Potential Interference To
Galileo From
23cm Band Operations
1. Contents.
2 Introduction
3 Galileo, History and Background
4 Galileo System description
5 The Politics of Galileo
6 Is there a requirement for Galileo PRS?
7 The Frequency Allocation Situation
8 Potential Interference from Galileo to 23cm Amateur Operations
9 The operation of Galileo receivers and their typical response to interference
10 Practical Interference Scenarios
11 What is likely to happen?
12 What can the Amateur Services do about it ?
13 References
2. Introduction
This paper describes the proposed Galileo system design and its applications
with particular reference to the E6 (1260-1300MHz) band. It covers some
of the political issues driving the programme and the frequency allocation
situation. It describes the operation of typical receivers and their ability
to deal with interference and gives practical illustrations of these effects.
The likely effect of the Galileo E6 channel transmissions on 23cm receivers
is analysed and found negligible. However there is the potential for 23cm
transmissions to interfere unless the Galileo receivers are designed and
built to withstand them when operating in the E6 channel. In order to
work robustly in the expected electromagnetic environment Galileo receivers
will need to use the most advanced technology available. Finally the likely
course of events is discussed and arguments that we might use to continue
our use of the band are presented.
3. Galileo, History and Background
The Galileo programme is intended to provide the European Union (EU)
with its own Global Navigation Satellite System (GNSS). Currently there
are two major systems, the USA’s Global Positioning System (GPS)
and the Russian GLONASS. GPS was designed as a military system and, until
2000, the open signal’s accuracy was intentionally degraded. The
US has now pledged to maintain the full capability, free, open service
signals and will give 6 years notice of any change to this position. Although
essentially a military system, the civil applications have been wide ranging
and are the basis of many businesses as well as supplementing and improving
many existing navigation systems even though the users recognise that
the US could degrade or jam the services should it judge that necessary
for its security. GLONASS will not be discussed further, as it does not
overlap our allocation and its future status is unclear.
Two programmes have been implemented to overcome some of the deficiencies
of GPS as they affect the civil aviation industry, these are the USA’s
Wide Area Augmentation System (WAAS) and the EU’s European Geostationary
Navigation Overlay System (EGNOS). Their purpose is to monitor the accuracy
and quality of the GPS signals and provide an instantaneous warning via
geostationary satellite and data link should they degrade.
The EU view is that having its own GNSS is essential to its economic
and infrastructure development and that it cannot rely on GPS for reasons
of availability and reliability of the signals. Furthermore, GPS gives
no performance guarantee. There is a benefit to both GPS and Galileo in
having more satellites in space, particularly in situations such as cities
where the view of the sky is restricted. Because both systems would operate
in the same frequency band and with comparable modulation schemes, it
will be relatively easy to build receivers to use all the satellites in
view.
In 1999, after many years of studies of candidate systems the EU launched
the Galileo programme. The definition phase ran from1999 to 2001 and covered
the definition of the architecture and services to be provided and the
development and validation phase started in 2002. In this phase, the European
Space Agency (ESA) will procure and launch two satellites, the first of
which will be launched at the end of 2005. In 2007 the plan is to launch
a mini constellation of four satellites to test the system in orbit. The
cost of this phase is estimated as €1.1Bn and will be EU funded.
The deployment phase, building and launching 26 satellites and building
and deploying the ground segment is estimated as €2.1Bn with two
thirds coming from industry and the rest from the EU. Full Commercial
operation is still planned to begin in 2008 according to the website even
though the award of the contract to the selected concessionaire is now
not expected before the second quarter of 2006. The four principal countries
involved in the work are France, Italy, Germany and the UK all of whom
will benefit under “juste retour” with jobs and the housing
of ground facilities.
Independent observers find this timescale unrealistic even without the
usual funding delays and full operation in 2010 at the very earliest is
probably more realistic.
The Galileo Joint Undertaking is, in essence, a body set up to organise
the funding, the business plan and the risk sharing arrangements. Organisations
of other nations outside the EU have been joining this body, most significantly
from China and Israel. This will, of course, help with the arrangements
for hosting ground facilities outside the EU. In 2005 the Galileo Supervisory
Authority was set up as an agency of the EU Commission to control and
manage all aspects of the project including security and all technical
matters.
4. Galileo System Description
The system will operate in essentially the same way as GPS. Thirty satellites
in 23,600 km orbits will carry atomic clocks and transmit accurate time
signals using spread spectrum modulation together with orbit data and
other messages. A receiver synchronises itself to the satellites in view
and by measuring the range to four of them can determine its position
in three dimensions and obtain standard time. Higher quality receivers
will use two or more frequencies making separate measurements to correct
for ionospheric delay. The ground system, fully duplicated to provide
resilience, will control the satellites through a series of uplink stations
around the globe.
The services planned to be offered by Galileo are the following:
l The Open Service (OS) provides position and timing free of user charge.
l The Safety of Life Service (SoL) improves the open service by providing
warnings to users when the OS fails to meet service standards.
l The Commercial Service (CS) provides access to two additional signals,
which can provide higher data rate throughput and help to improve accuracy.
It also provides a limited broadcast message capability from service centres
to users.
l The Public Regulated Service (PRS) provides position and timing to specific
users requiring high continuity of service with controlled access. Two
PRS signals with encrypted ranging codes and data will be available.
l The Search and Rescue Service (SAR) will enhance the international search
and rescue system by broadcasting globally the messages emitted from distress
beacons.
There is little more than this available about the services because of
course what is actually offered will by decided by those who are awarded
the concession to develop and operate Galileo. Somehow the services have
to generate an ecconomic return in the face of a free service (GPS) with
long established applications world wide.
The latest published information, reference [1], on the mapping of the
services to the frequency bands is from June 2003.
The three Galileo bands are as follows:
E5 1164 - 1215 MHz carrying CS, OS and SoL
E6 1260-1300 MHz carrying CS and PRS
E1-E2-L1 ( sometimes called L1) 1559 - 1591 MHz carrying CS, PRS and SoL
5. The Politics of Galileo
It is important to understand a few of the key issues around the development
and deployment of this system. It is being strongly backed by the European
Commission as part of the drive to be independent of the USA, but because
of its high cost (€3.2Bn to get it up and working is seen by some
as an underestimate and, of course, the running costs are additional to
this figure), it is essential to have industry involved in the funding
in a Public-Private Partnership (PPP).
The competition to choose the concessionaire to undertake the development
and running of the system was terminated in early 2005 and the two contenders
were asked to join forces and submit a combined proposal. The decision
is now scheduled for some time in mid 2006. Obviously there is currently
no information on what the concessionaire will offer; however, it is likely
that there will be two income streams, one from the IPR involved in equipment
licensing and one from the two subscription services, the CS and the PRS.
The fact that there is a free service already available from GPS, used
for years by many companies to offer enhanced services for profit (e.g.
differential GPS for oil prospecting, car navigation systems), must be
a problem for the concessionaire. The open GPS signals are being enhanced
by the addition of a second civil signal, called L2C, which will reach
full operational capability (FOC) in 2010 and eventually a third wide
bandwidth civil signal will be added.
Furthermore, the existence of EGNOS and WAAS enhances the reliability
of GPS for civil aviation and gives it much of what it wants without contributing
to the costs of Galileo. Everybody would like the Galileo satellites to
be available so that the coverage of GNSS, in urban canyons for example,
would be improved, but no one wants to pay for them.
6. Is there a Requirement for a Galileo PRS?
There are serious issues around the PRS concerning the extent to which
it will be used, for example, by European government agencies such as
customs and immigration or by the police and paramilitary. The advantage
being put forward to these agencies is that PRS will offer a more secure
service to them than the open GPS and that in the event that the open
services of both Galileo and GPS were jammed in order to prevent their
use by a hostile power, there would still be a service available. The
encryption and other tricks on the PRS signal would also give protection
against spoofing or meconing (see later). There is a cost involved however;
both in new equipment and in user charges and the agencies will have to
assess the costs against the risks. Some of the costs have probably not
been recognised, for example the costs of certifying a police helicopter
to use Galileo PRS rather than GPS as the input to its navigation system
will be frightening.
There are also persistent stories that some countries wish to use the
PRS for military purposes. Whilst there would be no objection to using
the Galileo signals for tracking material or for logistics purposes by
peacekeeping forces, the application to weapon guidance would raise serious
issues. Another factor often overlooked in the discussion of the PRS is
that to make the system robust requires much more than just protection
of the signal in space, it requires secure ground support facilities on
a regional basis ; this is costly. It all adds up to a lot of money to
pay for independence of the US system which is well established and which,
with the second civil frequency added in 2010, will have a high level
of robustness.
The recently published report of the UK House of Commons Transport Committee,
reference [2], voiced serious concerns about the PRS - “The uses
described for the PRS are hazy; the UK government has said it does not
want to use it… The Committee urges the UK government to ensure
that there is a real demand, that access can be properly controlled, and
that it would not allow the use of PRS for military applications”.
This situation will not be resolved or even clarified until the Concessionaire's
contract is available for examination. This will be a costly programme,
whichever way it is funded.
7. The Frequency Allocation Situation
At the World Radiocommunication Conference in 2003, (WRC-03) a Primary
status allocation was approved with no power flux-density (pfd) limits
for the radio navigation satellite service (RNSS) in the 1260 -1300 MHz
band.
The allocation was a result of studies conducted since WRC-2000 on sharing
between RNSS and the radiolocation service in this band. The WRC invited
interested parties to continue appropriate technical, operational and
regulatory studies (including an assessment of the need for a pfd limit)
on RNSS systems in the 1215 to 1300 MHz band. The purpose of the studies
was to ensure that the RNSS would not cause harmful interference to the
radiolocation (radar) service. All studies were to be conducted as a matter
of urgency and in time for WRC-07. They are reported under WP 8B.
There is a possibility for radar targets to be obscured by the signal
from a Galileo satellite because the high gain of the radar antenna and
tests carried out in the USA on working radars have demonstrated the potential
problem, reference [3]. Some proposed measures to achieve compatibility
include tailoring the RNSS signal to reduce overlap with the radar band,
pfd limits on the RNSS signal and frequency separation. It is clear from
the material already submitted to WP 8B that the USA is concerned about
interference to its L-band ATC radar network, however many countries operate
ATC and defence radars in this band so it is a much wider problem.
Wind profiling radars operate in the band 1270 to 1290 MHz and a recent
study examined the level of protection that these would require in the
presence of Galileo E6 signals.
It should be noted that the WRC appears to wish to achieve a mode of operation
and spectrum sharing in which up to five separate satellite GNSS systems
can operate in the allocated spectrum 1215 to 1300 MHz. The Galileo organisation’s
stated essential requirement is to have the same regulatory regime in
the whole of the band and to achieve regulatory protection of all radars
through a footnote in the Radio Regulations.
The position of the International Civil Aviation Organisation (ICAO)
is “To support the incorporation of a single regulatory mechanism
applicable to RNSS in the whole band 1215-1300 MHz as a necessary protection
for important radars used for civil aviation purposes, and to support
the incorporation of the agreed mechanism within an adequate regulatory
framework having full mandatory force for current and future RNSS systems”
The challenge to Galileo was to get a satellite up and running by April
2006 in order to claim the frequency allocation. This was achieved, on
schedule, on December 28 th 2005 by Giove, the satellite built by Surrey
Satellite Technology Ltd. (SSTL). The satellite carries a number of pieces
of equipment, such as atomic clocks, for trials purposes. The radiated
frequencies are not known but it is believed it is also able to monitor
the radiation environment, but whether this includes the radio spectrum
is unclear.
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