Department of Geomatic Engineering
Faculty of Geoinformation Science and Engineering
Universiti Teknologi Malaysia
mailto:[email protected];%[email protected]; [email protected]
Global Navigation Satellite Systems (GNSS) have evolved from an early period of limited programs such as the American Global Positioning System (GPS) and the Russian Global'naya Navigatsionnaya Sputnikovaya Sistem (GLONASS) to a point where a number of systems and their augmentations are underway. The European Geostationary Navigation Overlay Service (EGNOS) is one such augmentation system designed to provide greater accuracy for users of GNSS and at the same time increasing the integrity, availability and continuity of the system and providing information about the condition of the system. There have been several trials in Africa to ascertain the extent of EGNOS coverage and its performance. The outcome of the trials reveals that, by integrating with the European service area, complied with Approach with vertical Guidance-1 (APV-1) having a horizontal positional error of about 3meters, thus representing about 95% and vertical positional error around 4.5meters. However, there are pertinent issues such as international cooperation in the areas of technical, political, economic and legal that need to be addressed in order to successfully implement satellite navigation system in Africa. This paper proposes a possible extension architecture and institutional framework that will actualise the full implementation of the Global Navigation Satellite System in Africa.
The introduction and implementation of satellite navigation technology to the development of the African continent is a right step that needs to be pursued vigorously. In recognition of the strategic importance of satellite navigation, its potential applications and the need for the African states in joining the rest of the world to enjoy the benefits of the outer space; organisations such as the International Civil Aviation Organisation (ICAO), Africa and Indian Ocean (AFI), the Agency for Air Navigation Safety in Africa and Madagascar (ASECNA), the European Geostationary Navigation Overlay Service (ESA), and the European Organisation for Safety of Air Navigation (EUROCONTROL) have been actively involved in inspirational collaboration to ensure the introduction and implementation of GNSS in Africa.
EGNOS is an acronym for "European Geostationary Navigation Overlay Service". It is a Satellite-Based Augmentation System (SBAS) designed to improve GPS and GLONASS and the in-coming European Galileo services in terms of accuracy, integrity, availability and continuity. It is being implemented by the European Tripartite Group (ETG) comprising of European Space Agency (ESA), the European Commission (EC) and EUROCONTROL as Europe's contribution to the development of the Global Navigation Satellite System (GNSS-1) (EC, 2003). EGNOS consist of three geostationary satellites and a complex network of ground stations, which when fully operational will transmit GPS-like navigation signals containing integrity and differential corrections by the geosynchronous ranging satellites. The corrections are applied to GPS and GLONASS and EGNOS navigation signals and signals of other geosynchronous ranging satellites overlay systems to GNSS users within the area of coverage (Rane and Laurent, 2001).
2.0 Motivation for EGNOS
The goal of the international community is to achieve an internationally provided, funded and controlled Global Navigation Satellite System (GNSS). Although GPS and GLONASS are seen to constitute elements of an interim GNSS leading to a final international GNSS; they lack the accuracy, integrity, availability and continuity to satisfy many of the more-critical and safety-related applications. Similarly the dependency on this system that is solely owned and controlled by the military of one country has heightened the concern of the international community in terms of system availability especially during international crisis. This institutional uncertainty of a single state ownership and control, simultaneous dual military and civil use, couple with the technical limitations, particularly availability and vulnerability to interference has led to the development of various augmentation systems that will meet the requirement for safety-critical applications.
3.0 EGNOS System Architecture
The EGNOS system consists of the Space segment, Ground segment and User segment as shown in Figure 1
Figure 1: EGNOS segments (ESSP, 2004)
3.1 Space Segment
The space segment consists of navigation transponders onboard YHM, Inmarsat III Indian Ocean Region (IOR-E) at 64.50E and ESA ARTEMIS at 21.40E. They cover not only the whole of Europe but Africa, South America and most part of Asia.
The space segment therefore improves the geometry of the GPS constellation by broadcasting GPS-like signal thereby providing integrity and wide area differential corrections (Ventura-Traveset et al, 2001).
3.2 Ground Segment
The Ground segment is made of the Master Control Centres (MCC), Range and Integrity Monitoring Stations (RIMS), Navigation Land Earth Stations (NLES), Wide Area Networks (WAN) and Support facilities.
3.3 User Segment
The User segment is made of EGNOS Standard Receiver, which will verify the Signal-In-Space (SIS) performance, and a set of prototype user equipment for the various applications for which EGNOS is to provide which include; civil aviation, maritime and land (Rane and Laurent, 2001)
4.0 4.0Present EGNOS Service Area
The EGNOS coverage area includes all European states with a landmass. Figure 2 shows the European Service area for which EGNOS covers.
Figure 2: European Service Area with Inmarsat and Artemis Broadcast (ESA, 2004)
A pre-operational transmission of the EGNOS signal through the EGNOS test bed (ESTB) is currently going on. The EGNOS System Test Bed (ESTB) is the EGNOS prototype, which has been broadcasting a Signal in Space (SIS) since February 2000. It is meant to support and test the development of the EGNOS system, to demonstrate EGNOS to potential users, to prepare for the introduction of EGNOS and to test the possibility of extending this system outside Europe. However, the performance of this test bed is quite good achieving accuracy within few metres. This provides a GPS –augmentation signal so that users can determine their position (Mike, 2002).
5.0 Extension Requirements for Africa
The basic concept for the extension of EGNOS outside Europe is the enhancement of navigation performance that is only attainable by the user of EGNOS within the service area. This basic concept is achieved by transmitting ranging corrections that are applicable to GPS that are valid to users irrespective of their position. In the same vain, integrity data are broadcast to users within the service area. Users outside the service area will experience integrity information problem due to distance to the service area. Ionospheric corrections and other associated integrity data can be broadcast by EGNOS for the ionospheric grid within the service area. It is worth noting that if the user distance to the service area is large, then EGNOS will only monitor few number of ionospheric grid points which will result to degrading the performance (Legido, et al, 2001). As such, the extension of EGNOS is required.
5.1 Technical Requirement
One of the fundamental issues in the technical requirement is the ability to properly establish the size of the extension area. This requires analysis of the bandwidth that is available in the geostationary satellites (IMARSART and ARTEMIS).
Table 1:EGNOS bandwidth usage [Legido et al, 2001]
|Data type||No. of message instances||Maximum broadcast interval (sec.)||Bandwidth filling|
|Nominal Service area (ECAC)|
|SBAS in test mode||0||6||0,00%|
|Fast corrections GPS||2||6||33,33%|
|SBAS in test mode||0||6||0,00%|
|Geo ranging function data||1||120||0,83%|
|Fast correction degradation||1||120||0,83%|
|Ionospheric grid mask||4||300||1,33%|
|Ionospheric corrections, GIVEi||16||300||5,33%|
Table 1 provides information on the EGNOS bandwidth usage. About 17% of the total EGNOS bandwidth has been utilised mainly on the European serivce area (Legido et al, 2001). From the foregoing, there is the need for an increase in the bandwidth of the geostationary satellites to meet the extension requirements. Other aspect of the technical requirements include proper site location of the Range and Integrity Monitoring Stations (RIMS); modification of the current EGNOS Central Processing facilities software to compute the user differential range error; developing ionopsheric models that will mitigate the ionospheric effects; a real-time communication network (Wide Area Network) to allow data transfer to the processing centres and the navigation messages to the Navigation Land Earth Services (NLES) (Izquiew et al, 2001).
5.2 Environmental Requirement
Provision of an infrastructure for RIMS indoor equipment to meet up with the indoor environmental requirement, are necessary. This could be a building, and the building could contain some offices for administrative purposes. There should be an indoor canalisation to allow for separation of power and communication cables. Cable, which are made of metal that could cover all indoor interconnection cables. Considering relatively hot African climate, an air-conditioning system that will provide temperature in accordance with requirements need to be put in place (Zdzislaw, 2003).
6.0 On-going ESTB trials in Africa
Beginning from June 2003, there have been EGNOS mobile trials in Africa, known as EGNOS Signal Test Bed (ESTB). The aim of these trials is to assess the strength of the EGNOS signal with the view of preparing for the full implementation of the system. Africa is zoned into three namely; Central Africa as Zone A, Southern Africa as Zone B and Eastern Africa as Zone C. Two Inmarsat satellites (AOR-E and IOR-E), which are directly above Africa, are being used for transmission of signal-in-space. Mobile RIMS stations were installed at various locations in each of the zones. They are equipped with independent Very Small Aperture Terminal (VSAT) for communication purposes. In zone A the message type MT27 was used in 2003. However, there was a good accuracy but poor availability for Approach with Vertical Guidance -1 (APV-1). As a result of this, in February 2004, ESA integrated zone A into the ECAC area, but without the MT27. Sets of 24 hr data were collected for each week at the Douala (Cameroon) RIMS station
The results of the trials allows the coverage of continental AFI including Madagascar, except Mauritius and Seychelles. The result of the tests shows that the accuracy achieved after integrating with the ECAC service area complied with Approach with Vertical Guidance -1 (APV-1) having a horizontal positional error of about 3meters, representing 95% and vertical position error around 4.5m, which is also 95%. More than 98% was achieved for the Availability of APV-1 service.
7.0 Proposed Extension System Architecture
This section presents the proposed architecture for such extensions having considered the extension requirements.
Figure 3: EGNOS Extension Architecture to Africa
Fig 3 presents a design of an independent solution, where two Monitoring and Control Centres (MCC) with one Navigation Land Earth Station (NLES) for up-link of the message received from the MCC are implemented. The idea is that, the African Centres will perform real-time processing of the RIMS data that will allow an on-line monitoring of the African ground infrastructure. Such a real time-time processing includes the computation of the wide area corrections and also the provision of integrity data from those satellites (GPS/GLONASS) that are visible within the African region. Due to its independency, it would require a dedicated message type MT28 (provides availability inside service area and increase integrity outside) considering the fact that it provides an increased integrity outside the service area (ECAC). In view of this therefore, a Wide Area Network is required for transmission of messages. The African Monitoring and Control centres could also be linked to one of the European MCC, thus forming a network. The advantage of this design is that, there will be the provision of enough infrastructures within the African region for GNSS, similarly, it will provide independent for Africa not relying on Europe.
8.0 Institutional Framework
Considering the final architecture of EGNOS, the need for an international framework to support operation and exchange of information among system designers and operator and international user communities is very important.
Figure 4: Proposed Institutional Framework
The framework should include a collaborative mode among the providers, providing favourable and flexible mechanisms where there will be a shared interest in the use of the EGNOS system irrespective of the region in which they operate. Figure 4 shows the institutional framework for EGNOS extension to Africa.
8.1 Technical Cooperation
The technical cooperation allows the sharing of both expertise and the costs of developing the expertise. It involves conducting joint research and publication of the results. With the extension of EGNOS there will be the sharing of ideas between Europe and Africa researchers in space related research given the diversity of the two continents. It will be of immense advantage to the African scientist giving the opportunity to participate in space-related activities that have been previously seems impossible. The technical cooperation include among others the following:
- Spectrum management
- Man power development
- Cooperation among the service providers
- The provision of expert services.
8.2 Political Cooperation
EGNOS has political advantages that will foster the relationship between Europe and Africa. Such relationship will aid in the management of the airspace of both countries. Europe could help Africa in the area of capacity building as the safety of life services offered by EGNOS will be of much demand by the African States, this will therefore facilitate in the establishment of EGNOS in completing the first phase of GNSS-1, of the European policy on global navigation satellite system. The extension will therefore facilitate Galileo’s market launch in Africa, as EGNOS services are a precursor to future Galileo’s application.
8.3 Economic Motivation.
Regional economic motivation and integration is an important factor in fostering relationship. The relationship will strengthen regional economic integration bringing about sustainable development. Lack of or insufficiency of GNSS infrastructure in Africa justifies the urgent need for such cooperation. In addition to the infrastructure deficiency, financial resources mean another specific obstacle for the African States in addition to the technical and political constraints, hence the need for economic cooperation.
The extension of EGNOS requires heavy investments. Although the cost of the existing GNSS services is free, however, the provision of EGNOS would require funding from both nations. The funding cooperation would involve a capacity outlay for deployment and operational costs. This includes transmission cost, processing of data, provision of signal-in-space, monitoring and maintenance.
8.5 Legal Framework
It is important to note that the lack of legal framework for GPS has made it impossible for other nations to adopt the use of the Basic GNSS. An elaborate legal principle governing the extension of EGNOS to Africa is very essential. Such a legal framework should include series of private law contracts in which the relationship among various stakeholders involve in the implementation, operation, provision and use of the EGNOS signals and systems is be addressed. The legal framework should address issues such as unlawful interference with GNSS systems, outages and other legal principles relating to communications by satellite. It should also address the issue of ownership putting in place a legal ownership concept, management and control of the system. When this is put in place, there will that understand between Europe and Africa in an event of system failure and the- likes.
8.0 Benefits to Africa
The benefits of the proposed extensions will be experienced fully in all Surveying and Mapping services. Also military and defence operations will become more confident and precise. In aviation, and maritime transport system, there will be serious improvements in aircraft landing and take-off, thereby ensuring more safety. Ships and vessels will also experience less difficulty in sea navigation.
Further the agricultural areas and products will be better mapped and various decisions (or policies) on agriculture will be quick and timely. Again, the seemly boom in telecommunication industry will receive further boost to cover more areas and render quality services
9.0 Conclusion and Recommendations
The extension of EGNOS to Africa will enhance the services offered by GPS and GLONASS systems by increasing the accuracy, reliability and integrity.
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