Galileo Receiver Development
Kim O'Neil
Advanced Aviation Technology Ltd.
September 2004
Abstract
The Galileo satellite navigation system is a joint
public/private venture, initially funded by the EU and European industry. Many
other Nations outside the EU have now joined Galileo, including China and
India. A great many initiatives are underway to develop the system, including
activities within the EU's 6th Framework programme (6FP) and others within the
space industry. It is intended that the Galileo satellite navigation system
will offer improved accuracy, availability, continuity, integrity and general
robustness over the existing GPS system. Consequently, much rests on current
design and development efforts to ensure the intended performance of Galileo
and its value added services - particularly for the certified safety services.
Perhaps even more rests on the ability of Europe to put in place the legal
framework, institutional arrangements, standards, procedures and processes to
enable certification of these value added services.
This represents a daunting challenge for those
involved in launching a system that is still being designed and developed, but
which is planned to go into full operational service by 2010. Nevertheless, if
this can be achieved, Galileo will offer significant benefits over GPS - until
GPS itself is significantly upgraded in 2018 (whilst accepting the possibility
of slippage in both systems). Galileo will then have to contend with an
improved GPS - and may need to respond by further upgrades of its own. For the
wider community, the combined (and competitive) benefits of GPS and Galileo
will result in major improvements in navigation, timing and related
applications and services.
To realise these benefits, a range of Galileo
receivers (based on flexible system design principles and equally flexible
implementation) must be made available - in time to enable the commercial
exploitation and market penetration of the Galileo system and services.
1. Introduction
Recent negotiations between Europe and the US have
agreed a basis for the compatibility and interoperability of GPS and Galileo
(although Galileo and GPS have different modulation schemes). This has resulted
in a common baseline signal structure, interoperable time and geodesy
standards, agreements on non-discrimination in trade in satellite navigation
goods and services, commitment to preserve national security capabilities and
agreement not to restrict use of or access to respective GPS/Galileo open
services by end-users. However, these negotiations have also required some
compromises by Europe - specifically changes in Galileo frequencies to enable
the US to jam GNSS in geographical areas of military conflict (and perhaps in
times of political and economic conflict too).
Now that the negotiations with the US have provided a
basis for mutual agreement on the operation of GPS and Galileo, Europe is
moving forward to resolve the outstanding design and development issues prior
to the launch of an operational Galileo satellite navigation system. This short
paper provides an overview of some of these issues, whilst following articles
will address specific testing, verification and validation aspects.
2. Galileo Receiver Types
Market analysis has suggested a preliminary
classification of the likely types of Galileo receiver that will be required.
These include:
Consumer:
- A1 Stand alone ("Galileo Core Navigation
Receiver")
- A2 Communication Assisted (NAV/COM)
Professional:
- B1 Single frequency plus Local Element (LE)
- B2 Dual frequency plus LE
- B3 Triple frequency plus LE
- B4 Single frequency plus communication
assistance
Safety of Life:
- C1 Dual frequency plus LE (+EGNOS) with
integrity
- C2 Triple frequency plus LE (+EGNOS) with
integrity
This range of receiver types may look (at first)
commercially unlikely. However, note that a satellite navigation receiver
essentially consists of:
- Antenna
- RF Front-end
- Signal processing
- Navigation processing
Whilst the receiver front end - including the antenna,
RF integrated circuits, low noise amplifiers, and filters - are generally
hardware based, signal-processing solutions are primarily software-based.
Hence, it is possible to develop a range of receiver types merely by changing
the processing software (whilst using the same "front end"). All that is
required is careful and forward-looking design and some further advances in
technology! Some very significant factors likely to affect receiver design and
development include:
- Emerging S/W radio concepts and architectures
- Availability of associated digital chipsets
Software defined radios look set to be extremely
important in the development of Galileo receivers, enabling a wide range of
receiver types to be rapidly developed and manufactured. This technology may
even permit rapid and complete reconfiguration of the receiver by a simple
software update - without any changes to the underlying hardware.
Nevertheless, there are real cost and technology
issues associated with the level of large-scale integration (LSI) for packing
the necessary processing power onto silicon, to meet the requirements for
navigation applications.
3. Prototyping and Simulating Design
There are a great many issues in the design of future
Galileo receivers (too many to cover in this short article). Prototyping and
simulation provides a means of verifying and validating a given design
solution. As the cost of developing any hardware solution is so high, this
makes prototyping and simulation absolutely essential before any physical
implementation can be considered. The design methodology typically consists of
various stages including: specification, refinement, modeling and validation.
Each stage requires a range of hardware and software tools to be deployed -
requiring a very flexible platform.
Many parameters in the Galileo system design are still
subject to change, making the need for rapid and flexible prototyping and
simulation even more essential at this stage. Parameters where change is likely
to occur include: ranging codes, message formats, frame contents, page
sequencing and message data. The use of these tools has already given valuable
insights into the likely performance of Galileo. It has been especially helpful
for facilitating bread-boarding activities. Future articles will outline in
greater detail simulation and testing activities as these advance.
4. Certification
Whatever cooperation takes place between the EU and US
in delivering compatibility between both GPS and Galileo, Europe must take its
own specific and independent steps to enable the certification of Galileo.
Areas where action by the EU will be required include:
For Galileo itself:
- Establishment of the Legal Basis for the
Certification of Galileo
- Certification Standards for Galileo System
- Certification of the Galileo Signal in Space
- Certification of the Galileo Service provider
For Galileo derived products and services:
- Establishment of the Legal Basis for Certification
of Galileo Products
- Certification Standards for Galileo Products
- Appointment of "Notified Bodies" for
Certification
- International Mutual Recognition of Products and
Services
5. Safety of Life Receivers
Safety of Life Services (SoL) are targeted at users
who need real-time assurance of Galileo service performance. Certified SoL
provide additional integrity information. These integrity levels are tied to
particular operational and safety performance requirements, such as those for
'Approach with Vertical Guidance' (APV-II) as defined by ICAO. Consequently,
there are likely to be several categories of certified receivers.
However, for Galileo Receivers to be certified for
Safety of Life applications, this will require international agreements on:
- Safety Criteria
- Design Standards
- Documentation Standards
- Test and Qualification Procedures
- Certification Standards
Much preliminary regulatory material exists (gained
from experience with GPS), but since the use of satellite navigation has so far
been limited by concerns over accuracy, availability, continuity and integrity,
there is still a great deal to do. However, the formation of the European
Aviation Safety Authority (EASA) opens up the possibility that receiver
certification and qualification for airborne applications will take place
following publication of applicable standards.
6. Standardisation
European Standardization activities for commercially
available Galileo receiver equipment for the three main receiver categories
(consumer, professional and safety of life) are likely to be performed under
the direction of the official European Standardization Bodies CEN, CENELEC and
ETSI - according to an agreed partition of standardization work between these
bodies. Close coordination will be necessary between these standardisation
bodies and the Galileo Joint Undertaking (GJU) - consisting of EU, ESA and
Eurocontrol, to ensure the proper dissemination of Galileo core Technical
Standards and the continued future development of a broader range of Galileo
standards.
European standardisation processes have already had
many notable successes, such as the development of GSM telecommunication
services. It has also been very successful in opening up markets and removing
protectionist barriers to the free movement of goods and services. Accordingly,
Galileo Standardisation will require both specific and general mandates from
the EU to direct the development of a framework of vertical and horizontal
standardisation measures. This framework will be essential to avoid conflicting
or overlapping standards. This process will also expose the proposed Galileo
standards to public consultation, to ensure that the published standards are
robust, technically correct and meet the needs of the market.
A standardisation mandate has already been issued to
ETSI for the development of local components necessary to augment Galileo
performance for aircraft and airports. Discussions are underway for additional
mandates for the broad range of enabling standards that will be required.
Most importantly, CEN, CENELEC and ETSI have mutual
recognition agreements in place with many other States and International
organizations (including ICAO) extending the influence of these standards
considerably and ensuring that Galileo is able to reach the widest possible
market. |
