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Satellite Mobile System Architectures Report
of
The R&D Working Group 1 of the ASMS-TF
EXECUTIVE SUMMARY
The Satellite Mobile System Architectures Report is built upon contributions from Members of the
Working Group 1 on R&D (formerly the Technical Group) of the Advanced Satellite Mobile
Systems Task Force (ASMS-TF), and gives an overview of the architectures and enabling
technologies for the near future development of the next generation of advanced satellite mobile
systems (ASMSs), for broadband multimedia services provision. ASMSs will essentially be based
on the integration of communication systems with multimedia content delivery (broadband and
broadcast/multicast services), navigation and positioning, and terrestrial networks.
The focus is on the short term scenario (1-4 years), but the development into the long term scenario
(4-10 years) is also an important issue. For the short term scenario it has been concluded that
possible implementations must be based on existing technologies/architectures with minor
modifications. It has been anticipated that development will take place in several phases determined
by factors like market demand, the terrestrial evolution from 2.5G to 3G, and the potential of
available satellite technologies. The envisaged approach is based on the evolution from the present
situation for both satellite and terrestrial networks in the short term scenario. For the satellite
segment this means that only existing systems or systems planned for operation in the near future
are of interest for the short term. The long term scenario has possibilities for and must include a
transition into the future of multimedia communications with more advanced and complex
approaches depending on development in the first critical phase.
ASMSs will differ significantly from today’s mobile satellite systems in terms of supported services
and deployed technology. This implies moving from voice communication to an interactive
multimedia-based personal and business environment. ASMSs will enable faster transmission
speeds, providing mobile access to high-quality video, audio, graphics and multimedia. The ASMS
user will have a wide set of requirements, ranging from service cost to application performance.
The first part of the report is aimed at the embodiment of the requirements identified from the
ASMS-TF Commercial Group and their translation into the related technical requirements.
Chapter 2 of the Report enumerates the ASMS foreseen requirements. First, the overall user
requirements are identified; they are similar to those of the terrestrial UMTS system, i.e. reliability,
requiring stable and proven technology; affordability, requiring low tariffs and terminal costs,
achievable through open standards-based systems for a competitive market with compatible
products; voice, data and video services provision, requiring a flexible multi-service architecture,
with a single service interface; suitable display and user interface support; and everywhere
availability, requiring global coverage (with the critical issue of in-building penetration and urban
areas coverage).
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Then, specific requirements are illustrated for terminals, user interfaces, applications, pricing,
services and operators.
Terminals are grouped into four categories: handheld terminals; transportable terminals, including
briefcase, palmtop and laptop; vehicular terminals; and broadcast-only receivers. Each terminal type
has the possibility for multi-mode functionality (e.g., ASMS/GPRS/T-UMTS). From the terminals
point of view, the technology impact of terrestrial/satellite integration implies common user
interfaces, common control system, common modem functions, and common RF systems. To
reduce costs, reuse of terrestrial mobile system technology and use of adjacent frequency bands
with respect to the terrestrial allocation are suggested. The peculiar characteristics of each terminal
category are described in detail in the document. Apart the broadcast-only receivers, they all
provide telephony, messaging, Web/WAP browsing, audio, data and video streaming, e-commerce
and location-based services.
User interfaces requirements are different for the broadcasting and non-broadcasting cases.
Required user interfaces in non-broadcasting ASMSs are similar to the terrestrial counterpart:
research is directed towards friendly visual displays with miniaturized environments and the
replacement of the traditional keyboard as an input device. The user interfaces provided for
broadcasting applications will be a subset of those provided for non-broadcasting services.
The applications requirements identification from the technical point of view illustrates the
relationship between applications and bearer services, impact on user terminals, network
connectivity, service management and end-to-end service delivery. Non-broadcasting applications
comprise: Internet access, intranet/extranet access, customized infotainment, multimedia messaging,
location-based services, and rich voice. All the application will be IP-based. For
broadcasting/multicasting applications we mention real time/non real time video, audio, and data
streams, and short messages.
Pricing requirements identify the relations between service delivery and costs. ASMS services take
up will indeed be determined by the price of the service and of the terminal, and by the
attractiveness of the service bundle. Many different models for pricing are envisaged in the
document: billing on user profile or usage in the non-broadcasting case, and charging real-time
transactions (pay-per-view) or off-line processes in the broadcasting case.
From the service point of view, the document proposes that ASMSs follow the ITU-T B-ISDN
service classification: bearer services, tele-services, supplementary services, connected/nonconnected modes and access to other infrastructures (Internet, etc.). Also other service
characteristics have to be supported: positioning related services, “always on“ capability and service
availability at least equal to the existing comparable Inmarsat services. The document identifies in
detail the characteristics of non-broadcasting applications and underlines the ASMS complementary
role with respect to T-UMTS services, providing geographic extension of basic services and
functional extension services. The majority of broadcasting applications identified by the ASMS-TF
Commercial Group has little impact on the service requirements for broadcast services. They all use
the same standard bearers.
The operator requirements analysis distinguishes among infrastructure operators, service operators
and application operators. Infrastructure operators aim at maximizing service delivery capacity and
flexibility, with minimal costs, power consumption and adjustments. They tend to offer all-IP
solutions. Service operators provide users with terminals and services, and must interface with
infrastructure providers, considering terminal and infrastructure complexity. Application operators
provide the desired applications to the users, for instance internet surfing, gaming, e-business
applications etc., and this will necessitate interconnection with application servers distributed in
other networks.
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The second part of the report identifies the representative satellite systems that may support
ASMS applications in the initial phase, for communication and broadcast. The available systems in
the short term scenario are basically divided into two groups: satellite communication systems
(ACeS, Thuraya, Globalstar, Iridium, ICO, and Inmarsat-3) and satellite digital audio broadcasting
systems (WorldSpace, XMTM and Sirius). The main characteristics of these systems are the
following.
 Satellite communication systems
 ACeS is a satellite communication system for mobile and fixed applications. It is based on a
constellation of two GEO satellites (Garuda-1 already available and Garuda-2 in the near
future), with a payload that foresees on-board switching/routing. The 140 beams offer a
coverage that includes Western and Central Asia, Eastern Europe and parts of Northern
Africa. The provided services are voice, fax, standard-GSM services, data, short message
service (SMS), voice mail and high penetration alerting. Terminal are handheld or fixed, and
they are foreseen to operate in dual-mode. The Network Control Center (NCC), located in
Indonesia, controls the radio resources assignment to the gateways (GWs). The system
provides at least 11,000 simultaneous telephone channels.
 Thuraya is a satellite communication system that provides coverage for Europe, North and
Central Africa, Middle East, Central Asia and Indian subcontinent, through its 250-300 spot
beams. It consists of a constellation of three GEO satellites (only one is presently
operational), with a payload providing digital beam forming. Thuraya offers
telecommunication services like voice, fax and data, GSM supplementary services and value
added services. The available terminal types are handheld, vehicular and fixed terminals,
and payphones. The terrestrial segment comprises one primary GW and several regional
GWs. System capacity is 13,750 telephone channels.
 ICO represents one of the planned systems. The constellation comprises 10 MEO satellites
(plus two in-orbit spares), providing quasi-global coverage. The satellite architecture is bentpipe and each satellite generates 163 beams by digital beam forming. The payload is fully
digital. The bearer service set contains circuit-switched and packet-switched transmissions.
The network segment comprises 11 satellite access nodes (SANs) interconnected into the
ring-type network called ICONET. Terminal types are handheld, vehicular, maritime,
aeronautical and fixed.
 Globalstar is a satellite-based telephone system. It consists of 48 LEO satellites, offering
coverage in the world between 70o North and South latitudes, with satellite diversity. The
provided services are voice telephone, digital and fax data, paging, and short messages. The
terminal types are handheld, vehicular and fixed, and can operate in single or multi-mode.
 Iridium is based on a constellation of 66 LEO satellites, offering global coverage. Each
satellite generates 48 beams and is interconnected with four adjacent satellites through intersatellite links (ISLs). Services are voice, data, fax, paging, messaging and supplementary
services. Terminal types are handheld (dual-mode), vehicular and fixed. A small number of
GWs are envisaged for interconnection with other networks. Call routing employs the ISLs.
Capacity is 172,000 simultaneous users.
 Inmarsat consists of a GEO satellite constellation and offers global coverage. The Inmarsat
existing system is based on 5 third generation satellites (Inmarsat-3). The Inmarsat-3 system
is used by independent service providers to offer a range of voice and multimedia
communications. Keystone of the Inmarsat strategy is the new Inmarsat I-4 satellite system,
which from 2004 will support the Inmarsat Broadband Global Area Network (BGAN),
granting mobile data communications at up to 432 kbit/s for Internet access, mobile
multimedia and many other advanced applications. Inmarsat-3 services are categorized in
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several groups (A, B, GAN, mini-M, C, D+, E, Aero), and terminals vary according to that
subdivision. 40 land Earth stations are provided. Capacity is up to 210,000 terminals.
Digital audio broadcasting systems
 WorldSpace is the first satellite digital radio broadcasting system providing portable
reception. It offers a worldwide coverage, over developing countries, using 3 GEO satellites
and broadcasting in L-band. The service targets are mainly underserved radio markets where
low cost radio and radio portability are key. The coverage comprises Africa, middle East,
Asia and Latin America. Each satellite antenna provides 3 beams. In addition to the
satellites, the system provides a comprehensive ground infrastructure deployed on the five
continents, comprising various control centers (satellite, mission and broadcast) and service
provider feeder link stations. In addition to audio contents, WorldSpace is also providing
multimedia contents. To cope with the various broadcaster requirements, the WorldSpace
system uses two communication missions: a regenerative communication mission and a
transparent communication mission. The system offers up to 200 programs per beam.
 Sirius Radio System has been conceived to provide a digital audio radio service directly
from satellites to vehicles across the Continental United States (CONUS) region. Sirius
Radio offers a wide selection of music formats and program types using perceptive audio
coding techniques to efficiently digitally encode the analogue audio signal. The satellite
signals are received by the mobile platforms, particularly vehicular automobiles. Three
different types of diversity reception are present in the system concept: spatial diversity,
frequency diversity and time diversity. The system is capable of serving up to 300,000
terminals.
 XM™ Satellite Radio service is a digital audio radio service licensed for the United States.
It provides high-quality compressed audio, as well as text and other digital data to car,
home, and portable personal receivers via a pair of GEO satellites and a network of
terrestrial repeaters, over the United States. Distinctive features of this new radio service
include: a coast-to-coast coverage, creating a truly national listening audience in the United
States; a superior digital quality reception; and a superior choice of programming. The
system employs space and time diversity.
Chapter 3 concludes by describing satellite digital radio broadcasting from a general point of view.
It illustrates: the reasons underlining the fact that satellite digital radio broadcasting systems had
scarce success in Europe until recently; the advantages of digital broadcasting versus analogue
broadcasting; the reasons that suggest to adopt this technique in radio transmissions; and the
parameters characterizing this kind of transmission when it is performed via satellite.
Chapter 4 focuses on the enabling technologies and architectures for ASMSs in a longer term
scenario, starting with GSM/GPRS technologies, which are already becoming operational, and then
giving an overview of the S-UMTS/IMT-2000 technologies. Satellite broadcast systems can also
contribute with interactive broadcast/multicast and data communication.
The description of GSM/GPRS related technologies illustrates the Inmarsat Regional BGAN (RBGAN) and the Inmarsat BGAN concepts. The R-BGAN system makes use of the GEO Thuraya
satellite, and of the Geo-Mobile Packet Radio Service standard (GMPRS) air interface, built on the
circuit-switched Geo-Mobile Radio-1 (GMR-1) standard, which is based on the terrestrial GSM
standard. The BGAN system will provide near-global coverage overlay for the terrestrial network,
scheduled to enter service in 2004. The system will employ bandwidth-efficient modulation and
coding techniques, capable of supporting variable bit rate services and quality of service depending
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on the needs of the application. The BGAN system will be compatible with terrestrial 3rd
Generation UMTS/IMT-2000 services, enabling users equipped with BGAN terminals to access
these services over the near-global coverage provided by the BGAN system.
Enabling technologies and possible architectures for UMTS/IMT-2000 requires the distinction
between point-to-point and point-to-multipoint architectures.
In the point-to-point case, the Universal Mobile Telecommunication System is a member of the
IMT-2000 family of global systems and satellite-UMTS (S-UMTS) is an integral part of UMTS.
Some of the benefits to be gained from a fully integrated S-UMTS/T-UMTS system are seamless
service provision, re-use of the terrestrial infrastructure, and highly integrated multi-mode user
terminals. The satellite component of UMTS will provide services in areas covered by cellular
systems, complementary services, and be operational in those areas not planned to be served by
terrestrial systems. Different examples of architectures are envisaged according to different
combinations of regenerative/transparent satellites, GEO/non-GEO constellations, singlehop/double-hop architecture, and ISL/non-ISL presence.
In the point-to-multipoint case, a general approach for possible architectures is firstly pursued, and
then the specific architecture of S-DMB is described. In the general approach the vision of a
satellite/terrestrial integrated system intended to provide the point-to-point mobile communication
services as well as the multicast and the broadcast mobile services is presented. Within such an
integrated system it is possible to distinguish between a terrestrial and a satellite component. The
terrestrial component includes both a communication segment and a broadcast segment. The
satellite component complements the terrestrial UMTS by supporting the so-called multicast UMTS
services and cooperates with the future terrestrial digital mobile broadcast network in achieving a
very large coverage area at minimum total cost. Terminals will be multi-mode and some degrees of
interactivity are required. The peculiar characteristics of this kind of systems are described in detail
in the document. The drawn conclusion is that the proposed integrated system concept should
represent an efficient and cost-effective solution to support mobile wideband applications, by
maximizing synergies among services, infrastructures and technologies.
The particular case of S-DMB architecture is analyzed in detail. It is a satellite based multicast
system for 3G mobile networks relying on terrestrial UMTS standards and making use of the
allocated IMT-2000 bands to MSS systems. The S-DMB architecture aims at providing an efficient
and cost effective answer to solve the identified issues of multimedia services delivery on 3G
networks, inducing exciting market opportunities for 3G mobile operators. By relieving unicast
networks of the most cumbersome and less profitable traffic, the S-DMB delivery mechanisms will
provide 3G mobile operators with more efficient and more profitable usage of radio frequency
resources. The S-DMB concept is derived from content delivery network architectures developed
for fixed IP networks. The basic mission of the S-DMB system is to provide traffic optimization
mechanisms that rely on multicast content delivery to the user and are exclusively intended to
increase content transfer capacity over 3G networks. The main provided service is content delivery
service, based on different levels of capability: data streaming, push and store, user request
download, and peer-to-peer connections. Emergency services are provided, too.
Finally DVB-derived technologies for mobile users are investigated. The DVB-S standard
identifies the synergy between digital broadcasting and Web delivery, and specifies an option for a
return channel and interactive data services. The return link can be implemented using various
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media. The satellite return channel alternative is standardized as DVB-RCS (DVB-Return Channel
by Satellite). The DVB-S and DVB-RCS standards are defined for broadband fixed terminals
operating in Ku-band. However, with reasonable modifications to the air interface, DVB-based
systems may also be suitable for mobile/portable terminals operating in L/S-bands and offering data
rates of 400-2000 kbit/s. No standard has been developed for this yet. DVB-RCS provides a broad
spectrum of IP-based multimedia interactive applications and services. One of the major advantages
of DVB-RCS is efficient and low-cost implementation of multicasting and broadcasting services.
However, point-to-point services, such as voice-over-IP, can be supported as well. The generic
physical architecture of the overall DVB-RCS satellite interactive network is illustrated in the
document. The DVB-RCS system can be considered to be a self-standing system that includes all
functions needed to support internal mobility. In the minimum solution there is no location register
interworking with terrestrial mobile communication systems. Such interworking is possible if this is
an economically viable solution and if there is a demand for such interworking. The DVB-RCS
system can be interconnected to both fixed and mobile terrestrial communications systems as well
as to other mobile satellite communication systems.
Finally some conclusions are drawn. The identification of the uncertainties for the future
development of the ASMSs is pursued: the availability of reliable and low-cost equipments; the
development of the terrestrial UMTS market (for the time being, it is characterized by delays and
some skepticism); the fact that some of the requirements may be difficult to fulfill during the first
phase (this includes central topics like “always on” and multicast: “always on” is a bottleneck with
the limited availability for indoor and non line-of-sight areas, and this also affects the applicability
of multicast); standardization, a critical issue as the number of users is growing and they will
require interoperability of the user terminals with the different regional systems around the world;
finally, the interoperability/roaming with terrestrial networks.
In Annex1 GSM-based satellite systems are described in detail. Commonalities and differences
between terrestrial and satellite systems are identified. A detailed description of GMR-1 standard
and GMR-2 is given.