- Email: [email protected]
GPS to Galileo: A european path
/,i
e
+
GPS to Galileo: A European Path Herv~ BERTHELOT,Vidal ASHKENAZI
Navigation satellite systems such as GPS and GLONASS, which are capable of centimetric instantaneous positioning, have started a new era in navigation. Just as 20th century electronics and radar led to the development of radio navigation and the replacement of astro-navigation, satellite navigation is now targeted to become the main, if not the sole, means of multi-modal navigation in the 21st century. urthermore, satellite techniques are not only set to achieve millimetric accuracies for some nontransport applications, but also the mass production of electronic chips will create a mass market for these devices which are expected to retail for a few hundred ~ or less. This revolution will, in turn, create yet to be discovered new applications and even larger markets. Europe has to be ready for this challenge, and hence the Galileo initiative by the European Commission (EC, 1999) [21. This paper starts with the basic principles of satellite position fixing and the current applications. This is followed by a description of the ongoing projects in Europe and the market perspectives.
F
Satellite position fixing Basic Principles The fundamental observable of GPS is the pseudo-range. A pseudo-range is derived from the measured time of flight of the GPS signal from the satellite to a (fixed or mobile) receiver. By taking simultaneous measurements to at least four satellites, a GPS receiver is able to compute its three-dimensional position and time. In the current GPS, the satellites transmit on two L-band frequen-
cies, commonly referred to as L1 and L2. The precise P(Y) timing code, which is used to derive the pseudo-range, is modulated on both the L1 and L2 signals, whereas the coarse/acquisition C/A code is only modulated on the L1 signal. The civilian Standard Positioning System (SPS), which is based on the C/A code, has a specified accuracy of 100 metres (95%) for horizontal positioning and 150 metres for vertical positioning. The restricted Precise Positioning Service (PPS) is based on the precise P(Y) code, and has a specified accuracy of 16m SEP (50%). The GPS satellites continuously transmit a stream of information, consisting of timing codes and navigation data, which allows a user with a GPS receiver to calculate his position in real time. The timing codes, which are modulated on the two carrier frequencies, are received by the user and compared to two corresponding timing codes generated by the receiver, in a cross-correlation process. This results in the pseudo-ranges, which are then used in conjunction with the satellite ephemeris data which is also broadcast by the satellites, to compute the instantaneous position of the GPS receiver, whether fixed or moving.
Current systems: GPS and GLONASS The Global Positioning System (GPS) has now been fully operational for 66
around three years. At present (1999), there is an estimated 3 million users of GPS, covering a very wide range of applications. Although GPS was developed by the US Department of Defence (DOD) primarily for military purposes, the international civil community of users has been very active both in the development of the technology and in the commercial exploitation of the system. The last 10 years have also seen an increasingly active role for civilians in the management and future planning of GPS. Most notably, the establishment of the Interagency GPS Executive Board in 1996, to jointly manage GPS, formally acknowledged GPS as a civil/military dual-use system, at least in the USA. As of August 1998, there are 27 operational GPS satellites in orbit, of which 5 have minor problems. These constitute the GPS Block II/IIA satellites. Clearly, there is a constant requirement to replenish the system when satellites continually reach the end of their expected lifetime. The first satellite of a new generation of (Replacement) Block IIR satellites was launched in July 1997. A further generation of (Follow on) Block IIF, satellites are now being designed and will take the constellation well into the next century. The first phase of 6 Block IIF satellites were due to be delivered and launched in 2001/2002. This has now been postponed to 2004/2005.
................................................................................................................... The new Block IIF constellation will have several new features. Civilian users will be able to access two or possibly three frequencies, which will help considerably a number of applications, based on high accuracy carrier frequency phase measurements. The addition of more satellites to the constellation, a proposed transmitted integrity channel, increased transmission power, and aft facing antennas for geo-stationary satellite users, combine to make the Block IIF constellation a formidable system setting the standards. By contrast, the Russian Glonass system, which was originally designed as a stand-alone 24-satellite system, only had 15 satellites (including 1 back up and 1 not operational) in August 1998. Since then there has been a successful launch of 3 new satellites. It is now doubtful whether Glonass will achieve a standalone navigation capability.
Differential and carrier phase GPS The accuracy of positioning by GPS can be improved substantially by using a differential positioning technique. The differential GPS (DGPS) concept has now been proven under operational conditions for a number of years. The basic principle of DGPS is that a user is affected by satellite ephemeris, atmospheric propagation, Selective Availability (SA) and clock synchronisation errors to the same extent as a reference station, whose pre-determined position is known to a high accuracy. This can be used to calculate corrections to the measured pseudo-ranges measured to the various satellites, and transmitted to a multitude of users. The accuracy of DGPS positioning is generally quoted as being of the order of 1 to 3 metres. In fact, there are now not only a large number of commercial DGPS service providers, but the US military, which introduced Selective Availability (SA) to downgrade the GPS service available to civilians, uses its own DGPS whenever higher positioning accuracies are required. Since the mid 1980's civilian users have also developed a second method of positioning by using GPS satellites. This technique, which requires geodetic GPS
PROG.RAMMES.......
_.PROD.U.C.TS
~SS
i 0 sale411tes
I~M ¢~ ocK
Figure I. Galileo architecture.
receivers, is based on the use of the carrier frequency phase measurements. Geodetic receivers clear the pseudorange modulations, to access the two carrier frequencies. These correspond to wavelengths of about 19 cm and 24 cm respectively. The phase measurements, carried out in double difference mode, lead to the fractional part of the last wavelength in the distance from satellite to receiver. The required integer number of wavelengths in the satellite-to-receiver range, known as the 'integer ambiguity', is then solved through repeated measurements of the carrier phase. Carrier phase GPS can lead to very high relative positioning accuracies, ranging from several centimetres to a few millimetres.
Satellite and Ground Based Augmentations The 24-satellite basic GPS system provides a very wide range of navigation
and positioning applications. However, the system falls short of providing the necessary accuracy and integrity for a number of safety-critical applications, such as navigation in civil aviation. GPS was designed to provide two specified levels of positioning accuracy 50% and 95% of the time. These standards of accuracy, which were apparently considered adequate for, say, the navigation of military aircraft, fall well short of the required standards for civil airlines.
Even worse is the failure of the basic GPS constellation to meet the required level of integrity of a navigation system, before it can be used for a safety-critical application. Integrity is the ability of the system to detect an error and inform the user to stop using the system. A satellite navigation system can be adopted if it could be shown that the specified levels of accuracy and integrity were available not only anywhere along the flight path (availability), but also continuously during certain critical phases of the flight (continuity). To meet these requirements, GPS has to be augmented both through the provision of more satellites (space segment) and of stations on the ground (control segment). The Global Navigation Satellite System (GNSS-1) is made up of the basic GPS constellation (with or without GLONASS), augmented by a number of geo-stationary satellites, capable of broadcasting a GPS-like navigation signal, and a number of stations on the ground. The latter can be either (wide-area or local-area) DGPS reference stations, which contribute to improving the accuracy of the system, and Range Integrity Monitoring Stations (RIMS), which provide the system with an external integrity source.
Current applications Multi-modal transportation The Global Navigation Satellite System (GNSS) is likely to contribute signifi-
A I R & SPACE E U R O P E
• VOL.
I • N o 3 - 1999
cantly to sustainable mobility over a wide and increasing range of multimodal transport applications. The growing acceptance of GNSS technology by the transport community will not only generate substantial cost savings, but it will also contribute to safety through improved navigational performance of vehicles, vessels and airplanes. This, in turn, will lead to wider benefits to society, measured in terms of improved quality of life and wealth creation, through reduced delays, waiting times and the number of accidents, as well as reduced fuel consumption and its impact on the protection of the environment. Though crucial, GNSS is only one of the technological developments which are occurring within the wider field of transport telematics. The latter, which include not only navigation, but also communication and information technologies, are fundamental to the development of new and efficient transport information and management systems. GNSS provides the ability to continuously acquire real-time position and time information, which is necessary for
1000 9O0
location, monitoring, guiding and navigation in all transport modes. In the maritime community, GNSS technology is widely accepted as an essential component for the navigation of all types and sizes of vessels, from a small private craft to a large commercial tanker. Indeed, many countries are already implementing DGPS networks to provide increased accuracy and integrity, for coastal navigation and port entry. In civil aviation, GNSS will improve the efficiency of air transport, through the provision of a single global navigation system capable of meeting the most stringent requirements for all phases of flight. Efforts are already underway to introduce satellite and ground based GPS augmentation systems in North America, Europe and Japan to meet the requirements of the less stringent phases of flight. Of all sectors of transportation, roads constitute potentially the largest single market for GNSS services. Fitting all road mobile vehicles with GNSS receivers will reduce the strain of driv-
ing, by providing the driver with guidance information and thus assisting in decision making and route selection operations. Furthermore, when road accidents do occur, GNSS based telematics systems will notify the emergency services as soon as the vehicle's airbags are activated. The rail transport industry is perhaps the least interested in wanting to exploit the potential of GNSS. So far GNSS is considered only in a number of less important applications, such as passenger and timetable information. This may well be due to the considerable recent investments in trackside infrastructure for signalling. However, the increasing cost of maintaining such hardware in the future may well tilt the balance in favour of a GNSS based signalling system for rail transport.
Scientific applications The suggestion in the early 1980's by MIT radio astronomers that GPS could be used in measurements of the 'carrier frequency phase' of the signal, changed GPS from a limited military navigation
D lmua$ lIRe~reat,(mag Mmane a l m a n a c Sur~ e5
$00
OComa~rcml Maria,'
700 R^~cultur¢ 600
BI and .¢,urvey
~00
!'1Autca'n~l¢ Naviigali~m
400 30O
r'lHcct Mana$¢meat IIVI: R II1FR
200"
100"i O" i~7
1995
1999
Figure 2. The size of the market (1994-2004),
m
20f~
2001
2002
2003
2004
...........................................................................................................................................................................................................................
100 % 90%
"
70%
•
60~k Yg)%
# o
*
MobileTelephony
" * AirlFR
I.=--e-~ A i r V FR m
•
FleetManagement
"
4O%
"
AutoNav
L'andSurvey
3O%
----0--- A~iculturT~
;- Railways
20%
LandRe~Teational I O% 0% ~-
Figure 3. Penetration
rates b y s e g m e n t - GPS/GALILEO scenario.
tool to a highly flexible measurement system capable of literally hundreds of applications. GPS accuracies were no longer of the order of metres, but centimetres or even millimetres. Geodesy, geophysics, oceanography, land surveying, cartography, GIS, offshore exploration, civil engineering, agriculture, time synchronisation, astronomy and space navigation all benefit extensively from GPS. There are now in place dense global geodetic networks which act as reference points for the scientific applications of GPS. For example, interested scientists can now download from the Intemet continuous GPS measurements made on the IGS (international GPS Service) network. Meteorology is beginning to use GPS as a means for the measurement of water vapour content in the tropospheric layer of atmosphere, in preference to hitherto used less extensive and more expensive measurement systems. Water vapour content in the atmosphere is a crucial parameter for weather prediction and climate change. GPS is also used to monitor the relative vertical displacements of tide gauges which, in turn, are used to monitor the
change m mean-sea-level. There already are extensive GPS tide gauge networks in North America and Western Europe, and efforts are made to extend these to other regions of the world, for a more efficient monitoring of global sea level rise and climate change. Personal
Navigation
The availability of low cost GPS receivers has made this technology widely available for private usage, especially for walkers, climbers and sportsmen. It is easy to foresee even more extensive marketing of these devices, as part of a wristwatch, a tie pin or a mobile phone. The latter, in particular, could add a new dimension to inter-personal communications, especially in emergencies, when the provision and transmission of positional information could assist in life saving situations.
On-going projects in Europe EGNOS
In 1997 the European Commission, The European Space Agency and EuroconAIR
&
SPACE
trol established the European Tri-Partite Group (ETG), as a framework for taking the first major steps to involve Europe in satellite navigation. This was followed by a contract for the EGNOS project. The European Geostationary Navigation Overlay Service (EGNOS) is an ambitious development, valued at around ~165 million. The EGNOS contract, which is managed by the European Space Agency (ESA), was awarded towards the end of 1998 to a large industrial consortium, led by Alcatel Space Industries. The contract followed a two years definition phase, which derived the detailed architecture of the system and the requirements of the principal subsystems. EGNOS aims at deploying and operating by 2002 a space augmentation and ground infrastruc~re which, together with WAAS in North America and MSAS in Japan, will turn the basic GPS constellation of satellites into a Global Navigation Satellite System (GNSS-1). The latter will be able to provide a navigation service with a certifiable performance and an enhanced real-time positioning accuracy and integrity, compared with that EUROPE
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1999
offered by GPS and/or GLONASS (Benedicto et al, 1998) [1].
GALILEO In its quest to have an autonomous satellite positioning capability, independent from the availability of the GPS and GLONASS signals, the next step for Europe was inevitably the development and deployment of its own satellite constellation. Hence, the GALILEO initiafive, proposed by the European Commission in a communication dated 10 February 1999. This communication (EC, 1999, [2]) followed a very extensive process of consultation within Europe during 1998, through a GNSS Forum. The latter, which involved key representatives of European industry, government and academia, discussed user requirements, technical and financial aspects, civil-military interface, and legal certification issues. The core system of GALILEO is likely to consist of a constellation of Medium Earth Orbit (MEO) satellites, "representing low technical risk and known performance capabilities". In fact, this MEO approach, which was adopted by both the US and the USSR, has proved highly efficient and has therefore been retained for the next generation of the two existing satellite systems, known as Block IIF and GLONASS M respectively. The work to date, on an ESA contract to an industrial Consortium led by DaimlerChrysler Aerospace, and involving Alcatel, Alenia Aerospazio and Matra-Marconi Space, has focused on two broad options: A core constellation of 21 MEO and 3 GEO satellites, which could be integrated with GPS and wide area augmentation services (WAAS, EGNOS and MSAS), which would come close to meeting the requirements of Europe, or A core constellation of 36 MEO and 9 GEO satellites, which would meet the European requirements fully and independently. Clearly, both options would not preclude additional GEO and/or IGSO satellites, and an infrastructure of tracking, integrity, wide-area and local area ground stations, to produce a truly global satellite
navigation system, which could operate either together with or in parallel with GPS (figure 1). It is also proposed that the GALILEO signal will operate on two or three distinct carrier frequencies, thus improving significantly on the performance and the positioning accuracies provided currently by GPS and GLONASS.
A market perspective view for GALILEO The EC communication of 10 February 1999 (EC, 1999, [2]) mentions three projected service levels for GALILEO. A free 'mass market' Level I Service, similar to the GPS Standard Positioning Service (SPS), which would provide a 10-m horizontal positioning accuracy, a 'certifiable' Level 2 Service, and a 'safety-oflife and security-related' Level 3 Service. The latter two levels would have controlled access and probably a feebased use. Clearly, these three levels of service and likely corresponding feebased use would depend on the future policy of GPS, both in terms of interoperability with GALILEO and its own charging structure. The market potential for satellite navigation cannot just be assessed in terms of the sale of satellite receivers, but through the provision of value-added services which are more difficult to estimate. A forecast of the market size by application, is given in a study conducted by Frost and Sullivan (figure 2). Just a single business like road transport applications for cars and trucks has been assessed to generate an annual market of 7 million receivers by the year 2010. The Level 2 Service, which will offer enhanced levels of accuracy and integrity, will target markets where users will be prepared to pay for this added value. Payment could be affected, for example, in a manner similar to television services, which offer pay-per-view channels, on top of all the free channels received in parallel. The implementation of the Controlled Access Signal (CAS), in terms of space/ground infrastructure, ultimate performance levels
Ill
and geographical coverage, has yet to be settled. The Level 3 Service will represent the most stringent performance level of GALILEO, and will aim to satisfy safetyof-life related applications, such as aircraft precision landing, emergency crisis management, and search-and-rescue operations. GALILEO will offer the possibility to provide such public services to govemrnent agencies on a more economical basis than that offered currently by terrestrial systems, and in geographically difficult areas where satellite based systems are the only reliable solution. Finally, it is becoming clear that the development of local area augmentations and the coupling of GALILEO with communication systems, such as the 3rd mobile generation UMTS expected by 2003, will create additional markets. A forecast of the market penetration by segments, if GALILEO is implemented and used in parallel with GPS, is given in figure 3. For example, the combined usage of GPS and GALILEO, for rail applications, leads to a market penetration rate of 50%, compared to 10% for GPS alone. These estimates were established by KPMG during an ESA Comparative Study (ESA, 1999, [3]). Clearly, if in 10 years from now, GPS IIF is the sole satellite navigation system in place, this will be to the detriment of European industry and commerce.
Conclusion Satellites have progressively entered a wide field of our daffy life and affect it, without making us aware of their existence. Satellite telephones, digital TV, weather forecasting and earth resource management are some examples. 'Positioning' is one of the most important and promising applications, which will affect our lives, no less than 'time' does at present. Satellite receiver chips will make 'positioning' just as ubiquitous as wrist watches made 'time'. Given the right momentum, Europe should be able to play a decisive role in this field, through the GALILEO intiative. •
...................................................................................
PROGRAMMES
PRODUCTS
Acknowledgments The writers are grateful to Mr H H Fromm (European Space Agency) for permission to use the figures from the GNSS-2 Comparative Systems Studies (ESA, 1999, [3]).
References [1] Benedicto J, Michel P and Venture-Traveset J, 'EGNOS: Project Status Overview', GNSS 98 Conference, Toulouse (1998),and Air & Space Europe 1 (1) (1999),
[2] European Commission,'Galileo:InvolvingEurope ina New Generationof SatelliteNavigationServices', EC Communication, Brussels(1999),and Air& Space Europe I (2)(1999). [3] ESA Study by DaimlerChryslerAerospace, Matra Marconi, Alenia, Aerospazio and Alcatel Space Industries,'GNSS-2 Comparative System Studies, Phase I,Technical Note I,Macroeconomic Business Case' (1999),
AIR
& SPACE
EUROPE
• VOL.
I ° No
3 - 1999
e
+
GPS to Galileo: A European Path Herv~ BERTHELOT,Vidal ASHKENAZI
Navigation satellite systems such as GPS and GLONASS, which are capable of centimetric instantaneous positioning, have started a new era in navigation. Just as 20th century electronics and radar led to the development of radio navigation and the replacement of astro-navigation, satellite navigation is now targeted to become the main, if not the sole, means of multi-modal navigation in the 21st century. urthermore, satellite techniques are not only set to achieve millimetric accuracies for some nontransport applications, but also the mass production of electronic chips will create a mass market for these devices which are expected to retail for a few hundred ~ or less. This revolution will, in turn, create yet to be discovered new applications and even larger markets. Europe has to be ready for this challenge, and hence the Galileo initiative by the European Commission (EC, 1999) [21. This paper starts with the basic principles of satellite position fixing and the current applications. This is followed by a description of the ongoing projects in Europe and the market perspectives.
F
Satellite position fixing Basic Principles The fundamental observable of GPS is the pseudo-range. A pseudo-range is derived from the measured time of flight of the GPS signal from the satellite to a (fixed or mobile) receiver. By taking simultaneous measurements to at least four satellites, a GPS receiver is able to compute its three-dimensional position and time. In the current GPS, the satellites transmit on two L-band frequen-
cies, commonly referred to as L1 and L2. The precise P(Y) timing code, which is used to derive the pseudo-range, is modulated on both the L1 and L2 signals, whereas the coarse/acquisition C/A code is only modulated on the L1 signal. The civilian Standard Positioning System (SPS), which is based on the C/A code, has a specified accuracy of 100 metres (95%) for horizontal positioning and 150 metres for vertical positioning. The restricted Precise Positioning Service (PPS) is based on the precise P(Y) code, and has a specified accuracy of 16m SEP (50%). The GPS satellites continuously transmit a stream of information, consisting of timing codes and navigation data, which allows a user with a GPS receiver to calculate his position in real time. The timing codes, which are modulated on the two carrier frequencies, are received by the user and compared to two corresponding timing codes generated by the receiver, in a cross-correlation process. This results in the pseudo-ranges, which are then used in conjunction with the satellite ephemeris data which is also broadcast by the satellites, to compute the instantaneous position of the GPS receiver, whether fixed or moving.
Current systems: GPS and GLONASS The Global Positioning System (GPS) has now been fully operational for 66
around three years. At present (1999), there is an estimated 3 million users of GPS, covering a very wide range of applications. Although GPS was developed by the US Department of Defence (DOD) primarily for military purposes, the international civil community of users has been very active both in the development of the technology and in the commercial exploitation of the system. The last 10 years have also seen an increasingly active role for civilians in the management and future planning of GPS. Most notably, the establishment of the Interagency GPS Executive Board in 1996, to jointly manage GPS, formally acknowledged GPS as a civil/military dual-use system, at least in the USA. As of August 1998, there are 27 operational GPS satellites in orbit, of which 5 have minor problems. These constitute the GPS Block II/IIA satellites. Clearly, there is a constant requirement to replenish the system when satellites continually reach the end of their expected lifetime. The first satellite of a new generation of (Replacement) Block IIR satellites was launched in July 1997. A further generation of (Follow on) Block IIF, satellites are now being designed and will take the constellation well into the next century. The first phase of 6 Block IIF satellites were due to be delivered and launched in 2001/2002. This has now been postponed to 2004/2005.
................................................................................................................... The new Block IIF constellation will have several new features. Civilian users will be able to access two or possibly three frequencies, which will help considerably a number of applications, based on high accuracy carrier frequency phase measurements. The addition of more satellites to the constellation, a proposed transmitted integrity channel, increased transmission power, and aft facing antennas for geo-stationary satellite users, combine to make the Block IIF constellation a formidable system setting the standards. By contrast, the Russian Glonass system, which was originally designed as a stand-alone 24-satellite system, only had 15 satellites (including 1 back up and 1 not operational) in August 1998. Since then there has been a successful launch of 3 new satellites. It is now doubtful whether Glonass will achieve a standalone navigation capability.
Differential and carrier phase GPS The accuracy of positioning by GPS can be improved substantially by using a differential positioning technique. The differential GPS (DGPS) concept has now been proven under operational conditions for a number of years. The basic principle of DGPS is that a user is affected by satellite ephemeris, atmospheric propagation, Selective Availability (SA) and clock synchronisation errors to the same extent as a reference station, whose pre-determined position is known to a high accuracy. This can be used to calculate corrections to the measured pseudo-ranges measured to the various satellites, and transmitted to a multitude of users. The accuracy of DGPS positioning is generally quoted as being of the order of 1 to 3 metres. In fact, there are now not only a large number of commercial DGPS service providers, but the US military, which introduced Selective Availability (SA) to downgrade the GPS service available to civilians, uses its own DGPS whenever higher positioning accuracies are required. Since the mid 1980's civilian users have also developed a second method of positioning by using GPS satellites. This technique, which requires geodetic GPS
PROG.RAMMES.......
_.PROD.U.C.TS
~SS
i 0 sale411tes
I~M ¢~ ocK
Figure I. Galileo architecture.
receivers, is based on the use of the carrier frequency phase measurements. Geodetic receivers clear the pseudorange modulations, to access the two carrier frequencies. These correspond to wavelengths of about 19 cm and 24 cm respectively. The phase measurements, carried out in double difference mode, lead to the fractional part of the last wavelength in the distance from satellite to receiver. The required integer number of wavelengths in the satellite-to-receiver range, known as the 'integer ambiguity', is then solved through repeated measurements of the carrier phase. Carrier phase GPS can lead to very high relative positioning accuracies, ranging from several centimetres to a few millimetres.
Satellite and Ground Based Augmentations The 24-satellite basic GPS system provides a very wide range of navigation
and positioning applications. However, the system falls short of providing the necessary accuracy and integrity for a number of safety-critical applications, such as navigation in civil aviation. GPS was designed to provide two specified levels of positioning accuracy 50% and 95% of the time. These standards of accuracy, which were apparently considered adequate for, say, the navigation of military aircraft, fall well short of the required standards for civil airlines.
Even worse is the failure of the basic GPS constellation to meet the required level of integrity of a navigation system, before it can be used for a safety-critical application. Integrity is the ability of the system to detect an error and inform the user to stop using the system. A satellite navigation system can be adopted if it could be shown that the specified levels of accuracy and integrity were available not only anywhere along the flight path (availability), but also continuously during certain critical phases of the flight (continuity). To meet these requirements, GPS has to be augmented both through the provision of more satellites (space segment) and of stations on the ground (control segment). The Global Navigation Satellite System (GNSS-1) is made up of the basic GPS constellation (with or without GLONASS), augmented by a number of geo-stationary satellites, capable of broadcasting a GPS-like navigation signal, and a number of stations on the ground. The latter can be either (wide-area or local-area) DGPS reference stations, which contribute to improving the accuracy of the system, and Range Integrity Monitoring Stations (RIMS), which provide the system with an external integrity source.
Current applications Multi-modal transportation The Global Navigation Satellite System (GNSS) is likely to contribute signifi-
A I R & SPACE E U R O P E
• VOL.
I • N o 3 - 1999
cantly to sustainable mobility over a wide and increasing range of multimodal transport applications. The growing acceptance of GNSS technology by the transport community will not only generate substantial cost savings, but it will also contribute to safety through improved navigational performance of vehicles, vessels and airplanes. This, in turn, will lead to wider benefits to society, measured in terms of improved quality of life and wealth creation, through reduced delays, waiting times and the number of accidents, as well as reduced fuel consumption and its impact on the protection of the environment. Though crucial, GNSS is only one of the technological developments which are occurring within the wider field of transport telematics. The latter, which include not only navigation, but also communication and information technologies, are fundamental to the development of new and efficient transport information and management systems. GNSS provides the ability to continuously acquire real-time position and time information, which is necessary for
1000 9O0
location, monitoring, guiding and navigation in all transport modes. In the maritime community, GNSS technology is widely accepted as an essential component for the navigation of all types and sizes of vessels, from a small private craft to a large commercial tanker. Indeed, many countries are already implementing DGPS networks to provide increased accuracy and integrity, for coastal navigation and port entry. In civil aviation, GNSS will improve the efficiency of air transport, through the provision of a single global navigation system capable of meeting the most stringent requirements for all phases of flight. Efforts are already underway to introduce satellite and ground based GPS augmentation systems in North America, Europe and Japan to meet the requirements of the less stringent phases of flight. Of all sectors of transportation, roads constitute potentially the largest single market for GNSS services. Fitting all road mobile vehicles with GNSS receivers will reduce the strain of driv-
ing, by providing the driver with guidance information and thus assisting in decision making and route selection operations. Furthermore, when road accidents do occur, GNSS based telematics systems will notify the emergency services as soon as the vehicle's airbags are activated. The rail transport industry is perhaps the least interested in wanting to exploit the potential of GNSS. So far GNSS is considered only in a number of less important applications, such as passenger and timetable information. This may well be due to the considerable recent investments in trackside infrastructure for signalling. However, the increasing cost of maintaining such hardware in the future may well tilt the balance in favour of a GNSS based signalling system for rail transport.
Scientific applications The suggestion in the early 1980's by MIT radio astronomers that GPS could be used in measurements of the 'carrier frequency phase' of the signal, changed GPS from a limited military navigation
D lmua$ lIRe~reat,(mag Mmane a l m a n a c Sur~ e5
$00
OComa~rcml Maria,'
700 R^~cultur¢ 600
BI and .¢,urvey
~00
!'1Autca'n~l¢ Naviigali~m
400 30O
r'lHcct Mana$¢meat IIVI: R II1FR
200"
100"i O" i~7
1995
1999
Figure 2. The size of the market (1994-2004),
m
20f~
2001
2002
2003
2004
...........................................................................................................................................................................................................................
100 % 90%
"
70%
•
60~k Yg)%
# o
*
MobileTelephony
" * AirlFR
I.=--e-~ A i r V FR m
•
FleetManagement
"
4O%
"
AutoNav
L'andSurvey
3O%
----0--- A~iculturT~
;- Railways
20%
LandRe~Teational I O% 0% ~-
Figure 3. Penetration
rates b y s e g m e n t - GPS/GALILEO scenario.
tool to a highly flexible measurement system capable of literally hundreds of applications. GPS accuracies were no longer of the order of metres, but centimetres or even millimetres. Geodesy, geophysics, oceanography, land surveying, cartography, GIS, offshore exploration, civil engineering, agriculture, time synchronisation, astronomy and space navigation all benefit extensively from GPS. There are now in place dense global geodetic networks which act as reference points for the scientific applications of GPS. For example, interested scientists can now download from the Intemet continuous GPS measurements made on the IGS (international GPS Service) network. Meteorology is beginning to use GPS as a means for the measurement of water vapour content in the tropospheric layer of atmosphere, in preference to hitherto used less extensive and more expensive measurement systems. Water vapour content in the atmosphere is a crucial parameter for weather prediction and climate change. GPS is also used to monitor the relative vertical displacements of tide gauges which, in turn, are used to monitor the
change m mean-sea-level. There already are extensive GPS tide gauge networks in North America and Western Europe, and efforts are made to extend these to other regions of the world, for a more efficient monitoring of global sea level rise and climate change. Personal
Navigation
The availability of low cost GPS receivers has made this technology widely available for private usage, especially for walkers, climbers and sportsmen. It is easy to foresee even more extensive marketing of these devices, as part of a wristwatch, a tie pin or a mobile phone. The latter, in particular, could add a new dimension to inter-personal communications, especially in emergencies, when the provision and transmission of positional information could assist in life saving situations.
On-going projects in Europe EGNOS
In 1997 the European Commission, The European Space Agency and EuroconAIR
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trol established the European Tri-Partite Group (ETG), as a framework for taking the first major steps to involve Europe in satellite navigation. This was followed by a contract for the EGNOS project. The European Geostationary Navigation Overlay Service (EGNOS) is an ambitious development, valued at around ~165 million. The EGNOS contract, which is managed by the European Space Agency (ESA), was awarded towards the end of 1998 to a large industrial consortium, led by Alcatel Space Industries. The contract followed a two years definition phase, which derived the detailed architecture of the system and the requirements of the principal subsystems. EGNOS aims at deploying and operating by 2002 a space augmentation and ground infrastruc~re which, together with WAAS in North America and MSAS in Japan, will turn the basic GPS constellation of satellites into a Global Navigation Satellite System (GNSS-1). The latter will be able to provide a navigation service with a certifiable performance and an enhanced real-time positioning accuracy and integrity, compared with that EUROPE
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offered by GPS and/or GLONASS (Benedicto et al, 1998) [1].
GALILEO In its quest to have an autonomous satellite positioning capability, independent from the availability of the GPS and GLONASS signals, the next step for Europe was inevitably the development and deployment of its own satellite constellation. Hence, the GALILEO initiafive, proposed by the European Commission in a communication dated 10 February 1999. This communication (EC, 1999, [2]) followed a very extensive process of consultation within Europe during 1998, through a GNSS Forum. The latter, which involved key representatives of European industry, government and academia, discussed user requirements, technical and financial aspects, civil-military interface, and legal certification issues. The core system of GALILEO is likely to consist of a constellation of Medium Earth Orbit (MEO) satellites, "representing low technical risk and known performance capabilities". In fact, this MEO approach, which was adopted by both the US and the USSR, has proved highly efficient and has therefore been retained for the next generation of the two existing satellite systems, known as Block IIF and GLONASS M respectively. The work to date, on an ESA contract to an industrial Consortium led by DaimlerChrysler Aerospace, and involving Alcatel, Alenia Aerospazio and Matra-Marconi Space, has focused on two broad options: A core constellation of 21 MEO and 3 GEO satellites, which could be integrated with GPS and wide area augmentation services (WAAS, EGNOS and MSAS), which would come close to meeting the requirements of Europe, or A core constellation of 36 MEO and 9 GEO satellites, which would meet the European requirements fully and independently. Clearly, both options would not preclude additional GEO and/or IGSO satellites, and an infrastructure of tracking, integrity, wide-area and local area ground stations, to produce a truly global satellite
navigation system, which could operate either together with or in parallel with GPS (figure 1). It is also proposed that the GALILEO signal will operate on two or three distinct carrier frequencies, thus improving significantly on the performance and the positioning accuracies provided currently by GPS and GLONASS.
A market perspective view for GALILEO The EC communication of 10 February 1999 (EC, 1999, [2]) mentions three projected service levels for GALILEO. A free 'mass market' Level I Service, similar to the GPS Standard Positioning Service (SPS), which would provide a 10-m horizontal positioning accuracy, a 'certifiable' Level 2 Service, and a 'safety-oflife and security-related' Level 3 Service. The latter two levels would have controlled access and probably a feebased use. Clearly, these three levels of service and likely corresponding feebased use would depend on the future policy of GPS, both in terms of interoperability with GALILEO and its own charging structure. The market potential for satellite navigation cannot just be assessed in terms of the sale of satellite receivers, but through the provision of value-added services which are more difficult to estimate. A forecast of the market size by application, is given in a study conducted by Frost and Sullivan (figure 2). Just a single business like road transport applications for cars and trucks has been assessed to generate an annual market of 7 million receivers by the year 2010. The Level 2 Service, which will offer enhanced levels of accuracy and integrity, will target markets where users will be prepared to pay for this added value. Payment could be affected, for example, in a manner similar to television services, which offer pay-per-view channels, on top of all the free channels received in parallel. The implementation of the Controlled Access Signal (CAS), in terms of space/ground infrastructure, ultimate performance levels
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and geographical coverage, has yet to be settled. The Level 3 Service will represent the most stringent performance level of GALILEO, and will aim to satisfy safetyof-life related applications, such as aircraft precision landing, emergency crisis management, and search-and-rescue operations. GALILEO will offer the possibility to provide such public services to govemrnent agencies on a more economical basis than that offered currently by terrestrial systems, and in geographically difficult areas where satellite based systems are the only reliable solution. Finally, it is becoming clear that the development of local area augmentations and the coupling of GALILEO with communication systems, such as the 3rd mobile generation UMTS expected by 2003, will create additional markets. A forecast of the market penetration by segments, if GALILEO is implemented and used in parallel with GPS, is given in figure 3. For example, the combined usage of GPS and GALILEO, for rail applications, leads to a market penetration rate of 50%, compared to 10% for GPS alone. These estimates were established by KPMG during an ESA Comparative Study (ESA, 1999, [3]). Clearly, if in 10 years from now, GPS IIF is the sole satellite navigation system in place, this will be to the detriment of European industry and commerce.
Conclusion Satellites have progressively entered a wide field of our daffy life and affect it, without making us aware of their existence. Satellite telephones, digital TV, weather forecasting and earth resource management are some examples. 'Positioning' is one of the most important and promising applications, which will affect our lives, no less than 'time' does at present. Satellite receiver chips will make 'positioning' just as ubiquitous as wrist watches made 'time'. Given the right momentum, Europe should be able to play a decisive role in this field, through the GALILEO intiative. •
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Acknowledgments The writers are grateful to Mr H H Fromm (European Space Agency) for permission to use the figures from the GNSS-2 Comparative Systems Studies (ESA, 1999, [3]).
References [1] Benedicto J, Michel P and Venture-Traveset J, 'EGNOS: Project Status Overview', GNSS 98 Conference, Toulouse (1998),and Air & Space Europe 1 (1) (1999),
[2] European Commission,'Galileo:InvolvingEurope ina New Generationof SatelliteNavigationServices', EC Communication, Brussels(1999),and Air& Space Europe I (2)(1999). [3] ESA Study by DaimlerChryslerAerospace, Matra Marconi, Alenia, Aerospazio and Alcatel Space Industries,'GNSS-2 Comparative System Studies, Phase I,Technical Note I,Macroeconomic Business Case' (1999),
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