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ADVANCED
SATELLITE COMMUNICATION
TECHNOLOGY
Dr. S. PAL*
ISRO Satellite Centre,
BANGALORE - 560 017
10 July , 2003
* Author is Outstanding Scientist & Deputy Director, DCA
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For mankind to survive three things are essential:
LOVE
ENERGY COMMUNICATION
The last one becomes more important for present
days.
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When it come to communication, now-a-
days there are two buzz words:
Communication
Information Technology
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There is another word `information' which is also
closely related to communications means "contents" o
message. Claude Shannon defined "information" as"Reduction of Uncertainty". Information is also
described as "any difference that makes a difference".
Information is a notch on the spectrum with raw data
on low end and knowledge/wisdom on the high end. Itsuggests that the raw data when processed becomes
information. Information minus noise is intelligence or
understanding. Intelligence plus experience is
knowledge; and knowledge when further processed,
looked through scholastic eyes, gets philosophized andso becomes wisdom which is adored over ages. The
present day society is often referred as information
society.
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In the past few decades, persons and institutions
have been progressively unsettled by the rapid pace
of social and technological changes brought about
by Communications (telephony, TV etc.). In earlier
times the world around us seemed more stable andmajor changes in values, institutions and technology
evolved more slowly. It took centuries for the
Middle Ages to become the Renaissance, yet many
of us have experienced major technologicalrevolution in one life time in the last century.
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Many technological reversals have been seen like
the telephone which should have been on thewired network has become wireless, while the TV
which was wireless now works on cable. Many
individual spheres of working have become
almost universal, like education has come to thedrawing room from school and colleges, sectors
like banking, medicines, hospitals etc which were
location specific are available on net. There is
tremendous convergence and fusion o
communications, computers and associated
technology in the present era.
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We are presently getting on the crest of thethird wave which is INFORMATION &
COMMUNICATION REVOLUTION more
appropriately termed as `IT' -Information
Technology, the first being agriculture & thesecond being ``Industrial Revolution'. As we
become increasingly networked, our worlds will
grow smaller and bigger simultaneously.
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The conventional communication tools are:
Telegraphy using copper wire line
Telephony using copper wire line
Television
New papers, books, etc.
Means of Transport
All these have undergone a tremendous changes. A few new names
for the present day communication techniques are:
Electronic/Voice MailSpace Communications
Private Data Service using VAST
Auto Text Service
Video text service (Fascimile)Radio trunking/paging
Cellular Mobile Telephone (PCS)
Wireless in local loops
Local National & International information exchange
intelligent Networks & Integrated Services Networks
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New ones are:Mobile Satellite Telephone - Personal Communication
Systems INFOSAT (information satellite)
A major shift from analogue to digital domain
An increase in the value of software as opposed to
hardware content
Extension of optical technology towards the local loop
coupled with increasing use of optical switches and optical
processing
Use of wireless in access technology - New access &
Modulation codes
Ultra broad band services
Extensive use of spread spectrum and code division
multiple access techniques.
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Services planned / in existence are:
Virtual Private Networks. / PCS - PersonalCommunication Services
Call Collect Services / Desk top Video conferencing
Card Phone Services/ Tele-education/Telehealth/
TeleshoppingVideo Telephone / Interactive Video & Video on
demand
Multimedia transmission / reception /e-mail/e-
Governance/e-commerceGlobal positioning/timing system along with SATNAV
Digital TV, Direct TV to Home
MOST IMPORTANT - THE INTERNET & WORLD
WIDE WEB
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All these need either terrestrial or satellite channels to
serve the user. The present day scenario looks like:
Cable TV
Television
DVD
VideoCameraPrinter
PDA
Desktop PC
Cellular
Telephone
Fax
Pager
Internet
Cellular
Internet TV
Video on
Demand
Home Banking
Internet
Telephony
Network
Computing
Video
conferencing
Smart Card
Space
World
Wide
Web
Terrestrial
Credit Card
A FUTURE COMMUNICATION SCENARIO
AUDIO SYSTEM
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The situation changed considerably in eighties and the
communications requirements became really nerve-
racking. Imagine the transmission reception of signals
to satellites from:A ship pitching and rolling on the high seas
An aeroplane flying at a speed of >800 kms per
hour
An orbiting space vehicle/satellite with speeds >7to 8 kms per second
An aeroplane or a ship in distress
A mountaineer/A trekker/A forest guard/An
elephant/A tiger/A bird/A turtle/a dolphin
A man always on move / A motor vehicle.
If using satellites to communicate is a great marvel,
doing the same without stopping or even slowing down
is almost miracle.
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VARIOUS CONVENTIONAL SATELLITE
COMMUNICATION SERVICES:
Telephony/TV Broadcasting/Data reception anddistribution/Direct Television broadcasting/Disaster
warning/Continuous weather monitoring/Spacecraft
Vehicle Tracking and Commanding/ Intersatellite
links/ Mail /Internet/Data mining
Position (GPS) and time determination / Moving
motor vehicle tracking etc.
* The commercial communication satellite servicesare rapidly becoming a large & global business
increasing from $11 billion in 1992 to $20 billion in
1996 and $75 billion by year 2005. (Projections have
come down to $$66.5 billion due to iridium failureand overall slump in the market)
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Before one goes ahead with communication
satellites, it will be quite important & relevant
to talk about latest arrival on thecommunication technology scene : the
INTERNET & THE WEB. Internet the
new incarnation of mass
communication is becoming quitepopular. Internet the parasite which
has almost eaten away the host - the
telecom channels, is influencing our
every sphere of life.
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The next stage 3.0 has been denoted "The information
Super High Way". Internet 3.0 could provide
symmetrical, high bandwidth links that can
simultaneously carry telephone, video (Television) anddata. Ideally bandwidth could be at a maximum
capacity of the copper wire that link central offices &
homes at a minimum of 6-25 MBPS.
In assessing the societal implications of powerfulhistorical forces, it is essential to take the long view.
However, when events are developing as rapidly as they
are on the internet, it is meaningless to look out further
than 15 years.
The safest prediction is that by 2010 or 2015 the
Internet, as we know it, will no longer exist. There will
just be the Net a ubiquitous, broadband data dial-tone
provided by a cable telephone, wireless or satellite
operators.
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Teledesic, Skybridge, Cyber Star, Astrolink iPSTAR
etc., are planning to provide internet & multimedia
services through space. Clearly changes will have a big
impact on society.
How big according to The Economist, a conservative an
perceptive publication not normally known for
exaggeration, the impact is likely to be `ahead of thetelephone and television but behind the printing press
and the motorcar".
The point is that the Net is a phenomenon that cannot
be ignored. It is an agent of change in all sectors osociety.
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The changes won't occur in isolation, but they
will be going on simultaneously, resulting in
unpredictable, unanticipated synergy. In turn,
this will lead to truly profound changes in
society & the present technological paradigm.
To help all these & to spread the net at a faster
pace even to inaccessible & remote places
Satellite Communication plays a major role,
besides the conventional terrestrial links,
optical links etc., which cater to cities and
larger population bases owning to the
economics.
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Having talked about INTERNET let us come back to space
communications.
The most popular one is going to be :
MOBILE PERSONAL COMMUNICATIONS
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One may be forced to
say that the future
communication willbe dominated by theMOBILE PERSONAL
COMMUNICATION
SERVICES and the
overall system designwill be done around
the main dictating
factor: spacecraft
G/T independent o
orbital heights and
frequency.
Th d t ti hi h b i ll d
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The ground stations which are becoming smaller and
smaller day by day will be of pocket size calculator.
The size of the ground station & that of satellites have
gone a tremendous change over years.
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The satellites for mobile communication services could
be LEO/GEO/ICO. As of today the LEO (Low Earth
Orbiting) constellations have provided the services.
IRIDIUM SYSTEM
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Mobile Satellite Communications using LEO, MEO or Geo has
received a setback because of the commercial failure of Irridium
and Global Star. The failures were due to the fact that the
project was engineering led - rather than marketing led. Theastronomically high terminal & service cost as compared to
terrestrial based systems was another reason for its failures.
During the10 years of realization of the project the CELL
handset cost, airtime &size reduced considerably while no such
effort was made for iridium (handset cost $3000, airtime $3-9,
total no. of customers 15000). On engineering account the two
projects cannot be considered as failures. In spite of cellular
telephone & other mobile services, the two systems along with
Thuraya have shown their usefulness over others in Afghanistanand Iraq operations and also communications to inaccessible
places. INMARSAT has touched its 200000th customer very
recently. These figures should not make one think that there is
no future for MSS.
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Before commenting on any technology or the market it
is advisable to look on the s-curve
New technologies and markets are generally
characterized by an S- Shaped growth curve
STAGE 2 ----> Rapid growth driven by mass
adoption
STAGE 3 ---> Failing off with the adoption by
the most conservative population
STAGE 1 -->Emerging having slow growth
spurred by early adopters
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In the foreseeable future new equipments and
techniques will be used in satellite technology which
will extend and improve the possibilities of satellite
communications beyond our present imaginations.Some of these we discuss today:
The size of Geo satellite will continue to
increase . Incremental improvements are
foreseen in intelligent bus design whichtakes care of the spacecraft control traffic
control and particularly the thermal
control to allow the use of prime power
beyond 10 to 15 KWS.
Small GEOs for smaller capacity routes
will also be used (one may seriously start
thinking about I-2000 and even Met Sat
bus for Indian conditions).
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Greater Transmit
power and more
complex antennas onthe satellites will
make operations
possible with a large
number of very small
Earth stations.
DBS/DTH services
with 300 - 500
channels.The servicemay broadcast
multimedia &
internet .
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Phased array - orbit
re-configurable
antennas with digital
beam forming capable
of dynamically sharing
RF power, controlling
EIRPs and generating
large number of spotbeams will be used
extensively. This may
call for large
deployable antennas (>25 meter in diameter),
complex feed systems.
The similar systems
may be even needed
for ground networks.
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Efficient signal processors and switching equipment
will enable signal processing to be performed
onboard right down to operations similar to
switching in exchanges which will provide bettermesh connectivity. ATM switches onboard space
crafts may be used. Onboard multiplexing of digital
TV transmission may be done.
Networking technology for the seamless integration
of high data rate communication satellites &
terrestrial facilities.
Direct connections between satellites (Inter satellite
links) will shorten the transmission routes. The ISLs
could be in millimeter waves or even in optical
domain.
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The use of higher frequency bands (Ka band and V
band) & frequency reuse by multiple beams will
enlarge the available bandwidths and thus the
transmission capacity. Future even space laser
communication technique may be employed to
increase the data rates to giga bits.
Miniaturization of electronics will enhance the
launch capabilities & reduce the cost.
High speed two way INTERNET - through VSAT.
This avoids the installation of broad band access
through terrestrial network. It can provide upto
40 MBPS links.
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It was expected that the space based high speed
internet service would hit the services over $600million in 2001, reflecting triple digit growth rate.
Howevernon-start of some of the planned satellites
has brought this figure to ~ $400 million.
As of today internet is the greatest thing to happen
in the satellite industry; since some genius decided
he could deliver TV on cable. For many space
segment operators INTERNET is the biggestearner. As of today internet is going towards zero
tolerance for failure. The goal is more & more
critical services to NET.
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The LEO internet provider in pipe line are:
Skybridge (80 S/c - 4 S/C for 20 planes) 1496KMS,
Ku-Band 20 MBPS down & 2.5 MBPS up. Global
coverage
Teledesic
New ICO.
The GEO systems : Astrolink, Cyberstar,
Spaceway.
Non- starter
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The technology issues are: Bandwidth
availability.
Use of Ka & V-bands and their weather
dependence has to be examined. It should
follow TCP/IP standards.
It should be possible to integrate with land
mobile system GSM (TDMA), CDMA, the 3Gbased on wide band CDMA (W-CDMA).
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We have talked / heard / read that internet/IP
offers opportunities of convergence of data,video and voice on the same network. Most IPrelated ventures however, were badly hit by the
infamous Internet bubble in 2001. One of themost disappointing developments leveraging onconvergence of various technologies through IPand the power of vast geographical coverage of
satellite in the satellite market in the last 2years, is clearly the satellite IP multicast andcontent distribution market.
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There is no shortage of failed ventures and
nonstarters. Despite IPs promise of
convergence and cost efficiencies, loading
video on to core IP infrastructure networksis still taboo because of the BW hungry
nature of video transmission. The satellite
ISP backbone market, however is suffering.
The biggest threat is fibre.In spite of all these, broad band IP satellite
based services are going to grow up.ip-
STAR(launch 2004) & EUTELSATs European
based satellite broad band projectare going
ahead with their plans and developments.
Satellite broad band IP services are going to
grow up in the next couple of years
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The new breed of satellites will be agile, flexible,
intelligent & powerful. They will have digital
bandwidth. This makes the services they carry an
easy fit in the present digital networks with a specific
provider ground equipment. They will:
Switch & route high data rates instantaneously among
thousands of users.
Continuously change the antenna beam patterns/eirp
as traffic demands
Buffer and multiplex data
Null interference, providing a strong, clear signal &use of adaptic arrays & processing.
Cross link to other satellites (ISL: Optical or V-band)
Use of Soft radio
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The future satellites will be :
Small Geo - co-located at a single point. Suitablefor small transponder demands even suitable for
DTH-Ka Band
Large Geo - Suitable for multiple established
services/Ku & Ka Band Mini/micro/mono & pico satellites.
The satellite driven broadband system become more
popular because it provides the last mile solution whichis a great boon for developing countries.
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Satellites have innate advantage that make them an attractive
alternative or complement to terrestrial broadband circuits.
First is speed they can be built , launched and put into service
in as little as 12 to 24 months providing the last mileconnection. It also provides bandwidth on demand. User pays
for the time which he utilizes.
Although broad band satellites are considered to be poor
cousins of OFC - No country requires more than what satellitecannot give. Europe requirement is 450 Mbits/s and US bound
capacity is 3.5 Gbits/S.
Many times one feels that for the over capacity of the fibre one
has to pay while for space based links you pay for the time you
use.
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In my opinion SPACE COMMUNICATION SCENARIO will be:
The future Telecommunication spacecraft will be developed
from transmission in to Information Satellites (INFOSAT).
They will be given many of the properties of terrestrial
telephone exchanges and signal processing equipments and it
will be possible to integrate them directly into future global
networks.
They will thus permit immediate applications of many existingand future services. Because of their inherent built up
flexibility, these satellites will be able to support and speed up
the initial experimental phase of many new services before their
trial on terrestrial networks. These type of satellites will enablenew services to be tried out over a large area before being put in
to the market and optimally adapted to suit the most
appropriate transmission medium.
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The satellite platform will have multiple reconfigurable
antennas/transmitters with dynamic power sharing /
Receivers in various frequency ranges / large
reconfigurable switching matrices at baseband and at
RF level / intersatellite links permitting signals to be
exchanged between satellites according to changing
requirements / complex and efficient analog / optical /digital signal processors / New modulation technique
and multiple access techniques.
It will be sufficiently broadband systems & may haveeven optical space communication components.
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The satellites besides their autonomous control andpower generation equipment may have sensors to
observe the earths atmosphere and pass the data to an
appropriate station after processing. This will help to
deal with the situation like Orissa Cyclone. Such asystem will obviously have Geo synchronous spacecraft
with some orbiting satellites to take care of North/South
pole regions.
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Presently man is in a shrinking globe and also in
expanding universe with lots of technological surprises
for the technological pandits. We are becoming
increasing networked thereby our world is growingsmaller & bigger simultaneously. Space
Communication in all its forms will complement the
terrestrial technologies. Vision is always of one of hope
for human betterment.
OBP, ISL,Phased ArrayGP
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CONFUSION
CONVERGENCE and FUSION of
various Communication Technologies
Broad Band Satellite Links
Video Conferencing
DBS - 300 Channels Mobile
BroadbandIn
ternet
LifeTimeMovie
Network
OFC
CableT
V
Here
X A 0
GEO,MEO,LEOAda
ptiveA
rray
GPS
WAA
S,LAAS
SB
AS
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THANK YOU