GR67. A GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS)
Will Europe find its way?
Europe is engaged in developing a policy for satellite navigation to come to fruition around
2010. This paper presents an overview of the current situation in Europe, with the first and
second-generation systems, GNSS1 and GNSS2, covering organisational, commercial and
technical issues. Current plans are described in outline, together with the thinking behind
A little over ten years ago the United States launched its Navstar Global Positioning System
(GPS). It is now established as the primary system for determining time and position
Since then, there has been unprecedented interest in developing technologies to exploit the
system and a phenomenal growth in the commercial and private use of satellite-based time
and navigation information derived from GPS, and to a lesser extent the Russian GLONASS
system. Applications include aircraft and maritime navigation, road transport fleet
management, private in-car navigation, geo-surveying, sailing and other leisure pursuits,
animal tracking in wildlife conservation programmes, communications system timing.
This growth is unabated even though the present systems are, in effect, owned and
controlled by military authorities and the un-encrypted signal is degraded to limit the
accuracy available to civil users of GPS satellites. The performance that is available can still
satisfy many applications and - best of all - the basic service is free, a situation likely to
continue for some years.
In spite of the popularity of GPS and the number of applications that can be supported by the
basic system, it is accepted that the present system lacks the accuracy, integrity and
availability to satisfy many of the more critical transport and safety-related applications.
This has led to the development of techniques to augment the basic GPS service through
the use of differential corrections, improved integrity and additional GPS look-alike ranging
signals from geo-stationary satellites.
Augmentation takes several forms, from user-dynamic augmentation techniques to wide
area services providing regional coverage. Civil aviation has been the driver for the
development of wide area augmentation services, both in the US (WAAS - Wide Area
Augmentation Service) and Europe (EGNOS - European Geo-stationary Navigation Overlay
Service). The combination of GPS and the augmentation service is generally known as
GNSS1. These augmentation services overcome some of the shortcomings of present day
GPS, but are expensive and still depend entirely upon it.
For some time there has been concern about the dependence on a global navigation service
owned and controlled by one country. This concern is heightened in circumstances where
there is uncertainty over its long-term availability without interruption, or reduced capability
due to the requirements of national or military security interests.
Worldwide use of GPS has reached the point where it is probably no longer possible for the
US government to deny access to the civil community. Nevertheless, many still feel that if
the long term future dependence upon satellite technology is to be secured, it is important to
have an alternative system under separate civil, international ownership and control.
From a European perspective, there is a desire to secure a share in future lucrative markets.
In order to promote such strategic European business interests, the development of the next
generation GNSS is being planned. Following an initiative by the European Commission, a
programme of studies has been launched to define and develop a European satellite
navigation system that would satisfy the perceived objective of an independent, civil satellite
The development of GNSS1 in Europe and the studies now being undertaken to develop
and transition to its successor - Galileo, the European civil global system - will ensure
co-existence and interoperability with GPS.
The future of aeronautical navigation is now firmly wedded to satellite technology and in
recent years, the application and potential benefits to aviation from the available satellite
navigation systems have been well researched and publicised. Satellite technology has
already been found to be the ideal solution to satisfy operational requirements in some parts
of the world.
Yet civil aviation is estimated to represent only about 1% of the user market and road
transport is expected to become the largest and is probably the most important segment in
the mass market transport sector - perhaps representing over 60 % of the user community.
Service providers in this sector are already exploiting the technology and offering
value-added services, in addition to the simple position function available from basic GPS
Nevertheless there is also recognition of certain shortcomings in the quality of service
currently offered by the basic GPS, particularly for some safety-related applications. Integrity
and availability have been especially highlighted as areas that require performance
improvements and, although accuracy is not a problem, for some applications,
improvements in accuracy are needed. The attraction of satellite technology has spawned
the extensive development of augmentation techniques and technologies to overcome these
drawbacks and extend the range of applications that can be satisfied.
Whilst the concept of GNSS augmentations was originally developed for civil aviation
applications, in recent years it has become apparent that GNSS can be beneficial to the
enhancement of navigation and positional information for all modes of transportation.
These far-reaching applications pose several challenges for continued development of the
system. Each transport mode - and the various applications within each mode - have
different levels of requirements for system accuracy, integrity, and availability and
consequently the costs and benefits are also varied.
One augmentation service now under development is the European Geo-stationary
Navigation Overlay System, EGNOS - a project initiated by a European Tri-partite Group
(ETG) comprising the European Commission, the European Organisation for the Safety of
Air Navigation (Eurocontrol) and the European Space Agency (ESA). EGNOS is a
multi-modal approach to navigation, intended to satisfy the needs of aviation, maritime and
land transport user communities. However, analyses have confirmed the requirements of
aviation to be the principal driver of system design.
The pre-eminence of aviation as the driver of stringent performance standards may soon be
challenged as other transport services enter the field. Many feel that aviation is a niche
market with exaggerated requirements and the costs should not be borne by those with less
demanding performance requirements.
This is not a significant issue at present, while GPS is a free service, but it seems inevitable
that one day, user charges will be introduced - at least for identified value added services.
There have been a number of Commission studies into GNSS costs and benefits, most of
which have focused on the four primary modes of transportation - aviation, maritime, road
and rail. (Ref. 1) Most show positive benefits in varying degrees to the different user
communities. These studies have all been part of the ongoing work programme to pave the
way for decisions on the future shape of GNSS in Europe.
The ultimate test of user and provider interest will depend upon the extent to which
European administrations can engage in constructive dialogue and can develop equitable
bases for cost recovery that are acceptable to both sides. An important element is to identify
the appropriate service provider and equipment supplier representative bodies and to
identify the most appropriate means for financing a future system. A review of existing
European and global representative organisations carried out on behalf of the Commission
(Ref. 1) showed few organisations are currently constituted to be service providers or readily
act as a conduit for any cost recovery mechanism.
The European Commission is exploring options for funding the next generation system.
These include public/private financing (PPP) arrangements for development and operation.
Part of this exercise includes studies of potential revenue earning services. The principle
applied was that users of systems should pay for the services provided to them, when
possible. This causes additional challenges in setting user fees. The myriad of existing users
has different requirements, different population bases, various cost-recovery methods, and
different resources to draw upon for fee payment.
The final result must be a method of allocating costs fairly, across users of all applications.
So cost allocation methodologies have to be devised for the assessment of costs to users of
the system. This was an area studied by a special working group of the European
Commission‟s GNSS Forum (Ref. 3) which, inter alia, drafted proposals to formulate and
define a co-ordinating and institutional structure for the operation and regulation of a future
European based GNSS.
EGNOS Implementation and Functionality
The mission objective of EGNOS is to provide a full satellite navigation broadcast service to
augment GPS and GLONASS and enable GNSS to satisfy the Required Navigation
Performance (RNP) specified by ICAO for en-route through to Category I precision approach
and landing at aerodromes. The system will enhance GNSS integrity, availability, continuity
and accuracy of service throughout the European region, and more specifically, provide the
following primary functions:
supplementary geo-stationary ranging (R-GEO)
ground derived integrity (GIC)
wide area differential correction (WAD)
EGNOS comprises space, ground and user segments. Initially, the space segment will utilise
navigation payloads on two INMARSAT III geo-stationary satellites for broadcast of the
above three primary functions. The ground segment comprises a network of inter-connected
stations that monitor GPS and GLONASS transmissions, compute and up-link corrected
navigation messages and other data from Navigation Land Earth Stations (NLES) to
geo-stationary satellites for broadcast to the users. An overview of the EGNOS architecture
is shown in Figure 1.
STATIONS ORBIT DETERMINATION
IONOSPHERIC CORRECTION CORRECTION
TIME DETERMINATION NLES
WAD ORBIT CORRECTION
MONITORING IONOSPHERIC CORRECTION
STATIONS TIME CORRECTION
GIC CHECK CONTROL
Figure 1 - EGNOS Architecture
EGNOS development and implementation has been planned as a five-step deployment
strategy, in two distinct phases. Each step delivers an extended level of service. The
Advanced Operational Capability (AOC) phase comprises steps 1 to 3 and will provide the
GPS-like pseudo-range signals to augment the existing GPS constellation to
improve both overall GPS availability and the performance of Receiver
Autonomous Integrity Monitoring (RAIM).
Provision of a ground-derived, independent integrity channel that might arguably
be the most important function offered by EGNOS.
Wide area differential correction service to increase accuracy performance.
The AOC phase is scheduled for completion around 2002, at which time the full EGNOS
functionality should be available to augment both GPS and GLONASS. It is not planned that
the ground and space segment architectures will be fully developed until steps 4 and 5 have
been completed at Full Operational Capability (FOC).
FOC will provide essentially the same functionality as AOC, but improve service availability
and continuity through the addition of two further geo-stationary satellites and an increase in
the level of ground segment redundancy. FOC is beyond the scope of the current work being
sponsored by the ETG and currently, there is no definitive plan for the transition to FOC,
although it is estimated that completion could be achieved by 2005.
As mentioned earlier, the driver for EGNOS design has been the requirements of civil
aviation but like GPS, EGNOS will be available without user charges and there are no
barriers to any user taking advantage of the improved performance that will become
available. Opportunities will exist for other value added services to be introduced as a
complement to EGNOS. A performance summary for EGNOS is shown in Table 1. The
values shown are approximate, since the real values are too complicated for a simple table.
PARAMETER GPS EGNOS AOC EGNOS FOC
Coverage Global Europe Europe plus
Accuracy 100 m 6m 6m
Availability ? 99% 99.9%
Integrity ? 2x10-7/150s 2x10-7/150s
Time to Alarm hours 6s 6s
Continuity ? 8x10-5/150s 8x10-5/150s
Table 1 - EGNOS Performance
In 1998, the European Commission issued its first communication on developing a European
strategy for a global satellite navigation system – “Towards a Trans European Position
Navigation Network” (Ref. 2). It identified three key issues associated with a continued
reliance on GPS and/or GLONASS.
The sovereignty and security of Europe‟s safety-critical navigation systems were
outside European control
A need to ensure that European users were not at risk from changes in the
service or the introduction of future charges in a dominant, virtual monopoly
A need for EU industry to compete effectively in this lucrative global market
The Commission concluded that in order to redress the situation, there were three broad
A joint global system with all the major international players currently engaged in
The EU developing a GNSS with one or more international partners
Independent development by the EU of its own dedicated system
In order to arrive at a decision, the Commission established a GNSS2 Forum comprised of
leading experts from industry, governments of member States, service users, providers and
academia in the satellite navigation field, to study and advise the Commission on various
institutional, legal, technical, security and financial matters. The Forum produced its final
report in December 1998 and made the following observations:-
Co-operation with GPS was the preferred option
The systems should be independent but interoperable
National security must not be compromised
Other international partners could join, eg. Russia and Japan
A flexible organisational framework should be put in place
At least two levels of service should be provided
The system definition should proceed as soon as possible
Compatibility with EGNOS is essential
A public private partnership should be developed for funding and operating the
Taking these findings into account, together with the results of the international discussions,
the Commission concluded that it was possible to narrow the options. In February 1999, the
Commission issued its second communication (Ref. 4) which defined the concept for a future
GNSS and named it Galileo. It concluded that the preferred choice was a system that would
be independent from GPS but complementary to it and interoperable with it, and that it
should be multi-modal.
The Communication notes that the US is developing its next generation satellite navigation
system and the opportunity will be taken to co-ordinate these parallel activities as part of
GNSS2. At the same time, the Russian Federation is developing further its GLONASS
technology. Now that this system has been transferred to civilian control the European
Commission is exploring with Russia the possibilities of collaboration in the development of
GNSS2. There could be a particular advantage in co-operation with Russia due to the
scarcity of radio frequencies for radio-navigation satellite services and the strong competition
from other radio services seeking to use the same frequency band. The potential to utilise
the GLONASS frequencies for Galileo is perceived as a major benefit.
It is currently expected that the Galileo signal structure will permit a number of compatible
services to be provided including free to air, controlled access (value added), controlled
access (safety of life) and restricted access governmental services. The optimum funding
arrangement is still being studied but a PPP is perceived to be the most likely scheme and
efforts are now being made to attract private investment into the venture. It is hoped that the
prospect of a greater involvement of European industry in the applications market will
increase the willingness of private investors to participate in PPP.
Galileo comprises space, ground and user segments. The space segment will consist of
about 24 GPS-like Medium Earth Orbit (MEO) and Geo-stationary Earth Orbit (GEO)
satellites carrying navigation payloads. The ground segment comprises a network of
inter-connected stations that monitor satellite transmissions (OSS), compute and up-link
corrected orbit and synchronisation navigation messages to the satellites, for broadcast to
the users. A network of integrity monitoring stations (RIMS) collect integrity data on the
navigation signals for broadcast to the users. Satellite control stations (TTC) are also
included as part of the ground facilities. An overview of the Galileo architecture is shown in
In performance terms, aviation requirements still provide the baseline standard and it is
intended that Galileo will be designed to satisfy these standards and achieve equivalent or
better performance than that being considered by the US for its next generation GPS. In
addition, aviation certification requirements and its safety management and regulatory
regimes will have a considerable influence on system design, operation and even the
institutional framework that is established for Galileo. Aviation will use the safety of life
services. Other users, many of whom have not yet developed precise requirements, will not
require the stringent performance or regulatory strictness and will use one of the other civil
USER OSS network
Figure 2 - Galileo Architecture
The GNSS2 programme starts with an 18-month definition phase during which all the
outstanding performance issues will be resolved. Before full deployment, it is proposed that
a prototype system, which will test the performance of the full system, be implemented. This
should be in place by 2005. Between 2005 and 2010 the full system will be deployed and
made fully operational. It should be noted that the organisational arrangements will have to
keep pace with the system definition, test and deployment.
A performance summary for Galileo is shown in Table 2. The values shown here as the final
values are still being developed. System values assume co-operation with GPS.
PARAMETER GPS IIF Free Value Safety of
Coverage Global Global Global Global
Accuracy 15 m 10 m 2m 4m
Availability ? 99.5% 99.9% 99.999%
Integrity 1x10-7/150 - - 2x10-7/hr
Time to Alarm 10s - - 6s
Continuity 1x10-5/hr - - 8x10-6/150s
Table 2 - Galileo Performance
As mentioned earlier, one important aspect yet to be resolved relates to the institutional
framework that needs to be established to co-ordinate and manage the development and
operation of Galileo, in a manner that will satisfy the basic requirement for an international,
civil controlled system. In the Comparative System Studies currently being carried out under
contract to ESA in conjunction with the European Commission, an industry consortium has
proposed a possible framework, shown in Figure 3, which might be acceptable.
EU GNSS Policy Evolve
EU Treaty Evolve
Military EU Agency Evolve
Military OPERATOR REGULATOR SERVICE GUARANTOR
Controlled Access Controlled Access Open Access Controlled Access
SIS SIS SIS SIS
Security Value Added Value Added Open Access Safety
Services Services Services Services
Figure 3 - Proposed Institutional Framework
At present, and until the Galileo design is optimised and detailed costs are available, only
indicative costs can be given. Preliminary figures suggest Galileo will cost around 2,000
MEuro for development and implementation. Against this must be set the estimated
economic benefit to Europe if it operates its own satellite navigation system. This benefit has
been estimated to be around 80 BEuro over the next 25 years. This arises from the
additional business that can be developed with an improved system and from the larger
market share for European industry when it is more independent of the US. Obviously any
market forecasts over such a long period in a climate of rapid technological change must be
viewed with caution.
Security Requirements and Civil-Military Interface
Research has been undertaken to collect opinion from European defence authorities with
respect to accurate satellite navigation signals in the European area, under civil control. It
was generally concluded that the provision of such signals is not a significant issue, since
adequate techniques exist for the denial of such signals in space in the event that it is
justified by the needs of security.
Many of these concerns are already realised through the availability of GPS in Europe. GPS
issues are mitigated for as long as GPS remains under military control and, to an extent,
European concerns are likely to be reflected in US foreign policy. A European controlled
system can similarly be expected to be largely sympathetic to European security concerns.
With few exceptions, accuracy is not of particular concern provided that degradation and
denial are available as dictated by the security environment. On the other hand, if a more
accurate, secure service is included in GNSS2, most defence authorities consider that it
should be restricted to military use only, in a manner similar to the precise positioning
service (PPS) of GPS.
Some form of military control may be desirable in times of crisis. This should be
accommodated in the form of operating protocols, derived through some form of civil/military
liaison that would enable the development of appropriate operating protocols for times of
By 2010 EGNOS should be fully operational and Galileo beginning to be utilised by end
users. The organisational arrangements will be in place and everyone will settle down to
using a fully civil owned and operated, global navigation satellite system with no doubts over
its control. Some users, the extent of which is open to debate, will be paying for extra
services not provided by the free signal in space. As the system is developed it is likely that
other ideas will come into play to make satellite navigation even more attractive, much in the
same way as happened with GPS. What ideas are under discussion at present?
To derive full benefit from GNSS, some transport applications such as fleet management
require the availability of a two-way data communications link. In respect of a satellite-based
system, an integrated navigation and communication payload on a common spacecraft is
under consideration, though it is not necessarily a pre-requisite for a combined service. One
possibility is the use of the same geo-stationary satellites that may be part of GNSS2. Civil
aviation currently uses these satellites for air-ground communications supporting both
commercial and air traffic services. Future application development may consider more
economic satellite communications services such as Iridium in place of geo-stationary
The combined availability of Galileo and GPS should ensure that where coverage is difficult,
as in urban areas where the mask angle is high, there would be sufficient satellites in view to
provide good availability and reliable performance. Improvements in receiver technology (eg.
adaptive antennas) will also enhance the ability of users to operate in difficult reception
environments. This will encourage more users to take advantage of the services provided
and minimise the need for supplementary local area augmentation.
Carrier phase tracking, against a known local reference, has proved a useful technique for
local area augmentation where high accuracy and/or high rates of change are required.
However, carrier ambiguities have made it a difficult technique to implement. ESA has been
developing a technique for GNSS2 using three carriers known as Three Carrier Ambiguity
Resolution (TCAR) which overcomes these problems. A full description is given in Ref. 5.
For safety-critical applications it is likely that extra GNSS2 look-alike signals from
pseudolites, to improve integrity on a local basis, will be designed into the system. These
local signals will also enable the „time to alarm‟ to be reduced to less than the 2 seconds
which some applications require.
Most of these augmentations require extra spectra to be implemented. The availability of
adequate protected radio spectra for the services that are planned for Galileo is one of the
key issues that requires resolution. This issue is sensitive and controversial, as there are
several conflicting radio services that require additional spectra within the band to be used
by Galileo. The decisions to be taken at next year‟s International Telecommunications Union
(ITU) World Radio Conference will be crucial to the future of global radio navigation satellite
services. Fortunately, within the European Conference of Postal and Telecommunications
Administrations (CEPT), the European body co-ordinating preparations for this ITU
Conference, the importance of GNSS is well recognised and there seems to be a
convergence of members‟ views to persuade ITU delegates to give satellite navigation
services full, long-term protection.
Now there is the prospect of an internationally controlled, civil GNSS - for some a driver in
itself - and it can be reasonably assumed that system developers will wish to exploit the
technological developments and offer additional capabilities for which the users will be
expected to pay. There must be a clearly defined set of user requirements and system
solutions proposed by the engineers must be tailored to those needs, and not some more
esoteric application that seems nice to have.
It should be assumed that where a multi-modal system is being proposed for many different
applications and user communities, that each user is asked to pay only for the functions and
performance levels appropriate to his application. The proposed system features and
performance levels must be clearly mapped to each user application, and a cost-benefit
study conducted to determine that each system facet or performance level is justifiable and
The industry consortium engaged in the ESA Comparative System Studies will be
endeavouring to ensure these objectives are achieved and that development proceeds in a
cost effective manner. It can be envisaged that for GNSS there are a number of evolutionary
stages - the transition from the existing navigational aids to satellite technology, the
transition from GPS/GLONASS to augmented systems such as EGNOS, and the transition
from GNSS1 to GNSS2. Each stage must be justifiable in terms of the additional cost versus
the incremental benefit.
Whilst it may not be fashionable in some countries for governments to fund the development
and operating costs of new technologies out of general taxation, the European Commission
sees this as the only means of giving an incentive to transition to Galileo. It is proposed that
the cost of development and possibly the implementation of the basic system will be funded
jointly out of ESA and Commission resources, supported by private investment to the extent
that it is commercially justified by the potential revenue recoverable from the users.
1. „Core Area Cost Benefit Analysis‟ - Booze Allen & Hamilton, SA EC DG XIII GNSS
Support Task April 1997
2. „Towards a Trans-European Position Navigation Network‟ - EC Communication (98) 29
Final January 1998
3. „GNSS Forum Final Report‟ December 1998
4. „Involving Europe in a New Generation of Satellite Navigation Services‟ - EC
Communication 9 February 1998
5. „Analysis of TCAR Technique for Precise Relative Positioning in GNSS-2‟ - GNSS2
Conference, Toulouse October „98
The views of the author are his own. The UK Defence Forum holds no corporate view on
the opinions expressed therein. The Forum exists to enable politicians, industrialists,
members of the armed forces, academics and others with an interest in defence and security
issues to exchange information and views on the future needs of Britain‟s defence. It is
operated by a non-partisan, not for profit company.
UK Defence Forum papers generally fall into the following categories:
GR Grey Papers. Generally a single-author “expert opinion” on a defence-
CR Cream Papers. Either Grey Papers which have been moderated by other
military, civil servant or academic personnel or papers as presented and
debated at UK Defence Forum meetings.
RS Regional Study. Generally fact-based, single author.
FS Fact sheet. Generally draw on previously published data, and so sourced.
M Millibrief. A short single topic briefing of a factual nature.