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Transcript of African Satellite
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Telecommun Syst (2013) 52:121137DOI 10.1007/s11235-011-9464-x
Development and characteristics of African SatelliteAugmentation System (ASAS) network
D.S. Ilcev
Published online: 15 June 2011 Springer Science+Business Media, LLC 2011
Abstract This paper reports on an African Satellite Aug-
mentation System (ASAS) Space and Ground Segments asan integration part of Global Satellite Augmentation Sys-
tem (GSAS) for enhanced Traffic Control and Management
(TCM) globally at sea, on the ground (road and railway ve-
hicles) 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 Mid-
dle East region, according to the International Maritime Or-
ganization (IMO), its Global Maritime Distress and Safety
System (GMDSS) and International Civil Aviation Orga-
nization (ICAO) recommendations and requirements. Since
1995 few commercial Regional Satellite Augmentation Sys-
tem (RSAS) networks have been projected and developed toutilize 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 investiga-
tions are needed. Specific issues related to these challenges
are concluded and a set of solutions is proposed to maxi-
mize the availability of ASAS network capacity to the user
applications.
Keywords ASASGSASCNSRSAS GEOGNSS
GPSGLONASSWAASEGNOSMSASCNSO
SDCM SNASGAGANTABGMSGCSGES
LSASCMGCSMGC
D.S. Ilcev ()Mangosuthu University of Technology (MUT), 133 Bencorrum,183 Prince Street, Durban 4001, South Africae-mail:[email protected]
Acronyms
ADSS Automatic Dependent Surveillance SystemASS Augmentation Standards Service
ASTB African Satellite Test Bed
ATC Air Traffic Control
AVAS African VHF Augmentation System
CES Coast Earth Station
CMGC Coastal Movement Guidance and Control
CNS Communication, Navigation and Surveillance
CNSO Civil Navigation Satellite Overlay
CRS Coast Radio Station
DC Differential Corrections
DC Differential Corrections
DGPS Differential GPS
DME Distance Measuring Equipment
DOP Dilution of Precision
DSC Digital Selective Call
DST Department of Science and Technology
DST Department of Science and Technology
EGNOS European Geostationary Navigation Overlay
System
FAA Federal Aviation Administration
GAGAN GPS/GLONASS and GEOS Augmented
Navigation
GAS Ground Augmentation System
GBAS Ground-based Augmentation System
GCS Ground Control Stations
GEO Geostationary Earth Orbit
GES Ground Earth Station
GIC GNSS Integrity Channel
GMDSS Global Maritime Distress and Safety System
GMS Ground Monitoring Station
GNSS Global Navigation Satellite System
GRS Geostationary Ranging Station
GRS Ground Radio Station
mailto:[email protected]:[email protected] -
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122 D.S. Ilcev
GSAS Global Satellite Augmentation System
ICAA Integrity, Continuity, Accuracy and
Availability
ICAO International Civil Aviation Organization
IGP Ionospheric Grid Points
ILS Instrument Landing System
IMO International Maritime Organization
LAA Local Augmentation Area
LAS Local Augmentation System
LGS Light Guidance System
LSAS Local Satellite Augmentation System
LTC Land Traffic Control
LVAS Local VHF Augmentation System
MSAS MTSAT Satellite-based Augmentation System
MTC Maritime Traffic Control
NDB Non-Directional Beacons
NMS Navigation Management System
NPA Non-Precision Approach
NSI National Space Institute
PA Precision Approach
PVT Position, Velocity and Time
RAIM Receiver Autonomous Integrity Monitoring
RCS Radar Control Station
RDDI Radio Direction Distance Information
RDI Radio Direction Information
RFP Request for Proposal
RGIC Ranging GIC
RR Reference Receiver
RSAS Regional Satellite Augmentation System
Rx Receivers
SBAS Satellite-based Augmentation System (ICAO
nomenclature)
SDCM System of Differential Correction and
Monitoring
SMGC Surface Movement Guidance and Control
SNAS Satellite Navigation Augmentation System
TAB Transport Augmentation Board
TCC Traffic Control Centers
TCM Traffic Control and Management
TCS Terrestrial Communication SubsystemTTN Terrestrial Telecommunication Networks
VHF Very High Frequency
VOR VHF Omnidirectional Ranging
VPR Voice Position Reports
WAA Wide Augmentation Area
WAAS Wide Area Augmentation System
WADGNSS Wide Area Differential GNSS
WMS Wide Master Station
WRS Wide Reference Station
1 Introduction
The first generation of the Global Navigation Satellite Sys-
tem (GNSS) infrastructure are represented by old funda-
mental 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 andGLONASS are first generation of GNSS-1 infrastructures
giving positions to about 30 metres, using simple GPS re-
ceivers 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 applica-
tions. 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 determi-
nation precision in particular and are insufficient for certain
very critical navigation and flight stages [7,9].Because these two systems are developed to provide
navigation particulars of position and speed on the ships
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 ser-
vice of new CNS facilities. Besides of accuracy of GPS
or GLONASS, without new CNS is not possible to pro-
vide 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 in-ternational organizations would never be dependent on or
even entrust peoples safety to GNSS systems controlled
by one or two countries. However, augmented GNSS-1 so-
lutions 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 Avail-
ability (ICAA). These new operational CNS solutions are
the US Wide Area Augmentation System (WAAS), the Eu-
ropean Geostationary Navigation Overlay System (EGNOS)
and Japanese MTSAT Satellite-based Augmentation System
(MSAS), and there are able to provide CNS data from mo-biles to the TCC.
These three RSAS are integration segments of the GSAS
network and parts of the interoperable GNSS-1 architec-
ture of GPS and GLONASS and new GNSS-2 of the Eu-
ropean Galileo and Chinese Compass, including Inmarsat
CNSO (Civil Navigation Satellite Overlay) and new project
of ASAS infrastructure. The additional three GNSS-1 net-
works in development phase are the Russian System of Dif-
ferential Correction and Monitoring (SDCM), the Chinese
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Development and characteristics of African Satellite Augmentation System (ASAS) network 123
Fig. 1 GSAS networkconfiguration. Courtesy ofmanuscript for book:Aeronautical CNS by Ilcev [9]
Satellite Navigation Augmentation System (SNAS) and In-dian GPS/GLONASS and GEOS Augmented Navigation
(GAGAN). Only remain something to be done in South
America and Australia for establishment of the GSAS in-
frastructure globally, illustrated in Fig.1.
The RSAS networks are based on the GNSS-1 signals for
augmentation, which evolution is known as the GSAS net-
work 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 constella-
tion, to transmit overlay signals almost identical to those of
GPS and GLONASS and provide CNS service. The SouthAfrican 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 GNSS applications
The RSAS infrastructures are available globally to enhance
current standalone GPS and GLONASS system PVT perfor-
mances for maritime, land (road and railway) and aeronau-
tical transport applications. User devices can be configured
to make use of internal sensors for added robustness in thepresence 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 simi-
lar 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 [9,10].
Moreover, positioning accuracy can be improved by re-
moving the correlated errors between two or more satellites
GPS and/or GLONASS Receivers (Rx) performing rangemeasurements to the same satellites. This type of Rx is in
fact Reference Receiver (RR) surveyed in, because its geo-
graphical location is precisely well known. In such a man-
ner, one method of achieving common error removal is to
take the difference between the RR terminals surveyed posi-
tion 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 cor-
rection, 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 solu-
tions, the differential corrections can be stored along with
the users positional data and will be applied after the data
collection period, which is typically used in surveying ap-
plications [8].
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, sim-
ilar to the US Differential GPS (DGPS) for Maritime appli-
cations. In this way, as the distance increases between the
users and the GMS, some ranging errors become decorre-
lated. This problem can be overcome by installing a net-work consisting a number of GMS reference sites through-
out 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 Tele-
communication Networks (TTN) relay collected data to one
or more Ground Control Stations (GCS), where DC is per-
formed and satellite signal integrity is checked. Then, the
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124 D.S. Ilcev
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 im-
plementation of a local area differential, The LAA solution
is an implementation for seaports and airport including forapproaching 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 [10].
These three operational systems are part of the world-
wide 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 [6].
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 develop-
ment ASAS project. In this sense, development of forth-
coming RSAS projects in Australia and South America will
complete Augmented CNS system worldwide, known as an
GSAS Network [8].Three operational RSAS together with Inmarsat CNSO
are interoperable, compatible and each constituted of a net-
work 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 pre-
cision to within about 5 metres is operational from 2009.
In fact, it also constitutes the first steps towards forthcom-
ing Galileo, the future European system for civilian global
navigation by satellite. The EGNOS system uses leased In-
marsat AOR-E and IOR satellites and ESA ARTEMIS satel-
lite. Thus, the US-based WAAS is using Inmarsat satellitesand Japanese MSAS is using its own multipurpose MTSAT
spacecraft, both are operational from 2007 and 2008, respec-
tively. Although the global positioning accuracy system as-
sociated with the overlay is a function of numerous technical
factors, including the ground network architecture, the ex-
pected 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
[4,8].
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 sail-
ing 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 communicationsare since recently also in use, primarily for travel plan and
worldwide weather (WX) and navigation (NX) warning re-
porting. Apart from data service for cabin crew, cabin voice
solutions and passenger telephony have also been devel-
oped. Thus, all mobiles today are using traditional electronic
and instrument navigations systems and for surveillance fa-
cilities 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 Subsys-
tem in Fig.2. The VHF link between ships on one the hand
and Coast Radio Station (CRS) and TCC on the other, mayhave 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, unsta-
ble 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 fa-
cilities, shown by Previous Navigation Subsystem in Fig. 2.
This subsystem needs more time for ranging and secure nav-
igation at the deep seas, within the channels and approach-
ing 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 Fig. 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 traf-
fic 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 moun-
tains, see all three CNS Subsystems in Fig. 2. At this point,
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Development and characteristics of African Satellite Augmentation System (ASAS) network 125
Fig. 2 Current and newCNS/MTM system. Courtesy ofmanuscript, Maritime CNS byIlcev [7]
satellite voice communications, including a data link, aug-
ments a range and improves both the quality and capac-
ity of communications. The WX and NX warnings, sail-
ing planning and NAVAREA information may also be di-
rectly input to the Navigation Management System (NMS).
The new Navigation CNS/MTM System is providing im-proved 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 Subsys-
tem data provides a direct approaching line and the surveil-
lance information cannot be interfered by mountainous ter-
rain or bad weather conditions. The display on the screen
will eliminate misunderstandings between controllers and
ships Masters or Pilots [7].
The current communication facilities between aircraft
and ATC can be executed by traditional VHF/UHF and HF
voice (radiotelephone system), see the Present Communica-
tion Subsystem in Fig.3. The VHF voice link between air-
craft on one the hand and Ground Radio Station (GRS) and
TCC on the other, may have the possibility to be interferedwith high mountainous terrain. Moreover, the HF link may
not be established due to lack of available frequencies, be-
cause 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 Omnidirec-
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126 D.S. Ilcev
Fig. 3 Current and newCNS/ATM system. Courtesy ofbook: Global Mobile SatelliteCommunications by Ilcev [9]
tional Ranging (VOR) and Distance Measuring Equipment
(DME), illustrated by the Present Navigation Subsystem in
Fig.3. This subsystem needs more time for ranging and se-
cure 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 bySurveillance Radar and Ground HF Stations, respectively.
This subsystem may have similar HF voice communica-
tions problems or when airplanes are flying behind high
mountains they cannot be detected by Radar, see the Present
Surveillance Subsystem in Fig.3.
The issues of new CNS/ATM systems shown in Fig. 3for
Communication, Navigation and Surveillance have the sim-
ilar improved impacts introduced in the previous Maritime
CNS/MTM system [9].
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 [9].
To start with realization of the project it will be neces-
sary to form Augmentation Standards Service (ASS) and to
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Development and characteristics of African Satellite Augmentation System (ASAS) network 127
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 Mid-
dle East region. The TAB team has to be instrumental in the
project and development of the criteria, standards and proce-dures for the use of unaugmented and as well an augmented
GNSS signals by the ASAS and Local Satellite Augmen-
tation System (LSAS). If there is not developed yet some
RSAS network, it can be also used Local VHF Augmenta-
tion System (LVAS) for seaports and airports also known as
a current DGPS developed in US for Coast Guard MTC.
4.1 Overview of ASAS Project
Among the GNSS-1 elements and characteristics stan-
dardized by the ICAO board the complements to GPS or
GLONASS augmented solutions are as follows:
(a) Regional RSAS ProjectIn this paper, the use of the
ICAO nomination Satellite-based Augmentation Sys-
tem (SBAS), which appear in the classification of the
acronyms, will be replaced by Regional Satellite Aug-
mentation System (RSAS) as better convenient nomen-
clature. The RSAS complementary information is dif-
fused 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 ProjectThe Local Satellite Augmen-
tation System (LSAS) nomenclature also convenientmuch better than Ground-based Augmentation System
(GBAS) nomination of ICAO. The complementary in-
formation is valid over a limited area, such as seaport or
airport and can use satellite diffusion to provide connec-
tion 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 pro-
vide 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 posi-
tioning service of the GPS or GLONASS. It has to be de-
signed 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 monitor-
ing (to ensure that errors are within tolerable limits with
a very high probability and thus ensure safety) and rang-
ing (to improve availability). Therefore, separate differen-
tial corrections are broadcasting by RSAS to correct GPS or
GLONASS satellite clock errors, ephemeris and ionospheric
errors. At this point, Ionospheric corrections are broadcast-
ing 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 Govern-
ment or leased Inmarsat-3 and Artemis GNSS satellite pay-
loads, 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 constella-
tions [8].
The TAB team, IS Marine Radio with partners from Rus-
sia and Ukraine, NovAtel, Leica and research institutions
such as National Space Institute (NSI) together with South
African Department of Science and Technology (DST), hasto perform all feasibility studies and research for develop-
ment 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 algo-
rithms (error boundings).
On the other hand, TAB will assist to establish perfor-
mance 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 techni-
cal 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 insti-
tution 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 im-
pacts 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 sys-
tem (i.e., orbiting sensors) and to help also to determine
operational strategies for dealing with low performance ar-
eas [10].
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 neces-
sary to establish one GES in Senegal, one in Kenya and one
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128 D.S. Ilcev
in South Africa or to utilize service of the existing CSIR
Satellite Centre [8].
The TAB can initiate a 3-phase developmental approach
to complete the ASAS network:
1. Phase 1 (20112012)Will start with initial ASAS com-
missioned 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 sea-
ports, while for Land application will enable precise nav-
igation facilities for road and rail vehicles and for Aero-
nautical solutions will provide en-route navigation, mo-
bile terminal navigation and NPA. In addition, this sys-
tem will support Category I PA within a limited coverage
area as well.
2. Phase 2 (20122015)Will initiate with full ASAS in-
frastructures and with additional GMS up to 55. Redun-
dant coverage of the entire initial ASAS operational re-
strictions will be removed. The ALAS ground structures
will be deployed at major African seaports and airports.
Precisely surveyed ground stations with multiple GPS re-
ceivers and processors will be established, including one
or more pseudolites and VHF data link-supports Cate-
gory 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 availabil-
ity is required than ASAS network can provide. In the
proper manner, the reduction of ground-based NAVAIDS
infrastructure, such as VOR and Non-Directional Bea-
cons (NDB) will be initiated, and the added 2nd and 3rd
civil radio frequencies will improve GPS robustness and
ICAA.
3. Phase 3 (20152018)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 constel-
lations of GPS/GLONASS with 2nd and 3rd civil fre-
quency band available for ASAS/ALAS have to be mod-
ified accordingly to: Dual-frequency avionics to mitigate
unintentional jamming and complete phase-out of all on-
airport NAVAIDS (VOR, NDB).
4.2 ASAS system configuration
The ASAS will be designed and implemented as the pri-
mary 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 vehi-
cles 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 navi-
gation, channels and passages, approachings to anchorages
and ports, and inside of ports, and for land (road and rail-
ways) solutions. It was intended to provide the following
services [10]:
(1) The transmission of integrity and health information on
each GPS or GLONASS satellite in real time to en-
sure all users do not use faulty satellites for navigation,
known as the GNSS Integrity Channel (GIC).
(2) The continuous transmission of ranging signals in addi-
tion to the GIC service, to supplement GPS, thereby in-
creasing GPS/GLONASS signal availability. Increased
signal availability also translates into an increase in Re-
ceiver Autonomous Integrity Monitoring (RAIM) avail-
ability, which is known as Ranging GIC (RGIC).
(3) The transmission of GPS or GLONASS wide area dif-
ferential 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 Fig. 4. As observed previous figure, all mo-
bile 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 governmen-
tal 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 processedto 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 lo-
cated in GEO Inmarsat and Artemis spacecraft (8), the aug-
mented 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
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Development and characteristics of African Satellite Augmentation System (ASAS) network 129
Fig. 4 ASAS networkconfiguration. Courtesy of book:UnderstandingGPSPrinciples andApplications by Kaplan(modified by authors) [10]
Fig. 5 ASAS space segment.Courtesy of book: GlobalMobile SatelliteCommunications by Ilcev [9]
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 [ 6].
The ASAS space constellation could be formally con-
sisted 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 120-138).
An ASAS ground segment consists of a network of cer-
tain 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 1575.42 MHz GPS frequency.
The ASAS signal is modulated on a GPS look-alike sig-
nal 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 po-
sition corrections and ionospheric mapping terms. This data
message separates ASAS from normal GPS or GLONASS
by increasing integrity (satellite health), improving the accu-
racy (vector corrections) and also enhancing the availability
(additional pseudo range) of the System. The ASAS network
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130 D.S. Ilcev
Fig. 6 ASAS space and groundsegments. Courtesy ofmanuscript for book:Aeronautical CNS by Ilcev [9]
improves accuracy in two ways by reducing the range mea-
surement error by sending differential corrections for each
satellite and by adding new ranging signals thereby improv-
ing the geometry [9,10].
The vector corrections include fast corrections contain-
ing the satellite clock error; long-term corrections contain-ing more slowly varying errors of satellite location and iono-
spheric 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.
4.3 ASAS space segment
The ASAS Space Segment can be designed by using own
project of GEO satellite constellation, what is more expen-
sive solution, or by leasing existing GEO Inmarsat-3 and
Artemis spacecraft. The operational system can use 3 GEOsatellites: Inmarsat-3 AORE at 15.5W; Inmarsat-3 IOR at
position 64E, and ESA Artemis at 21.5E over equator, il-
lustrated in Fig.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 Fig.6. The ASAS
system can use service of existing Geostationary Ranging
Station (GRS) infrastructures and to implement a wide trian-
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Development and characteristics of African Satellite Augmentation System (ASAS) network 131
gular observation base for ranging purposes with the stations
located in Aussaguel (France), Kourou (French Guiana) and
Hartebeeshoeck (South Africa) [4,8].
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 groundand for use in user Rx to improve performance (reliabil-
ity, accuracy) with GPS and GLONASS signals.
As mentioned earlier, GEO is able to augment the perfor-
mances 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 [1].In response to improve this need, Inmarsat decided to em-
bark a new navigation transponder to support RSAS func-
tions on its last generation of GEO Inmarsat-4 at the begin-
ning 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 con-
cept, 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 ar-
eas. In fact, more GEO will be necessary to assure a proper
replenishment policy when the Inmarsat-3 birds terminate
their operational life [2].
In the meantime, the US made a commitment to support
civil applications of GPS including the modification of fu-
ture generations of spacecraft to meet civil requirements.
The GPS modernization initiatives will make two new civil
signals available: a second signal at 1227.60 MHz (L2) and
a third civil signal at 1176.45 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 secu-
rity services and other precision positioning and navigation
applications [6].
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 sig-
nals in two separate bands. In such a way, Inmarsat designed
its Inmarsat-4 navigation transponder to be, as far as possi-
ble, backward compatible with the existing RSAS and suit-
able for the future RSAS projects. It also recognized that
Fig. 7 EGNOS professional ESA 1 and Personal-Nav 400 Rx.Courtesy of WebPages: EGNOS Test Bed User Equipment fromInternet [4]
dual user downlink RF are an important advance over the
current Inmarsat-3 satellite augmentation capabilities.However, the satellite communication design had to re-
spect the technical constraints imposed by the Inmarsat-
4 space segment primary communications mission. In the
proper manner, the Inmarsat-4 navigation payload will trans-
mit satellite navigation signals at the GPS L1 and L5 fre-
quencies and allow the real-time relay from a single ground-
monitoring network of integrity and accuracy augmentation
data for orbiting GNSS constellation [8].
The L1 and L5 downlink signals can be received in in-
tegrated L1/L5 GPS/RSAS receiver (Rx), see two Rx pro-
totypes. The ASAS users will have at their disposal a few
models of multimodal prototype Rx units. The multimodalprototypes 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 Fig.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 pro-
totype equipment will be used to validate and eventually cer-
tify ASAS for the different applications being considered. Insuch 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 near-
est pizza restaurant in an unfamiliar city, as shown in the
Personal-Nav 400 in Fig.7(B).
Precise position via the Internet and ASAS system will be
possible anytime after completing and testing the ASAS net-
work, thanks to the SIS technology developed by the ESA.
This technology combines the powerful capabilities of satel-
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132 D.S. Ilcev
Fig. 8 ASAS ground segments.Courtesy of manuscript forbook: Aeronautical CNS byIlcev [9]
lite navigation and the Internet. As a result, the highly ac-
curate navigation information that comes from the ASAS
SIS will be available on the Web in real time over the Inter-
net [2].
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 iono-
sphere, or can also be disrupted by jamming.
The ASAS network, shown in Fig. 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 trian-
gles), 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 Fig. 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 pre-
cisely surveyed monitoring reference station receives GPS
signals and determines if any errors exist, while 5 GCS col-
lect data from these GMS reference terminals, assess signal
validity, compute all corrections and create the ASAS cor-
rection message [6].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 mon-
itored satellite and for each IGP. The bounds on the resid-
ual errors are used to establish the integrity of the rang-
ing 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 communica-
tion satellite. The GEO downlinks this data to the users via
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Development and characteristics of African Satellite Augmentation System (ASAS) network 133
Fig. 9 RSAS ground stations.Courtesy of WebPages:WAAS from Internet [4]
the current GPS L1 frequency with GPS type modulation
[9,10].
Therefore, the message is broadcasting on the same fre-
quency 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 addi-
tional navigation constellation providing supplemental sig-
nals 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 air-
craft, combines the GPS signals with the ASAS message to
arrive at a more accurate position. Otherwise, each ASAS
ground-based station or subsystem configuration communi-
cates with TCC infrastructure via terrestrial landline [6].
The GMS is a special ground reference station with an-
tenna and adequate equipment located at a precisely sur-
veyed position, as shown in Fig.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 [3]. 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 [4]. 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 satel-
lites using a ground uplink system on the GPS L1 frequency,
while the next generation of GPS will provide L5 as well [5].
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 Fig. 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 re-
ceivers (possibly 50 US$ or more). Thus, some type of GPS
receivers or chart plotters can be upgraded with RSAS spe-
cial 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 [2].
6 LSAS System configuration
The LSAS is intended to complement the ASAS service us-
ing a single differential correction that accounts for all ex-
pected common errors between a local reference and mobileusers. 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 net-
works developed in Northern Hemisphere.
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 Con-
tinent 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, Sea-floor 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;
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134 D.S. Ilcev
Fig. 10 CMGC subsystem.Courtesy of paper, SatelliteCNS for MaritimeTransportation AugmentationSystem (MTAS), by Ilcev [7]
7. Meteorological, Cadastral and Seismic Surveying; and8. 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
Fig.4is illustrated scenario that all mobiles and GMS di-
rectly are using not augmented signals of GPS or GLONASS
satellites. To provide augmentation will be necessary to pro-
cess not augmented signals in GCS, to eliminate all errors
and produce augmented signals. In this stage any RSAS orASAS network standalone will be not able to produce aug-
mented service for seaports, airports or any ground infras-
tructures. Meanwhile, it will be necessary to be established
some new infrastructure known as an LSAS, which can pro-
vide 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 es-
tablishment 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 air-
port known as a Surface Movement Guidance and Control
(SMGC) [8,11].
6.1 Coastal Movement Guidance and Control (CMGC)
The new LSAS network can be implemented as a Coastal
Movement Guidance and Control (CMGC) system inte-
grated in the ASAS or any RSAS infrastructure. It is a
special maritime security and control system that enablesa port controller from Control Tower at shore to collect all
navigation and determination data from all ships and vehi-
cles, 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 landvehicles in port and around the ports 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 informa-
tion in the vicinity detected via satellites and by sensors on
the ground, shown in Fig.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 ports sur-
face. This position is measured by GNSS, using data from
GPS/GLONASS and GEO satellite constellation. A con-troller is also able to show the correct ship course to Mas-
ters 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 Fig.10:
(1) GPS or GLONASS GNSS Satellite measures the vessel
or port vehicles exact position.
(2) GEO MSC Satelliteis integrated with the GPS position-
ing data network caring both communication and navi-
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Development and characteristics of African Satellite Augmentation System (ASAS) network 135
Fig. 11 SMGC subsystem.Courtesy of book: GlobalMobile SatelliteCommunications by Ilcev[6,9]
gation payloads, In addition to complementing the GPSsatellite, it also has the feature of communicating data
between the ships or vehicles and the ground facilities,
pinpointing the mobiles 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 ports coastal surface. The location
of each vessel and ground vehicle is displayed on the
command monitor of the port control tower. The con-
troller performs sea-controlled distance guidance and
movements for the vessels and ground-controlled dis-
tance vehicles and directions based on this data.
(4) Light Guidance System (LGS) is managed by the con-
troller who gives green light or red light guidance
whether the ship should proceed or not by pilot in port,
respectively.
(5) Radar Control Station (RCS) is a part of previous sys-
tem for MTC of ship movement in the channels, ap-
proaching areas, in port and around the ports 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 satellitecommunications 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 Instrumentof each vessel displays the ship posi-
tion and course [7].
6.2 Surface Movement Guidance and Control (SMGC)
The new LSAS network can be also implemented as a Sur-
face Movement Guidance and Control (SMGC) system inte-
grated in the ASAS or any RSAS infrastructure. It is a spe-
cial aeronautical security and control system that enables
an airports controller from Control Tower on the ground
to collect all navigation and determination data from all air-
craft, 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 traf-fic controller provide essential control, traffic management,
guide and monitor all aircraft movements in the vicinity of
the aircraft, approaching areas to the airport, aircraft move-
ment in airport, including land vehicles in airport and around
the airport, even in very poor visibility conditions at an ap-
proaching to the airport. Thus, the controller issues instruc-
tions to the aircrafts Pilots with the reference to a command
surveillance display in a Control Tower that gives all air-
craft position information in the vicinity detected via satel-
lites and by sensors on the ground, shown in Fig. 11.
The command monitor also displays reported position in-
formation of landing or departing aircraft and all auxiliaryvehicles moving onto the airports 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 Fig. 11:
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136 D.S. Ilcev
(1) GPS or GLONASS Satellitemeasures the aircraft or air-
port 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, pinpoint-
ing the aircrafts exact position.
(3) Control Toweris the centre for monitoring the traffic sit-uation on the landing strip around the airports environ-
ment. The location of aircraft and vehicles is displayed
on the command monitor of the control tower. The con-
troller 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 pro-
ceed to the runway by turning on and off the central
guidance line lights and stop line lights as a signal, in-
dicating 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 airportand 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 com-
munications system.
(7) Ground Earth Station (GES) is a main part of satel-
lite communications system between GES terminals and
ground telecommunication facilities via GEO satellite
constellation.
(8) Aircraft Cockpitdisplays the aircraft position and routes
on the headwind protective glass (head-up displays) and
instrument panel display (head-down display) [6,9].
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 re-
port their positions verbally by voice or have them automati-
cally sent through a relay station. For the controller, surveil-
lance equipment, primarily radar, detects the position of the
many moving ships, vehicles and aircraft in the traffic cov-
erage area. Otherwise, the radar monitoring the movement
of ships, aircraft and other vehicles spins much faster thanthose radars covering.
New tools, like satellite surveillance, have been devel-
oped as part of GSAS combined with surface radars, to help
the controllers to move increased number of vessels, air-
craft and land vehicles more safely through the transporta-
tion augmentation system environment. In the proper man-
ner, this additional navigational accuracy now available on
the ships 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 tak-
ing 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 orGLONASS signal accuracy from about 30 metres to approx-
imately 3 metres. For example, the current US WAAS sys-
tem provides 12 metres horizontal accuracy and 23 me-
tres vertical accuracy throughout the contiguous US. Un-
fortunately, 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.
In the future will be possible to integrate new satel-
lite systems in ASAS network such as already mentioned
Inmarsat-4 space configuration or new SA Space Constella-tion and forthcoming GNSS-2 systems.
Although the global positioning accuracy system associ-
ated with the overlay is a function of numerous technical
factors and ground network architecture, the expected accu-
racy for the ASAS will be in the order of 12 metres hori-
zontal accuracy and 23 metres vertical accuracy throughout
the contiguous Africa and Middle East region.
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http://www.leica-geosystems.com/http://www.leica-geosystems.com/http://www.novatel.com/http://www.novatel.com/http://www.esa.int/http://www.gps.faa.gov/http://www.gps.faa.gov/http://www.esa.int/http://www.novatel.com/http://www.leica-geosystems.com/http://www.leica-geosystems.com/ -
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Development and characteristics of African Satellite Augmentation System (ASAS) network 137
D.S. Ilcev received two B.Eng. de-grees in Mobile Radio Engineeringand in Maritime Navigation fromthe Faculty of Maritime Studiesat Kotor of Podgorica University,Montenegro; received BSc. Eng.(Hons) degree in Maritime Com-munications from the Maritime Fac-ulty of University at Rijeka, Croatia;
and received M.Sc. degree in Elec-trical Engineering from the Facultyof Electrical Engineering, Telecom-munication department of Univer-sity at Skopie, Macedonia, in 1971,1986 and 1994, respectively. His
Doctoral dissertation in Satellite Communications, Navigation andSurveillance (CNS) was positive evaluated in 2000 by Telecommuni-
cation department of Faculty of Electrical Engineering Nikola Teslaof Belgrade University, Serbia.He also passed in Spring 1995 an on-site GMDSS training course onPoseidon simulator at Military Maritime Training Centre in Varna, Bul-garia. He holds the certificates for Radio operator 1st class (Morse); forGMDSS 1st class Radio Electronic Operator and Maintainer; for Mas-ter Mariner, and he was Reserve Staff in CNS of Former YugoslavArmy.Prof. Ilcev is currently working as a Research Professor in Space
Science at Mangosuthu University of Technology (MUT) in Durban,South Africa, and as Director for establishment of National Space In-stitute (NSI). His research concentrated over 45 years on all aspects ofRadio and Satellite CNS systems, networks, technology transfer, navi-gation and logistics, including safety and security in all transportationsystems.
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C o p y r i g h t o f T e l e c o m m u n i c a t i o n S y s t e m s i s t h e p r o p e r t y o f S p r i n g e r S c i e n c e & B u s i n e s s
M e d i a B . V . a n d i t s c o n t e n t m a y n o t b e c o p i e d o r e m a i l e d t o m u l t i p l e s i t e s o r p o s t e d t o a
l i s t s e r v w i t h o u t t h e c o p y r i g h t h o l d e r ' s e x p r e s s w r i t t e n p e r m i s s i o n . H o w e v e r , u s e r s m a y p r i n t ,
d o w n l o a d , o r e m a i l a r t i c l e s f o r i n d i v i d u a l u s e .