this presentation is about satellite communication which includes working of gps ,vsat ,frequency bands ,needs of communication satellite ,types of satellite ,working ,orbits ,elements involved in working ,transponder ,satellite control center ,satellite network

1. Satellite Communications
Ppt for Computer Networks

2. Topics of Presentation
How it
works
How it
works
Applications
Launching
How it
works
Frequency
Bands
Intro
Satellites
Types
VSAT
GPS

3. What are Communication Satellites?
• A satellite is an object that orbits another large
object like planet.
• A communication satellite is a station in space
that is used for telecommuncation, radio and
television signals.
• The first satellite with radio transmitter was in
1957.

4. Need for communication satellite.......
• Early 1950’s and 1960’s,satellite communication by
mettallized weather baloons..
•Moon as an artificial satellite.In 1954, the US Naval
Research Laboratory successfully transmitted the first
voice message.
•Disadvantage using moon as a
satellite….Communications via the Moon is limited by
simultaneous visibility of the Moon by both the transmit
and the receive stations
•For further progress,had to wait for an Artificial satellite.

5. Early Satellites
Syncom
• In October 1957, the first
artificial satellite Sputnik -I was
launched.
• 1963 Clark’s idea became a
reality when the first
geosynchronous satellite
SYNCOM was successfully
launched by NASA.
•India launched its first satellite
Aryabhatta on 19 April 1975

7. Types of Satellites
•In 1950’s both Active and Passive satellites were
used.
• The principle of communication by passive
satellite is based on the properties of scattering of
electromagnetic waves from different surface
areas.
•Thus an electromagnetic wave incident on a
passive satellite is scattered back towards the
earth and a receiving station can receive the
scattered wave.

8. Active replaces Passive
The disadvantages of passive satellites for
communications are:
• The large attenuation of the signal.
• Earth Stations required high power (10 kW) to
transmit signals strong enough to produce an
adequate return echo.
• Large Earth Stations with tracking facilities were
expensive.
• A global system would have required a large number
of passive satellites accessed randomly by different
users
• Control of satellites not possible from ground.

9. Active satellites
• In active satellites, which amplify and
retransmit the signal from the earth have
several advantages over the passive
satellites.
The advantages of active satellites are:
1.Require lower power earth station
2.Less costly
3.Not open to random use
4.Directly controlled by operators from ground.

10. How Does a Satellite Work?
• Consider the light bulb example:

12. Orbital Options
• A Geosynchronous satellite(GEO)
completes one revolution around the world
every 23 hrs and 56 minutes in order to
maintain continuous positioning above the
earth’s sub-satellite point on the equator.
• A Medium earth orbit
satellite(MEO) requires a constellation
of 10 to 18 satellites in order to maintain
constant coverage of the earth.
•A Low earth orbit satellites(LEO)
offers reduced signal loss since these
satellites are 20 to 40 times closer to the
earth in their orbits thus allowing for
smaller user terminals/antennas.

13. Geostationary orbits
• What are they?
Geostationary orbits is fixed position to an earth-based observer.
• When was the first use?
The first truly geostationary sateliite was the SYNCOM3 in 1964.
• Why they are important in communications?
- The antennas in the ground don’t need equipment to track the satellite.
- Lower cost & complexity.
• Disadvantages?
- Not always suitable for providing services at high latitudes.
- Molniya satellite was introduced as a solution.

14. Geostationary Orbit (GEO)
Characteristics of Geostationary(GEO) Orbit System
• User terminals do not have to track the satellite
• Only a few satellites can provide global coverage
• Maximum life-time (15 years or more)
• Above Van Allen Belt Radiation
• Often the lowest cost system and simplest in terms of
tracking and high speed switching.
Challenges of Geostationary(GEO) Orbit System
• Transmission latency or delay of 250 millisecond to
complete up/down link
• Satellite antennas must be of larger aperture size to
concentrate power and to create narrower beams for
frequency reuse
• Poor look angle elevations at higher latitudes

15. Medium Earth Orbit (MEO)
Characteristics of Medium-Earth Orbit system
• Less latency and delay than GEO (but greater than LEO)
• Improved look angle to ground receivers in higher latitudes
• Fewer satellites to deploy and operate and cheaper TTC&M
systems than LEO (but more expensive than with GEO)
• Longer in-orbit lifetime than LEO systems (but less than
GEO)
Challenges of Medium-Earth Orbit System
• More satellites to deploy than GEO (10 to 18 vs. 3 to 4)
• Ground antennas are generally more expensive and complex
because of the need to track satellites. Or, one must use
lower-gain, quasi-omni antennas.
• Increased exposure to Van Allen Belt radiation

16. Low Earth Orbit (LEO)
Characteristics of Low-Earth Orbit (LEO) Systems
• Low latency or transmission delay
• Higher look angle (especially in high-latitude
regions)
• Less path loss or beam spreading
• Easier to achieve high levels of frequency re-use
• Easier to operate to low-power/low-gain ground
antennas.
Challenges of Low-Earth Orbit (LEO) Systems
• Due to Larger number of satellites (50 to 70
satellites). Thus higher launch costs to deploy, build,
and operate.
• Harder to deploy, track and operate. There is
higher TTC&M costs even with cross links.
• Shorter in-orbit lifetime due to orbital degradation

17. Properties of Orbits

19. Satellite-Fiber Comparison
capability Fiber optic
cable systems
Geo satellite in
a global
system
Meo satellite in
a global
system
Leo satellite in
a global
system
Transmission
speed
10 Gbps-3.2
Terabits/second
Single sat
1Gbps-10Gbps
Single sat
0.5Gbps-5Gbps
Single sat
1Gbps-2Gbps
Quality of
service
10-11
-10-12
10 -6
-10-11
10-6
-10-11
10-2
-1091
Transmission
latency
25 to 50 ms 250 ms 100-150 ms 25-75 ms
System
availability w/o
backup
93 to 99.5% 99.8%(C-Ku
band)
99% (Ka band)
99.9%(C-Ku
band)
99% (Ka band)
99.5%(L-c-Ku
band)
99% (Ka band)
Broadcasting
capabilities
Low to Nil High Low Low
Multi-casting
capabilities
Low High High Medium
Trunking
capabilities
Very High High Medium Low

20. ELEMENTS OF SATELLITE COMMUNICATIONS
SYSTEM
•Space Segment
Satellite (transponders etc)
Means for launching satellite
Satellite control centre for station keeping of the satellite
•Ground Segment
Earth Stations
Rear Ward Communication links
User terminals and interfaces
Network control centre

21. Elements

22. Transponders
•The Transponder (short-for Transmitter-responder) is the
“BRAIN” of the satellite that provides connection between the
satellite’s Receive and Transmit antennas.
•Satellites can have 12 to 96 transponders plus spares,
depending on the size of the satellite.
•A transponder bandwidth can frequently be 36 MHz, 54 MHz,
or 72 MHz or it can be even wider.
•A transponders function is to
•Receive the signal, (Signal is one trillion times weaker then when
transmitted)
•Filter out noise,
•Shift the frequency to a down link frequency (to avoid interference
w/uplink)
•Amplify for retransmission to ground

23. Transponder

24. Satellite Power SystemsSatellite Power Systems
• Main source of power is solar cell panels - new solar cells
are increasingly efficient
• The solar cell system is backed up by battery system that
provides energy during solar eclipses and other periods of
outages.
• Typical power levels of 2 to 5 KWs for Fixed Satellite
Systems and 10 to 12 KWs for Mobile and Broadcast
Satellite Systems.
Batteries
• latest battery technology is represented by Lithium Ion
systems that can provide a greater power density for
longer periods of time and survive a greater depth of
discharge

25. Launching Satellites
• How does a satellite stay in it’s orbit?

26. Launching cntd…
The launch process can be divided into two
phases:
• The Launch Phase
- Satellite placed into the transfer orbit.
• The Orbit Injection Phase
- Satellite transferred from elliptical transfer orbit to
geosynchronous orbit.

27. Launch Vehicle
• Function-Place the satellite into the desired Orbit.
• Two types
Expandable
• Launch vehicles can be used only once.
• Most of the satellite are of this type.
Reusable
• Only one reusable launch vehicle available.

28. Satellite ejected from the cargo
compartment.
• The Space Shuttle
performs the functions
of the first two stages of
an expendable launch
vehicle.
• The satellite and third
stage assembly are
ejected after reaching
elevation of 150 to 200
miles.

29. Launching contd….
• By riding on a rocket or in the
cargo bay of the Space
Shuttle.
• At about 120 miles (193 km)
up, the rocket's navigational
system fires small rockets, just
enough to turn the launch
vehicle into a horizontal
position.
• Inertial guidance system
mechanism is used to
calculate adjustments to tilt the
rocket

30. Path followed by a satellite.

31. SATELLITE CONTROL CENTRE
Satellite Control Centre performs the following function:-
1. Tracking of the satellite
2. Receiving data
3. Determining Orbital parameters from Tracking and Ranging data
4. Commanding the Satellite for station keeping
5. Switching ON/OFF of different subsystems as per the operational
requirements
6. Thermal management of satellite.
7. Eclipse management of satellite
8. Communications subsystems configuration management.
9. Satellite Bus subsystems configuration management etc.

32. CONTROL ROOM

33. Satellite Frequencies
•There are specific frequency ranges used by commercial
satellites.
L-band (Mobile Satellite Services)
1.0 – 2.0 GHz
S-band (MSS, DARS – XM, Sirius)
1.55 – 3.9 GHz
C-band (FSS, VSAT)
3.7 – 6.2 GHz
X-Band (Military/Satellite Imagery)
8.0 – 12.0 GHz
Ku-band (FSS, DBS, VSAT)
11.7–14.5 GHz
Ka-band (FSS “broadband” and inter-satellite
links)
17.7 - 21.2GHz and 27.5 – 31 GHz

34. Frequency Efficiency
•The vital resource in satellite communications is spectrum.
•As the demand for satellite services has grown, the solution has
been;
•To space satellites closer together,
•Allocate new spectrum in higher bands,
•Make satellite transmissions more efficient so that more bits/Hz can be
transmitted, and
•To find ways to re-use allocated spectrum such as through geographic
separation into separated cells or beams or through polarization
separation
•Today the satellites systems transmit more efficiently than ever
before but interference is now a bigger problem - there is a basic
trade off;
•The higher the frequency the more spectrum that is available
•But, the higher the frequency the more problems with interference
from other users terrestrial, unlicensed, etc.

35. VSAT(VERY SMALL APERTURE TERMINALS)
What is VSAT???
• A new development in the communication satellite
world is the development of low-cost microstations,
sometimes called VSATs.
• These tiny terminals have 1-meter or smaller antennas
(versus 10 m for a standard GEO antenna) and can
put out about 1 watt of power.
• In many VSAT systems, the microstations do not have
enough power to communicate directly with one
another (via the satellite, of course). In many VSAT
systems, the microstations do not have enough power
to communicate directly with one another (via the
satellite, of course).

36. Transmission process of VSAT

37. Working of VSAT
The uplink is generally good for
19.2 kbps, but the downlink is
more often 512 kbps or more.
Direct broadcast satellite
television uses this technology
for one-way transmission.
In this mode of operation, 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.

38. What is GPS???
• The Global Positioning System (GPS)
is a space-based
global navigation satellite system that
provides reliable location and time
information in all weather and at all
times and anywhere on or near the
Earth when and where there is an
unobstructed line of sight to four or
more GPS satellites.

39. Global Positioning System

40. Structure
• GPS consists of three parts: the space
segment, the control segment, and the
user segment.
• The U.S. Air Force develops, maintains,
and operates the space and control
segments.
• GPS satellites broadcast signals from
space, which each GPS receiver uses to
calculate its three-dimensional location
(latitude, longitude, and altitude) plus the
current time.[1]

41. Structure contd……
• The space segment is composed of 24 to 32
satellites in medium Earth orbit and also includes the
boosters required to launch them into orbit.
• The control segment is composed of a master control
station, an alternate master control station, and a
host of dedicated and shared ground antennas and
monitor stations.
• The user segment is composed of hundreds of
thousands of U.S. and allied military users of the
secure GPS Precise Positioning Service, and tens of
millions of civil, commercial, and scientific users of
the Standard Positioning Service.

42. Satellite Network
Branch Offices
Corporate Data
Center/HQ
Network HUB
Corporate Offices
Gas Stations
Apartment
Buildings
Residential
Internet
Some large scale corporate networksSome large scale corporate networks
have as many as 10,000 nodeshave as many as 10,000 nodes

43. Applications
• Telephony
- Fixed points< earth station> Satellite> earth station> fixed points.
• Televesion & Radio
- e.g. Direct broadcast satellite (DBS) & Fixed service satellite (FFS).
• Mobile satellite technology
- Special antenna called mobile satellite antenna.
- No matter where or how this antenna is mounted on.

44. Applications
• Amateur radio
- Access to OSCAR satellite.
- Low earth orbits.
• Internet
- High Speed.
- Useful for far away places.
• Military
- Uses geostationary satellites.
- Example: The Defense Satellite Communications System (DSCS).

45. Disadvantages
• The antenna noise due to energy
- Unwanted radiation sources (stars – galaxies - …etc).
- Worsen S/N ratio.
• Atmosphere behaves as a resistive medium
- Supplies noise power to the antenna.
•Meteors
- Have to be programmed to avoid any rock or any harmful thing.
- Rules of orbits.
• Expensive
- only for governments or large organizations.

46. In Conclusion
Satellites remain the best utilizationSatellites remain the best utilization
used for communications due to theirused for communications due to their
speed and other advantagesspeed and other advantages
mentioned in this presentation.mentioned in this presentation.