used for onboard navigation for all forms of transport, including ocean and coastal navigation, port approach and port manoeuvres. Galileo™s characteristics, which make it suitable even for today™s most demanding applications, will permit the definition and development of new applications,such as the Automated Identification System (AIS), to improve safety in navigation.
Finance, Banking and Insurance :
As online financial transactions become an increasingly common part of daily life, the integrity, authenticity and security of transmitted data have emerged as major issues in the electronic exchange of documents. This usually calls for a dedicated encryption system.Similarly, e-banking suffers from risks such as falsified transactions and unauthorised access to documents,accounts and credit cards...Online systems have created the need for accurate and legally accepted documentation that provides detailed information on the user and the type and size of transaction

Agriculture and Fisheries:
With food security climbing ever higher up the decision-makersâ„¢ agenda, together with food risks and consumer concerns, achieving traditional productivity targets at all costs is no longer the main driver in agriculture.On the contrary, farmers aim for better quality agricultural products,while respecting the environment and maintaining acceptable income.Navigation can contribute to yield monitoring and the spraying of fertilisers, herbicides and insecticides to replenish low- yield areas and control of weeds and pests.Galileo receivers can be installed easily on harvesters, tractors and self-propelled sprayers.Proper yield monitoring entails not only effective resource management and consequently significant return, but also contributes to safeguarding the agrienvironment,which, in turn, is often regulated by a series of rules.

Personal Navigation:

Galileo opens the door to several location-based services by integrating positioning with communications,typically in handheld terminals. Ahandset will determinine its position using either Galileo alone or in conjunction with other systems.Location-based services depend on service providers or network operators knowing the position of the mobile caller in order to provide appropriate information. Data sent to a userâ„¢s handset can be automatically customised to provide on-demand services such as information about nearby restaurants, hotels and theatres, and weather forecasts.
Environmental Management:
Galileo is expected to play an important role for the scientific community. The availability of new frequencies and different signals will increase the possibilities of analysing data for different purposes.. Galileo can contribute to ocean and cryosphere mapping, including the determination of the extent of polluted, studies of tides, currents and sea levels, and tracking of icebergs. It will help to monitor the atmosphere,including the analysis of water vapour for weather- forecasting and climate studies, and ionospheric measurements for radio communications, space science and even earthquake prediction.


The surveying sector covers a very wide and heterogeneous set of users: land and maritime survey for cartography, mapping, cadastral survey,hydrography, natural resources, geodesy, marine seismic exploration,etc.Galileo will open new opportunities in this market by offering a global worldwide service, with sub-metre accuracy thanks to the additional dissemination of encrypted navigation-related data,ranging and timing. Recreation: The leisure market will see a tremendous surge in developments that we cannot even imagine today. Galileo will extend them to personal navigation via handsets with map displays and secondary communication functions. Integration with mobile communications technology will open up new scenarios and applications for personal mobility. Attractive tourist packages can be based on Galileo coupled with interactive multimedia communications linked to local information providers.


Galileo will provide the first satellite positioning and navigation system specifically for civil purposes. Its profitable applications will spread into many areas of all our lives “ starting with safe and efficient transport. Using only small receivers,we will all be able to determine our locations to within a few metres.It will provide information concerning the positioning of users in many sectors such as transport, social services, the justice system and customs services, public works, search and rescue systems. Galileo is designed for civil use and will be operational by 2008.


2) ieeeportal/site/tionline
3) aat1publications/galileo.htm
4) Forbeshome/feeds/afx/2005/12/28/afx2416597.html
5) Galileo to be led by a Europe-wide consortium(21 june 2005) “Magazine

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