Fugro has introduced its high-accuracy G2+ service, designed to benefit offshore operators around the globe who require positioning and measurement accuracy at centimeter level.
G2+ is an enhancement of Fugro’s G2 service (based on GPS and GLONASS). The service uses highly advanced GNSS augmentation algorithms developed in house. The code and carrier-phase signals transmitted by GPS and GLONASS satellites are monitored globally by Fugro’s worldwide network of reference stations.
These observations are processed centrally in real-time using the company’s proprietary algorithms to generate precise corrections which are used to augment the standard signals broadcast by GPS and GLONASS satellites.
Customers receive corrections via seven high-powered communications satellites, providing at least two independent G2+ data sources. The new satellite positioning service will be particularly beneficial when seeking to measure latitude, longitude, elevation and speed with high accuracy in real-time, Fugro said.
Applications include offshore construction, survey services, vessel monitoring and structural monitoring. The ultra-high accuracy enables the real-time correction of tidal changes — which impact the accuracy of seabed mapping — as well as the real-time monitoring of the motion of floating and fixed structures.
The 3D accuracies of the system approach those of GNSS RTK (real-time kinematic) systems while avoiding the need for an RTK base station or local transmission link, overcoming the logistical challenges and range limitations associated with coastal RTK systems, Fugro said.
The launch of G2+ follows the recent launch of Fugro’s G4 satellite correction service, which takes advantage of all four global navigation satellite systems: GPS, GLONASS, BeiDou and Galileo.
Fugro has launched the G4 service, designed to provide GNSS augmentation for offshore positioning applications. The new satellite correction service takes advantage of all four GNSS: GPS, GLONASS, BeiDou and Galileo.
By using all available GNSS satellites, Fugro’s G4 service is designed to improve availability and reliability of offshore positioning and thus enhance the safety and productivity of a wide range of survey and other activities offshore. G4 represents a significant advancement compared to augmentation systems which are based on GPS-only or GPS + GLONASS, the company said.
The BeiDou system operated by China currently provides coverage in the Asia-Pacific region. Fugro’s G4 service already utilises the first BeiDou satellites and is ready to start using the Galileo satellites as soon the EU announces Initial Operational Capability (IOC) status for this system. Galileo and future BeiDou satellites will be automatically included as they come online, steadily increasing availability and robustness of the integrated augmentation service.
The new G4 service will be particularly beneficial when the line-of-sight to certain satellites is obstructed by offshore structures – a key consideration during critical positioning operations. The G4 augmentation signals, transmitted via seven high–powered communication satellites to provide at least two independent broadcast channels anywhere in the world, will offer Fugro’s customers unrivalled coverage and availability.
By Ugo Celestino, European Commission, Antonella Di Fazio, Telespazio SpA, Vicente José Giner Herrera, Ineco, Patrizio Vanni, ENAV SpA, and Francisco Javier Deblas, ESSP.
This article describes a live demonstration of an aviation application in Tunisia, to help the local aviation community in validating the use of the European Geostationary Navigation Overlay Service (EGNOS) to guide airplanes during landing operations. This activity constitutes the first complete experience of EGNOS Safety of Life (SoL) service for aviation approaches outside Europe. We present here the obtained results that are useful not only for Tunisia, but as a valuable case study for other countries outside Europe interested in using EGNOS in aviation.
EGNOS, operational since 2009, has a European regional coverage that could be quite easily extended to areas adjacent to European Union through the deployment of limited additional ground infrastructure elements, but sharing the same existing space segment and leveraging the other core ground infrastructure.
The European Commission has put in place a series of actions since 2006 to support the EGNOS service extension in neighbouring areas. The MEDiterranean follow-Up for EGNOS Adoption (MEDUSA) is an on-going European initiative related to EGNOS extension in the Euromed region, including North African and Middle East countries around the Mediterranean basin: Algeria, Egypt, Israel, Jordan, Lebanon, Libya, Morocco, Palestine, Syria, and Tunisia. MEDUSA runs a program of technical assistance action in these Euromed countries, in order to prepare them for an optimal adoption and exploitation of European GNSS services in their priority market segments.
The Mediterranean Extension of EGNOS
EGNOS is Europe’s first venture into satellite navigation and paves the way for Galileo, Europe’s independent global satellite navigation system currently under deployment.
EGNOS is a satellite-based augmentation system (SBAS), whose signal is compliant to the international SBAS interoperability standards: standards – MOPS (Minimum Operational Performance Standards) and ICAO SARPs (International Civil Aviation Organization Standard and Recommended Practices). In its current version (V2) it augments the open public service offered by the American Global Positioning System (GPS), by providing correction data that enables to improve GPS position accuracy, and provides integrity information about the GPS system (integrity information is fundamental for aeronautical applications like approaches). EGNOS is interoperable with the other equivalent regional systems. Today other SBASs are the U.S Wide Area Augmentation System (WAAS), the Japanese Multi-functional Satellite Augmentation System (MSAS), the Indian GPS Aided Geo Augmented Navigation (GAGAN) and the Russian System for Differential Correction and Monitoring (SDCM). The future version (V3) of EGNOS will augment Galileo signal as well.
Today EGNOS is operational, and available for use in aviation since 2011, giving opportunities for users to have more accurate and reliable positioning for enhancing existing applications, developing new applications and particularly the safety critical ones. Already more than 150 landing procedures are operational across Europe (some of them also in countries out of the European Union, such as Switzerland, Norway, Guernsey), with many others under development to reach 100 percent Approaches with Vertical Guidance (APV) coverage in the European instrumental runways as per ICAO recommendation.
EGNOS provides three services:
EGNOS Open Service (OS), launched in 2009, is delivered free of charge. It is open for use to anyone with an EGNOS-enabled receiver. This can be any receiver compatible with satellite-based augmentation systems. Being based on GPS, the EGNOS signal does not require major changes for receivers. Today, many mass market receivers available on the market are also EGNOS enabled. EGNOS OS is particularly suitable for mass market and some applications like surveying.
EGNOS Safety-of-life Service (SoL) is authorized for European civil aviation and operational since March 2011. EGNOS SoL delivers the integrity message providing the verification of the GPS system and timely warnings (within six seconds), when the system or its data should not be used for navigation. Since integrity relates to the trust that can be placed in the correctness of the location information supplied by GPS, thanks to this feature EGNOS is able to meet the demands of safety-critical applications in sectors such as aviation.
EGNOS Data Access Service (EDAS) launched in 2012, delivers a terrestrial commercial data service. It consists of a server that gets the data directly from EGNOS system and disseminates it via terrestrial networks in real time, within guaranteed maximum delay, security and performance. EDAS is particularly suitable for professional applications. It provides EGNOS raw data and corrections enabling software solutions that implement products and value added services built on them.
EGNOS infrastructure consists of three geostationary satellites over Europe and a network of ground stations (Ranging and Integrity Monitoring Station – RIMS) located to provide services whose coverage includes southern Europe, North Africa and some Middle East countries.
The EGNOS RIMS network supports a flexible network geometry that gradually adapts to service coverage requirements evolution. From the originally envisaged coverage over European Union’s countries, the EGNOS RIMS network is being expanded over Europe’s neighbouring areas, thus increasing the number of beneficiary countries. EGNOS SoL service is highly sought by several non-EU countries for the benefits it can bring to their civil aviation, in providing a solution to comply with ICAO requirements for Performance Based Navigation (PBN).
The present layout of the EGNOS RIMS network is presented in Figure 1.
Figure 1. EGNOS ground segment.
Figures 2 and 3 show respectively today’s coverage of EGNOS OS availability (source: European Satellite Services Provider, the service provider of EGNOS) and the APV-I availability performance commitment provided by EGNOS SoL (source: EGNOS Safety of Life Service Definition Document, EGN-SDD SoL, V2.0, European Commission, 2013), obtained relying on the above presented ground segment.
Figure 2. EGNOS OS Availability.
EGNOS OS Availability. The Figure 2 map is obtained by projecting the error at pseudorange level into the position domain. The computed error assumes that the GPS satellites used are those with an elevation angle above the local horizon (with a mask angle of 5º) and does not consider any possible factor depending on local characteristics that could produce different results (optimistic or pessimistic) with respect to the results computed using real receivers located in the considered areas. Moreover, it represents an estimation of EGNOS OS availability during a very limited period of time being an estimation, thus it does not imply any commitment or reference for the performances which can be obtained during different periods.
Figure 3. EGNOS APV-I Availability.
Other initiatives for a further extension in North Africa and Middle East are already being developed, under the umbrella of the Euromed GNSS programme. In parallel with the infrastructure deployment, the Euromed GNSS programme also includes actions to support the introduction and exploitation of EGNOS services. The first stage was completed in the frame of the Euromed GNSS I/MEdiTerranean Introduction of GNSS Services (METIS) project in the period 2006-2009, the second stage is presently running in the frame of the Euromed GNSS II/MEDUSA project. Further initiatives are being planned for 2015 and beyond.
EGNOS Use in Aviation
EGNOS was initially designed and developed to be used in aviation, similarly to the U.S. Federal Aviation Administration WAAS, to support different types of aviation applications and, in particular, to meet the performance requirements set by the International Civil Aviation Organization (Annex 10) for the implementation of APV-I, which enable the implementation of LPV final approaches, as reported in Table 1.
Table 1. ICAO Operational Requirements.
EGNOS is one of the GNSS elements recognised by ICAO (Annex 10) as a radionavigation aid. It is an important element of a global SBAS systems mosaic, that started with the American system WAAS in 2003, and that is gradually completed by other more recent SBAS: EGNOS itself, MSAS (Japan), GAGAN (India), SDCM (Russia), and some countries like Australia and South Korea that have launched feasibility studies to develop their own SBAS.
It is expected that, in a not too far future, most parts of the world will profit from SBAS services, following the current coverage extension plans and SBAS system evolutions. The final objective, as also shared at ICAO level, is that as many airdromes worldwide, as possible, can offer instrument approaches with vertical guidance, with an outstanding increase in global safety rates.
Additionally, the use of EGNOS allows taking full advantage of GNSS for all phases of flight, including final approach. Therefore, EGNOS means for aviation a fundamental and strategic tool to help meet ICAO’s recommendations, aimed at the adoption of a PBN oriented airspace use policy, for all countries. The 37th Assembly of ICAO (28 September – 8 October 2010) resolved that APV procedures should be implemented as either a primary or backup strategy for precision approaches at all instrument runway ends by 2016.
APV is a major safety initiative. ICAO recognises SBAS and Barometric Vertical Navigation (Baro-VNAV) as the two acceptable (and often complementary) means of implementing APV procedures, which are safer than NPA (Non Precision Approach).
GNSS based navigation enables RNAV (aRea NAVigation) with a higher cost effectiveness in comparison with the old conventional, sensor ground-based, navigation procedures. This is especially true for wide, even desert unequipped areas (or difficult to maintain) like those in North Africa and Middle East.
EGNOS benefits are maximized in final approach manoeuvres, providing GNSS lateral and vertical guidance, and enabling APV-I approaches.
Final approach procedures based on GNSS are classified as RNP approaches (RNP APCH, as shown in the next figure), namely: Lateral Navigation (LNAV) with GPS lateral guidance and no vertical guidance; LP with GPS + SBAS (EGNOS) for lateral guidance (CAT-I localizer performance) and no vertical guidance; Lateral Navigation/Vertical Navigation (LNAV/VNAV) with GPS lateral guidance and Baro-Vertical Navigation (VNAV) vertical guidance (Baro-VNAV approach procedures can be flown with SBAS vertical guidance upon the approval of the Air Navigation Service Provider (ANSP)) and the LPV (Localizer Performance with Vertical Guidance) with GPS + EGNOS for both lateral and vertical guidance.
Figure 4. RNP approaches.
Those procedures not including vertical guidance are intended to be flown with the Constant Descent Final Approach (CDFA) technique (to avoid dangerous dive and drive practices), supported by most Flight Management Systems (FMS).
Regarding the operational LPV main figures, the European regulation (EU OPS -REGULATION (EC) No 859/2008 usually known as EU OPS) allows LPV operational minima (Decision Height – DH) down to 250 ft, expected to be possibly lowered down to 200 ft by 2015 (LPV-200), similarly to what is already permitted by the FAA, in the United Sates for WAAS based LPV approaches (a DH of 200 ft would make LPV approaches very competitive, when benchmarked against ILS CAT-I, precision approach, or even Ground Based Augmentation System (GBAS) CAT-I precision approach).
In the last few years, about 150 LPV procedures (status as of July 2014) have been published in European airports, and the number of procedures and countries introducing EGNOS is continuously increasing.
Euromed GNSS I/METIS and Euromed GNSS II/MEDUSA
In parallel with the development of the infrastructures necessary for extending EGNOS availability across the Euromed region, the European Commission has put in place initiatives to prepare and assist the Euromed countries for the optimal use and adoption of the relevant services.
These consist in two sequential projects, the first being Euromed GNSS I/METIS project and the second being Euromed GNSS II /MEDUSA.
Running from mid 2006 up to the end of 2009, METIS acted as a pioneer in the Euromed countries and built national/regional liaisons with decision-makers and key stakeholders, interested in sharing experience and absorbing know-how. The project assisted the 10 Euromed countries to identify their priorities in relation to the use of EGNOS services, to validate the relevant opportunities from the strategic/social and economic perspectives, and to elaborate a suitable strategy and a plan of actions for facilitating EGNOS adoption and exploitation.
MEDUSA Case Study in Tunisia: LPV Approaches in the Airport of Monastir Using EGNOS
As part of the technical assistance actions programme in the priority domains, MEDUSA implements demonstrations and validations of EGNOS services in concrete applications.
For EGNOS SoL, the technical assistance action consisted in the validation of GNSS approaches, including LPV approaches, designed and constructed in MEDUSA along with the relevant safety assessment and business case for the airport of Monastir in Tunisia (35°45’29’’ N 10°45’17’’ E). The selection of the airport was driven by a trade off between the EGNOS service availability with required APV-I performances and the specific needs of the Tunisian Air Navigation Service Provider – ANSP (OACA, Office de l’Aviation Civile et des Aéroports). According to OACA, Monastir is among the airports in Tunisia presenting favourable conditions, in terms of operational constraints and traffic, for concretely proving the added value of EGNOS for final approaches.
The airport has two runways, RWY 07 and RWY 25, the former is equipped with an ILS CAT-I, the latter only supports NPA approaches. The installation of an ILS in RWY 25 was discarded due to technical constraints. This infrastructure has proven to be insufficient to fully cover the airport needs, that suffers some Delays-Diversions-Cancellations (DDCs) as a result of local specific meteorological conditions, frequent fog banks entering from the sea in the early morning, combined with desert haze. These conditions make LPV ideal procedures, as backups to RWY 07, and enabling APV approaches to RWY 25. Finally, Monastir’s TWR ATC (Tower Air Traffic Control ) staff has been involved in OACA’s PBN development, for which they were ideal candidates to evaluate the benefits possibly achievable from the use of EGNOS.
This MEDUSA’s technical assistance action is the first complete experience for the use of EGNOS SoL service outside Europe. It was conceived as a realistic exercise of RNP APCH procedures implementation, following the guidelines provided by ICAO in the “EUR RNP APCH Guidance Material (EUR Doc 025)” and including all the activities required, from the scenario adequacy study to flight validation and the requirements analysis for the final publication in the AIP (Aeronautical Information Publication). OACA was directly involved in all activities, providing inputs/feedbacks and for training purposes.
A set of three GNSS based approach procedures was produced for each RWY, following ICAO 8168 PANS OPS design principles. The next figures show the combined charts type elaborated, that include minima boxes for three RNP approaches (LNAV, LNAV/VNAV and LPV). The procedures construction preserves the current Monastir arrivals structure, following airspace management principles and facilitating the operational approval. As illustrated in the charts, in both cases for the three minima the calculated OCH (Obstacle Clearance Height) values improve with respect to the already existing conventional approaches, providing significant operational and safety benefits.
Figure 5. GNSS approaches for RWY 07.Figure 6. GNSS approaches for RWY 25.
An on-site GNSS performance monitoring campaign was performed by OACA, with the support of GEMCO’s staff, 3 months before the flight trials schedule, covering both EGNOS and GPS signal performances. Besides, an APV-I availability study for the area and specifically for Monastir airport during 1 month before the flight validation was purposely elaborated by the European EGNOS service provider (ESSP). Both analyses, confirmed suitable APV-I performance in terms of availability and continuity, making feasible the implementation of LPV approach procedures in line with ICAO prescriptions.
The next figures show the EGNOS APV-I availability and continuitymeasured on one day during the period of the flight validation (conducted from 30 January to 1 February 2014), in particular at Monastir airport for the considered time-lag:
APV-I availability was over 99%;
APV-I continuity presented a total value lower than 5×10-4/15s;
95th percentile of Horizontal APV-I accuracy was between 1.1 and 1.2 meters and the 95th percentile of Vertical APV-I Accuracy is around 1.4 meters, thus showing a very good accuracy level;
Horizontal and Vertical safety indexes were lower than 0.25, representing a very good integrity margin.
Additionally, the results of the on-site GNSS performance monitoring campaign showed quite stable performances with small fluctuations during the whole period of observation, and no problems or outages were observed.
(EGNOS APV-I Availability is defined as the percentage of epochs in a month in which the Protection Level are below Alert Limits for this APV-I service (HPL<40m and VPL<50m) over the total period (source: ESSP).
EGNOS APV-I Continuity Risk is defined as the result of dividing the total number of single continuity breaks using a time-sliding window of 15 seconds by the number of samples with valid and available PA navigation solution. A single continuity break occurs if the system is available at one epoch and becomes not available for the following 15 seconds (source: ESSP).)
Figure 7. APV-I availability on 31.01.2014.Figure 8. APV-I continuity on 31.01.2014.
The flight validation campaign was carried out according to ICAO doc 9906 with a Piaggio P180 Avanti II (from ENAV flight inspection department) suitably equipped with UNIFIS 3000 system and a Rockwell Collins FMS 3000 with SBAS LPV approach capabilities.
Figure 9. Piaggio P180 Avanti II aircraft and the FMS messages during the flight validation.
The outcomes of this concrete experience have allowed the Tunisian authorities to identify the main elements for the publication of the validated procedures in their national AIP. They have also contributed to the analysis of the necessary process for the operational adoption of GNSS, including EGNOS, in aviation in countries beyond the EU boundaries.
The activities performed on performance assessment have been preparatory for discussions on GNSS monitoring and data recording on going at ICAO Navigation System Panel level, that would produce ICAO guidelines for States.
Therefore, this Tunisia’s “case study” represents a practical and realistic example that could be beneficial for the other non-EU countries in terms of best practice and lesson learnt. Moreover, methodology and guidelines have been derived to be possibly injected to other non-European countries interested to introduce EGNOS operations in aviation.
Lessons Learned and Outlook
Through its achievements, MEDUSA is opening the way for the introduction of EGNOS SoL service in North Africa and Middle-East region, and it is also defining a suitable path to be followed by other interested non-European countries. Overall, MEDUSA is continuing to confirm the ability to foster cooperation and involvement in EGNOS programme of the great majority of the Euromed countries. Further to Tunisia, other Euromed countries have already expressed their interest in relation to the EGNOS use in aviation, considering each country’s strategy and also in the light of a common shared regional perspective. Besides, the results obtained by MEDUSA are useful also for other regions interested to use EGNOS in aviation.
Additionally, MEDUSA is clearly showing that Euromed region, presently lacking the full support of SBAS technologies, represents an opportunity for EGNOS service extension, with many benefits for the countries of the region and for Europe.
On one hand, being SBAS an effective and efficient technology to enable the aviation community of the Euromed countries to comply with ICAO recommendations on PBN implementation by year 2016 across the region, the services coverage extension of existing SBAS systems (EGNOS in the case of the Euromed countries) can be one of the most efficient ways to move forward. In fact, the Euromed national ANSPs consider the readiness of EGNOS SoL service as one of the main drivers and factors when designing their PBN strategy. EGNOS, which is already operational since 2009 and available for use in aviation since 2011, can deliver added-value services to the Euromed region, just by leveraging the existing European infrastructure with only incremental, marginal and natural extension. The EGNOS coverage extension across the Euromed region can provide significant benefits and particularly to those Euromed countries with few ILS or reduced navaids coverage, and enhance safety and efficiency to the whole aviation community.
On the other hand, the European Union has to gain from an EGNOS-based long term links with its neighbouring regions, by increasing bilateral/multilateral cooperation and interaction (e.g. assistance, mutual cooperation) among public and semi-public bodies (e.g. ANSPs, Civil Aviation Authorities), by strengthening EGNOS SoL coverage in the southern/peripheries of EU (e.g. Malta, Cyprus, Greece, Southernest Italian islands, Canary islands), by pursuing and supporting other EU policies in several sectors (like transports, e.g. harmonizing aviation safety standards across the Mediterranean, Transport Policy of the Mediterranean Partners), and last but not least by achieving a first step towards EGNOS extension to the whole African continent which will bring in similar, additional benefits just described above.
The third IRNSS satellite heads into orbit. Photo: ISRO
India has successfully launched IRNSS-1C, the third satellite in the Indian Regional Navigation Satellite System (IRNSS), early on October 16. The satellite was launched aboard the Polar Satellite Launch Vehicle (PSLV) C26 at 2002 GMT (4:02 p.m. EDT) from Satish Dhawan Space Centre, Sriharikota.
After the lift-off of PSLV-C26 with the ignition of the first stage, the important flight events — namely, stage and strap-on ignitions, heat-shield separation, stage and strap-on separations and satellite injection — took place as planned, according to the Indian Space Research Organization (ISRO). After a flight of about 20 minutes, 18 seconds, the IRNSS-1C satellite, weighing 1425 kg, was injected to an elliptical orbit of 282.56 km x 20,670 km, which is very close to the intended orbit.
After injection, the solar panels of IRNSS-1C were deployed automatically. ISRO’s Master Control Facility (at Hassan, Karnataka) assumed the control of the satellite. In the coming days, four orbit maneuvers will be conducted from the Master Control Facility to position the satellite in the geostationary orbit at 83 degrees East longitude.
IRNSS-1C is the third of the seven satellites constituting the space segment of the Indian Regional Navigation Satellite System. IRNSS-1A and IRNSS-1B, the first two satellites of the constellation, were successfully launched by PSLV on July 02, 2013, and April 04, 2014, respectively. Both IRNSS-1A and 1B are functioning satisfactorily from their designated geosynchronous orbital positions.
IRNSS is an independent regional navigation satellite system designed to provide position information in the Indian region and 1,500 kilometers around the Indian mainland. IRNSS will provide two types of services, namely, Standard Positioning Services (SPS) — provided to all users — and Restricted Services (RS), provided to authorized users.
A number of ground stations responsible for the generation and transmission of navigation parameters, satellite control, satellite ranging and monitoring, etc., have been established in as many as 15 locations across the country.
This is the 27th consecutively successful mission of the PSLV, which used the XL configuration of PSLV for the seventh time. Honorable Minister of State (Space) Jitendra Singh, witnessed the launch from the Mission Control Centre at SDSC, Sriharikota.
The next satellite of this constellation, IRNSS-1D, is scheduled to be launched by PSLV in the coming months. The entire IRNSS constellation of seven satellites is planned to be completed by 2015.
Below is a slideshow with images from the launch preparations and launch.
Nozzle end segment of PSLV-C26 being hoisted for assembly. Photo: ISRO
Nozzle end segment of PSLV-C26 being hoisted for assembly with launch pedestal. Photo: ISRO
IRNSS-1C being assembled with PSLV-C26 in the mobile service tower. Photo: ISRO
PSLV-C26 inside the mobile service tower prior to satellite integration. Photo: ISRO
IRNSS-1C being assembled with PSLV-C26. Photo: ISRO
The PSLV-C26, carrying IRNSS-1C, lifts off. Photo: ISRO
Assembly of PSLV-C26, third and fourth Stages. Photo: ISRO
The third IRNSS satellite heads into orbit. Photo: ISRO
On October 21, Jordan will host a Euro-Mediterranean Partnership (EUROMED) regional event focused on the use of GNSS, particularly European GNSS, for freight and road transport. The Euromed GNSS II/MEDUSA meeting will be held in Amman, Jordan, at the Sheraton Al Nabil Hotel.
Organized by the Euromed GNSS II/MEDUSA project, under the auspices of the Ministry of Transport of Jordan, the event will aim to share experiences and best practices, and to discuss strategies and possible ways forward in relation to the use of the satellite navigation for freight and road transport in the region.
At the event, MEDUSA will present the results of its case study, which was conducted with Royal Jordanian Customs and with the aid of the Ministry of Transport of Jordan. Since April, supported by European companies involved in MEDUSA, Royal Jordanian Customs have had the opportunity to test and validate the use of European GNSS, and specifically of EGNOS, for tracking and tracing containers shipped across the Mediterranean Sea and vehicles transporting goods in Jordan.
The case study is one of the technical assistance actions implemented by MEDUSA, and it represents the first life experience of EGNOS services’ usage in areas distant from Europe.
MEDUSA belongs to the EU Euromed Transport Program. Its objective is to promote the adoption of the European GNSS by the Euromed countries, which include Algeria, Egypt, Israel, Jordan, Lebanon, Libya, Morocco, Palestine, Syria (suspended due to political unrest), and Tunisia.
GNSS technology is applied to several user applications, and transport is one of the most important, including aviation, road, maritime, rail, freight transport and logistics. The MEDUSA project includes a program of specific technical assistance actions for the Euromed countries, to facilitate the introduction and exploitation of GNSS services in their markets.
The wide adoption of advanced technology, also including satellite navigation, for freight and road transport applications (such as Intelligent Transport Systems, or ITS) enables the implementation of smart mobility and the enhancement of goods transportation/traffic volumes increasing.
During the event, the participants from the Euromed countries will share lessons learned from the Jordan case study, and learn about relevant best practices in Europe and in the Euromed region, as well as debate strategies and possible ways forward in the light of national interests and common regional perspectives.
Opened by an institutional panel, with representatives of the Jordan Ministry of Transport and the European Commission, the event will consist of a session dedicated to the case study and a session addressing opportunities in other Euromed countries, including the presentation of European success cases as examples of suitable paths to guide the GNSS operational introduction and adoption.
At the conclusion of the event, the participants will elaborate guidelines and recommendations, to be possibly translated into action plans for the Euromed countries.
The Japan News is reporting that the Japanese Committee on the National Space Policy has compiled a draft proposal that includes increasing the number of quasi-zenith satellites (QZSS), Japan’s satellite navigation system, from the current single satellite to a total of four.
Currently, Japan is operating only one quasi-zenith satellite, named Michibiki.
The increase would be made to strengthen Japan’s overall surveillance systems, in light of developments such as China’s maritime expansion. “China’s high-pressure maritime advances have become a menace to the security of countries in Asia. Continued vigilance is also required against North Korea’s missile launches and nuclear weapons development program,” according an editorial published by The Japan News.
The additional QZSS satellites would presumably supplement Japan’s surveillance satellites with positioning information. Japan currently has four information-gathering satellites, which lack the flexibility to boost the accuracy of ground surveillance activities and swiftly grasp movements of objects such as vessels at sea.
“For surveillance activities, acquisition of high-precision positioning information using space technology is also important. Only the global positioning system (GPS) run by the United States is currently reliable for this purpose,” the editorial said.
A four-satellite QZSS system will allow positioning surveillance of all regions around the clock. Based on the proposal, the government is expected to revise the Basic Plan on Space Policy within the year.
The proposal also stipulates that the country should aim to operate seven quasi-zenith satellites as early as possible, which would allow stable management of the system, according to The Japan News.
“What can we do to reduce the vulnerability [of GPS] and ensure that the expectations of the public are going to be met?” asked Dr. Bradford Parkinson as he opened his presentation this morning (Tuesday, April 15) at the European Navigation Conference, ENC-GNSS 2014 in Rotterdam, The Netherlands.
Parkinson went through his 61-slide, 50-minute briefing on what he called “PTA” — Protect, Toughen, and Augment — a proposal concerning not only GPS but PNT systems globally. An article by Parkinson based on this talk will highlight the special 25th Anniversary edition of GPS World, to appear in conjunction with this year’s July issue.
Brad Parkinson
After briefly overviewing the many worldwide applications of GPS and its penetration and participation in several vital markets, Parkinson stated “If we want to ensure the economic benefits of GPS, there are some essential needs that a user has. The first need is availability, and I’m defining availability in a certain way. It’s at the required accuracy for the application involved, and it has a bound on the random events that happen out there.
“The second required aspect is integrity, as in ‘I know I’m getting this accuracy, the system is not lying to me.’ In many cases, it’s required that the system not lie to you more often than once in 10 to the seventh (10 million) times.”
Parkinson developed his Protect, Toughen, and Augment proposal in part in response to a remark he heard from a high U.S. government official who opined that “GPS is much too vulnerable, we need to replace it.” While agreeing that the system is vulnerable, Parkinson has strived for a more constructive approach to the problem.
At the end of his presentation, Parkinson introduced one of his colleagues in the audience, from his early days on the GPS Program, and stated that if it was not for Hugo Fruehauf’s expertise with atomic reference systems in 1973, there might never have been a GPS program.
Parkinson was among attendees at an ENC event at City Hall hosted by the Mayor of Rotterdam, The Netherlands. From left are Hugo Fruehauf, Mrs. Bradford “Ginny” Parkinson, Professor Bradford Parkinson, Don Jewell — GPS World Defense Editor, Jac Spaans — Chairman of the Organizing Commitee of the ENC, and Adrianna Spaans.
By Mirko Stanisak, Mark Bitter, and Thomas Feuerle
INNOVATION INSIGHTS by Richard Langley
GPS = SAFER FLIGHT. While reviewing material for an article celebrating the 25th anniversary of the launch in February 1989 of the first Block II or operational GPS satellite, I was yet again annoyed by many articles on the Web stating that GPS only became available for civil use after the launch of this satellite. Some sources get closer to the truth when they say that GPS was opened for civil use in 1983, following the shoot-down of the Korean Airlines Flight 007. In fact, GPS was designed to serve the needs of both the military and civil communities from the outset. A government memo from April 1973 clearly states: “Civil user needs should be considered in the design of the spaceborne equipment.”
One of the first demonstrations of the use of GPS for aircraft navigation occurred in July 1983, when a Sabreliner business jet was flown in stages from Cedar Rapids, Iowa, to the Paris Air Show, flying only when a sufficient number of the experimental or Block I satellites were in view. The first standalone GPS receivers certified for aviation use (with Receiver Autonomous Integrity Monitoring or RAIM) became available by the mid-1990s. But already the Federal Aviation Administration had been looking into the development of a system to provide higher accuracies and better integrity than that afforded by standalone receivers. In 1994, the FAA announced the development of the Wide Area Augmentation System, its brand of a system generically known as satellite-based augmentation. Geostationary satellites transmit corrections and integrity information to GPS receivers, permitting GPS use for en route navigation all the way down to traditional Category I approach and landing. CAT I approaches can be flown down to a decision height of 61 meters (200 feet). WAAS was declared operational on July 10, 2003, but enhancements to the system continue. Japan, Europe, and India also have operational SBAS based on GPS.
Ground-based GPS augmentation was first developed for maritime applications with the U.S. Coast Guard’s low-frequency system coming on line in the mid-1990s. Also in the mid-1990s, the FAA began the development of the Local Area Augmentation System, generically known as a ground-based augmentation system (GBAS), to provide aircraft with approach and landing capabilities from CAT I down through CAT II (30-meter or 100-foot decision height) and CAT III (no decision height but certain visual range minima) using a VHF datalink. Initial CAT I systems are being operated at Bremen, Germany, and at Newark Liberty International Airport and Houston George Bush Intercontinental Airport.
While a GPS-based GBAS will definitely offer improved navigation services for aircraft, might these services be even better if the systems were to use satellites from other constellations besides GPS? In this month’s column, we look at a straw-man concept for modifying the GBAS protocols to accommodate multiple constellations and the results of preliminary tests using GPS, GLONASS, and Galileo simultaneously.
“Innovation” is a regular feature that discusses advances in GPS technology and its applications as well as the fundamentals of GPS positioning. The column is coordinated by Richard Langley of the Department of Geodesy and Geomatics Engineering, University of New Brunswick. He welcomes comments and topic ideas. Write to him at lang @ unb.ca.
Ever since the declaration of Full Operational Capability (FOC) of the U.S. Global Positioning System in April 1995, GPS has dominated satellite navigation, especially in aviation applications. By contrast, the Russian GLONASS system cannot be used in western aviation because no approval guidelines exist for GLONASS equipment. Thus GPS has been the de-facto standard in aviation for years.
However, within the last few years, major changes have evolved in the field of GNSS, providing a wide variety of useable satellite navigation systems. The European Union launched its Galileo project, which will provide global multi-frequency services in the near future. China is upgrading its BeiDou system (formerly called Compass) to provide global coverage with more medium-Earth-orbit (MEO) satellites. The operators of GPS and GLONASS have started modernization programs that will enable multi-frequency operations in the future, too. Therefore, a large number of usable satellites and signals from multiple systems will soon be available.
In aviation, almost all phases of flight can be assisted by satellite navigation systems nowadays. The most challenging phase of flight with respect to accuracy, continuity, availability, and integrity is the approach and landing phase. The Ground Based Augmentation System (see FIGURE 1; courtesy of the European Organization for Civil Aviation Equipment) allows precision approaches to be performed using satellite navigation. It uses a VHF data link to broadcast differential GNSS corrections, integrity information, and approach definitions to approaching aircraft. These aircraft combine the differential corrections with their own GNSS measurements, calculate a GBAS-corrected position solution, and determine path deviations based on the selected approach.
FIGURE 1. GBAS principle. (Source: EUROCAE WG 28, ED-114)
From a technical perspective, GBAS can use either GPS or GLONASS for differential corrections. For this, the International Civil Aviation Organization (ICAO) Standards and Recommended Practices (SARPs) include GPS and GLONASS side by side. On the other hand, some standardization documents (for example, those from RTCA) are limited to GPS only, effectively excluding GLONASS from being used in the western world. Nevertheless, Russian GBAS systems provide differential corrections for GPS and GLONASS, and are expected to be certified in Russia in the near future. Additional GNSS such as Galileo or BeiDou are not yet included within these documents, as these systems are not approved for aviation use themselves. This article will focus on how a multi-constellation GBAS with GPS, GLONASS, and Galileo could work.
GBAS installations can provide multiple services for different kinds of operation, based on GNSS L1 corrections only. On the one hand, the differentially corrected positioning service (DCPS) is intended to be a generic service for high accuracy positioning. On the other hand, two different GBAS approach services have been defined. GBAS Approach Service Type C (GAST-C) allows Category I (CAT I) procedures and is already in operation. GAST-D is still under development and will enable precision approaches and landings down to CAT II/III minima once certified. To mitigate all possible hazards, GAST-D will require some additional broadcast messages.
VHF Data Broadcast
The VHF Data Broadcast (VDB) is used to communicate binary GBAS messages to approaching aircraft. It operates in the VHF band (108.025 – 117.975 MHz) and uses time-division multiple access (TDMA) to allow the operation of multiple GBAS ground stations on a single frequency. As shown in FIGURE 2, VDB uses UTC time to have a common time frame. Two frames are transmitted each second, lasting 0.5 seconds each. Within each frame, eight slots with durations of 62.5 milliseconds can be used for transmission. Binary application data is encoded using a differentially encoded eight-phase-shift-keying modulation (D8PSK) and a symbol rate of 10,500 symbols per second. With three bits transmitted per symbol, up to 31,500 bits per second can be transmitted. Each slot can contain up to 222 bytes of binary application data. Usually, only a subset of slots is allocated to a particular ground facility. This way, multiple GBAS ground facilities can share a common VDB frequency.
Within each slot, multiple VDB messages can be transmitted as application data. The coding of information in VDB messages is defined in the RTCA’s GNSS-Based Precision Approach Local Area Augmentation System (LAAS) Signal-in-Space Interface Control Document (ICD) and depends on the VDB message type. (LAAS is the U.S. GBAS.) Currently, message types (MT) 1, 2, 3, 4 and 11 are defined. Figure 2 is derived from this document.
Message Type 1 – MT1. Within VDB Message Type 1, differential corrections based on 100-second smoothing are transmitted. These corrections are required by all GBAS approach services (GAST-C and GAST-D). Aside from the differential corrections, additional information for the first broadcast satellite is transmitted. This includes an ephemeris cyclic redundancy check (CRC), mitigating the effects of wrongly received GNSS navigation data, and the Issue of Data (IOD) flag, indicating the time of applicability for the ephemeris data to be used. To transmit this information for all satellites, the satellite for which differential corrections are transmitted first has to be alternated continuously.
Each MT1 message can contain up to 18 pseudorange- and range-rate corrections for individual satellites. Nevertheless, it is possible to link two consecutive MT1 messages using the Additional Message Flag (AMF). The value of this parameter indicates whether this is a single message (0), or the first (1) or second (3) part of a linked MT1 message. Up to 36 differential corrections can be transmitted using two consecutive VDB time slots with 18 corrections each.
All MT1 measurement blocks must be transmitted at least once per frame. The maximum transmission rate is once per slot for all measurement blocks.
Message Type 2 – MT2. VDB Message Type 2 contains station and integrity parameters such as the coordinates of the reference point to which all differential corrections refer. MT2 messages can include (next to a “core” MT2 message) multiple Additional Data Blocks (ADBs) to transmit information required for different GBAS services. At the moment, the Additional Data Blocks 1, 3, and 4 are defined.
ADB1 contains the maximum distance to the reference point at which the corrections may be used (Dmax) as well as parameters to calculate the remaining risk of incorrect GNSS ephemeris data (Kmd,e). Within ADB3, additional information required for GAST-D is transmitted. ADB4 implements the VDB authentication feature. If this ADB is broadcast by a ground facility, MT2 messages must be transmitted first and contain additional indications about which VDB slots are allocated to the ground facility.
MT2 messages must be transmitted at least each 20th frame, but may be repeated up to once per frame.
Message Type 3 – MT3. The VDB Message Type 3 is a fill message, which is only used in conjunction with the GBAS authentication feature (MT2, ADB4). Among other things, this feature requires a minimum slot occupancy of at least 95 percent. Thus, MT3 messages are broadcast only by ground facilities that support the authentication feature and are completely ignored by airborne GBAS receivers.
Message Type 4 – MT4. With VDB Message Type 4, approach information can be broadcast to approaching aircraft. A pilot can select a specific approach by simply tuning to a given channel number.
Currently, GBAS only uses Instrument Landing System look-alike straight-in approaches called Final Approach Segments (FAS). Each FAS represents one approach. This way, a single GBAS ground facility can provide multiple approaches for all runways of an airport. All approaches must be broadcast at least once per 20 consecutive frames.
Message Type 11 – MT11. The VDB Message Type 11 provides differential corrections in a way very similar to MT1 messages. The main difference is that MT11 corrections are based on 30-second smoothing, which is required for GAST-D service. As for MT1, all MT11 measurement blocks must be transmitted at least once per frame.
Enhancements for GBAS with Galileo
At the moment, the GBAS standardization documents include information on GPS, GLONASS, and SBAS ranging sources. No information on Galileo or other constellations has been added yet. Thus, to include Galileo for GBAS, some Galileo-specific experimental additions to the standards are necessary. These proposed modifications have been made in such a way as to keep as close to the other system standards as possible to preserve consistency. This way, hardly any new functionality is added, but additional satellites can be used. The additional Galileo signals (E5a, E5b, E6) are not used at the moment; however, they might be highly beneficial for multi-frequency applications in the future.
All modifications presented here are purely experimental and will most probably not be exactly the same as those in future standards documents. Nevertheless, they provide a way to test Galileo together with GPS and GLONASS for GBAS on an experimental basis.
Ranging Source ID. The Ranging Source ID uniquely addresses a single satellite. It is used in MT1 and MT11 to transmit the differential corrections and other information for each ranging source. In ICAO Annex 10, Standards and Recommended Practices, the Ranging Source ID is defined for GPS, GLONASS, and SBAS only. To provide Galileo corrections as well, an experimental mapping for Galileo satellites was added; see TABLE 1.
TABLE 1. GBAS Ranging Source IDs.
In this way, up to 36 Galileo satellites can be addressed.
Navigation Data. Galileo provides two different sets of navigation data. The I/NAV data corresponds to the Safety-of-Life (SoL) service and is broadcast on E1 and E5b. The F/NAV data corresponds to the Open Service (OS) and is broadcast on E5a. In order to remain as close as possible to the legacy navigation systems, we selected the I/NAV navigation data for use, as it is broadcast on the E1 frequency and can thus be received with an L1-only GNSS receiver.
The navigation data is primarily used in VDB MT1. For the first transmitted correction in this message, the ephemeris set that shall be used in the aircraft is identified via the Issue of Data (IOD) field. To be consistent with the GPS ephemeris, we used Galileo’s IODnav parameter.
Together with the identification of the navigation data, a CRC parameter is transmitted in MT1 for the first satellite within the differential corrections. This parameter ensures that the receiver as well as the ground facility use identical navigation data for all calculations. The CRC algorithm uses the raw navigation data to generate a distinct CRC value.
For GPS and GLONASS, two ephemeris masks are defined. These masks ensure that only information relevant for GBAS processing are covered by the CRC. For Galileo, a similar mask had to be designed.
Additional Data Blocks in MT2. Within VDB MT2, station parameters and integrity information are transmitted. Some parameters for the over-bounding of possible ephemeris errors are specific to each satellite navigation system.
To extend MT2 to Galileo, parameters for the DCPS, GAST-C, and GAST-D must be added for Galileo. For downward compatibility, these parameters cannot be included in the existing Additional Data Blocks beside the existing parameters. Thus, a new Additional Data Block (ADB5) was defined on an experimental basis. This Additional Data Block is dedicated to Galileo and is structured as shown in TABLE 2. The coding of all values corresponds to the coding of the parameters for the existing systems.
TABLE 2. Additional Data Block 5 in Message Type 2 for Galileo parameters.
Optimized VDB Transmission Scheme
Having available a large number of ranging sources for differential corrections, the VHF VDB is a bottleneck for the transmission of this data. To demonstrate this, we first consider the number of visible satellites that there will be in the future. This leads to construction rules for an optimal VDB transmission scheme, which allows transmitting the maximum number of differential corrections.
Number of Satellites Available. To demonstrate the number of differential corrections enabled by the different systems in the future, we computed the number of visible satellites over a day for a stationary GNSS receiver in Braunschweig, Germany. Even though only four Galileo satellites were in orbit at that time, up to 26 different satellites (GPS, GLONASS, and Galileo) were in view simultaneously. Keeping in mind the preliminary Galileo constellation, it is obvious that more than 30 satellites will be available simultaneously in the future — considering only GPS, GLONASS, and Galileo. Adding BeiDou satellites for GBAS would further boost these numbers.
The broadcast of such a large number of differential corrections is limited by the capacity of the VDB and thus by the number of slots assigned to a GBAS ground facility. The number of assigned slots for a facility should be limited as far as possible to be able to use the same frequency for other GBAS ground facilities. Thus, the available capacity must be used as effectively as possible.
Number of Bytes Required. Each VDB message is framed by a message block header (6 bytes) and the message block CRC (4 bytes).
The length of each message depends on the message type and the amount of information to be transmitted. The resulting length for a message of each type is given in TABLE 3.
TABLE 3. Size of different VDB message types (including message block header and CRC). Variable length message types are dependent on the number of corrections, N.
VDB Constraints. A GBAS ground facility must transmit the VDB data following some constraints. These are:
MT2 messages (including all Additional Data Blocks required) must be transmitted at least each 20th frame (that is, every 10 seconds).
If authentication is required, each MT2 message must be transmitted in the first slot assigned to the GBAS ground facility.
All differential corrections (both MT1 and MT11) must be transmitted at least once in each frame. However, it is possible to split the differential corrections into two adjacent slots using the Additional Message Flags in MT1 and MT11 messages.
Within each MT1 message, the ephemeris decorrelation parameter (Peph), the Issue of Data (IOD), and the ephemeris CRC is transmitted for the first satellite in the message. Thus, the first satellite must be alternated in order to broadcast the ephemeris information for all satellites.
Approach definitions are transmitted in MT4 messages. All MT4 messages must be transmitted within at least each 20th slot.
Based on these constraints, a VDB encoding scheme has been developed, which allows us to fulfill all the requirements listed above while optimizing the number of differential corrections that can be transmitted. Even though it is optimized for GAST-D-like services (including authentication parameters, MT11 messages, and experimental Galileo extensions), it can be used for legacy GAST-C systems, too.
Rules for Optimal VDB Transmission. To fulfill the requirement for the MT2 message to be transmitted first, a complete MT2 message must be transmitted each 20th frame at the beginning of the first slot assigned. If no MT2 message has to be transmitted, an MT4 message is transmitted instead. Thus, all messages are arranged in proper order by three simple rules:
MT2 (each 20th frame) or MT4 (otherwise)
MT11 (all corrections; can be split into two messages)
MT1 (all corrections; can be split into two messages).
Additionally, two more rules must be fulfilled. On the one hand, if supporting the authentication feature, each slot in which the ground facility may transmit VDB data must be filled to at least 95 percent. For this, MT3 null messages may be used to ensure that each slot is filled sufficiently. On the other hand, an additional rule for MT1 messages is necessary if more than three slots are assigned to the GBAS ground facility. In this case, to maximize the number of differential corrections the MT1 messages may be transmitted in the last two assigned slots only. This rule is necessary because the Additional Message Flag is limited to two slots for differential corrections.
Using this transmission scheme, the number of differential corrections is maximized while fulfilling the minimum requirements on the VDB data. Even in case of the maximum number of differential corrections, MT4 approach definitions can still be broadcast. However, in this case, the number of transmittable FAS segments is limited to 19. If more approaches (or different approach types such as Terminal Area Paths (TAPs)) have to be transmitted, the VDB generation scheme must be adapted.
Number of Transmittable Corrections. Using the optimized transmission scheme explained earlier, the number of transmittable corrections can be calculated easily for different numbers of assigned slots for GAST-C as well as for GAST-D services (see TABLE 4).
TABLE 4. Number of differential corrections that can be broadcast.
The exact distribution of VDB messages for the maximum number of differential corrections (18) is shown in FIGURE 3 for an MT1/MT11 configuration and two assigned slots.
FIGURE 3. VDB messages for two slots and 18 satellites (MT1 and MT11).
Experimental Realization of Multi-Constellation GBAS
The experimental GBAS multi-constellation extensions described earlier have been implemented in software for further testing. As these enhancements are purely experimental and might change in the future, we have ensured that these definitions can be changed easily.
Navigation Software. The Institute of Flight Guidance at Technische Universität Braunschweig has been developing an experimental navigation framework for many years. This software, called TriPos, can handle and combine different navigation technologies. TriPos can be used for simulations, post-processing of recorded data, and even for live (online) processing. It is written in C++ and supports various platforms.
The navigation framework can be extended easily. Originally, only GPS was supported within the software, but support for GLONASS and Galileo as well as augmentation systems like SBAS and GBAS were added over the past few years. Additionally, the software handles GNSS data of multiple frequencies internally and can thus be used for multi-constellation and multi-frequency applications. TriPos includes decoders for the binary protocols of most GNSS receivers currently available.
For GBAS research, two components can be simulated using the software. On the one hand, the Ground Facility simulation calculates the differential corrections and provides simulated VDB data. On the other hand, the GBAS receiver simulation emulates the behavior of an airborne GBAS receiver and uses VDB data and GNSS measurements to calculate a GBAS solution. Both simulations can use either recorded data in post-processing or live data for online-processing. This allows complete simulation of GBAS.
Multi-Constellation GBAS Ground Facility Simulation. The GBAS ground facility simulation uses raw binary data from multiple stationary GNSS receivers to calculate binary VDB data. The simulation can be freely configured to process either live or pre-recorded GNSS data. Even though it features all algorithms required by the standards, it does not contain additional monitor algorithms at the moment.
Nevertheless, it can provide a valid VDB signal-in-space (SIS), which can be used by GBAS receivers and simulation tools (such as Eurocontrol’s PEGASUS tool). The ground facility simulation supports legacy GBAS CAT-I (GAST-C) as well as GAST-D (including all additional VDB information required) using GPS and GLONASS. Support for Galileo has been added according to the experimental definitions described earlier. In addition to FAS data blocks, the ground facility simulation is also capable of providing curved approaches using TAP data blocks.
Multi-Constellation Airborne GBAS Receiver Simulation. The GBAS receiver simulation has been used for various GBAS-related projects. It supports GAST-C as well as GAST-D and can be configured flexibly to use GPS, GLONASS, and/or Galileo (using the experimental enhancements as described earlier). For GAST-D, all airborne monitoring algorithms required are present. Thus, the aircraft-specific parameters (for example for the airborne geometry screening) can be configured together with the other parameters.
Flight Trials
The practicability of the multi-constellation GBAS approach has been tested in flight trials. To ensure that all four Galileo satellites were in view and capable of providing valid data during our trials, an orbit prediction tool and the Notice Advisory to Galileo Users (NAGU) service of the European GNSS Service Center (GSC) were used prior to the flight.
The data processing configuration is shown in FIGURE 4 and includes the GBAS simulation components explained earlier. All processing is done in real time while recording all data for later post processing.
FIGURE 4. Schematic data processing for the flight experiments (ground components in orange, airborne components in blue).
Ground Processing. On the ground, two Septentrio AsteRx3 GNSS receivers connected to two roof-top antennas were used. The GNSS receivers were connected to the GBAS ground facility simulation via a network and provided binary GPS, GLONASS, and Galileo raw measurements with an update rate of 2 Hz as well as navigation data. Using this data, the ground facility simulation generated binary VDB data. The GBAS ground facility simulation was configured to generate multi-constellation GAST-D VDB data for a three-slot configuration. All required messages (MT1, MT2 including all required ADBs, MT3, MT4 and MT11) were generated and sent to the telemetry facility via the network.
Telemetry. Official VHF data broadcasts operate in a frequency band between 108 and 118 MHz, which is reserved for authorized aviation applications. However, for our experimental system, an alternative data link was used. The Institute of Flight Guidance operates a full-duplex telemetry system to share data between ground and aircraft. Even though the operating frequencies are different, the telemetry system allows the generated binary VDB data to be transmitted to research aircraft. The airborne telemetry receiver outputs data as if it were a VDB receiver to allow us to switch between a real VDB receiver and the telemetry receiver easily.
Research Aircraft. The Institute of Flight Guidance operates the research aircraft of the Technische Universität Braunschweig. The Dornier Do 128-6 with the call sign D-IBUF (see FIGURE 5) is a twin-engine turboprop aircraft without a pressurized cabin and has been used multiple times for GBAS-related research over the years.
FIGURE 5. Research aircraft D-IBUF (Dornier Do 128-6).
The research aircraft allows us to flexibly integrate experimental equipment for specific flight trials. For the multi-constellation GBAS flights, a JAVAD Delta GNSS receiver (capable of multiple constellations and frequencies), a telemetry receiver, and an experimental cockpit display were installed temporarily.
Airborne Processing. The online GBAS receiver simulator uses GNSS data from the JAVAD Delta GNSS receiver together with the VDB data received via telemetry. The receiver was configured to output raw GPS, GLONASS, and Galileo measurements with an update rate of 10 Hz. The simulator was configured to use this data to calculate a multi-constellation GAST-D solution. Based on the selected approach definition, the resulting information (deviations, distance to threshold, and so on) was displayed in the cockpit using an experimental cockpit display.
Results. The flight test was conducted in the evening of November 6, 2013 (16:52 – 17:58 UTC), at Research Airport Braunschweig (EDVE). We performed five approaches with a 10 nautical mile final segment. The flight path as calculated by the GBAS receiver subsystem is shown in FIGURE 6.
FIGURE 7 shows the number of satellites used for the GBAS receiver simulation, and distinguishes between the different satellite navigation systems used. Up to 22 satellites have been used simultaneously for GBAS processing, including up to 10 GPS satellites, eight GLONASS satellites, and four Galileo satellites.
FIGURE 7. Number of satellites used by the multi-constellation GBAS receiver simulation.
Even though no certified GBAS equipment was used for the flight trials, FIGURE 8 shows the resulting vertical and lateral protection levels (VPL and LPL) of the online multi-constellation GBAS receiver simulation. Both values fluctuate due to the differences between 100- and 30-second smoothing position solutions, which have to be added to the protection levels for GAST-D. Nevertheless, both sets of values remain clearly below the corresponding Alert Limits (FAS Lateral Alarm Limit (FASLAL): 40 meters, FAS Vertical Alarm Limit (FASVAL): 10 meters). A valid GAST-D service was achieved continuously.
FIGURE 8. Vertical and lateral protection levels (VPL and LPL).
FIGURE 9 shows a vertical integrity diagram, commonly known as a Stanford plot, for the integrity of the multi-constellation GBAS simulation. This plot shows the Vertical Protection Level (VPL) as determined by the GBAS receiver simulation against the actual Vertical Position Error (VPE). The Vertical Position Error is a direct measure for the Vertical Navigation System Error (V-NSE). This has been determined using a precise point positioning reference trajectory. Both values are normalized by the current VAL as these values change during the approaches. During the flight, the GBAS online processing ran at a rate of 10 Hz, resulting in 43,670 GAST-D epochs and an availability of 100 percent.
FIGURE 9. Normalized vertical Stanford plot of flight trials (GAST-D using GPS, GLONASS, and Galileo). Color scale indicates number of occurrences.
Of course, these results must not be misinterpreted as a multi-constellation GBAS performance assessment. The ground facility simulation was highly experimental and lacked any kind of long-term analysis. Even the GNSS antennas used do not meet formal requirements. However, aside from a quantitative judgment, these results show the practicability of this multi-constellation GBAS approach on an experimental basis.
Conclusion and Outlook
In this article, experimental extensions to GBAS have been developed to support GPS, GLONASS, and Galileo simultaneously. Based on these extensions, an optimized VDB transmission scheme has been created. In this way, the number of transmittable differential corrections could be maximized. Using flight trials, the multi-constellation GBAS concept has successfully been verified. The experimental airborne GBAS subsystem was able to calculate a valid GBAS solution including GPS, GLONASS, and Galileo satellites continuously.
It has been shown that multi-constellation GBAS is possible from a purely technical perspective. On the other hand, neither operational nor approval aspects for satellite navigation systems other than GPS have been addressed yet. Additionally, further testing would be necessary to ensure the compatibility with legacy GPS-only GBAS equipment. However, in theory, all modifications for Galileo are backward compatible. Nevertheless, it has to be assured that certified GBAS multi-mode receivers only use the GPS part of the VDB data and are not disturbed by additional VDB messages or additional ranging sources, for example. The required tests are planned for the future.
The operational benefit of multi-constellation GBAS systems cannot be foreseen yet. A certification for this will take several years and could only be addressed by the GBAS community after the completion of the GAST-D certification. Most probably, the use of GNSS signals on multiple frequencies could provide a highly improved GBAS service and will allow much more operational benefit. Many of the satellite navigation systems have already introduced additional frequencies, including signals in the protected L5 aviation band. The use of multiple frequencies for satellite navigation in aviation can remove most ionospheric errors effectively and mitigate a major source of uncertainty. Thus, multi-constellation GBAS can just be seen as a preliminary step on the way towards multi-frequency GBAS. The concepts and infrastructure described in this article will serve as a basis for more research in this area.
Acknowledgments
Most of our work on multi-constellation GBAS was done within the research project “Bürgernahes Flugzeug,” which was established in 2009 and is partly funded by the German federal state of Lower Saxony. This is gratefully acknowledged by the authors. Additionally, the authors would like to thank all colleagues involved for constructive discussions and their support. This article is based on the paper “Mulitple Satellite Navigation for the Ground Based Augmentation System” presented at ITM 2014, The Institute of Navigation 2014 International Technical Meeting, held in San Diego, California, January 27-29, 2014.
MIRKO STANISAK is a research assistant at the Institute of Flight Guidance (IFF) at the Technische Universität (TU) Braunschweig in Germany. He received his diploma in mechanical engineering (Dipl.-Ing.) in 2009 from TU Braunschweig.
MARK BITTER holds a Dipl.-Ing. in mechanical engineering from TU Braunschweig and has been employed as a research engineer at TU Braunschweig IFF since 2003.
THOMAS FEUERLE received his Dipl.-Ing. in mechanical engineering in 1997 from TU Braunschweig. He joined the TU Braunschweig IFF in May 1997. Since 2005, he has been the leader of the Air Traffic Management Team at the IFF. In April 2010, he completed his Ph.D. dissertation at TU Braunschweig.
FURTHER READING
• Authors’ Conference Paper
“Multiple Satellite Navigation Systems for the Ground Based Augmentation System,” by M. Stanisak, M. Bitter, and T. Feuerle in Proceedings of ITM 2014, the 2014 International Technical Meeting of The Institute of Navigation, San Diego, California, January 27–29, 2014, pp. 254–264.
• Standards Documents
Aeronautical Communications, Vol. 1, Radio Navigation Aids, Annex 10 to the Convention on International Civil Aviation, International Standards and Recommended Practices, International Civil Aviation Organization, Montreal, Draft Version, May 2010.
GNSS-Based Precision Approach Local Area Augmentation System (LAAS) Signal-In Space Interface Control Document (ICD), DO-246D, RTCA Special Committee 159, Global Positioning Systems, RTCA Inc. Washington, D.C., December 2008.
Minimum Operational Performance Standards for GPS Local Area Augmentation System Airborne Equipment, DO-253C, RTCA Special Committee 159, Global Positioning Systems, RTCA Inc. Washington, D.C., December 2008.
Minimum Operational Performance Specification for Global Navigation Satellite Ground Based Augmentation System Ground Equipment to Support Category I Operations, ED-114, EUROCAE Working Group 28 on Global Navigation Satellite System, European Organisation for Civil Aviation Equipment, Malakoff, France, September 2003.
• GBAS Research and Development
“Conception, Implementation and Validation of a GAST-D Capable Airborne Receiver Simulation” by M. Stanisak, R. Schork, M. Kujawska, T. Feuerle, and P. Hecker in Proceedings of ION GNSS 2012, the 25th International Technical Meeting of the Satellite Division of The Institute of Navigation, Nashville, Tennessee, September 17–21, 2012, pp. 250–257.
“Initial GBAS Experiences in Europe” by A. Lipp, A. Quiles, M. Reche, W. Dunkel, and S. Grand-Perret in Proceedings of ION GNSS 2005, the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation, Long Beach, California, September 13–16, 2005, pp. 2911–2922.
Signs Point Toward Early Services in December, If ESA Delivers
Europe’s Galileo satnav system.
A February conference on the European Union’s space policy in Brussels sought to set a course for 2020 and close official ranks behind the prospect of early Galileo services at the end of this year. Much in the business community’s perception of the new system — critical for device availability and mass- and professional-market adoption of Galileo — will depend on meeting the projected unveiling of early services in December. This is turn depends on an operational 10-satellite constellation; the fleet now stands at four.
Among trends noted at the meeting: the growing importance of the European GNSS Agency (GSA) as Galileo service provider, with perhaps more authority — and budget — than it has had in the past to get the job done. “The GSA will gradually assume responsibility for the operational management of the programmes while ESA will remain responsible for the deployment of Galileo, and the design and development of new generation of systems,” announced the European Commision (EC).
EC Vice President Antonio Tajani reiterated there will be three Galileo launches in 2014 to reach the requisite year-end total. “The first will come in June. Two satellites have passed the necessary tests. We need to keep this up, and continue to raise our game.”
Trouble on the Equator. The next two Galileo satellites may be ready to ship to Europe’s spaceport in South America by early April. But a large European commercial satellite customer is crowding the schedule, pressuring launch operator Arianespace to lift its satellites first. This could delay the Galileo birds, now set for June rise.
ESA’s year-end plan calls for two more dual-satellite launches in October and December on Russian Soyuz rockets — new partners to the Galileo dance, bringing perhaps new technical connectivity issues.
It’s Not Easy. With Galileo and EGNOS financed to the tune of €7 billion for 2014–2020, expectations are high, yet the European Commission brings a decidely conservative approach to expenditure on new ventures.
“To take a chance, to do what no one has ever done — it’s not easy in a culture that doesn’t like risk,” said ESA director Jean-Jacques Dordain.
Other conference speakers pointed to the securely established European Geostationary Navigation Overlay Service (EGNOS), the first generation of Europe’s GNSS, now fully operational.
Carlo des Dorides, executive director of the GSA, responsible for operating EGNOS through the EGNOS Service Provider (ESSP), elaborated on his big job in 2014: maintaining and improving EGNOS performance and maximizing user adoption, particularly in the aviation, maritime transport, and rail transport sectors.
“The experience we gain through our work with EGNOS will be instrumental as we move towards Galileo service delivery.”
As well as organizational experience with EGNOS, user adoption of the GNSS precursor augurs much for Galileo. With one eye on the present and another on the future, the GSA has a big serving coming to its plate by December: management of a long-awaited, heavily invested system that has been in discussion since the 1990s and in various stages of gestation since 2000.
PNT Advisory Board Hears Air Force CNAV Plan
The U.S. National Space-Based Positioning, Navigation, and Timing (PNT) Advisory Board published the minutes of its December 2013, detailing a report from Air Force Space Command on the road ahead for implementation of the GPS Civil Navigation (CNAV) message on L2C and L5. The subject has stirred some controversy of late, particularly between the U.S. Departments of Transportation (DoT) and Defense (DoD), and DoT is currently seeking public comments on the plan.
The minutes relay the gist of General Whelan’s CNAV remarks as follows: “CNAV has been under discussion for a considerable time. Currently, L2C and L5 signals are being transmitted, but without a navigation message. AFSPC is working hard to activate these messages as soon as possible. One of the reasons for the delay is that additional time was needed to complete testing prior to activation. Testing began in late summer 2013 and, based on initial test results, a ‘way ahead’ has been plotted. . . . Current plans are to begin initial broadcasting in the spring of 2014. CNAV uploads will occur twice weekly. The signal will meet GPS Standard Positioning System (SPS) standards, but may not achieve current accuracy levels until full implementation in late 2014.
“CNAV live-sky testing occurred in June [2013] and was conducted in cooperation with civil, industry, and international partners. The two-week test series included independent assessment and verification. The tests identified four errors that required action. The first, which was addressed in real time, related to implementation of the test series. The second required improvement to the tools suite, which should be totally integrated into the ground segment by December 2014. The third and fourth errors required patches to satellite software. All four issues are now regarded as closed.”
DOT Speaks. A subsequent presentation from the Department of Transportation did not directly mention CNAV, according to the meeting minutes, but did include this update on civil signal monitoring, taken from the meeting minutes:
“DOT is responsible for performance monitoring of GPS civil signals. The International Committee on GNSS’s (ICG’s) transparency principle states that ‘Every GNSS provider should publish documentation that describes the signal and system information, the policies of provision, and the minimum levels of performance offered for its open service.’
Currently, this is only done on GPS L1 C/A signals. Performance standards for L2C and L5 have not yet been established. The crucial function of signal/service monitoring is to verify that commitments to GNSS performance are being met. Additionally, monitoring improves the situational awareness for GNSS operators, and provides assurance that any civil service failure is detected and resolved promptly.”
Opposing Activation. At the close of 2013, a departing DOT assistant secretary wrote a letter to the Air Force opposing activation of the CNAV signal in April 2014. In March, DOT opened a 30-day comment period on the proposed CNAV message on L2C and L5. The comment period closed on April 4, after press time for this magazine so no results are yet known.
Bright New IIF Aloft
A United Launch Alliance Delta IV lifts off from Space Launch Complex-37 with the Air Force’s Global Positioning System (GPS) IIF-5 satellite. This launch marked the 25th Delta IV flight since the first flight in 2002.
The latest GPS IIF satellite was successfully launched into orbit on February 21. GPS IIF-5 will replace the vintage 1997 spacecraft known as GPS IIA-28 in Plane A, Slot 3 of the constellation. IIA-28 will go into a reserve role in the network for the remainder of its useful life.
This is the first of three GPS launches planned through July to replace aging craft in the constellation. The IIF generation will form the backbone of the GPS space fleet for the next 15 years, providing greater navigational accuracy through improvements in atomic clock technology, a new, more robust, third civil signal, L5, for commercial aviation and safety-of-life applications, a second civil signal, L2C, for the dual-frequency GPS receivers, and improved anti-jam capabilities for military and civil users around the world.
The GPS Block IIF satellites are built by Boeing. Earlier IIF satellites were launched in 2010, 2011, 2012, and 2013. All 12 satellites in the GPS IIF series have completed production. The Air Force plans to launch the remaining IIF satellites by 2016.
Downstream Dialog, Tests in Europe
With Galileo services set to take effect in December, the two European entities charged with the program are engaging manufacturers — the European Space Agency (ESA) in consumer markets, and the European GNSS Agency (GSA) in the government security sector, respectively.
“We put out an open call to satnav manufacturers offering testing with our laboratory facilities,” said the head of ESA’s Radio Frequency Systems, Payload, and Technology Division. “We have gone on to work with five mass-market chipset makers and a comparable number of professional receiver manufacturers.”
Available ESA facilities include:
a hybrid localization solution rack for receiver plug-in; it generates simulated constellations of multiple satnav systems along with Wi-Fi or mobile networks. It can also simulate inputs from inertial devices.
the octobox, a mini anechoic chamber into which phones or mobile devices can be placed, to feed them simulated satnav and cellular network signals.
a telecommunications and navigation testbed vehicle for field tests, carrying its own extremely accurate receivers to assess the performance of the consumer devices under test.
“Thanks to earlier collaboration with ESA and the EU, the millions of multi-constellation satnav chips we sell annually have been equipped for Galileo signals since 2009,” stated Philip Mattos of ST Microelectronics, whose Teseo II receiver chips are used in satnavs and embedded in cars (see detailed technical article on page 36). “It will take only a software update to enable them to start using Galileo. This cooperation allows us to optimize our software based on access to actual signals and background technical information.”
Regulated Service. The GSA invited European industries and member states’ Public Regulated Service (PRS) authorities to share views and ideas on technologies at the user segment level for the adoption of the PRS. The PRS uses encrypted signals designed to resist jamming, involuntary interference, and spoofing. GSA’s objective is to ensure that PRS service is affordable and secure for all interested users while also ensuring that European industry maintains its competitive edge in the global satellite navigation marketplace.
GSA consultations will focus on:
steps transforming technologies into products competitive enough in terms of cost, power, dimension;
euro-manufacturing capability and capacity, especially nanotechnology;
how to build the manufacturing lines capable of serving PRS user segment needs;
main domains, elements, and interfaces that will benefit from standardization, allowing for a stronger market adoption of PRS.
GPS III Alternative Payloads Canvassed
GPS III prime contractor Lockheed Martin has heard from six companies concerning alternate designs for the GPS III satellite payload, according to reports. A company spokesperson said “constantly canvassing the industrial base to see what’s out there” is merely part of Lockheed’s standard business practice.
Lockheed Martin partner Exelis Geospatial Systems currently supplies the payload, as it has for all previous GPS generations. Earlier this year, Gen. William Shelton, Air Force Space Command, said the first GPS III launch date had slipped from late 2015 into 2016, and confessed to “patience wearing thin” at a press breakfast.
Part of the delay may have been due to signal crosstalk in the new, as yet unlaunched, payload. Crosstalk occurs when a signal broadcast on one circuit creates an undesired effect on another circuit.
The Story So Far. In December 2013, Lockheed Martin turned on power to the bus and network communications payload of the second GPS III satellite, SV-02, at its test facility in Denver. This demonstrated the satellite’s mechanical integration, validated its interfaces, and opened the way for electrical and integrated hardware-software testing. The first GPS III satellite (SV-01) was powered on in February 2013.
In October, the Lockheed Martin GPS III Nonflight Satellite Testbed (GNST), a full-sized, functional satellite prototype at Cape Canaveral Air Force Station, successfully communicated via cross-links to Air Force simulators of the current GPS constellation in orbit. Testing also demonstrated the ability of an Air Force receiver to track navigation signals transmitted by the GNST.
Exelis Advances. In mid-March, Exelis announced successful completion and full testing of six transmitter assemblies, which are integral payload components for the GPS III satellites. The test program includes random vibration, pyroshock, and thermal vacuum testing, replicating space-like conditions through deployment and on-orbit environments. In January, Exelis received three rubidium atomic frequency standard clocks from Excelitas Technologies specifically designed for GPS III.
Next-Gen SBAS Will Be a Multi-Constellation Affair
Plans to harness Galileo and other satnav systems for next-generation satellite augmentation systems for aviation and other high-performance uses took a step forward at the 126th Satellite-Based Augmentation Systems (SBAS) Interoperability Working Group (IWG) in New Delhi, India, in February, with plans to move to a multi-constellation design adding Galileo, BeiDou, and GLONASS systems in the post-2020 era.
International experts began converging on a standard message definition for the L5 channel of the planned second-generation SBAS systems, which will utilize dual-frequency, multi-constellation signals.
“Two solutions had been put forward, one by ESA based on work by European industry and one from the U.S. Federal Aviation Administration and Stanford University,” explained ESA’s Didier Flament, co-chair of the IWG.
“A single definition coordinated between both bodies has been presented, combining the benefits of both solutions. The formal IWG review and approval loop has now been started with the objective of finalizing it for September’s IWG meeting.
“The aim is to have it ready to submit to the official international SBAS standardization bodies — the International Civil Aviation Organization and the Radio Technical Commission for Aeronautics — as soon as October.”
GAGAN to the Mix. The meeting also marked the significant progress made by India’s own SBAS system GAGAN, which underwent its final stability test in summer 2013, followed by its safety certification in December.
At this point GAGAN was declared certified for non-precision approach users , followed by its safety-of-life service being formally offered to civil aviation users on February 14.
SBAS Services Worldwide
GAGAN is the fourth certified SBAS to enter service worldwide. Europe has the European Geostationary Navigation Overlay Service (EGNOS), which was designed and built by ESA then turned over for operation by the European Satellite Service Provider, ESSP, overseen by the European GNSS Agency (GSA) — both of whom also participated in the meeting. ESA retains responsibility for the future evolution of EGNOS.
The U.S. has the Wide Area Augmentation System (WAAS), developed and operated by the Federal Aviation Administration, with an extension over Canada called CWAAS (Canadian WAAS). WAAS celebrated its 10th anniversary of operational life in July 2013.
Japan has the Multi-functional Satellite Augmentation System (MSAS), developed and operated by Japan’s Civil Aviation Bureau. Japan is discussing plans to merge this capability with its new home-grown satnav system, QZSS.
Along with GAGAN, the meeting covered the progress made by the other SBAS systems under definition or development — the Russian SDCM, Chinese SNAS, and Korean K-SBAS.
The next IWG meeting will take place in September in Tampa, Florida.
The satellite ASTRA 5B, which will become part of the European Commission’s European Geostationary Navigation Overlay Service (EGNOS), launched successfully after a one-day delay. It lifted off on March 22 aboard an Ariane 5 ECA rocket at 2204 GMT (6:04 p.m. EDT) from the Guiana Space Center near Kourou, French Guiana.
Officials from Arianespace, the French launch services company, declared the mission a success following the rocket’s deployment of the ASTRA 5B and Amazonas 4A communications satellites about a half-hour after liftoff, reports Spaceflight Now.
ASTRA 5B carries a hosted L-band payload for EGNOS. It will also extend transponder capacity and geographical reach over Eastern Europe and neighboring markets for DTH, direct-to-cable, and contribution feeds to digital terrestrial television networks.
“Today’s successful launch, the 59th in a row for Ariane 5, confirms the unrivaled reliability and availability of the European launcher,” said Stephane Israel, chairman and CEO of Arianespace. “We take particular pride in being able to offer this service excellence to two leading European operators, SES and Hispasat, both long-standing customers of Arianespace, as well as the European Commission, which has an EGNOS satellite navigation payload integrated on the ASTRA 5B satellite.”
The spacecraft, based on the Airbus Defence and Space Eurostar E3000 satellite bus, is flying with a hosted L-band navigation payload for EGNOS, which augments GPS navigation signals over Europe for specialty users such as the aviation and surveying industries.
“EGNOS will be able to continue to provide valuable positioning services to users all over Europe, be it in the field of aviation, transport or agriculture,” said Christoph Kautz, deputy head of the European Commission’s enterprise and industry unit.
ASTRA 5B was built by Airbus Defence and Space (formerly Astrium) in Toulouse, France, using a Eurostar E3000 platform. The multi-mission satellite will be located at 31.5 degrees East.
The ASTRA 5B is installed in preparation for launch Friday, March 21. (Photo credit: Arianespace)
The launch of the satellite ASTRA 5B, which will become part of the European Commission’s European Geostationary Navigation Overlay Service (EGNOS), is scheduled for Friday, March 21, according to satellite company SES. It will be launched into space from the European Space Centre in French Guiana on board an Ariane 5 ECA rocket between 19:05 p.m. and 20:02 p.m. local time (23.05 – 00.02 CET; 18.05 – 19.02 EDT).
ASTRA 5B will carry a hosted L-band payload for EGNOS. It will also extend transponder capacity and geographical reach over Eastern Europe and neighboring markets for DTH, direct-to-cable, and contribution feeds to digital terrestrial television networks.
ASTRA 5B was built by Airbus Defence and Space (formerly Astrium) in Toulouse, France, using a Eurostar E3000 platform. The multi-mission satellite will be located at 31.5 degrees East.
“The launch of ASTRA 5B will be the 39th launch of an SES satellite on board a European Arianespace launch vehicle,” said Martin Halliwell, chief technology officer of SES. “Our long-standing relationship is based on this proven track record and shows the continuous confidence we have in Arianespace and our commitment to Ariane as a launch vehicle. We look forward to a successful mission with this longstanding launch partner.”
More than 30 specialists overseeing the world’s five satellite navigation augmentation systems gathered in Russia last week, planning for a high-performance future with many more navigation satellites in orbit, reports the European Space Agency.
The Satellite-Based Augmentation Systems (SBAS) Interoperability Working Group was hosted June 25–27 in St. Petersburg by Russia’s Roscosmos space agency and the Russian Academy of Sciences.
With augmentation, additional ground monitoring stations and satellite transponders are applied to sharpen satnav accuracy and reliability across given geographical regions. This enhancement makes satnav suitable for the guidance of aircraft and other precision applications.
Today there are three certified SBAS in operation worldwide: the U.S. Wide Area Augmentation System (WAAS), Japan’s Multi-functional Satellite Augmentation System (MSAS), and Europe’s Geostationary Navigation Overlay Service (EGNOS), the last designed by ESA then turned over for operation by the European Satellite Service Provider, ESSP.
Participants of the 25th Satellite-Based Augmentation Systems (SBAS) Interoperability Working Group, taking place on 25–27 June in St Petersburg, Russia, photographed beside Russia’s Svetloe Radio Astronomy Observatory. Equipped with a 32 m-diameter antenna, this site is part of the Very Long Baseline Interferometry network for high-resolution radio astronomy. It is also hosting a reference station for the System of Differential Correction and Monitoring, Russia’s forthcoming SBAS network.
Two more are under development in Russia and India: the Roscosmos-designed System of Differential Correction and Monitoring (SDCM), and the GPS and Geo-Augmented Navigation (GAGAN) system, the work of Indian Civil Aviation and India’s ISRO space agency.
Meeting twice yearly, the task of the Working Group is to ensure that the various systems work together on a standardized
basis, so end-users can pass seamlessly between them.
“The Group’s terms of reference include developing a shared vision for future generations of these systems,” commented Didier Flament, representing ESA.
“The future will see many more navigation satellites in place. So among the most important achievements of the meeting was agreeing on a common SBAS message based on dual-frequency multi-constellation (DFMC) signals from up to four constellations — GPS, Galileo, Compass, and GLONASS — for the post-2020 era.
“Field tests by our Japanese colleagues using GPS and GLONASS combined with MSAS are confirming the improved performance expected from this DFMC concept,” Flament said. “Two solutions have been studied in parallel, one by ESA and one by the U.S. Federal Aviation Authority (FAA). Both have been compared, with a final single definition to be made before the end of this year. This represents a major step forward towards providing a quasi-global SBAS service.”
Comparing current worldwide SBAS coverage – based on WAAS, EGNOS and MSAS – to the situation envisaged for 2020–25: near-global coverage based on WAAS, EGNOS, MAAS, SDCM and GAGAN, with an expanded network of stations in the southern hemisphere, all based on a common dual-frequency/dual satnav standard being finalised by the SBAS Interoperability Working Group.
