Development and Characteristics of African Satellite Augmentation System (ASAS) Network

Transcription

1 1 Development and Characteristics of African Satellite Augmentation System (ASAS) Network By St. D. Ilcev Durban University of Technology (DUT) Abstract: This paper reports on an African Satellite Augmentation System (ASAS) Space and Ground Segments as an integration part of Global Satellite Augmentation System (GSAS) for enhanced Traffic Control and Management (TCM) globally at sea, on the ground (road and railway vehicles) and in the air. The ASAS network can be used as solely systems for covering and providing TCM and Safety and Security service for entire African Continent and Middle East region, according to the International Maritime Organization (IMO), its Global Maritime Distress and Safety System (GMDSS) and International Civil Aviation Organization (ICAO) recommendations and requirements. Since 1995 few commercial Regional Satellite Augmentation System (RSAS) networks have been projected and developed to utilize Communication, Navigation and Surveillance (CNS) service for Maritime Traffic Control (MTC), Land Traffic Control (LTC) and Air Traffic Control (ATC), including for improved Safety and Security in all transportation systems. The proposed Space Segment of Geostationary Earth Orbit (GEO) constellation and Ground Segment of ASAS network are discussed, and areas examined where further investigations are needed. Specific issues related to these challenges are concluded and a set of solutions is proposed to maximize the availability of ASAS network capacity to the user applications. Key Words: ASAS, GSAS, CNS, RSAS, GEO, GNSS, GPS, GLONASS, WAAS, EGNOS, MSAS, CNSO, SDCM, SNAS, GAGAN, TAB, GMS, GCS, GES, LSAS, CMGC, SMGC 1. Introduction The first generation of the Global Navigation Satellite System (GNSS) infrastructure are represented by old fundamental solutions for Position, Velocity and Time (PVT) of the satellite navigation and determination systems such as GPS and GLONASS for the US or Russian (former-soviet Union) military requirements, respectively. The GPS and GLONASS are first generation of GNSS-1 infrastructures giving positions to about 30 metres, using simple GPS receivers onboard chips or aircraft, and they therefore suffer from certain weaknesses, which make them impossible to be used as the sole means of navigation for ships, particularly for land (road and railway vehicles) and aviation applications. In this sense, technically GPS or GLONASS GNSS-1 systems used autonomously are incapable of meeting civil maritime, land and especially aeronautical mobile very high requirements for integrity, position availability and determination precision in particular and are insufficient for certain very critical navigation and flight stages. [01, 02]. Because these two systems are developed to provide navigation particulars of position and speed on the ship s bridges or in the airplane cockpits, only captains of the ships or airplanes know very well their position and speed, but people in Traffic Control Centers (TCC) cannot get in all circumstances their navigation or flight data without service of new CNS facilities. Besides of accuracy of GPS or GLONASS, without new CNS is not possible to provide full TCM in every critical or unusual situation. Also these two GNSS systems are initially developed for military utilization only, and now are also serving for all transport civilian applications worldwide, so many countries and international organizations would never be dependent on or even entrust people s safety to GNSS systems controlled by one or two countries. However, augmented GNSS-1 solutions of GSAS were recently developed to improve the mentioned deficiencies of current military systems and to meet the present transportation civilian requirements for high-operating Integrity, Continuity, Accuracy and Availability (ICAA). These new operational CNS solutions are the US Wide Area Augmentation System (WAAS), the European Geostationary Navigation Overlay System (EGNOS) and Japanese MTSAT Satellitebased Augmentation System (MSAS), and there are able to provide CNS data from mobiles to the TCC. These three RSAS are integration segments of the GSAS network and parts of the interoperable GNSS-1 architecture of GPS and GLONASS and new GNSS-2 of the European Galileo and Chinese Compass, including Inmarsat CNSO (Civil Navigation Satellite Overlay) and new project of ASAS infrastructure. The additional three GNSS-1 networks in development phase are the Russian System of Differential Correction and Monitoring (SDCM), the Chinese Satellite Navigation Augmentation System (SNAS) and Indian GPS/GLONASS and GEOS Augmented Navigation (GAGAN). Only remain something to be done in South America and Australia for establishment of the GSAS infrastructure globally, illustrated in Figure 1. The RSAS networks are based on the GNSS-1 signals for augmentation, which evolution is known as the GSAS network and which service provides an overlay function and supplementary services. The future ASAS Space Segment will be consisted by existing GEO birds, such as Inmarsat-4 and Artemis or it will implement own satellite constellation, to transmit overlay signals almost identical to those of GPS and GLONASS and provide CNS service. The South African firm IS Marine Radio, as designer of the Project will have overall responsibility for the design and development of the ASAS network with all governments in the region.

2 Figure 1. GSAS Network Configuration 2 2. GNSS Applications Courtesy of Manuscript for Book: Aeronautical CNS by Ilcev [01] The RSAS infrastructures are available globally to enhance current standalone GPS and GLONASS system PVT performances for maritime, land (road and railway) and aeronautical transport applications. User devices can be configured to make use of internal sensors for added robustness in the presence of jamming, or to aid in vehicle navigation when the satellite signals are blocked in the urban canyons of tall city buildings or mountainous environment. In the similar sense, some special transport solutions, such as maritime and especially aeronautical, require far more CNS accuracy and reliability than it can be provided by current military GPS and GLONASS GNSS-1 space infrastructures [01, 03]. Moreover, positioning accuracy can be improved by removing the correlated errors between two or more satellites GPS and/or GLONASS Receivers (Rx) performing range measurements to the same satellites. This type of Rx is in fact Reference Receiver (RR) surveyed in, because its geographical location is precisely well known. In such a manner, one method of achieving common error removal is to take the difference between the RR terminals surveyed position and its electronically derived position at a discrete time point. These positions differences represent the error at the measurement time and are denoted as the differential correction, which information may be broadcast via data link to the user receiving equipment. In this case the user GPS or GLONASS augmented Rx can remove the error from its received data. Alternatively, in non-real-time technique GNSS solutions, the differential corrections can be stored along with the user s positional data and will be applied after the data collection period, which is typically used in surveying applications [04]. If the RR or Ground Monitoring Station (GMS) of the future ASAS service coverage is within of the mobile users, the mode is usually referred to as local area differential, similar to the US Differential GPS (DGPS) for Maritime applications. In this way, as the distance increases between the users and the GMS, some ranging errors become decorrelated. This problem can be overcome by installing a network consisting a number of GMS reference sites throughout a large geographic area, such as a region or continent and broadcasting the Differential Corrections (DC) via GEO satellites. In such a way, ASAS network has to cover entire African Continent and the Middle East region. Therefore, all GMS sites connected by Terrestrial Telecommunication Networks (TTN) relay collected data to one or more Ground Control Stations (GCS), where DC is performed and satellite signal integrity is checked. Then, the GCS sends the corrections and integrity data to a major Ground Earth Station (GES) for uplink to the GEO satellite. This differential technique is referred to as the wide area differential system, which is implemented by GNSS system known as Wide Augmentation Area (WAA), while another system known as Local Augmentation Area (LAA) is an implementation of a local area differential, The LAA solution is an implementation for seaports and airport including for approaching utilizations. The WAA is an implementation of a wide area differential system for wide area CNS maritime, land and aeronautical applications, such as Inmarsat CNSO and the newly developed Satellite Augmentation WAAS in the USA, the European EGNOS and Japanese MSAS [03].

3 3 These three operational systems are part of the worldwide GSAS network and integration segments of the future interoperable GNSS-1 architecture of GPS and GLONASS and GNSS-2 of Galileo and Compass, including CNSO as a part of GNSS offering this service via Inmarsat-3/4 and Artemis spacecraft. The author of this paper for the first time is using more adequate nomenclature GSAS than Satellite-based Augmentation System (SBAS) of ICAO, which has to be adopted as the more common designation in the field of CNS [06]. As discussed earlier, the current three RSAS networks in development phase are the Russian SDCM, Chinese SNAS and Indian GAGAN, while African Continent and Middle East have to start at the beginning of 2011 with development ASAS project. In this sense, development of forthcoming RSAS projects in Australia and South America will complete Augmented CNS system worldwide, known as an GSAS Network [04]. Three operational RSAS together with Inmarsat CNSO are interoperable, compatible and each constituted of a network of GPS or GLONASS observation stations and own and/or leased GEO communication satellites. Namely, the Inmarsat CNSO system offers on leasing GNSS payload, while the European system EGNOS, which will provide precision to within about 5 metres is operational from In fact, it also constitutes the first steps towards forthcoming Galileo, the future European system for civilian global navigation by satellite. The EGNOS system uses leased Inmarsat AOR-E and IOR satellites and ESA ARTEMIS satellite. Thus, the US-based WAAS is using Inmarsat satellites and Japanese MSAS is using its own multipurpose MTSAT spacecraft, both are operational from 2007 and 2008, respectively. Although the global positioning accuracy system associated with the overlay is a function of numerous technical factors, including the ground network architecture, the expected accuracy for the US Federal Aviation Administration (FAA) WAAS will be in the order of 7.6 m (2 drms, 95%) in the horizontal plane and 7.6 m (95%) in the vertical plane [04, 05]. 3. Status and Weaknesses of the Current CNS System Business or corporate shipping and airways companies have used for several decades HF communication for long-range voice and telex communications during intercontinental sailing and flights. Meanwhile, for short distances mobiles have used the well-known VHF onboard ships and VHF//UHF radio on aircraft. In the similar way, data communications are since recently also in use, primarily for travel plan and worldwide weather (WX) and navigation (NX) warning reporting. Apart from data service for cabin crew, cabin voice solutions and passenger telephony have also been developed. Thus, all mobiles today are using traditional electronic and instrument navigations systems and for surveillance facilities they are employing radars. The current communication facilities between ships and MTC are executed by Radio MF/HF voice and telex and VHF voice system; see Previous Communication Subsystem in Figure 2. The VHF link between ships on one the hand and Coast Radio Station (CRS) and TCC on the other, may have the possibility to be interfered with high mountainous terrain and to provide problems for MTC. The HF link may not be established due to lack of available frequencies, high frequency jamming, bad propagation, intermediation, unstable wave conditions and to very bad weather, heavy rain or thunderstorms. The current navigation possibilities for recording and processing Radio Direction Information (RDI) and Radio Direction Distance Information (RDDI) between vessels and TCC or MTC centre are performed by ground navigation equipment, such as the shore Radar, Racons (Radar Beacon) and Passive Radar Reflectors, integrated with VHF CRS facilities, shown by Previous Navigation Subsystem in Figure 2. This subsystem needs more time for ranging and secure navigation at the deep seas, within the cannels and approachings to the anchorages and ports, using few onboard type of radars and other visual and electronic navigation aids. The current surveillance utilities for receiving Radar and VHF Voice Position Reports (VPR) and HF Radio Data/VPR between ships and TCC can be detected by Radar and MF/HF/VHF CRS. This subsystem may have similar propagation problems and limited range or when ships are sailing inside of fiords and behind high mountains Coastal Radar cannot detect them; see the Surveillance Subsystem in Figure 2. The very bad weather conditions, deep clouds and heavy rain could block radar signals totally and on the screen will be blanc picture without any reflected signals, so in this case cannot be visible surrounded obstacles or traffic of ships in the vicinity, and the navigation situation is becoming very critical and dangerous causing collisions. On the contrary, the new Communication CNS/MTM System utilizes the communications satellite and it will eliminate the possibility of interference by very high mountains, see all three CNS Subsystems in Figure 2. At this point, satellite voice communications, including a data link, augments a range and improves both the quality and capacity of communications. The WX and NX warnings, sailing planning and NAVAREA information may also be directly input to the Navigation Management System (NMS). The new Navigation CNS/MTM System is providing improved GPS/GLONASS navigation data, while Surveillance CNS/MTM System is utilizing augmented facilities of GPS or GLONASS signals. Thus, if the navigation course is free of islands or shallow waters, the GPS Navigation Subsystem data provides a direct approaching line and the surveillance information cannot be interfered by mountainous terrain or bad weather conditions. The display on the screen will eliminate misunderstandings between controllers and ship s Masters or Pilots [02].

4 Figure 2. Current and New CNS/MTM System 4 Courtesy of Manuscript, Maritime CNS by St. D. Ilcev [02] The current communication facilities between aircraft and ATC can be executed by traditional VHF/UHF and HF voice (radiotelephone system), see the Present Communication Subsystem in Figure 3. The VHF voice link between aircraft on one the hand and Ground Radio Station (GRS) and TCC on the other, may have the possibility to be interfered with high mountainous terrain. Moreover, the HF link may not be established due to lack of available frequencies, because many users are working on the same frequency band, intermediation, unstable wave conditions and to very heavy rain or thunderstorms. The current navigation possibilities for recording and processing RDI and RDDI between aircraft and ATC are performed by ground landing navigation equipment, such as the Instrument Landing System (ILS), VHF Omnidirectional Ranging (VOR) and Distance Measuring Equipment (DME), illustrated by the Present Navigation Subsystem in Figure 3. This subsystem needs more time for ranging and secure landing, using an indirect way of flying in a semicircle. The current surveillance utilities for receiving Radar and HF Voice signals between aircraft and TCC are detected by Surveillance Radar and Ground HF Stations, respectively. This subsystem may have similar HF voice communications problems or when airplanes are flying behind high mountains they cannot be detected by Radar, see the Present Surveillance Subsystem in Figure 3. The issues of new CNS/ATM systems shown in Figure 3 for Communication, Navigation and Surveillance have the similar improved impacts introduced in the previous Maritime CNS/MTM system [01].

5 5 Figure 3. Current and New CNS/ATM System Courtesy of Book: Global Mobile Satellite Communications by D.S. Ilcev [01] 4. Development of ASAS Network As stated earlier, the basic GPS and GLONASS service fails to meet the high-operating ICAA requirements that are needed by many civilian mobile users. In order to meet the requirements for better ICAA of GPS or GLONASS over African Continent and Middle East is necessary to design the ASAS network. The ASAS service will improve the ICAA requirements of the basic GPS or GLONASS signals and allows them to be used as a primary means of ships navigation at coastal waters and precision approach to the anchorages and for en-route flight of airplanes, Precision Approach (PA) and Non-Precision Approach (NPA) in the African and Middle East coverage area [01]. To start with realization of the project it will be necessary to form Augmentation Standards Service (ASS) and to establish Transport Augmentation Board (TAB). The TAB team together with IS Marine Radio, as a designer of ASAS project, will be responsible for providing the leadership role in engineering, realization and coordination the operational implementation of existing and emerging modern satellite CNS technologies into the African Continent and the Middle East region. The TAB team has to be instrumental in the project and development of the criteria, standards and procedures for the use of unaugmented and as well an augmented GNSS signals by the ASAS and Local Satellite Augmentation System (LSAS). If there is not developed yet some RSAS network, it can be also used Local VHF Augmentation System (LVAS) for seaports and airports also known as a current DGPS developed in US for Coast Guard MTC.

6 Overview of ASAS Project Among the GNSS-1 elements and characteristics standardized by the ICAO board the complements to GPS or GLONASS augmented solutions are as follows: a. Regional RSAS Project In this paper, the use of the ICAO nomination Satellite-based Augmentation System (SBAS), which appear in the classification of the acronyms, will be replaced by Regional Satellite Augmentation System (RSAS) as better convenient nomenclature. The RSAS complementary information is diffused by GEO satellite by means of a pseudo-gps or GLONASS signals and covers a wide geographical area of GSAS systems, such as ASAS project for entire African Continent and Middle East region. b. Local LSAS Project - The Local Satellite Augmentation System (LSAS) nomenclature also convenient much better than Ground-based Augmentation System (GBAS) nomination of ICAO. The complementary information is valid over a limited area, such as seaport or airport and can use satellite diffusion to provide connection between mobiles and TCC. In similar instances, the local scenario can employ LVAS diffused by using VHF Radio system, similar to the US DGPS. On this basis, the TAB team has to launch the development of regional ASAS, whose objective has ultimately to provide one single navigation system over the whole Africa and Middle East. The ASAS program has to be a combination of ground and space equipment to augment the standard positioning service of the GPS or GLONASS. It has to be designed as a milestone of the next generation civil maritime, land and aviation CNS service. However, the fundamental mission of ASAS is to provide a primary means of improved navigation for maritime and also for land and aeronautical applications. The functions have to be provided by RSAS missions are: DGPS corrections (to improve accuracy), integrity monitoring (to ensure that errors are within tolerable limits with a very high probability and thus ensure safety) and ranging (to improve availability). Therefore, separate differential corrections are broadcasting by RSAS to correct GPS or GLONASS satellite clock errors, ephemeris and ionospheric errors. At this point, Ionospheric corrections are broadcasting for selected Ionospheric Grid Points (IGP), which are lattice points of a virtual grid of lines of constant latitude and longitude at the height of the ionosphere. The ASAS network will integrate the Space Segment of own constellation developed by South African Government or leased Inmarsat-3 and Artemis GNSS satellite payloads, and the Ground Segment, which consists in a primary and secondary GMS, GCS, GES and Traffic Control Centre (TCC) to attain improved availability, accuracy and integrity beyond the standard GPS or GLONASS GNSS constellations [04]. The TAB team, IS Marine Radio with partners from Russia and Ukraine, NovAtel, Leica and research institutions such as National Space Institute (NSI) together with South African Department of Science and Technology (DST), has to perform all feasibility studies and research for development of regional ASAS prototype including participating in the early tests of an experimental ASAS. This team with TAB has to analyze the accuracy of the experimental system when it will be used to provide guidance to ships and aircraft performing approaches on the four coasts of the African continent. Feasibility studies will include a few performance tests of alternative ionospheric correction and integrity algorithms (error boundings). On the other hand, TAB will assist to establish performance demands for the ASAS and provide technical data to other teams that will evaluate contractor responses to the ASAS Request for Proposal (RFP). After the contract award, TAB will assist in the transfer of technology project to the prime contractors. The TAB team has also to provide technical advice to the contractors on the ASAS design in the areas of performance and safety since the contract award, and has also to be involved in the design, modeling prototype and simulation of ASAS availability performance. The all institution parties of ASAS will be used in sensitivity analyses to help determination of optimal mix and location of land resources, such as GMS and GES, and to determine the impacts of design changes that alter equipment performance or location. It will be also used as a tool to demonstrate to air traffic planners the behavior of a space navigation system (i.e., orbiting sensors) and to help also to determine operational strategies for dealing with low performance areas [03]. At first has to be established the African Satellite Test Bed (ASTB) that includes the all above mentioned parties, then minimum 55 ATSB GMS over African continent and both existing Inmarsat GES in a ground uplink centre Maadi in Egypt and Jeddah in Saudi Arabia. In addition, it is necessary to establish one GES in Senegal, one in Kenya and one in South Africa or to utilize service of the existing CSIR Satellite Centre [04]. The TAB can initiate a 3-phase developmental approach to complete the ASAS network: 1. Phase 1 ( ) Will start with initial ASAS commissioned with 44 GMS, 5 GCS uplinks, 5 GES and 3 leased GEO satellites. In the next stage will be upgraded GMS infrastructures to maximum 55 and perhaps can be provided own GEO satellites. The ASAS ground network will enable wide civilian Maritime deep sea and coastal navigation including approaching to anchorages and seaports, while for Land application will enable precise navigation facilities for road and rail vehicles and for Aeronautical solutions will provide en-route navigation, mobile terminal navigation and NPA. In addition, this system will support Category I PA within a limited coverage area as well.

7 7 2. Phase 2 ( ) Will initiate with full ASAS infrastructures and with additional GMS up to 55. Redundant coverage of the entire initial ASAS operational restrictions will be removed. The ALAS ground structures will be deployed at major African seaports and airports. Precisely surveyed ground stations with multiple GPS receivers and processors will be established, including one or more pseudolites and VHF data link-supports Category II/III PA locally at all runway ends of an airport. An additional approach lighting system will be deployed, the Cat I precision approach and where higher availability is required than ASAS network can provide. In the proper manner, the reduction of ground-based NAVAIDS infrastructure, such as VOR and Non-Directional Beacons (NDB) will be initiated, and the added 2nd and 3rd civil radio frequencies will improve GPS robustness and ICAA. 3. Phase 3 ( ) To continue reducing ground-based NAVAIDS, when VOR and DME will support only operations along principal air routes and NPA at many airports. Furthermore, the ILS will support PA at high-activity airports for ATC and Management. Full constellations of GPS/GLONASS with 2nd and 3rd civil frequency band available for ASAS/ALAS have to be modified accordingly to: Dual-frequency avionics to mitigate unintentional jamming and complete phase-out of all on-airport NAVAIDS (VOR, NDB) ASAS System Configuration The ASAS will be designed and implemented as the primary means of satellite CNS for aviation routes in corridors over African Continent and Middle East region, control of airports approachings and managing all aircraft and vehicles movements on airports surface. In this sense, it will also serve for maritime course operations such as ocean crossings, navigation at open and close seas, coastal navigation, channels and passages, approachings to anchorages and ports, and inside of ports, and for land (road and railways) solutions. It was intended to provide the following services [03]: 1) The transmission of integrity and health information on each GPS or GLONASS satellite in real time to ensure all users do not use faulty satellites for navigation, known as the GNSS Integrity Channel (GIC). 2) The continuous transmission of ranging signals in addition to the GIC service, to supplement GPS, thereby increasing GPS/GLONASS signal availability. Increased signal availability also translates into an increase in Receiver Autonomous Integrity Monitoring (RAIM) availability, which is known as Ranging GIC (RGIC). 3) The transmission of GPS or GLONASS wide area differential corrections has, in addition to the GIC and RGIC services, to increase the accuracy of civil GPS and GLONASS signals. Namely, this feature has been called the Wide Area Differential GNSS (WADGNSS). The combination of the Inmarsat overlay services and Artemis spacecraft will be referred to as the ASAS network illustrated in Figure 4. As observed previous figure, all mobile users (3) receive navigation signals (1) from GNSS-1 of GPS or GLONASS satellites. In the near future can be used GNSS-2 signals of Galileo and Compass satellites (2). These signals are also received by all reference GMS terminals of integrity monitoring networks (4) operated by governmental agencies in many countries within Africa and Middle East. The monitored data are sent to a regional Integrity and Processing Facility of GCS (5), where the data is processed to form the integrity and WADGNSS correction messages, which are then forwarded to the Primary GNSS GES (6). At the GES, the navigation signals are precisely synchronized to a reference time and modulated with the GIC message data and WADGNSS corrections. The signals are sent to a satellite on the C-band uplink (7) via GNSS payload located in GEO Inmarsat and Artemis spacecraft (8), the augmented signals are frequency-translated to the mobile user on L1 and new L5-band (9) and to the C-band (10) used for maintaining the navigation signal timing loop. The timing of the signal is done in a very precise manner in order that the signal will appear as though it was generated on board the satellite as a GPS ranging signal. The Secondary GNSS GES can be installed in Communication CNS GES (11), as a hot standby in the event of failure at the Primary GNSS GES. The TCC ground terminals (12) could send request to all particular mobiles for providing CNS information by Voice or Data, including new Voice, Data and Video over IP (VDVoIP) on C-band uplink (13) via Communication payload located in Inmarsat or Artemis spacecraft and on C-band downlink (14) to mobile users (3). The mobile users are able to send augmented CNS data on L- band uplink (15) via the same spacecraft and L-band downlink (16). The TCC sites are processing CNS data received from mobile users by Host and displaying on the surveillance screen their current positions very accurate and in the real time [13]. Therefore, the ASAS will be used as a primary means of navigation during all phases of traveling for all mobile applications [06]. The ASAS space constellation could be formally consisted in the 24 operational GPS and 24 GLONASS satellites and of 2 Inmarsat and 1 Artemis GEO satellites. The GEO satellites downlink the data to the users on the GPS L1 RF with a modulation similar to that used by GPS. Information in the navigational message, when processed by an ASAS Rx, allows the GEO satellites to be used as additional GPS-like satellites, thus increasing the availability of the satellite constellation. At this point, the ASAS signal resembles a GPS signal origination from the Gold Code family of 1023 possible codes (19 signals from PRN ).

8 8 Figure 4. ASAS Network Configuration Courtesy of Book: Understanding GPS - Principles and Applications by E.D. Kaplan (Modified by Authors) [03] An ASAS ground segment consists of a network of certain GMS cites that monitor the satellite signals and send their observations to one or more GCS, which generate the augmentation message. This is in turn sent to uplink GES, which transmit it to the navigation transponders on board the GEO spacecraft payload. Finally, these satellites broadcast the ASAS message to the mobile users at the L1 or MHz GPS frequency. The ASAS signal is modulated on a GPS look-alike signal using a spread-spectrum code thus providing an ASAS pseudo range measurement. This means that, with slightly modified equipment, GPS or GLONASS users can receive integrity and more accurate position information. In such a way, the ranging signals improve Dilution of Precision (DOP) and RAIM. In fact, the ASAS signal will be modulated with a 250 b/s data message containing GPS health information, vector position corrections and ionospheric mapping terms. This data message separates ASAS from normal GPS or GLONASS by increasing integrity (satellite health), improving the accuracy (vector corrections) and also enhancing the availability (additional pseudo range) of the System. The ASAS network improves accuracy in two ways by reducing the range measurement error by sending differential corrections for each satellite and by adding new ranging signals thereby improving the geometry [01, 03]. The vector corrections include fast corrections containing the satellite clock error; long-term corrections containing more slowly varying errors of satellite location and ionospheric corrections (Van Dierendonck). The fast corrections are sent every 10 to 12 seconds and only one correction per satellite is sufficient for the entire ASAS coverage area. Long-term and ionospheric corrections are sent much less frequently (about every 2 minutes) as they do not vary much over the entire ASAS network. The GEO satellites reduce the need to update these corrections as rapidly as a normal GPS or GLONASS satellite. Figure 5. ASAS Space Segment Courtesy of Book: Global Mobile Satellite Communications by D.S. Ilcev [01]

9 ASAS Space Segment The ASAS Space Segment can be designed by using own project of GEO satellite constellation, what is more expensive solution, or by leasing existing GEO Inmarsat-3 and Artemis spacecraft. The operational system can use 3 GEO satellites: Inmarsat-3 AORE at 15.5ºW; Inmarsat-3 IOR at position 64ºE, and ESA Artemis at 21.5ºE over equator, illustrated in Figure 5. The navigation payloads on these GEO spacecraft are essentially bent-pipe transponders, so that a data message uploaded to a satellite is broadcast to all users in the GEO broadcast area of the satellite over entire African Continent and the Middle East region, see Figure 6. The ASAS system can use service of existing Geostationary Ranging Station (GRS) infrastructures and to implement a wide triangular observation base for ranging purposes with the stations located in Aussaguel (France), Kourou (French Guiana) and Hartebeeshoeck (South Africa) [04, 05]. In general, navigation payloads of GEO spacecraft for augmentation systems must fulfill 2 key roles: 1) Transmission of a spread-spectrum timing and ranging signal on 1 or 2 navigation L-band RF; 2) Relay in near-real-time of data originated on the ground and for use in user Rx to improve performance (reliability, accuracy) with GPS and GLONASS signals. As mentioned earlier, GEO is able to augment the performances of GPS and GLONASS by providing a separate ranging channel to transmit integrity and correction data. This concept dates back to the late eighties and has evolved to its current form known as RSAS. In this sense, RSAS data will allow GNSS to meet the stringent reliability, availability and integrity requirements set by MTC and ATC. Land users will also be able to improve in positioning accuracy by Land Traffic Control (LTC) for road and railway applications [07]. Figure 6. ASAS Space and Ground Segments Courtesy of Manuscript for Book: Aeronautical CNS by Ilcev D. St. [01]

10 10 Figure 7. EGNOS Professional ESA 1 and Personal-Nav 400 Rx Courtesy of WebPages: EGNOS Test Bed User Equipment from Internet [05] In response to improve this need, Inmarsat decided to embark a new navigation transponder to support RSAS functions on its last generation of GEO Inmarsat-4 at the beginning of 2005, which it is now developing to provide new broadband services and which can be used for ASAS space segment as well. Throughout the evolution of the RSAS concept, Inmarsat played an active role in GNSS. In November 1990, it decided to include navigation transponders on its third generation of GEO satellites, Inmarsat-3, developed to provide the space capacity needed by WAAS and EGNOS. Inmarsat-3 satellites alone, however, do not give sufficiently redundant coverage for EGNOS and WAAS systems to offer operational services throughout their respective service areas. In fact, more GEO will be necessary to assure a proper replenishment policy when the Inmarsat-3 birds terminate their operational life [08]. In the meantime, the US made a commitment to support civil applications of GPS including the modification of future generations of spacecraft to meet civil requirements. The GPS modernization initiatives will make two new civil signals available: a second signal at MHz (L2) and a third civil signal at MHz (L5) RF. Moreover, in 2004 FAA expressed its intention to have the L5 signal also available on GPS augmentation satellites planed to be launched in 2005 for civil aviation safety-of-life and security services and other precision positioning and navigation applications [06]. The Inmarsat-4 satellite navigation payload is a dual-channel bent-pipe transponder that converts two C-band (C1 and C5) uplink signals from one GES to two downlink signals in two separate bands. In such a way, Inmarsat designed its Inmarsat-4 navigation transponder to be, as far as possible, backward compatible with the existing RSAS and suitable for the future RSAS projects. It also recognized that dual user downlink RF are an important advance over the current Inmarsat-3 satellite augmentation capabilities. However, the satellite communication design had to respect the technical constraints imposed by the Inmarsat-4 space segment primary communications mission. In the proper manner, the Inmarsat-4 navigation payload will transmit satellite navigation signals at the GPS L1 and L5 frequencies and allow the real-time relay from a single ground-monitoring network of integrity and accuracy augmentation data for orbiting GNSS constellation [04]. The L1 and L5 downlink signals can be received in integrated L1/L5 GPS/RSAS receiver (Rx), see two Rx prototypes. The ASAS users will have at their disposal a few models of multimodal prototype Rx units. The multimodal prototypes will enable users to carry out few tests on the ASAS system: static and/or dynamic platform testing; user ASAS Rx validation and system performance demonstration comparison with reference position: geodetic marks (static), trajectography data (dynamic), such as the model of EGNOS Rx ESA 1 prototype shown in Figure 7 (A). The ASAS Standard Rx will be also developed to verify the Signal-In-Space (SIS) performance. In the meantime a set of prototype user equipment has been manufactured for civil maritime, land and aeronautical applications. That prototype equipment will be used to validate and eventually certify ASAS for the different applications being considered. In such a way, a handheld personal receiver (like a cell phone) would use satellite navigation to avoid traffic jams in city centres, find the nearest free parking space, or even the nearest pizza restaurant in an unfamiliar city, as shown in the Personal-Nav 400 in Figure 7 (B).

11 11 Figure 8. ASAS Ground Segments Courtesy of Manuscript for Book: Aeronautical CNS by Ilcev D. St. [01] Precise position via the Internet and ASAS system will be possible anytime after completing and testing the ASAS network, thanks to the SIS technology developed by the ESA. This technology combines the powerful capabilities of satellite navigation and the Internet. As a result, the highly accurate navigation information that comes from the ASAS SIS will be available on the Web in real time over the Internet [08]. 5. ASAS Ground Segment The ASAS service will correct GNSS-1 signals from the 24 GPS and 24 GLONASS orbiting satellites, respectively, which can be in error because of satellite orbit and clock drift or signal delays caused by the atmosphere and ionosphere, or can also be disrupted by jamming. The ASAS network, shown in Figure 8, can be based on 55 GMS spread over entire Africa and Middle East (see red cubes), 5 GCS (see red circles) and 5 GES (see red triangles), covering large area and monitors GPS data. The GCS and GES sites will be located in South Africa, Saudi Arabia, Kenya, Egypt and Senegal, see prototype of WAAS ground monitoring station in Figure 9 (A). In such a manner, signals from GPS are received and processed at 55 GMS, which are distributed throughout the African territory and linked to form the ASAS network. In this instance, each of this precisely surveyed monitoring reference station receives GPS signals and determines if any errors exist, while 5 GCS collect data from these GMS reference terminals, assess signal validity, compute all corrections and create the ASAS correction message [06].

12 12 Figure 9. RSAS Ground Stations Courtesy of WebPages: WAAS from Internet [05] Furthermore, data from the GMS are forwarded to the GCS, which process the data to determine the differential corrections and bounds on the residual errors for each monitored satellite and for each IGP. The bounds on the residual errors are used to establish the integrity of the ranging signals. Hence, the corrections and integrity information from the GCS are then sent to each GES and unlinked along with the GPS navigation message to the GEO communication satellite. The GEO downlinks this data to the users via the current GPS L1 frequency with GPS type modulation [01, 03]. Therefore, the message is broadcasting on the same frequency as GPS to receivers that are within the broadcast coverage area of the entire ASAS network. In fact, these three GEO communications satellites also act as an additional navigation constellation providing supplemental signals for position determination. Each satellite covers a part of the hemisphere, except for both Polar Regions. The user receiver, installed aboard a boat, ships, land vehicles or aircraft, combines the GPS signals with the ASAS message to arrive at a more accurate position. Otherwise, each ASAS ground-based station or subsystem configuration communicates with TCC infrastructure via terrestrial landline [06]. The GMS is a special ground reference station with antenna and adequate equipment located at a precisely surveyed position, as shown in Figure 9 (A). The ASAS network will use 55 GMS, while the current WAAS configuration uses only 25 Wide Reference Stations (WRS) spread over the entire territory of the Continental US, covering as well as eastern Canada. The WRS infrastructure continuously receives and collects GPS data for various satellites and then sends the data to their Wide Master Station (WMS), which interpret the data from each WRS and calculate the errors and health of each satellite [05]. The ASAS network will use 5 GCS, while WAAS uses only two WMS calculate observed satellite errors for the entire WAAS network and then forward these corrections to a primary GES. The GES receives GPS corrections and transmits them to GEO satellites using a ground uplink system on the GPS L1 frequency, while the next generation of GPS will provide L5 as well [10]. The GEO satellite receives corrections and forwards them to users, who are equipped with special Rx equipment, as shown in the Raytheon GPS/WAAS Rx 2 in Figure 9 (B). The WAAS satellite signal type is compatible with GPS or GLONASS systems, so new RSAS-enhanced GPS receivers will not be much more expensive than unaugmented GPS receivers (possibly 50 US$ or more). Thus, some type of GPS receivers or chart plotters can be upgraded with RSAS special hardware modem or software without additional cost, by contacting the manufacturer to be converted for RSAS signal utilization [11]. The GPS signal can be received by integrated GPS/RSAS Rx for processing pseudorange, pseudorange-rate and accumulated Doppler measurements. These measurements control the phase and frequency (code and carrier) of the corresponding signal generator, SG-L1 and SG-L5, to generate two individually controlled uplink signals. Inmarsat plans to develop prototype equipment for proper navigation signal generation and control that will be used for the ground and in-orbit test campaign in order to conduct end-to-end system tests [08]. 6. LSAS System Configuration The LSAS is intended to complement the ASAS service using a single differential correction that accounts for all expected common errors between a local reference and mobile users. The LSAS will broadcast navigation information in a localized volume area of seaport or airport using satellite service of ASAS network or any of mentioned RSAS networks developed in Northern Hemisphere.

13 13 As stated earlier, the ASAS network will consist 55 GMS (Reference Stations), 5 GCS (Master Stations) and 5 GES (Gateways), which service has to cover entire African Continent and Middle East region. Inside of this coverage the ASAS network will also serve to any other customers at sea, on the ground and in the air users who need very precise determinations and positioning, such as: 1. Maritime (Shipborne Navigation and Surveillance, Seafloor Mapping and Seismic Surveying); 2. Land (Vehicleborne Navigation, Transit, Tracking and Surveillance, Transportation Steering and Cranes); 3. Aeronautical (Airborne Navigation and Surveillance and Mapping); 4. Agricultural (Forestry, Farming and Machine Control and Monitoring); 5. Industrial, Mining and Civil Engineering; 6. Structural Deformations Monitoring; 7. Meteorological, Cadastral and Seismic Surveying; and 8. Government/Military Determination and Surveillance (Police, Intelligent services, Firefighting); etc. However, all above fixed or mobile applications will be able to use ASAS or any RSAS service directly by installing new equipment known as augmented GPS receivers (Rx), and so to use more accurate positioning and determination data. In Figure 4 is illustrated scenario that all mobiles and GMS directly are using not augmented signals of GPS or GLONASS satellites. To provide augmentation will be necessary to process not augmented signals in GCS, to eliminate all errors and produce augmented signals. In this stage any RSAS or ASAS network standalone will be not able to produce augmented service for seaports, airports or any ground infrastructures. Meanwhile, it will be necessary to be established some new infrastructure known as an LSAS, which can provide service for collecting augmented data from ships, land vehicles, airplanes or any ground user. The navigation data of mobiles can be processed in the TCC cites and shown on the surveillance screen similar to the radar display and can used for traffic control system at the see, on the ground and in the air. This scenario will be more important for establishment MTC or ATC service using augmented GNSS-1 signals from the ships or aircraft, respectively. In this sense, the LSAS network can be utilized for seaport known as a Coastal Movement Guidance and Control (CMGC) and airport known as a Surface Movement Guidance and Control (SMGC) [04, 11] Coastal Movement Guidance and Control (CMGC) The new LSAS network can be implemented as a Coastal Movement Guidance and Control (CMGC) system integrated in the ASAS or any RSAS infrastructure. It is a special maritime security and control system that enables a port controller from Control Tower at shore to collect all navigation and determination data from all ships and vehicles, to process these signals and display on the surveillance screens. On the surveillance screen can be visible positions and courses of all ships in vicinity sailing areas, so they can be controlled, informed and managed by traffic controllers in any real time and space. In this case, the LSAS traffic controller provide essential control, traffic management, guide and monitor all vessels movements in coastal navigation, in the cramped channel strips and fiords, approaching areas to the anchorage and harbours, ship movement in the harbours, including land vehicles in port and around the port s coastal environment, even in poor visibility conditions at an approaching to the port. The controller issues instructions to the ship Masters and Pilots with reference to a command surveillance display in a Control Tower that gives all vessels position information in the vicinity detected via satellites and by sensors on the ground, shown in Figure 10. The command monitor also displays reported position data of coming or departing vessels and all auxiliary land vehicles (road and railways) moving into the port s surface. This position is measured by GNSS, using data from GPS/GLONASS and GEO satellite constellation. A controller is also able to show the correct ship course to Masters and sea Pilots under bad weather conditions and poor visibility or to give information on routes and separation to other vessels in progress. The following segments of CMGC infrastructure are illustrated in Figure 10: 1) GPS or GLONASS GNSS Satellite measures the vessel or port vehicle s exact position. 2) GEO MSC Satellite is integrated with the GPS positioning data network caring both communication and navigation payloads, In addition to complementing the GPS satellite, it also has the feature of communicating data between the ships or vehicles and the ground facilities, pinpointing the mobile s exact position. 3) Control Tower is the centre for monitoring the traffic situation on the channel strips, approaching areas, in the port and around the port s coastal surface. The location of each vessel and ground vehicle is displayed on the command monitor of the port control tower. The controller performs sea-controlled distance guidance and movements for the vessels and ground-controlled distance vehicles and directions based on this data. 4) Light Guidance System (LGS) is managed by the controller who gives green light or red light guidance whether the ship should proceed or not by pilot in port, respectively.

14 14 Figure 10. CMGC Subsystem Courtesy of Paper, Satellite CNS for Maritime Transportation Augmentation System (MTAS), by St. D. Ilcev [02] 5) Radar Control Station (RCS) is a part of previous system for MTC of ship movement in the channels, approaching areas, in port and around the port s coastal environment. 6) Very High Frequency (VHF) is Coast Radio Station (CRS) is a part of RCS and VHF or Digital Selective Call (DSC) VHF Radio communications system. 7) Coast Earth Station (CES) is a main part of satellite communications system between CES terminals and shore telecommunication facilities via GEO satellite constellation. 8) Pilot is small boat or helicopter carrying the special trained man known as a Pilot, who has to proceed the vessel to the anchorage, in port, out of port or through the channels and rivers. 9) Bridge Instrument of each vessel displays the ship position and course [02] Surface Movement Guidance and Control (SMGC) The new LSAS network can be also implemented as a Surface Movement Guidance and Control (SMGC) system integrated in the ASAS or any RSAS infrastructure. It is a special aeronautical security and control system that enables an airport s controller from Control Tower on the ground to collect all navigation and determination data from all aircraft, to process these signals and display on the surveillance screens. On the surveillance screen can be visible positions and courses of all aircraft in vicinity flight areas, so they can be controlled, informed and managed by traffic controllers in any real time and space. In such a way, the LSAS traffic controller provide essential control, traffic management, guide and monitor all aircraft movements in the vicinity of the aircraft, approaching areas to the airport, aircraft movement in airport, including land vehicles in airport and around the airport, even in very poor visibility conditions at an approaching to the airport. Thus, the controller issues instructions to the aircraft s Pilots with the reference to a command surveillance display in a Control Tower that gives all aircraft position information in the vicinity detected via satellites and by sensors on the ground, shown in Figure 11. The command monitor also displays reported position information of landing or departing aircraft and all auxiliary vehicles moving onto the airport s surface. This position is measured by GNSS, using data from GPS and GEO ASAS or RSAS satellites. An airport controller is able to show the correct taxiway to pilots under poor visibility, by switching the taxiway centreline light and the stop bar light on or off. Otherwise, the development of head-down display and head-up display in the cockpit that gives information on routes and separation to other aircraft is in progress. The following segments of SMGC are shown in Figure 11: 1) GPS or GLONASS Satellite measures the aircraft or airport vehicles exact position. 2) RSAS is integrated with the GPS satellite positioning data network. In addition to complementing the GPS satellite, it also has the feature of communicating data between the aircraft and the ground facilities, pinpointing the aircraft s exact position.

15 15 Figure 11. SMGC Subsystem Courtesy of Book: Global Mobile Satellite Communications by D.S. Ilcev [01, 06] 3) Control Tower is the centre for monitoring the traffic situation on the landing strip around the airport s environment. The location of aircraft and vehicles is displayed on the command monitor of the control tower. The controller performs ground-controlled distance guidance for the aircraft and vehicles based on this data. 4) Stop Line Light System is managed by the controller, who gives guidance on whether the aircraft should proceed to the runway by turning on and off the central guidance line lights and stop line lights as a signal, indicating whether the aircraft should proceed or not. 5) Ground Surveillance Radar (GSR) is a part of previous system for ATC of aircraft approaching areas, in airport and around the airport air environment. 6) Very High Frequency (VHF) is Ground Radio Station (GRS) is a part of ARC via VHF or UHF Radio communications system. 7) Ground Earth Station (GES) is a main part of satellite communications system between GES terminals and ground telecommunication facilities via GEO satellite constellation. 8) Aircraft Cockpit displays the aircraft position and routes on the headwind protective glass (head-up displays) and instrument panel display (head-down display) [01, 06]. 7. Conclusion The current radios and traffic control are based on 1960s technology. In fact, there is no radar coverage over the ocean areas, so ship captains and aircraft pilots must report their positions verbally by voice or have them automatically sent through a relay station. For the controller, surveillance equipment, primarily radar, detects the position of the many moving ships, vehicles and aircraft in the traffic coverage area. Otherwise, the radar monitoring the movement of ships, aircraft and other vehicles spins much faster than those radars covering. New tools, like satellite surveillance, have been developed as part of GSAS combined with surface radars, to help the controllers to move increased number of vessels, aircraft and land vehicles more safely through the transportation augmentation system environment. In the proper manner, this additional navigational accuracy now available on the ship s bridge and aircraft cockpit will be used for other system enhancements and for surface control in area of ports and airports. This is the Automatic Dependent Surveillance System (ADSS), currently being evaluated and which is taking advantage of this improved accuracy of traffic control for all mobile applications. By the way, South Africa (SA) is building fast Gauteng train and new Dube airport in Durban not implementing CNS technology. Using this enhanced chain, the new ASAS system of GSAS with navigational message will improve the GPS or GLONASS signal accuracy from about 30 metres to approximately 3 metres. For example, the current US WAAS system provides 1 2 metres horizontal accuracy and 2 3 metres vertical accuracy throughout the contiguous US. Unfortunately, to receive an ASAS signal, an ordinary GPS or GLONASS receiver must be upgraded by hardware module or software and be capable of receiving and decoding ASAS signals.

16 16 In the future will be possible to integrate new satellite systems in ASAS network such as already mentioned Inmarsat-4 space configuration or new SA Space Constellation and forthcoming GNSS-2 systems. Although the global positioning accuracy system associated with the overlay is a function of numerous technical factors and ground network architecture, the expected accuracy for the ASAS will be in the order of 1 2 metres horizontal accuracy and 2 3 metres vertical accuracy throughout the contiguous Africa and Middle East region. 8. Acronyms: ADSS ASS ASTB ATC AVAS CES CMGC CNS CNSO CRS DC DC DGPS DME DOP DSC DST DST EGNOS FAA GAGAN GAS GBAS GCS GEO GES GIC GMDSS GMS GNSS GRS GRS GSAS ICAA ICAO IGP ILS IMO LAA LAS LGS LSAS LTC LVAS MSAS MTC NDB NMS NPA NSI PA PVT RAIM RCS RDDI Automatic Dependent Surveillance System Augmentation Standards Service African Satellite Test Bed Air Traffic Control African VHF Augmentation System Coast Earth Station Coastal Movement Guidance and Control Communication, Navigation and Surveillance Civil Navigation Satellite Overlay Coast Radio Station Differential Corrections Differential Corrections Differential GPS Distance Measuring Equipment Dilution of Precision Digital Selective Call Department of Science and Technology Department of Science and Technology European Geostationary Navigation Overlay System Federal Aviation Administration GPS/GLONASS and GEOS Augmented Navigation Ground Augmentation System Ground-based Augmentation System Ground Control Stations Geostationary Earth Orbit Ground Earth Station GNSS Integrity Channel Global Maritime Distress and Safety System Ground Monitoring Station Global Navigation Satellite System Geostationary Ranging Station Ground Radio Station Global Satellite Augmentation System Integrity, Continuity, Accuracy and Availability International Civil Aviation Organization Ionospheric Grid Points Instrument Landing System International Maritime Organization Local Augmentation Area Local Augmentation System Light Guidance System Local Satellite Augmentation System Land Traffic Control Local VHF Augmentation System MTSAT Satellite-based Augmentation System Maritime Traffic Control Non-Directional Beacons Navigation Management System Non-Precision Approach National Space Institute Precision Approach Position, Velocity and Time Receiver Autonomous Integrity Monitoring Radar Control Station Radio Direction Distance Information

17 17 RDI RFP RGIC RR RSAS Rx SBAS SDCM SMGC SNAS TAB TCC TCM TCS TTN VHF VOR VPR WAA WAAS WADGNSS WMS WRS Radio Direction Information Request for Proposal Ranging GIC Reference Receiver Regional Satellite Augmentation System Receivers Satellite-based Augmentation System (ICAO nomenclature) System of Differential Correction and Monitoring Surface Movement Guidance and Control Satellite Navigation Augmentation System Transport Augmentation Board Traffic Control Centers Traffic Control and Management Terrestrial Communication Subsystem Terrestrial Telecommunication Networks Very High Frequency VHF Omnidirectional Ranging Voice Position Reports Wide Augmentation Area Wide Area Augmentation System Wide Area Differential GNSS Wide Master Station Wide Reference Station 9. References [01] Ilcev D. St. Aeronautical Communications, Navigation and Surveillance (CNS), Manuscript for Book, John Wiley, Chichester, [12] Ilcev D. St. Satellite CNS for Maritime Transportation Augmentation System (MTAS), CriMiCo Conference, IEEE Catalog Numbers CFP09788, Sevastopol, Ukraine [03] Kaplan E.D. Understanding GPS Principles and Applications, Artech House, Boston, [04] Ilcev D. St. Maritime Communications, Navigation and Surveillance (CNS), DUT, Durban, [05] Group of Authors, Website of EGNOS ( WAAS ( GSAS, [06] Ilcev D. St. Global Mobile Satellite Communications for Maritime, Land and Aeronautical Applications, Book, Springer, Boston, [07] El-Rabbany A. Introduction to GPS, Artech House, Boston, [08] Grewal M.S. and others, Global Positioning Systems, Inertial Navigation, and Integration, Wiley, London, [09] Group of Authors, Website of Leica ( & NovAtel ( [10] Group of Authors, MTSAT Update, NextSAT/10 CG, Japan Civil Aviation Bureau, MSAS, Tokyo, [11] Prasad R. & Ruggieri M., Applied Satellite Navigation Using GPS, GALILEO, and Augmentation Systems, Artech House, Boston, Author: Stojce Dimov Ilcev received two BEng degrees in Mobile Radio Engineering and in Maritime Navigation from the Faculty of Maritime Studies at Kotor of Podgorica University, Montenegro; received BSc Eng (Hons) degree in Maritime Communications from the Maritime Faculty of University at Rijeka, Croatia; and received MSc degree in Electrical Engineering from the Faculty of Electrical Engineering, Telecommunication department of University at Skopie, Macedonia, in 1971, 1986 and 1994, respectively. His Doctoral dissertation in Satellite Communications, Navigation and Surveillance (CNS) was positive evaluated in 2000 by Telecommunication department of Faculty of Electrical Engineering Nikola Tesla of Belgrade University, Serbia. He also passed in Spring 1995 an on-site GMDSS training course on Poseidon simulator at Military Maritime Training Centre in Varna, Bulgaria. He holds the certificates for Radio operator 1st class (Morse); for GMDSS 1st class Radio Electronic Operator and Maintainer; for Master Mariner, and he was Reserve Staff in CNS of Former Yugoslav Army. Prof. Ilcev is currently working as a Research Professor in Space Science at Durban University of Technology (DUT) in Durban, South Africa. During past 40 years his research is concentrated on fundamental aspects of Radio and Satellite CNS systems, networks, technology transfer and innovations, navigation and logistics, including safety and security in all transportation systems. Prof. Ilcev is actual IEEE member.

18 18 Your article in Telecommunication Systems is now online at SpringerLink Springer Sent: Saturday, June 18, :22 AM Dear Prof. Ilcev, Congratulations, your article Development and characteristics of African Satellite Augmentation System (ASAS) network has just been published and is now as 'Online First' on SpringerLink It is fully accessible to libraries, institutions and their patrons that have purchased a SpringerLink license. If your article is published under one of our Open Access programs it will be freely accessible to any user. Citation Information