Telecom/1996-04-telecom-walnutcreek.iso/technical/iridium

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Subject:  TELECOM Digest Special: Iridium Cellular Service
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TELECOM Digest     Sat, 4 Aug 90 17:00:00 CDT    Special: Iridium Cellular

Inside This Issue:                         Moderator: Patrick A. Townson

    IRIDIUM - Motorola's New Cellular Phone System [Andrew Peed]
----------------------------------------------------------------------

From: Andrew Peed <motcid![e-mail]>
Subject: IRIDIUM: Motorola's New Cellular Phone System
Date: 2 Aug 90 19:57:40 GMT
Organization: Motorola Inc. - Cellular Infrastructure Div., Arlington Hgts, IL


The contact person for the Iridium project is:

    Lawrence Moore
    Motorola, Inc.
    Government Electronics Group
    8201 E. McDowell Rd.
    Scottsdale, AZ 85252
    [phone]


IRIDIUM BACKGROUNDER

System Description:
    Iridium is a worldwide digital, satellite-based, cellular
personal communications system primarily intended to provide
commercial, rural, mobile service via either handheld mobile or
transportable user units, employing low-profile antennas, to millions
of individual users throughout the world. The system includes a
constellation of 77 small, smart satellites in low-earth orbit which
are networked together as a switched digital communications system
utilizing the principles of cellular diversity to provide continuous
line-of-sight coverage from and to any point on the earth's surface,
as well as all points within an altitude of about 100 miles. The
system also includes space-to-earth gateways which interface into the
public switched telephone network (PSTN). Service will be available on
a country-by-country switched basis as negotiated with the individual
governments and/or the individual telephone companies. Unlike the
terrestrial cellular telephone system, Iridium is best suited for
areas where the traffic density is low -- sparsely populated areas,
the oceans, and areas where personal communications is just emerging.
In these emerging markets, Iridium can be used as a primer for the
eventual terrestrial system.

Voice:
    The system is designed as an entirely digital communications
system with 8KHz bandwidth available for each voice channel. Vocoders
operating at 4.8 kilobits per second are employed in the user units to
recreate the audio signals and in the gateways to couple to the analog
PSTNs.

Data:
    The system is designed to allow a user to substitute a data
link in lieu of a voice link which would operate at a rate of 2400
baud.

Modulation:
    The user links use PSK modulation with a multiplexing scheme
that will be compatible with digital terrestrial cellular systems.

Spectrum:
    The system is designed to operate in the 1 to 2 GHz region
with a capability of up to 29 MHz for the uplink and 29 MHz for the
downlink with the expectation that spectrum allocation may grow as the
system demand grows. Gateways and crosslinks will operate at
approximately 20 GHz.

Subscriber Unit:
    The system is designed to operate with a subscriber unit
similar to the Motorola Dyna-Tac.

Constellation:
    The constellation of 77 satellites at a height of 413 nautical
miles was chosen to assure that every point on the earth's surface is
continuously in line of sight of one or more of the satellites. The
constellation includes 7 planes of 11 satellites each in circular
polar orbits. The satellites all "travel in the same direction,"
meaning that the seven planes of satellites co-rotate towards the
north pole on one side of the earth and "cross over" the pole,
traveling down to the south pole on the other side of the earth. The
11 satellites in each plane are equally spaced around their planar
orbit, with the satellites in planes 1, 3, 5 and 7 in phase with one
another, and those in planes 2, 4, and 6 in phase with each other and
halfway out of phase with 1, 3, 5 and 7. (In order to prevent the
satellites from colliding at the poles, a tolerance on the term "in
phase," as used above, is employed and a minimum miss distance is
maintained.) Each of the seven co-rotating planes are separated by
slightly more than 27 degrees, and the "seam" between planes 1 and 7,
which represents plane 1 satellites going up on one side of the earth
and plane 7 satellites coming down in the adjacent plane, is separated
by slightly more than 17 degrees.

Cells:
    Each Iridium satellite has the capacity to operate 37 cells
which are projected onto the earth's surface. These separate cells
allow for higher gain antenna beams and for spectral efficiency in the
system since different cells are able to reuse frequencies and service
different customers with the same channel. These cells are spatially
separated by the main mission antenna on board each satellite.

    The 37 cells are created in a contiguous hexagonal pattern
with one center cell surrounded by three rings of smaller cells. The
three rings consist of 6, 12, and 18 cells respectively, and each of
the 37 cells are created such that each is of approximately the same
shape and size. The cells are approximately 360 nautical miles in
diameter, and the ensemble of cells covers the earth's surface. In
operation, cells will be turned on and off to singly cover all points
within which operation is desired, as well as all necessary gateways,
and to conserve energy on board the satellites.

    The constellation of satellites and its projection of cells is
somewhat analogous to a cellular telephone system. In the case of
cellular telephones, a static set of cells serves a large number of
mobile users; in the case of Iridium, the users move at a relatively
slow pace relative to the spacecraft, which move at about 7,400 meters
per second, so the users appear static and the cells move. The
advantage for Iridium, given this situation, is that the handoffs
required as a call migrates from cell to cell are more deterministic
in that, with the spacecraft's high velocity, handoffs are largely in
one direction and the potential handoff is not to one of six adjacent
cells but more commonly to one of two.

Crosslinks:
    Each satellite operates crosslinks as a medium used to support
internetting. These operate at approximately 20 GHz and include both
forward and backward looking links to the two adjacent satellites in
the same orbital plane. These are nominally at a fixed distance and
angle 2,173 nautical miles away. Up to 6 interplane crosslinks are
also maintained and these links vary in angle and distance from the
satellite with a maximum distance of 2,500 nautical miles.

Gateways:
    Each satellite has the capacity to interlink (via the
crosslink network) to earth-based gateways that employ high-gain
antennas. The initial system will use 20 gateways. Gateways employ
standard cellular switches and interface both to the various local
PSTNs and to the local billing offices.

Delay:
    Unlike geostationary satellite communications systems,
interconnect distances in the Iridium system are on the order of the
wireless telephone and echo effects are minimized.

Spacecraft Life:
    The Iridium spacecraft are designed for a 5 year mean mission
duration (MMD) with expandables sized for 8 years. A small expandable
launch vehicle, such as Pegasus, will service the Iridium
constellation, which, in its steady-state mode (after initial
deployment), will replace satellites on a routine basis and emergency
replacements within 36 hours.

Growth:
    With such a dynamic constellation, constantly being
refurbished, the system design takes on a unique freshness in its
baseline. High reliability is designed into the system to assure the 5
year MMD, but redundancy, per se, is avoided wherever possible. The
initial system is sized to handle the system capacity expected, with
some margin, for the first 8 years -- the system design, however,
incorporates all the necessary "hooks" to allow for capacity growth in
subsequent "blocks" of satellites. Technological improvements in power
available on board spacecraft, launch, weights, antenna technology,
electronic technology and other areas will allow for system growth
within the overall system design. This will provide for a natural
evolution as Iridium matures.

                   ----------------------

MOTOROLA UNVEILS NEW CONCEPT FOR GLOBAL PERSONAL COMMUNICATIONS; BASE
IS CONSTELLATION OF LOW-ORBIT SATELLITES

    In a move that heralds a new era in personal communications,
Motorola, Inc., Schaumburg, Ill., announced a global communications
system that will allow people to communicate by telephone anywhere on
earth -- whether on land, at sea or in the air -- via portable
radiotelephones operating as part of a satellite-based system.

    Callers using the new system will not need to know the
location of the person being called; they will simply dial that
person's number to be connected instantly.

    Motorola calls the new system Iridium and has established a
satellite communications business unit to develop it. The heart of
Iridium is a "constellation" of 77 satellites in low-earth orbit,
working together as a digital switched communications network in
space. The system will be able to handle both voice and data.

    "Iridium brings personal communications to the world -- it
represents the potential for any person on the planet to communicate
with any other," said John F. Mitchell, vice chairman of Motorola Inc.
"For this reason, Iridium marks the next major milestone in global
communications."

    "It is an ambitious concept, which will bring us significantly
closer to 'the global village' As such, Iridium boldly extends the
Motorola tradition of innovation in personal communications recognized
through our leadership in cellular telecommunications, private two-way
radio and radio paging."

IRIDIUM ADVANTAGES:
    Motorola's Iridium system provides several key improvements
over the geosynchronous satellites currently used for international
communications. The low altitude of Iridium satellites allows easy
radio links with portable radiotelephones on earth, using small
antennas rather than satellite dishes. It also supports reuse of radio
frequencies, in a similar fashion to land-based cellular systems.

    In addition, the system solves the problem of low-orbit
satellites "disappearing over the horizon" by combining a large number
of satellites in a space-based, inter-satellite switching system.

    Although Iridium uses cellular communications principles, it
is designed to complement, not compete with, land-based cellular
systems. Land-based cellular will remain the most efficient way to
serve high-density areas, whereas Iridium will bring communications to
remote or sparsely populated areas that lack communications. Iridium
and terrestrial cellular will work together to eventually provide a
seamless communications service for the entire world.

SMALL SATELLITES:

    The satellites are small (approximately one meter in diameter
and two meters tall) and lightweight (approximately 315 kilograms, or
700 pounds). They are considered "smart" because they can switch and
route calls in space.

    Each satellite antenna pattern will project 37 cells onto the
earth's surface. Each cell will provide communications coverage for an
area of the earth's surface roughly 350 nautical miles in diameter;
people will communicate with the satellites using equipment operating
at frequencies of 1.5/1.6 Gigahertz. In addition to voice, the digital
system can transmit data at a rate of 2400 baud.

    The Iridium satellites can be placed into orbit by a variety
of launch vehicles. The U.S. Delta and Atlas rockets, and the European
Ariane, could launch multiple satellites. The new Pegasus air-launched
vehicle could launch individual satellites. Each satellite is expected
to have a lifespan of five to six years.

    Another key component of the system will be a network of
"gateway" surface facilities in various countries that will link
Iridium with the public switched telephone network. These gateways
will store customer billing information and will constantly keep track
of each user's location. An Iridium system control facility will
maintain the satellite network and the overall operation of the
system.

LIGHTWEIGHT, PORTABLE SUBSCRIBER UNITS:
    Subscriber units for Iridium are similar to Motorola's
original cellular radiotelephones and will offer additional features
such as latitude, longitude, altitude, and Greenwich Mean Time.

    In addition to the lightweight portables, Iridium subscriber
units will be available as mobiles or small fixed units.

ANTICIPATED USERS:
    The Iridium system will support millions of users worldwide,
with a total capacity more than 10 times greater than current
geosynchronous satellite systems.

    For low-density areas not economically feasible for cellular
phone networks, Iridium will be an ideal alternative for mobile
telephone service. In sparsely populated or underdeveloped areas
lacking basic telephone service, Iridium can be a foundation for an
eventual ground telephone system.

    For ships and aircraft, Iridium will provide voice or data
links and positioning information without the sophisticated on-board
telecommunications hardware now required. Since Iridium is not
dependent on land-based communications links, it also would play a
crucial role in disaster-recovery efforts following earthquakes,
hurricanes, or other natural calamities.

OPERATING PLAN:
    Motorola envisions that the Iridium system will be operated by
one or more international consortia whose members have the necessary
licenses to operate in each country.

    Motorola will serve as the supplier of the system itself. This
will include the satellites, the communications links and all
necessary support. Motorola's plan for an open architecture is
expected to provide the opportunity for significant international
participation in the development and manufacture of Iridium.

    Plans call for two demonstration satellites to be placed into
orbit in 1992. Implementation of the entire system is planned to begin
in 1994, and full service will begin as early as 1996.

                      --------------------

MOTOROLA SIGNS AGREEMENTS TO EXPLORE NEW SATELLITE-BASED PERSONAL
COMMUNICATION SYSTEM

    Motorola, Inc. has signed memoranda of understanding with
three organizations -- the London-based International Maritime
Satellite Organization (Inmarsat), the American Mobile Satellite
Corporation (AMSC), based in Washington, D.C., and Telesat Mobile Inc.
(TMI) of Canada -- to jointly explore the potential of Motorola's
Iridium satellite communications system.

    Iridium is a network of 77 small satellites in low-earth orbit
that will allow people with portable radiotelephones to communicate
anywhere on earth, whether on land, at sea, or in the air.

    In each memorandum of understanding, the parties agree to
cooperate in studying the potential of the Iridium satellite network,
including an analysis of the technical and business issues involved.

    "This system ushers in a new era of global personal
communications," said John F. Mitchell, vice chairman of Motorola,
Inc. "We're delighted that these organizations recognize the
importance of Iridium to the future of worldwide telecommunications."

    Inmarsat, organized in 1979 as an international consortium to
provide satellite communications for ships at sea, now includes
representatives of 59 nations and has expanded its services in
several countries to include aviation and land-mobile communications.

    AMSC is licensed to provide mobile communications via
satellite for the United States, and TMI is licensed to provide a
similar service for Canada.

    Motorola is continuing discussions with other potential
partners, including British Telecom in London and organizations in
Australia, Hong Kong and Japan.

        Motorola Inc. is one of the world's leading providers of
electronic equipment, systems, components and services for worldwide
markets. Products include two-way radios, pagers, cellular telephones
and systems, semiconductors, defense and aerospace electronics,
automotive and industrial electronics, computers, data communications
and information processing and handling equipment. Motorola was a
winner of the first annual Malcom Baldrige National Quality Award, in
recognition of its superior company wide management of quality
processes.

                   ----------------------

Andrew B. Peed          Motorola, Inc.
...!uunet!motcid!peed     Cellular Infrastructure Division
[phone]          1501 W.Shure Dr., Arlington Heights, IL, 60074

------------------------------

End of TELECOM Digest Special: Motorola's Iridium
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