This document discusses communication satellites and their properties. Geosynchronous satellites orbit at the same rate as the Earth's rotation, maintaining a fixed position above the same location on Earth. They contain multiple transponders that receive and rebroadcast signals at different frequencies to avoid interference. New developments include very small aperture terminals and spot beams that allow multiple simultaneous transmissions to focused geographical areas. While fiber optics provide more bandwidth than all satellites launched, satellites remain advantageous for mobile communications, broadcasting, and situations where infrastructure is limited. Both terrestrial and satellite systems will likely continue competing on price as technologies advance.

1. Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft

2. ABOUT…..
 Communication Satellites have many
interesting properties that make them easy
and attractive for many applications.
 Can be thought of as a big microwave
repeater in the sky.
 Contains several transponders, each of which
listens to some portions of spectrum amplifies
the incoming signals and then rebroadcasts it
at another frequency to avoid interference…

3. GEOSYNCHRONOUS SATELLITES
 They are those satellites that travel at the same
direction as our earth moves and have the same time
period as earth(24 Hrs).
 A typical satellite has 12-20 transponders, each with a
36-50-MHz bandwidth. A 50-Mbps transponder can
be used to encode a 50-Mbps data streams and various
other combinations.
 In the earliest satellites the division of transponders
was static, by splitting the bandwidth into Fixed
Frequency Bands (FDM).
 But now TDM facility is also used due to its greater
flexibility…

4. CONTD….
 The first satellite had a single spatial beam that
illuminated the entire earth. Each satellite is
equipped with multiple transponders and
antennas.
 Each downward beam can be focused on a small
geographical area so that multiple upward and
downward transmissions can take place
simultaneously.
 These are called as Spot Beams and they are
elliptically shaped…

5. DEVELOPMENT…
 VSAT (Very Small Aperture Terminals) which
are low cost micro station is the new development
in the in the field of Communication Satellites.
These tiny terminals have miniature antennas.
 In many VSAT systems, the microstations do
not have enough power to communicate directly
with one another.
 For this they use hub with a large antenna. In
this mode either the sender or the receiver has a
large antenna and a powerful amplifier.
 The trade-off is a longer delay in return for
having cheaper end-user stations…..

6.  There are many properties that make the
communication satellites different from the
point-to point links.
 The large round trips introduces a
substantial delay.
 From the security and privacy point of view
satellites are a complete disaster.
 Encryption is essential when security is
required…

7. ADVANTAGES…
 Cost of transmitting a message is
independent of the distance traversed.
 A call across an ocean is same as a call across
a street.
 Have excellent error rates and can be
deployed almost instantly.
 This is a major consideration for many
military applications…

8. LOW-ORBIT SATELLITES
 For the first 30 years of satellite eras, low
orbit satellites were rarely used for
communication because they zip into and out
of view so quickly.
 Later in 1990 a plan was devised for the
above, as soon as a satellite went out of view
another would replace it.
 The Iridium system is an example.

9. IRIDIUM SYSTEM
 Basic goal:-
Provide worldwide telecommunications
service using hand held devices that
communicate directly with Iridium Satellites.
It provides voice, data, paging, fax and
navigation services all over the earth. It uses
ideas from cellular radios…

10. CONTD….
 Normally the cells are fixed, but the users are
mobile. Here each satellite has a substantial
number of spot beams that scan the earth as
the satellite moves.
 Thus both the cells and the users are mobile
in this system

11. CONTD….
 The projected cost for the end user is about 3
dollars/minutes.
 If this technique can provide universal service all
through the world for that price, it is unlikely
that project would die for lack of services.
 Business and other travelers who want to be in
touch all time can sign in even if they are in
undeveloped areas.
 This system can face stiff competitions from
PCS/PCN….

12. SATELLITES VS FIBERS
۩ It was all of a sudden that the terrestrial fiber
connections looked like the long time winner.
۩ Communication Satellites have some major
niche markets that the fiber does not and
sometimes cannot address…
First Niche
۩ A single fiber has more potential bandwidth than
all the satellites ever launched.
۩ The fibers that are now being installed are used
within the telephone system to handle many long
distance calls at once.

13. CONTD….
۩ With satellites, it is practical for the user to erect an antenna on the roof of the
building and completely bypassing the phone system.
Second Niche
۩ Is for mobile communications. Many people now a days want to communicate
while moving. Fiber link optics are of no use now. But Satellite links potentially
are…

14. CONTD…
Third Niche
۩ Situations in which broadcastings are essential. A
message sent by the satellites can be received by
thousands of stations at once.
۩ Broadcasting facility through the satellite system
is much cheaper than simulating a broadcast on
the ground…
Fourth Niche
۩ Communications in place with hostile or poor
terrain infrastructure.
۩ Launching one satellite was much more easier
than stringing thousands of undersea cables…

15. CONTD…
Fifth Niche
۩ Obtaining the right way for laying fiber is difficult or unduly expensive.
۩ When rapid deployment is critical, as in military communication systems in
time of wars, satellites win very easily…

16. CONCLUSIONS
 The main stream of communications for future use
will be terrestrial fiber optics combined with cellular
radios, but for some specialized uses satellites are
better.
 Although fiber optics offer more bandwidth it is
certainly possible that terrestrial and satellite
communications will compete belligerently on price.
 If advances in technology radically reduces the cost
of deploying the satellites or low orbit satellites catch
on, it is not certain that fibers win an all markets…

17. Shashwat Shriparv
dwivedishashwat@gmail.com
InfinitySoft