TABLE OF CONTENTS
1. The Future of Wireless Telecommunications 1
2. Iridium System Overview 2
3. Iridium System History 3
3.1 Iridium Timeline 4
4. Industrial Partners 5
5. Space Segment 6
6. Ground Segment 9
6.1 Gateway 9
7. Subscriber Equipment 12
8. The Call Process 13
9. Controlled System Access and Gateway Roles 14
10. Market Outlook 15
11. Conclusions 17
12. Index - Iridium System Facts 18
13. References 19
TABLE OF FIGURES
Figure 1. Intersatellite crosslinks. 7
Figure 2. Satellite footprints. 7
Figure 3. Gateway block diagram. 10
Figure 4. Iridium in action 11
Figure 5. Mobile exchange units (MXUs). 11
Figure 6. Dual-mode in operation. 12
Figure 7. Composition of a subscriber number. 14
Wireless telecommunications services have grown steadily since
introduction. In the mid 1980's, terrestrial wireless telephone
services was offered only in a few major metropolitan cities.
Today, wireless communications is commonplace - inaugurated in
large and small cities, towns and villages, and selected rural
corridors, as an efficient means of providing telecommunication
services.
Growth inspires varying degrees of standardisation. There are
now various different wireless communication standards which are
fighting with each others. Analogue technology is slowly replaced
by digital technology. GSM standard has taken over Europe and
got a foothold in Asia and the US Anyway, AMPS standard is still
strong especially in the Americas, and CDMA is raising its head
in different parts of the world. Also, there are other systems
like PHS in Japan which have also supporters. Currently there
are not any systems which allow the subscriber to travel world-wide
with a single compatible telephone.
In 1998, the Iridium system is supposed to harmonise world-wide communications standards by providing service to hand-held, pocket-sized telephones located virtually anywhere on the surface of the earth.
The Iridium system is a satellite-based, wireless personal communication
network designed to permit any type of telephone transmission
- voice, data, fax, paging - to reach its destination anywhere
on earth, at any time. It will bring a new dimension of capability
to the commercial, rural and mobile sectors by providing universal,
portable service.
The system is being financed by a private international consortium
of telecommunications and industrial companies and is expected
to begin initial operation in 1998. Motorola is the prime contractor
and creator of the original system concept.
Subscribers will use wireless, pocked-sized Iridium telephones,
transmitting through digital facilities, to communicate with any
other telephone in the world. Unlike conventional telecommunications
networks, the 66-satellite system will track the location of the
telephone hand-set, providing global transmission even if subscriber's
location is unknown. In areas where compatible cellular service
is available, the dual-mode phone will provide the option of transmitting
a call via the cellular system.
Iridium uses many of the techniques that have been in use with
GSM terrestrial mobile systems. As these satellites are relatively
near the earth's surface, small low powered hand-sets can be used
providing full duplex voice services covering all oceans, deserts
and polar regions
Applications for the system vary widely including business use for persons who must stay in touch with the offices located continents away, service for developing nations with lack telecommunications infrastructure, communications for rescue and supply efforts during natural disasters, and personal use.
The Iridium system was conceived in 1987 by engineers at Motorola's
Satellite Communications Division, in Arizona, USA. With the goal
of providing truly global communications coverage, engineers determined
that the system would require a constellation of low earth orbiting
(LEO) satellites with sophisticated electronics. The satellites
would be relatively small and simple constructed so they could
be build, launched and replaced economically.
As the system concept was being considered, Motorola conducted
market analyses to determine the requirements for system capacity
and financing. The analyses projected the existence of a strong
potential market for a system that would provide high quality
service at reasonable rates. A constellation of small satellites
made particularly sound financial sense because the entire system
could be upgraded in as little as three years to increase capacity
and technical sophistication, research showed.
Working quietly, Motorola and its industrial partners spent more
than US$ 150 million on research and developed on the project.
In 1990, Motorola filed a request with the US Federal Communications
Commission (FCC) for a license to construct and launch satellites
for a world-wide system.
Representatives of the World administrative Radio Conference affirmed
the importance of LEO satellites for global personal communications
with allocation of global radio frequency for LEO mobile satellites
services in February 1992. These actions ensured that the same
spectrum will be available around the world, pending local licensing.
They also established guidelines for the international co-ordination
of mobile satellite systems like the Iridium system.
Also in 1992, the FCC granted an experimental license to construct
and launch five satellites to demonstrate the feasibility of the
Iridium system, with authorisation for full construction expected
later. The launch of these satellites is planned for 1997.
In August that same year, it was announced that the Iridium system
design had been enhanced by reducing the number of satellites
from the original 77 to the current 66. The changes increased
to 48 the number of beams each satellite would project on the
ground, improving system performance and ensuring less electronic
interference during calls.
To gain equity, Iridium Inc. issued a private placement memorandum
to potential investors world-wide. In August 1993, the company
announced that it had obtained $US800 million in binding commitments
and initial cash payments from investors, closing its first-round
equity offering. The investment announcement was seen as a strong
show of confidence in the Iridium system. In September 1994, Iridium
Inc. completed its equity financing, bringing the total capital
committed to the Iridium system to $US1.6 billion.
Shares in Iridium, Inc. were purchased by telecommunications operators
and industrial companies world-wide. Countries represented include
Brazil, Canada, China, Germany, Italy, Japan, Korea, the Russian
Federation, Saudi Arabia, Taiwan, Thailand, the United States
and Venezuela.
Iridium, Inc. in 1993 signed a $US3.4 billion contract to purchase
the Iridium space systems from Motorola's Satellite Communications
Division. The company also signed a $US2.8 billion follow on contract
with Motorola for operation and maintenance of the Iridium system
over five years, beginning approximately in 1998. Motorola has
signed a $US700 million contract with Lockheed Missiles &
Space Co., Inc. for development of key elements of the program.
Among many other subcontractors, Raytheon Corporation will design
the phased array antenna for communications between ground stations
and Iridium telephones. The Canadian firm, Com Dev, will develop
hardware for intersatellite conversation. Bechtel, Scientific
Atlanta, Siemens, telespazio, and many others also will provide
key elements of the system.
McDonnell Douglas Co. will launch the majority of the satellites
on its Delta 2 launch vehicle. Khrunichev Space Center of the
Russian Federation also will provide launch services aboard its
Proton vehicles, and China Great Wall Industry Co. will provide
services aboard its Long March 2c vehicles.
The Iridium network of 66 satellites will orbit approximately
420 nautical miles above earth's surface. The constellation will
include six orbital planes, with 11 operational satellites and
one on-orbit spare per plane. Compared to geostationary communications
satellites 22,300 nautical miles above the earth, the low orbit
of the satellites will allow communications to low-power hand
units on the ground with negligible time delay.
Echo will be minimised due to the satellites' low orbit, and the
receiving antenna will be small enough to be carried on a hand-held
subscriber unit. The satellites, weighing about 689 kilograms,
will be electronically interconnected to provide continuous world-wide
coverage. Communications will be relayed via satellite and through
terrestrial gateways, where billing information and user location
data will be stored.
In the Iridium system switching can be organised in the satellites.
This is one of the major advantage compared to its rival mobile
satellite systems, which are using "ground switching".
The Iridium system's use of intersatellite links is essential
to provide truly global coverage. The system will cover the vast
portions of the world where telecommunications networks cannot
be economically justified, but also will serve polar and ocean
areas. Through use of these links, the system will be capable
of locating subscribers anywhere in the world.
Further, the ability to hand off a call from satellites in the
same or adjacent orbiting planes will allow a user to maintain
a call indefinitely, preventing the dropping of calls as will
occur on systems in which satellites are not linked.
The Iridium system will use a combination of Frequency Division
Multiple Access and Time Division Multiple Access (FDMA/TDMA)
multiplexing to make the most efficient use of limited spectrum.
Intersatellite transmissions and transmissions to ground gateway
locations and the system control segment - responsible for tracking
and telemetry - will take place in the Ka-band frequencies. Communications
between the satellites and Iridium subscriber units, pagers or
solar-powered phone booths will use L-band frequencies.
Communications traffic will be routed throughout the Iridium network
by intersatellite crosslinks, enabling call delivery regardless
of terrestrial network availability. These K-band broadband crosslinks
operating between 23.18-23.38 GHz will provide reliable, high-speed
communications between neighbouring satellites, allowing call
routing and administration to occur most efficiently within orbiting
network.
Figure 1. Intersatellite
crosslinks.
Each satellite will cast a footprint consisting of 48 spot beams
onto the surface of the earth. These discretely focused and concentrated
beams will support high voice quality between the Iridium satellites
and pocked-sized telephones. The cluster of 48 hexagons beneath
each satellite represent the theoretical cells formed by phase-array
L-band antennas aboard the satellite.
Figure 2. Satellite footprints.
Satellite crosslinks provide the flexibility to place gateways
virtually anywhere in the world. Even though there is not a gateway
showing with one of the pictured hexagons, the crosslinks provide
multiple possible paths between the subscriber and the gateway
which "lands" his conversation. These multiple possible
paths offer the Iridium network additional robustness and reliability.
It should also noted that while crosslinks make it theoretically
possible for just one gateway to serve the entire planet, higher
quality and reliability in service will be obtained through geographic
diversity.
Once Iridium subscriber unit is activated, the nearest satellite,
in conjunction with the Iridium network, automatically will determine
account validity and the location of the user. The subscriber
will select among terrestrial wireless or satellite transmission
alternatives, depending on compatibility and system availability,
to dispatch a telephone call.
If the subscriber's local terrestrial wireless system is not available,
the telephone will communicate directly with a satellite overhead
through an L-band frequency and the call will be transferred from
satellite to satellite through the network to its destination,
either another Iridium telephone, or an Iridium ground station.
The ground stations, or gateways, will connect the network with
land-based Public Switched Telephone Networks (PSTN) to reach
fixed or wireless system world-wide.
Connections between the Iridium system and land-based PSTN will
be achieved by Iridium gateway installations. The Iridium constellation
will be connected to the gateway using high gain 3.048 meter parabolic
tracking antennas operating at K-band feederlink frequencies in
the 28GHz range , and housed in radomes approximately five meters
in diameter. These co-located antennas will provide the necessary
geographic diversity to overcome weather and atmospheric signal
fading and blocking.
Individual L-band cells and channels are not "owned"
by any particular gateway. Consequently, calls can be routed to
the Iridium gateway most advantageously located. This flexibility
permits efficient, cost effective call delivery and additional
system delivery.
Figure 3. Shows a block diagram of an Iridium gateway. At the
heart of the gateway is the Mobile Switching Center (MSC), a Siemens
GSM-D900 switch. The MSC has two "sides", a land side
which connects to the local telephone network, and a mobile side
which connects to an Earth Terminal Controller (ETC). The ETC
is analogous to the Base Side System (BSS) of a terrestrial GSM
system, and it controls a set of Earth Terminals (ETs) which communicate
with the constellation using 28 GHz K-band radio links. Information
for physical subscriber equipment is kept in the Equipment Identification
Register (EIR).
The gateway Message Origination Controller (MOC) supports a variety
of messaging services such as direct messaging to Iridium pagers.
The Gateway Management System (GMS) provides operations, administration,
and maintenance support for each of the gateway subsystems.
Figure 3. Gateway block diagram.
The continuous, global coverage of the Iridium system will extend
from the earth's surface to an altitude of 160 km, providing service
to government and general aviation, and to high-altitude hypersonic
transports of the future.
Local service providers will act as the intermediaries between
Iridium gateways and individual system users. These service providers
will be responsible for marketing Iridium services and billing
and servicing subscribers. Rights to act as a service provider
will be granted only by gateway operators, consistent with selection
and performance criteria.
Because Iridium users can be located anywhere in the world, cellular,
wireless and telephone operators may include Iridium services
as an integral part of their service offerings.
Through co-operation with Iridium, Inc., telecommunications equipment
manufacturers and providers will be able to offer world-wide
roaming service, and to manufacture, sell and service Iridium-compatible
hand-sets.
Semiportable multi-line units, or MXUs, will provide remote location
with access to telecommunications.
Figure 5. Mobile exchange
units (MXUs).
Working with the local earth-based wireless systems, the dual-mode
Iridium phone will search for and use compatible ground-based
wireless systems whether they are available - with user charges
at prevailing local wireless rates. Whenever the local terrestrial
wireless system is unavailable or non-existent, the dual-mode
phone will route the call through the Iridium satellite constellation
to its destination.
Figure 6. Dual-mode in operation.
The Iridium hand-set will be of digital design for maximum clarity
and signal integrity. Voice, paging, fax, and data modem capability
will be built in, as will data storage features. The phone will
be pocket-sized and similar in design to many of Motorola's popular
cellular phones.
Iridium services also will be available through solar-powered Iridium "phone booths" that will provide widely scattered populations with world-class communications capability virtually overnight.
The call processing architecture of the Iridium system is patterned
after the GSM standard. GSM is a popular digital cellular standard
which offers a wealth of features to subscribers, and its continuously
being enhanced new features. By adopting this standard, Iridium
subscribers will benefit as appropriate advances in the GSM standard
are transferred to the Iridium system. The flexibility of the
GSM architecture will enable multiple value-added subscriber features
including:
Each Iridium subscriber will be assigned a "Home Gateway".
A permanent record of subscriber service information will be kept
at this Home Gateway in the Home Location Register (HLR). Iridium
subscribers may be identified by any of the following numbers,
all but one of which are transparent to the subscriber:
Irrespective of the location of the subscriber, the Home gateway
can be determined by examining the "Iridium Numbering Plan
Area" (INPA) fields of the MSISDN or INSI, which can be derived
from Gateway lookup of a TMSI. Figure x shows the structure of
an MSISDN number, and its associated INPA fields.
Figure 7. Composition of
a subscriber number.
The current growth of cellular service and the market outlook
for broader personal communications suggests a strong demand for
Iridium services. The world-wide market for personal communications
will account for annual revenues of up to $US60 billion by the
year 2000, and the number of cellular subscribers could reach
200-300 million world-wide according to industry predictions.
The largest single potential group of Iridium system users is
expected to be business travellers. Top-level executives can be
connected to their home offices no matter where they are - on
a remote oil platform, in a major city without compatible terrestrial
wireless infrastructure, or somewhere in the sky. A travelling
business person's call from Tel Aviv will be as simple as making
a call from home.
High-income customers and members of the press who want the convenience
of global communications also will use the Iridium system, and
it will be an invaluable tool for aeronautical and marine users.
For undeveloped areas in which telephone system infrastructure
costs have been prohibitive, the Iridium system is aiming to provide
governments and telecommunications providers with an economical
alternative or interim service.
The system, which will be virtually impervious to earthquakes,
floods, hurricanes and other natural disasters, also will be an
important asset for disaster response. Unaffected by weather and
damage to local telephone systems and power lines, portable, satellite-linked
Iridium hand-sets can be air-dropped or carried to speed and simplify
disaster relief efforts anywhere in the world.
Land mobile communication represents a significant opportunity
within the developed and developing world. Here are some of the
services which mobile satellite communications could provide:
Technology is advancing at a rapid pace and it will not be long before small hand portable telephones can be used over a satellite link. Already, there are a range of small earth stations that will fit inside a briefcase.
It is expected that satellite mobile communication systems will
gain 1-3% market share of the total mobile communications markets.
This is not much when considering that the satellite infrastructure
requires quite huge investments to implement and to maintain.
Anyway it is aimed that the very special group of users is willing
and capable to pay clearly higher service charges.
One important factor for the increasing popularity of mobile satellite
communications in the future might be the development of the third
generation mobile communications systems; UMTS/ FPLMTS. These
new systems will be launched approximately in the year 2002 and
they are projected to be capable to operate hand-by hand with
satellite systems as well.
Global services will lead to universal benefits as service providers
and subscribers make use of the Iridium system's seamless connectivity.
Business travellers will have the freedom to roam world-wide with
a single telephone. Previously remote and unserved regions will
be able to interact with the rest of the world. Relief organisations,
members of the press and countless other markets will have access
to an unprecedented array of features, including voice, paging,
fax, data services.
The Iridium system will represent much more than its satellites,
ground stations, pocketable telephones and other infrastructure.
It will become the ultimate instrument of global connectivity
by connecting anyone, anywhere, anytime. For that goal the Iridium
"project" needs excellent co-operation between the major
bodies involved in the development. If international operators,
technology suppliers and standardisation organisations were capable
to have required "chemistry" , there could be enough
space for the success of the Iridium system.
Space Segment
Number of satellites 66 Interconnected
Number of orbital planes 6
Orbit height 780 kilometers
Inclination of orbital planes 86.4 degrees
Orbital period 100 minutes, 28 seconds
Coverage 5.9 square miles /satellite
Satellite weight 700kg
Spot beams/satellite 48
Link margin 16 decibels
Lifetime 5-8 years
Frequency Bands
L-Band service links 1616-1626.5 MHz, L-Band
Intersatellite links 23.18-23.38 GHz, Ka-Band
Gateway/TT&C links
Downlinks 19.4-19.6 GHz, Ka-Band
Uplinks 29.1-29.3 GHz, Ka-Band
Switching Equipment
Siemens GSM-D900
Signalling
GW to ISC PCM transmission and SS7-ISUP or MFCR2
Iridium Telephone Frequency Division/Time Division (FDMA/TDMA), Quaternary Phase Shift Keying (QPSK)
Transmission Rates
Voice Full-duplex, 2.4 kilobits per second
Data/Facsimile 2400 baud
Launch
McDonnell Douglas delta 2. Five Iridium satellites/launch
Khrunichev Proton Seven Iridium satellites/launch
China Great Wall Long March Two Iridium satellites/launch
All the information for this study was collected from Iridium
Inc. company and project information booklets, and the special
Iridium Magazines.