satellite system

1. Class Work-8
Topic Name : Satellite System
Course Title:Computer Networks Theory
Course Code: CSE-317
Submitted To
Pranab Bandhu Nath
Senior Lecturer
Department Of CSE
City University
Submitted By
Khondoker Sadia
Id:1834902542
Semester:8th
Batch:49th

2. Satellite System
An artificial satellite is an object that people have made and launched into orbit using rockets. A
communications satellite is an artificial satellite that relays and amplifies radio
telecommunication signals via a transponder; it creates a communication channel between a
source transmitter and a receiver at different locations on Earth. Most communications satellites
are in geostationary orbit 22,236 miles (35,785 km) above the equator, so that the satellite
appears stationary at the same point in the sky; therefore the satellite dish antennas of ground
stations can be aimed permanently at that spot and do not have to move to track the satellite.
Approximately 2,000 artificial satellites orbiting Earth relay analog and digital signals carrying
voice, video, and data to and from one or many locations worldwide.
Development of satellite communication
• The idea of communicating through a satellite first appeared in the short story titled “The
Brick Moon,” written by the American clergyman and author Edward Everett Hale and
published in The Atlantic Monthly in 1869–70.
• The first practical concept of satellite communication was proposed by 27-year-old 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.
• The first artificial satellite, Sputnik 1, was launched successfully by the Soviet Union on
October 4, 1957.
• The first satellite to relay voice signals was launched by the U.S. government’s Project
SCORE (Signal Communication by Orbiting Relay Equipment) from Cape Canaveral,
Florida, on December 19, 1958.
• American engineers John Pierce of American Telephone and Telegraph Company’s
(AT&T’s) Bell Laboratories and Harold Rosen of Hughes Aircraft Company developed key
technologies in the 1950s and ’60s that made commercial communication satellites possible.
• NASA’s first project was the Echo 1 satellite that was developed in coordination with AT&T
’s Bell Labs. Pierce led a team at Bell Labs that developed the Echo 1 satellite, which was
launched on August 12, 1960
• Echo 2, managed by NASA’s Goddard Space Flight Center in Beltsville, Maryland, was
launched on January 25, 1964.
• Pierce’s team at Bell Labs also developed Telstar 1, the first active communications satellite
capable of two-way communications. Telstar 1 was launched into low Earth orbit on July 10,
1962, by a Delta rocket.
• Rosen’s team at Hughes Aircraft attempted to place the first satellite in geostationary orbit,
Syncom 1, on February 14, 1963. Syncom 2, the first satellite in a geosynchronous orbit (an

3. orbit that has a period of 24 hours but is inclined to the Equator), on July 26, 1963, and
Syncom 3, the first satellite in geostationary orbit, on August 19, 1964. Syncom 3 broadcast
the 1964 Olympic Games from Tokyo, Japan, to the United States, the first major sporting
event broadcast via satellite.
• On April 6, 1965, the first Intelsat satellite, Early Bird (also called Intelsat 1), was launched;
it was designed and built by Rosen’s team at Hughes Aircraft Company. Early Bird was the
first operational commercial satellite providing regular telecommunications and broadcasting
services between North America and Europe.
Earth-Satellite Parameters
Orbit
• An orbit is the curved path that an object in space (such as a star, planet, moon, asteroid or
spacecraft) takes around another object due to gravity.
• The orbits of satellite could be elliptical or circular. Rotation time depends on the distance
between the satellite and the earth. For satellites following circular orbits, applying Newton’s
gravitational law:
Fg (attractive force) = mg (R/r)2
Fc (centrifugal force) = mrω2
ω = 2πf
Where, m= mass of the satellite
g= gravitational acceleration (9.81 m/s2)
R= radius of the earth (6,370 kms)
r= distance of the satellite to the center of earth
ω = angular velocity of satellite
f = rotational frequency
Elevation and Footprint
• The area inside the circle is considered to be an isoflux area and this constant intensity area is
taken as the footprint of the beam. A satellite consists of several illuminated beams. These
beams can be seen as cells of the conventional wireless system.
• Angle between center of satellite beam and surface of the earth is called elevation. Elevation
needed to at least communicate with the satellite is Minimal elevation. The elevation angle
between the satellite beam and the surface of earth has an impact on the illuminated area
(footprint).
Different Frequency Bands
The satellites operate in different frequencies for the uplink and the downlink:

4. Band Uplink (GHz) Downlink (GHz)
C 3.7-4.2 5.925-6.425
LIS 1.610-1.625 2.483-2.50
Ka 17.7-21.7 27.5-30.5
Ku 11.7-12.2 14.0-14.5
• C band frequencies have been used in the first-generation satellites and has become
overcrowded because of terrestrial microwave networks employing these frequencies.
• Ku and Ka bands are becoming more popular, even though they suffer from higher
attenuation due to rain.
Characteristics of Satellite Systems
• Satellites weigh around 2,500 kgs.
• The GEO satellites are at an altitude of 35,768 kms which orbit in equatorial plane with 0
degree inclination.
• They complete exactly one rotation per day.
• The antennas are at fixed positions and use an uplink band of 1,634.5-1,660.5 MHz and
downlink in the range of 1,530-1,559 MHz.
• Ku band frequencies (11 GHz and 13 GHz) are employed for connection between the BS and
the satellites.
• A satellite typically has a large footprint – 34% of earth’s surfaceis covered. Therefore it is
difficult to reuse frequencies.
• There is a high latency (about 275 ms) due to global coverage of mobile phones.
• LEO satellites are divided into little and big satellites.
• Little LEO satellites are smaller in size, in the frequency range 148-150.05 MHz (uplink) and
137-138 MHz (downlink).They support only low bit rates (1 kb/s) for two way messaging.
• Big LEO satellites have adequate power and bandwidth to provide various global mobile
services like data transmission, paging etc.
• Big LEO satellites transmit in the frequency range of 1,610- 1,626.5 MHz (uplink) and
2,483.5-2,500 MHz (downlink).
• It orbits around 500-1,500 kms above the earth’s surface.
• The latency is around 5-10 ms and the satellite is visible for 10-40 min
Application Areas of Satellite System

5. Traditionally
• Meteorological satellites
• Radio and TV broadcast satellites
• Military satellites
• Satellites for navigation and localization (e.g GPS)
Telecommunications
• Global telephone connections
• Backbone for global networks
• Connections for communication in remote places
• Global mobile communication
How satellites work
A satellite is basically a self-contained communications system with the ability to receive signals
from Earth and to retransmit those signals back with the use of a transponder—an integrated
receiver and transmitter of radio signals. A satellite has to withstand the shock of being
accelerated during launch up to the orbital velocity of 28,100 km (17,500 miles) an hour and a
hostile space environment where it can be subject to radiation and extreme temperatures for its
projected operational life, which can last up to 20 years. In addition, satellites have to be light, as
the cost of launching a satellite is quite expensive and based on weight. To meet these
challenges, satellites must be small and made of lightweight and durable materials. They must
operate at a very high reliability of more than 99.9 percent in the vacuum of space with no
prospect of maintenance or repair.
The main components of a satellite consist of the communications system, which includes the
antennas and transponders that receive and retransmit signals, the power system, which includes
the solar panels that provide power, and the propulsion system, which includes the rockets that
propel the satellite.
A satellite in orbit has to operate continuously over its entire life span. It needs internal power to
be able to operate its electronic systems and communications payload. The main source of power
is sunlight, which is harnessed by the satellite’s solar panels. A satellite also has batteries on
board to provide power when the Sun is blocked by Earth. The batteries are recharged by the
excess current generated by the solar panels when there is sunlight.
Satellites operate in extreme temperatures from −150 °C (−238 °F) to 150 °C (300 °F) and may
be subject to radiation in space. Satellite components that can be exposed to radiation are
shielded with aluminum and other radiation-resistant material.

6. The tracking telemetry and control (TT&C) system of a satellite is a two-way communication
link between the satellite and TT&C on the ground. This allows a ground station to track a
satellite’s position and control the satellite’s propulsion, thermal, and other systems. It can also
monitor the temperature, electrical voltages, and other important parameters of a satellite.
Classification of Satellites
The commonly used altitude classifications of geocentric orbit satellites are:
1. Geostationary orbit (GEO)
2. Low Earth orbit (LEO)
3. Medium Earth orbit (MEO)
4. Highly Elliptical orbit (HEO)
1. GEO satellites are positioned 35,786 km (22,236 miles) above Earth, where they complete
one orbit in 24 hours and thus remain fixed over one spot. They circle Earth above the equator
from west to east following Earth’s rotation.
Advantages
• Few satellites and few earth stations required for quasi-global coverage Antenna pointing
is trivial
• Tracking antenna not required from a fixed location
• Terminals don’t need to do a handover between satellites unless the terminals move out
of a footprint
Disadvantages
• Can’t cover polar regions
• High latency
• Requires relatively large high-gain (typically parabolic) antennas to achieve meaningful
data rates
2. LEO satellites are positioned at an altitude between 160 km and 1,600 km (100 and 1,000
miles) above Earth. Unlike satellites in GEO that must always orbit along Earth’s equator, LEO
satellites do not always have to follow a particular path around Earth in the same way.
Advantages
• As it is near to the earth, LEO satellites provide better signal strength
• Very low latency

7. • High data rates even with low price equipment.
• Truly global coverage achievable with polar orbits
Disadvantages
• Terminal “handover” between satellites an absolute necessity for unbroken connectivity,
which for directional antennas means two antennas required for one always to be online
• Great number of satellites required
• Requires either a large number of earth stations, or a complex cross-link between
satellites to ensure users on every satellite has a data path to the Internet/other intended
target network on the ground
• Antenna pointing with directional antennas non-trivial
• Directional antennas must be of the tracking type
3. MEO satellites operate from 10,000 to 20,000 km (6,300 to 12,500 miles) from Earth. It is
very commonly used by navigation satellites.
Advantages
• Latency is typically lower than GEO,
• Data rates for a given antenna size is higher than GEO
• As they are in higher altitude fewer satellites recquired than LEO
Disadvantages
• More transmission power is required due to higher altitude
• The system is more expensive compare to LEO.
• Multiple MEO satellites are needed to cover a region continuously
4. HEO orbit is a geocentric orbit with an altitude entirely above that of a geosynchronous orbit
(35,786 kilometers (22,236 mi)). The orbital periods of such orbits are greater than 24 hours.
Advantages
• Not limited to equatorial orbits like the geostationary orbit and the resulting lack of high
latitude and polar coverage.
• Faces less exposure to atmospheric drag
• Coverage and path is smaller on one side and larger on the other
Disadvantages
• Position from a point on the Earth does not remain the same
• High latency on one side of earth

8. • High costs of manufacturing and launching a satellite into this orbit.
The future of satellite communication
In a relatively short span of time, satellite technology has developed from the experimental
(Sputnik in 1957) to the sophisticated and powerful. Mega-constellations of thousands of
satellites designed to bring Internet access to anywhere on Earth are in development. Future
communication satellites will have more onboard processing capabilities, more power, and
larger-aperture antennas that will enable satellites to handle more bandwidth. Further
improvements in satellites’ propulsion and power systems will increase their service life to 20–
30 years from the current 10–15 years. In addition, other technical innovations such as low-cost
reusable launch vehicles are in development. With increasing video, voice, and data traffic
requiring larger amounts of bandwidth, there is no dearth of emerging applications that will drive
demand for the satellite services in the years to come. The demand for more bandwidth, coupled
with the continuing innovation and development of satellite technology, will ensure the long-
term viability of the commercial satellite industry well into the 21st century.
References
[1] https://www.britannica.com/technology/satellite-communication/How-satellites-work
[2] http://faculty.csie.ntust.edu.tw/~hwferng/file_dir/MblCpt03/Chapt-11
[3] https://www.esa.int/Enabling_Support/Space_Transportation/Types_of_orbits