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SATELLITE COMMUNICATIONS
UNIT-I : INTRODUCTION
Space: (Raja Rao)
 Space can be defined as a Place free from obstacles.
 Air Space: Region below 100 km from the earth’s surface.
 Outer space: This is also called cosmic space and falls between 100 km to 42,000 km. In
this region, aerodynamic lift is ineffective and is taken over by the centrifugal force.
 Deep Space: Regions beyond 42,000 km fall in this category which is not use for the
communication satellites.
Orbit: (Internet)
 An orbit is a regular, repeating path that one object in space takes around another one.
 An object in an orbit is called a satellite.
 A satellite can be natural, like Earth or the moon. Many planets have moons that orbit
them.
 A satellite can also be man-made, like the International Space Station.
Definition of satellite: (Internet)
 an artificial body placed in orbit round the earth or another planet in order to collect
information or for communication.
 A satellite is an object which has been sent into space in order to collect information or
to be part of a communications system. Satellites move continually round the Earth or
around another planet.
 It can also be defined as a heavy object which goes around another object in space due to
the effect of mutual gravitational forces.
Basics: How do Satellites Work: (PPT: Satellite Communications CSC 490: Wireless Networking Author Michael Charles)
 Two Stations on Earth want to communicate through radio broadcast but are too far
away to use conventional means.
 The two stations can use a satellite as a relay station for their communication
 One Earth Station sends a transmission to the satellite. This is called a Uplink.
 The satellite Transponder converts the signal and sends it down to the second earth
station. This is called a Downlink.
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Basics: Advantages of Satellites:

 The advantages of satellite communication over terrestrial communication are:
 The coverage area of a satellite greatly exceeds that of a terrestrial system.
 Transmission cost of a satellite is independent of the distance from the center of
the coverage area.
 Satellite to Satellite communication is very precise.
 Higher Bandwidths are available for use.
Basics: Disadvantages of Satellites:
 The disadvantages of satellite communication:
 Launching satellites into orbit is costly.
 Satellite bandwidth is gradually becoming used up.
There is a larger propagation delay in satellite communication than in terrestrial
communication.
Basics: How Satellites are used:
 Service Types:
 Fixed Service Satellites (FSS)
• Example: Point to Point Communication
 Broadcast Service Satellites (BSS)
• Example: Satellite Television/Radio
• Also called Direct Broadcast Service (DBS).
 Mobile Service Satellites (MSS)
• Example: Satellite Phones

Types of Satellites:
 Satellite Orbits
 GEO
 LEO
 MEO
 Molniya Orbit
 HAPs
 Frequency Bands
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Geostationary Earth Orbit (GEO):

 These satellites are in orbit 35,863 km above the earth’s surface along the equator.
 Objects in Geostationary orbit revolve around the earth at the same speed as the earth
rotates. This means GEO satellites remain in the same position relative to the surface of
earth.
 Advantages;
 A GEO satellite’s distance from earth gives it a large coverage area, almost a
fourth of the earth’s surface.
 GEO satellites have a 24 hour view of a particular area.
These factors make it ideal for satellite broadcast and other multipoint applications.
 Disadvantages:
 A GEO satellite’s distance also cause it to have both a comparatively weak signal
and a time delay in the signal, which is bad for point to point communication.
 GEO satellites, centered above the equator, have difficulty broadcasting signals to
near polar regions.
Low Earth Orbit (LEO):
 LEO satellites are much closer to the earth than GEO satellites, ranging from 500 to
1,500 km above the surface.
 LEO satellites don’t stay in fixed position relative to the surface, and are only visible for
15 to 20 minutes each pass.
 A network of LEO satellites is necessary for LEO satellites to be useful.
 Advantages:
 A LEO satellite’s proximity to earth compared to a GEO satellite gives it a better
signal strength and less of a time delay, which makes it better for point to point
communication.
 A LEO satellite’s smaller area of coverage is less of a waste of bandwidth.
 Disadvantages:
 A network of LEO satellites is needed, which can be costly
 LEO satellites have to compensate for Doppler shifts cause by their relative movement.
 Atmospheric drag effects LEO satellites, causing gradual orbital deterioration.
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Medium Earth Orbit (MEO):

 A MEO satellite is in orbit somewhere between 8,000 km and 18,000 km above the
earth’s surface.
 MEO satellites are similar to LEO satellites in functionality.
 MEO satellites are visible for much longer periods of time than LEO satellites, usually
between 2 to 8 hours.
 MEO satellites have a larger coverage area than LEO satellites.
 Advantage:
 A MEO satellite’s longer duration of visibility and wider footprint means fewer
satellites are needed in a MEO network than a LEO network.
 Disadvantage:
 A MEO satellite’s distance gives it a longer time delay and weaker signal than a
LEO satellite, though not as bad as a GEO satellite.
Other Orbits:
 Molniya Orbit Satellites
 Used by Russia for decades.
 Molniya Orbit is an elliptical orbit. The satellite remains in a nearly fixed position
relative to earth for eight hours.
 A series of three Molniya satellites can act like a GEO satellite.
 Useful in near polar regions.
 High Altitude Platform (HAP)
 One of the newest ideas in satellite communication.
 A blimp or plane around 20 km above the earth’s surface is used as a satellite.
 HAPs would have very small coverage area, but would have a comparatively
strong signal.
 Cheaper to put in position, but would require a lot of them in a network.
Frequency Bands: (PPT Michael Charles)
 Different kinds of satellites use different frequency bands.
 L–Band: 1 to 2 GHz, used by MSS
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 S-Band: 2 to 4 GHz, used by MSS, NASA, deep space research

 C-Band: 4 to 8 GHz, used by FSS
 X-Band: 8 to 12.5 GHz, used by FSS and in terrestrial imaging, ex: military and
meteorological satellites
 Ku-Band: 12.5 to 18 GHz: used by FSS and BSS (DBS)
 K-Band: 18 to 26.5 GHz: used by FSS and BSS
 Ka-Band: 26.5 to 40 GHz: used by FSS
 Satellites are specifically made for telecommunication purpose. They are used for mobile
applications such as communication to ships, vehicles, planes, hand-held terminals and
for TV and radio broadcasting.
 They are responsible for providing these services to an assigned region (area) on the
earth. The power and bandwidth of these satellites depend upon the preferred size of the
footprint, complexity of the traffic control protocol schemes and the cost of ground
stations.
 A satellite works most efficiently when the transmissions are focused with a desired
area. When the area is focused, then the emissions don’t go outside that designated area
and thus minimizing the interference to the other systems. This leads more efficient
spectrum usage.
 Satellite’s antenna patterns play an important role and must be designed to best cover the
designated geographical area (which is generally irregular in shape). Satellites should be
designed by keeping in mind its usability for short and long term effects throughout its
life time.
 The earth station should be in a position to control the satellite if it drifts from its orbit it
is subjected to any kind of drag from the external forces.
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Introduction : History of Satellites

• Communicating through a satellite first appeared in the short story titled “The Brick
Moon,” written by Edward Everett Hale and published in The Atlantic Monthly in 1869–
70.
• The first practical concept of satellite communication was proposed by Royal Air
Force officer Arthur C. Clarke in a paper titled “Extra-Terrestrial Relays: Can Rocket
Stations Give World-wide Radio Coverage?” published in the October 1945 issue
of Wireless World.
• In October 1957 communications stations started picking up a regular beeping noise
coming from space.
• The signals were coming from Russia's Sputnik 1, the world's first man-made satellite.
• It was January 1958, before a Jupiter rocket successfully launched Explorer 1, the first
American satellite.
• In July 1963 the Hughes Aircraft Corporation launched the experimental Syncom 2 for
NASA, the world's first geosynchronous communications satellite
It carried the first live two-way satellite call between heads of state when President John F.
Kennedy in Washington, D.C., telephoned Nigerian Prime Minister Abubaker Balewa in Africa.
• The third Syncom satellite transmitted live television coverage of the 1964 Olympic
Games from Tokyo.
• The world's first commercial communications satellite was Early Bird, built for the
Communications Satellite Corporation (COMSAT) by Hughes.
• It was launched on April 6, 1965, and placed in commercial service after moving into
geosynchronous orbit 36,000 Km above the equator.
• That meant it was always on station to provide line of sight communications between
Europe and North America.
Early Bird didn't have a battery - and worked only when its solar panels were exposed to the
sun.
• The launch of the Intelsat 3 satellites in 1969 created a global TV and speech
communications network that spanned the Atlantic, Pacific and Indian Oceans.
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• The introduction of multiple-beam antennas in the 1980s brought new improvements in

efficiency, as a satellite's power could now be concentrated on small regions of the Earth,
making possible smaller-aperture (coverage area), lower-cost ground stations.
• The Capacity (the number of simultaneous television and speech channels carried) grew
as well.
Introduction : How Satellites Work
1. A Earth Station sends message in GHz range. (Uplink)
2. Satellite Receive and retransmit signals back. (Downlink)
3. Other Earth Stations receive message in useful strength area. (Footprint)

Advantages of Satellite communication

• Satellite links are unaffected by the propagation variations that interfere with HF radio.
• Free from the high attenuation of wire or cable facilities
• Capable of spanning long distances.
• The numerous repeater stations required for line-of-sight or troposcatter links are no longer needed.
• They furnish the reliability and flexibility of service that is needed to support a military operation.
• The system is capable of handling thousands of communications channels.
• Frequencies are not dependent upon reflection or refraction and are affected only slightly by
atmospheric phenomena.
• Destruction of a single communication satellite would be quite difficult and expensive.
• A high degree of freedom from jamming.
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Disadvantage of satellite communication

• With the Satellite in position the communication path between the terrestrial transmitter and receiver is
approximately 75000 km long.
• There is a delay of 0.25 sec between the transmission and reception of a signal because the velocity of
electromagnetic wave is 3* 10^5 Km/second.
• The time delay reduces the efficiency of satellite in data transmission and long file transfer, which
carried out over the satellites.
• Over-crowding of available bandwidth due to low antenna gains is occurred.
• High atmosphere losses above 30 GHz limit the carrier frequency.

Services provided by satellites

FREQUENCY ALLOCATION FOR SATELLITE

 Allocation of frequencies to satellite services s a complicated process which requires
international coordination and planning. This is done as per the International
Telecommunication Union (ITU). To implement this frequency planning, the world is
divided into three regions:
 Region1: Europe, Africa and Mongolia
 Region 2: North and South America and Greenland
 Region 3: Asia (excluding region 1 areas), Australia and south-west Pacific.
 Within these regions, he frequency bands are allocated to various satellite services. Some
of them are listed below.
 Fixed satellite service: Provides Links for existing Telephone Networks Used for
transmitting television signals to cable companies
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 Broadcasting satellite service: Provides Direct Broadcast to homes. E.g. Live Cricket
matches etc
 Mobile satellite services: This includes services for:
Land Mobile, Maritime Mobile, Aeronautical mobile

 Navigational satellite services : Include Global Positioning systems

 Meteorological satellite services: They are often used to perform Search and Rescue
service
o Below are the frequencies allocated to these satellites: Frequency Band (GHZ)
Designations:
 VHF: 01-0.3
 UHF: 0.3-1.0
 L-band: 1.0-2.0
 S-band: 2.0-4.0
 C-band: 4.0-8.0
 X-band: 8.0-12.0
 Ku-band: 12.0-18.0 (Ku is Under K Band)
 Ka-band: 18.0-27.0 (Ka is Above K Band)
 V-band: 40.0-75.0
 W-band: 75-110
 Mm-band: 110-300
 μm-band: 300-3000
o Based on the satellite service, following are the frequencies allocated to the
satellites:
Frequency Band (GHZ) Designations:
 VHF: 01-0.3 ---Mobile & Navigational Satellite Services
 L-band: 1.0-2.0 --- Mobile & Navigational Satellite Services
 C-band: 4.0-8.0 --- Fixed Satellite Service
 Ku-band: 12.0-18.0 --- Direct Broadcast Satellite Services
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Orbits : Low-Earth-Orbit (LEO)

• Altitude (375-1000 miles)
• 0.8 GHz – 30 GHz range
• Revolution time: 90 min - 3 hours.
• Advantages:
• Reduces transmission delay
• Small, low-cost
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• Eliminates need for bulky receiving equipment.

• Handles Broad band data
• Disadvantages:
• Smaller coverage area.
• Shorter life span (5-8 yrs.) than GEOs (10 yrs).
• Subdivisions: Little, Big, and Mega (Super) LEOs.
• Application : Vehicle tracking, environmental monitoring and two-way data
communication. Used for short, narrowband communications

Middle-Earth-Orbiting (MEO)
• MEOs orbits between the altitudes of 5,600 and 9,500 miles.
• These orbits are primarily reserved for communications satellites that cover the North and
South Pole.
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Geosynchronous-Earth-Orbit (GEO)
• Orbit is synchronous with the earths rotation.
• From the ground the satellite appears fixed.
• Altitude is about 36000 km.
• Coverage to 40% of planet per satellite.

Polar Orbiting Satellites

• Orbit the earth to cover the north and south polar regions.
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Features offered by Satellite Communications

1. Large areas of the earth are visible from the Satellite, thus the satellite can form the star
point of a communications net linking together many users simultaneously, users who
may be widely separated geographically.
2. Provide communications links to remote communities.
3. Remote sensing, detection of pollution, weather conditions, search and rescue operations.

APPLICATIONS OF SATELLITES
1) Weather Forecasting: Certain satellites are specifically designed to monitor the climatic
conditions of earth. They continuously monitor the assigned areas of earth and predict the
weather conditions of that region. This is done by taking images of earth from the
satellite. These images are transferred using assigned radio frequency to the earth station.
(Earth Station: it’s a radio station located on the earth and used for relaying signals from
satellites.) These satellites are exceptionally useful in predicting disasters like hurricanes,
and monitor the changes in the Earth's vegetation, sea state, ocean color, and ice fields.
2) Radio and TV Broadcast: These dedicated satellites are responsible for making 100s of
channels across the globe available for everyone. They are also responsible for
broadcasting live matches, news, world-wide radio services. These satellites require a 30-
40 cm sized dish to make these channels available globally.
3) Military Satellites: These satellites are often used for gathering intelligence, as a
communications satellite used for military purposes, or as a military weapon. A satellite
by itself is neither military nor civil. It is the kind of payload it carries that enables one to
arrive at a decision regarding its military or civilian character.
4) Navigation Satellites: The system allows for precise localization world-wide, and with
some additional techniques, the precision is in the range of some meters. Ships and
aircraft rely on GPS as an addition to traditional navigation systems. Many vehicles come
with installed GPS receivers. This system is also used, e.g., for fleet management of
trucks or for vehicle localization in case of theft.
5) Global Telephone: One of the first applications of satellites for communication was the
establishment of international telephone backbones. Instead of using cables it was
sometimes faster to launch a new satellite. But, fiber optic cables are still replacing
satellite communication across long distance as in fiber optic cable, light is used instead
of radio frequency, hence making the communication much faster (and of course,
reducing the delay caused due to the amount of distance a signal needs to travel before
reaching the destination.
Using satellites, to typically reach a distance approximately 10,000 kms away, the
signal needs to travel almost 72,000 kms, that is, sending data from ground to satellite
and (mostly) from satellite to another location on earth. This cause’s substantial amount
of delay and this delay becomes more prominent for users during voice calls.
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6) Connecting Remote Areas: Due to their geographical location many places all over the
world do not have direct wired connection to the telephone network or the internet (e.g.,
researchers on Antarctica) or because of the current state of the infrastructure of a
country. Here the satellite provides a complete coverage and (generally) there is one
satellite always present across a horizon.
7) Global Mobile Communication: The basic purpose of satellites for mobile
communication is to extend the area of coverage. Cellular phone systems, such as AMPS
and GSM (and their successors) do not cover all parts of a country. Areas that are not
covered usually have low population where it is too expensive to install a base station.
With the integration of satellite communication, however, the mobile phone can switch to
satellites offering world-wide connectivity to a customer. Satellites cover a certain area
on the earth. This area is termed as a „footprint‟ of that satellite. Within the footprint,
communication with that satellite is possible for mobile users. These users communicate
using a Mobile-User-Link (MUL). The base-stations communicate with satellites using a
Gateway-Link (GWL). Sometimes it becomes necessary for satellite to create a
communication link between users belonging to two different footprints. Here the
satellites send signals to each other and this is done using Inter-Satellite-Link (ISL).
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