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between 1998 and 2000, allowing EGNOS to reach Advanced Operational Capability in 2001. At
this point, it can be used as a primary source of navigation and positioning for such applications
as aircraft landing approaches.
This phased service entry for EGNOS was decided to optimise the development effort needed,
to minimise technical risks, and provide initial benefits to users as soon as possible.
Full Operational Capability is to be achieved in 2002. At this point EGNOS will have sufficient
redundancy to be considered as stand-alone navigation system for the most demanding
applications. To this end, EGNOS will be expanded to include EGNOS navigation transponders,
navigation uplink stations and Ranging and Integrity Monitoring Stations. 8
The European Union is also developing the user segment and in particular receivers for all
modes of transport. To ensure compatibility of these receivers with those developed in other
regions of the world, discussions have begun with ICAO and the International Maritime
Organisation IMO.
4.3 ABAS
Aircraft-based augmentation system (ABAS-ICAO definition) augments and/or integrates the
information obtained from the GNSS elements with other information available on board the
8 Note : AOC = Accuracy +Integrity (2003)
FOC = AOC + Availability + Continuity (probably 2006)
Document prepared by EVP Europe, August 1999 Page 8 of 14
aircraft. The aim is to enhance the overall performance of the GPS equipment on board in terms
of integrity, (continuity), availability and (accuracy).See chapter A2 CNS/ATM.
5. European Tripartite Group (ETG)
To best manage Europe’s contribution to the GNSS, the ETG was formed: it brings together the
European Organisation for the Safety of Air Navigation (EUROCONTROL), the European Space
Agency (ESA) and the European Commission. Each organisation is contributing with their
experience, expertise and funding to the programme.
The ETG’s mandate is supported by government decisions at national and European Union level.
In particular, the European Union is drafting an Action Programme to set up an institutional and
technical framework for the introduction of GNSS for civilian use.
Military use and control over the navigation signals from both the United States’ GPS and
Russia’s GLONASS satellites means there can never be a guarantee that signals from the two
systems will always be available on an unrestricted basis, or that a guaranteed level of
performance will be maintained. Furthermore, satellites used in the GPS and GLONASS
constellations carry a number of non-navigation payloads of considerable military importance.
Consequently, it is unlikely that control over these satellites’ operations would ever be
relinquished by their respective military establishments.
This clearly shows that to make the best and earliest possible use of satellite navigation, a civil
successor to GPS and GLONASS must evolve that will not suffer from the technical and
institutional limitation of these two current systems.
6. Frequency spectrum
ICAO has stated an intention to move to GNSS as the basis for radio navigation in the 21st
century. As discussed, GNSS-1 will be formed from the US GPS and the Russian GLONASS
combined with one or more augmentation schemes. To provide the sole means of navigation or
even the sole means of radio navigation, GNSS must be protected against interference and
states must ensure that no harmful transmissions are present or radiated from their territory.
There is a study available carried out by the Eurocontrol Experimental Centre looking at GNSS
Frequency Protection requirements (EEC Report No. 337). This study reviews the effect of
interference and derives a protection mask for GPS and GLONASS receivers. Protection
requirements for the proposed European Navigation Satellite system are also evaluated.
High-powered ground transmitters, such as TV broadcasts, could generate sufficient spurious
power to jam a GNSS receiver. However in the en-route phase of flight the aircraft’s altitude,
combined with reduced antenna gain beneath the azimuth plane and/or distance from the
transmitter, provides a large attenuation factor; moreover, such accidental interference is likely to
last only for a few minutes, unless deliberate ‘jamming’ is present. Test flights by UK NATS
demonstrated that interference from ground transmitters in some parts of Europe reduced the
signal to noise in a GPS receiver, but did not prevent it navigating. Satellite communications in
the 1625 MHz band were identified as a problem and precautions taken in the design of the
aircraft installation, diplexer and frequency planning to eliminate interference into GPS.
　
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