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07-03-2008
GATE: Galileo Test Environment
Gateway to a Successful Start of Galileo
 
GATE (Galileo Test Environment) is the only Galileo test and development environment worldwide where already today navigation is possible with realistic Galileo Signals on all frequencies in an outdoor area. Six transmission stations, deployed on top of six mountains in the German Alps, and two monitoring stations in the valley are the components making GATE a unique test environment. Receivers and applications being operated on the test ground receive the transmitted signals in such a way as if they were radiated from real Galileo satellites in the earth orbit. Thus, GATE enables an early development of technologies, receivers, applications and services, which will decisively influence the navigation market and so fosters the development in nearly all fields of Galileo products.
 
By Simon Plum
 

The Future of Satellite Navigation in South-East Bavaria
The test area is located at Berchtesgaden in the outermost southeast of Germany close to the Austrian border. It offers a branched road network with all kinds of streets except motorways and outside the town various landscape conditions, like, for example, woods, acreage and unimproved fields. The transmitting stations are located near the mountain tops of Gr¸nstein (see the middle Figure), Toter Mann, Hochthron, Kneifelspitze, Kehlsteinhaus and Jenner.

GATE operates following the same physical principles like Galileo and GPS to allow users finding their position, velocity and time (PVT): The signals with accurate information on position and current time are being radiated to the reception area. There a receiver can determine its PVT by calculating the distance to the transmitter and finding the intersection point. Through its infrastructure, GATE is able to radiate the navigation signals from Galileo satellites, to simulate natural influences like ionosphere or troposphere delays, to change characteristic parameters of signals and to adapt the signal strength as required. The altitude profile determined by the surrounding mountains show a difference of up to 1.250 meters and makes Berchtesgaden an ideal location to have contact to at least four transmitters at any time. Since the mountains are located around Berchtesgaden, a good horizontal accuracy can be achieved (HDOP between 1.5 and 2.5). The arrangement of the transmitters can be seen on the next page.

The stages of development of Galileo also influence GATE. Continuously all respective stages are being integrated into the GATE system. So it will be possible to carry out tests using additionally the four spacecrafts belonging to the In-Orbit Validation (IOV) phase of the Galileo program once they are available. The combination of IOV and GATE signals enables the reception of ten "satellites" long before the full operational capability of Galileo is achieved.

After its completion, Galileo will transmit four different services and one search and rescue (SAR) channel with different specifications. The services comprise the Open Service (OS), the Commercial Service, the Safety of Life (SoL) Service and the Public Regulated Service. At first, GATE offers the OS and SoL Service on all foreseen frequencies with a restriction on the functionality of the SoL Service as there is no real integrity calculation within GATE. Information on the different Galileo Services can be found at the official website of the European Union (EU) - or the European Space Agency (ESA), see at the end of this article.


The transmitting stations are located near the mountain tops. One of these locations is Grnstein, shown in this picture.

For application developers, who do not have their own receiver, GATE offers three Galileo/GPS receivers, which are able to receive Galileo signals on all three frequencies and GPS on L1 at the same time. These receivers are well tested receivers of IFEN GmbH. They provide standard outputs as specified by the National Marine Electronics Association (NMEA), the University of Bern (Receiver Independent Exchange Format; RINEX) and other observation data. Details on the GATE User Receiver (GUT) can be provided on request. So, there is hardly a scenario that can not be tested in GATE.


The locations of all the transmitters are marked with yellow triangle symbols on this 3D image.

GATE Operations
The deployment phase of the GATE system is already finalised. Currently the system is in an experimental test phase which will last until the end of 2007 to verify all kinds of performance parameters. By the end of 2007 the GATE system and its crew will have at least one year of experience in operating the test environment and execution of GNSS experiments.


DLR measurement vehicle in front of the mountains of Berchtesgaden during a test campaign inside
the GATE test area in summer 2007.

GATE will be operated by the German Space Operations Center (GSOC) in Oberpfaffenhofen, which is part of the German Aerospace Center (DLR). GSOC is one of the leading space operations centres worldwide. It has over 40 years of experience in satellite and ground system operations. The operable divisions fulfil their projects related to operational tasks associated with manned and unmanned space missions. The main tasks include the planning and preparation of projects, the definition of ground system requirements, mission planning, the generation of operation procedures as well as tests, trainings and simulations for scientific, commercial, security and human-spaceflight missions. Additionally GSOC is currently building one Galileo Control Center and is in charge of operating the four spacecrafts belonging to the so called In-Orbit Validation (IOV) phase, which will belong to the Galileo system itself. It also houses the GATE Control Center, which is the central access point to the GATE system. The GATE Control Center monitors and controls remotely the GATE infrastructure in Berchtesgaden from Oberpfaffenhofen.
Therefore GSOC, as operator of GATE, can offer an excellence support for every kind of user. Various planning and simulation tools, scientific support from the DLR institute for communication and navigation as well as support of the leading GATE developer, IFEN GmbH, will assure optimised test preparation and exactly tailored experiments to the needs of the users. This includes, if desired, the usage of a very powerful signal generation environment, which can be used to cover the full test range from laboratory to realistic outdoor testing.


Overview of the GATE performance.

How to Use GATE
GATE closes the gap between pure lab-based test constellation and the real Galileo system, which will be available not earlier than 2012. Its infrastructure enables an early development of all kind of Galileo and GNSS products as GPS and GLONASS can obviously be used during a test campaign within GATE as well. Due to its variable structure, GATE is at the disposal of a broad range of users. The target groups mainly consist of companies, research institutions and universities wanting to test and optimise their products. The objective of GATE is to enable these developing entities to provide well tested products to the market once Galileo’s full operational capability is achieved.


A screenshot of the GATE User Receiver (GUT) shows different windows of the GUT software, running on a laptop to control the GUT.
Every use of GATE starts with a conversation with the GATE team at GSOC. Once the contact is established a user will be guided through two planning phases. First all user’s needs will be analysed and discussed with the experts of the GATE crew. After clarifying all issues related to usability and feasibility a rough experiment plan will jointly be developed. Before the second planning phase a contract needs to be signed between GSOC and the user. Afterwards the detailed experiment planning will take place, which includes the generation of a schedule for the testing period to map every test scenario to a feasible timeline and to cover any other organisational topics. This includes a briefing on the handling of the GATE User Receiver (GUT), if the GUT will be used during experimentation.

With completion of the second planning phase the test phase of any user starts in the test area of Berchtesgaden. If desired, an onsite support of GSOC can be provided while usually the system is monitored and controlled remotely from the GATE Control Center in Oberpfaffenhofen without GSOC interaction in Berchtesgaden. To harmonise ongoing experiments in the test area with the GATE Control Center a permanent voice loop is activated between Berchtesgaden and Oberpfaffenhofen.

Once the experiments are completed the user can get access to all data from the two monitoring stations with its reference receivers and from the GUT, which log every observation during the experiment execution.

Testing within GATE
Testing within GATE is simply comparable to any other satellite navigation measurement campaign. The system itself will be powered-up long before the measurement campaign takes place and so a user is not affected by the turn-on procedure of the system. Once he reached the test region of GATE, he just needs to switch-on his equipment and start with the execution of the planned tasks. The big advantage of GATE is the possibility to reconfigure the system at any time to cover the user needs. For example, the power levels of the radiated navigation signals can be adjusted to an optimal or, if designated, to a suboptimal configuration. The simulated satellite constellation can also be adapted to special purposes by setting up the used almanac period. So, any user has the flexibility to customise the navigation environment GATE as if he would have a direct link to the satellite control centre of Galileo.
To get an impression of the test area above shows a picture of the DLR measurement vehicle in front of the mountains of Berchtesgaden during a test campaign in summer 2007. A screenshot of the GUT taken at the current position is displayed in Figure 4. The screenshot presents different windows of the GUT software running on a laptop to control the GUT. It indicates parameters like the current signal to noise ratio, elevation and azimuth angles, measured ranges and Doppler frequencies for every signal in track and displays the position by using the information provided by GPS and Galileo (GATE) signals.

Conclusion
With its very flexible infrastructure GATE offers a GNSS development environment for all kinds of satellite navigation products. It enables users to demonstrate their capabilities for the growing market of satellite navigation and allows them to integrate and test the advantages of Galileo in their newly developed receivers, applications or services: "GATE tested - Galileo Ready!".

Simon Plum  is working in the space mission operations area. He is part of the Galileo operations department in the German Space Operations Center of the German Aerospace Center DLR, which is in charge of the preparation and operations of the four spacecrafts for the Galileo In-Orbit Validation (IOV) phase. Since 1995 he is project manager for GATE operations. In the GATE project he is responsible for the reliable system take over from the developing industry and for the overall GATE routing operations phase. See more on the GATE project at www.gate-testbed.com, www.dlr.de/rb and the Galileo project at. http://ec.europa.eu/dgs/energy_ transport/galileo and www.esa.int/esaNA/galileo.html.