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|  | | | | | | | | The ITU regulates radio frequencies | |
Frequency filing for Galileo
If you have ever tried to listen to a distant radio station while driving your car under a tram line or near a badly-tuned motor-cycle, you will understand radio interference. The fact that radars do not interrupt television broadcasts or that microwave ovens do not disturb cell-phones is the result of the careful regulation of radio communications systems by the International Telecommunications Union (ITU), a treaty organisation of the United Nations.
The ITU requires that any radio transmitter broadcasting across national boundaries which could cause interference in other countries be registered in an International Master Frequency Register. Before this may be done, the operator must ensure that his system respects ITU regulations and recommendations. After this is done, the operator can expect that his signals will be received without interference.
Satellite systems, by their natural ability to provide international communications, are invariably able to cause widespread interference but are, once launched, difficult or impossible to modify or adjust to mitigate any such interference. The ITU therefore requires that details of any satellite system be published in advance, so that other radio users can review and discuss its characteristics before it is registered, prior to launch. However, in order to prevent indefinite reservation of frequencies in space, the ITU places a time limit on the validity of each advance publication.
The ITU maintains the Radio Regulations. These are designed to ensure that all the different radio systems (television, radio, cell-phone, radar, air traffic control, satellite broadcasting, GPS and Galileo and even microwave ovens) can all operate in the same radio spectrum.
In the first instance, separate frequency bands are allocated to each radio service. However, each part of the frequency spectrum is only suitable for specific services. Low frequencies have limited bandwidth and require large antennas. Very high frequencies can only be used either over very short ranges or, using directional antennas, along specific lines of sight. Mobile and portable receivers using omni-directional antennas all need to use the range between approximately 30 MHz and 3 GHz, which as a result is so congested that in many cases, services must share. Before any such sharing is permitted by the Radio Regulations, ITU Study Groups discuss and agree the conditions under which the services can operate together, either in the same region or in different countries.
When Galileo was first under study, ESA identified the availability of spectrum as a priority. Fortunately, GPS expansion was also under study at the same time, and Europe and the United States were able to work together in the ITU to devise a plan for extra spectrum, which was allocated by the World Radio Communications Conference held in Istanbul during June 2000.
The time limit for Galileo to obtain maximum protection from its early advance publication was 10 June 2006. For this reason, ESA made a major effort to ensure that a GIOVE satellite was in orbit and operating by this date. Because of the ever-present risk of launch failure, two different satellites, GIOVE-A and GIOVE-B, were constructed. GIOVE-A was launched on 28 December 2005 and transmitted its first signals on 12 January 2006.
GIOVE-B is scheduled for launch towards the end of 2007. An additional satellite, GIOVE-A2, has been ordered - to be ready for launch in the second half of 2008, in case anything should happen to its sister satellites - guaranteeing the Galileo frequency filing with the permanent presence of a Galileo satellite in space.
Last update: 16 August 2007 | |
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