Zakia Sultana Components A microwave repeater in the sky consisting of transmitter receiver amplifier regenerator mux demux antenna and so on Space segment The transponder Earth segment ID: 796979
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Slide1
Satellite Communication
Kazi
Zakia
Sultana
Slide2Components
A microwave repeater in the sky consisting of transmitter, receiver, amplifier, regenerator,
mux
,
demux
, antenna, and so on.
Space segment
The transponder
Earth segment
The Ground Station
Transmitting station
Receiving station
An interface between space and earth segment for transmission and reception of terrestrial communication traffic
Slide3History
In 1962, the American telecommunications giant AT&T launched the world's first true communications satellite, called Telstar.
Since then, countless communications satellites have been placed into earth orbit, and the technology being applied to them is forever growing in sophistication.
Slide4How do Satellites Work
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
.
Slide5Basics:
Advantages:
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
.
Disadvantages:
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.
Slide6Kepler’s Law
The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus. (The Law of Ellipses) (Figure 14-1 a)
An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. (The Law of Equal Areas) (Figure 14-1 b)
The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. (The Law of Harmonies)
Slide7Slide8Third Law
Planet
Period
(s)
Average
Dist. (m)
T
2
/R
3
(s
2
/m
3
)
Earth
3.156 x 10
7
s
1.4957 x 10
11
2.977 x 10
-19
Mars
5.93 x 10
7
s
2.278 x 10
11
2.975 x 10
-19
Slide9ProGrade
Orbit
Satellite orbits at the same direction of the earth’s and at more angular speed than earth’s.
Retrograde Orbit
Satellite orbits at the opposite direction of the earth’s and at less angular speed than earth’s.
Slide10Types of Satellites
Satellite Orbits
GEO
LEO
MEO
Slide11Geostationary 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.
Slide12Advantages
A GEO satellite’s distance from earth gives it a large coverage area, almost a fourth of the earth’s surface.
No expensive tracking equipment is required
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
Require higher transmit power and sensitive receivers
High precision
spacemanship
is required to place
Slide13Low 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.
Slide14LEO (cont.)
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.
Disadvantages
Relatively costly
Atmospheric drag effects LEO satellites, causing gradual orbital deterioration.
Slide15Medium 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.
Slide16MEO (cont.)
Advantage
A MEO satellite’s longer duration of visibility
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.
Slide17Several Terms
Ascending Node
Descending Node
Line of Nodes
Orbits
Inclined
Equatorial
Angle of inclination is 0
No ascending or descending node
No line of nodes
Polar
Angle of inclination is 90
100% coverage area
Slide18Slide19Basics: Factors in satellite communication
Elevation Angle: The angle of the horizontal of the earth surface to the center line of the satellite transmission beam.
This effects the satellites coverage area. Ideally, you want a elevation angle of 0 degrees, so the transmission beam reaches the horizon visible to the satellite in all directions.
However, because of environmental factors like objects blocking the transmission, atmospheric attenuation, and the earth electrical background noise, there is a minimum elevation angle of earth stations.
Coverage Angle: A measure of the portion of the earth surface visible to a satellite taking the minimum elevation angle into account.
Slide20Geosynchronous Satellites
No special antenna tracking equipment is
necessary
Completes one revolution around the earth in 24 hours
Orbits are circular, so speed of rotation is constant throughout the orbit
Follow equatorial orbit, angle of inclination must be 0
Same angular speed and same direction as that of the earth
Orbital Velocity