Satellite Communication

1. BASIC PRINCIPLE
OF SATELLITE
COMMUNICATION
ENG : AHMED AYMAN FAHMY

2. AGENDA
• What is satellite?
• Basic satellite system elements
• How satellite work?
• Satellite configurations
• Link frequency allocations
• Classification of satellite orbits

3. WHAT IS
SATELLITE?
• Satellite is an artificial body placed in
orbit around the earth to collect
information or for communication.

4. BASIC SATELLITE SYSTEM ELEMENTS
• The satellite communications are
compromised of two major elements
The satellite
Ground station

5. HOW SATELLITE WORK?
• Uplink : Earth station sends signal
to the satellite in GHz range.
• Downlink : satellite retransmit the
signal back to the earth.

6. GROUND STATION
• Collection of equipment which located on the earth surface to
perform communication with the satellite.
Simplest : satellite TV reception.
Complex : terminal station used for international
communication network.

7. SPACE SEGMENT
• The main parts in the space segment are :
The payload : Transponders , Antennas
Bus : Physical platform , Remote control

8. PAYLOAD
• It is all the equipment's which the satellite needs to do its job like camera,
antennas, radar and electronic circuits.
• The payload is different for every satellite
Weather satellite includes camera to take picture for the cloud formations.
Communication satellite includes large antennas to transmit TV or telephone
signal to the Earth.

9. BUS
• Consists of all the subsystems
which permit the payload to
operate :
• Electric power supply
• Temperature control
• Attitude and orbit control
• Propulsion equipment
• Tracking, telemetry and
command (TT & C) equipment

10. SATELLITE CONFIGURATIONS
• Point to Point
Signals transmitted from a
single station in one part of the
world to another individual
station

11. SATELLITE CONFIGURATIONS
• Point to Multi point
Signal transmits from one
station to an unlimited number
of independent receiving
stations (e.g. Satellite TV
broadcasting)
• Multi point to point
From many individual stations
to a single controlling station
(e.g. Maritime satellite)

12. LINK FREQUENCY ALLOCATIONS
• 4/6-GHz band
• Uplink: 5.925 to 6.425 GHz
• Downlink: 3.7 to 4.2 GHz
• 12/14 GHz band
• Uplink: 14 to 14.5 GHz
• Downlink: 11.7 to 12.2 GHz
• 20/30 GHz band
• Uplink: 27.5 to 30 GHz
• Downlink: 17.7 to 20.2 GHz

13. LINK FREQUENCY ALLOCATIONS
• Interference
• Satellites using the same frequency bands can affect
one another if they are closely spaced
• Limit on distance between satellites
• Angular displacement measured from the earth
• A 4o spacing required in 4/6-GHz band
• A 3o spacing required in 12/14-GHz band

14. CLASSIFICATION OF SATELLITE ORBITS
• Orbit : the path which satellite follows in its
rotation
Physical Shape
Circular with center at the earth center
Elliptical with one Foci at the earth center

15. CLASSIFICATION OF SATELLITE ORBITS (CONT.)
Angle of inclination : Angle between
the equatorial plane of the earth and the
orbital plane of the satellite
Equatorial orbit above the earth equator
Polar orbit passes over both poles
Other orbits referred to inclined orbits

16. CLASSIFICATION OF SATELLITE ORBITS (CONT.)
Altitude of satellites
Low Earth Orbit (LEO)
Medium Earth Orbit (MEO)
Geostationary orbit (GEO)

17. LOW EARTH ORBIT (LEO)
• Altitude : 500 – 1500 km
• Revolution time : 90 min – 3 hours
• Characteristics
o Reduce transmission delay
o Smaller footprints, better frequency reuse
o Stronger signal can be received
o More handovers necessary from one satellite to
another
o More satellites necessary for global coverage
o More complex systems due to moving satellites
o Shorter life span
• Subdivisions : Little, Big, Mega (Super) LEO.

18. MEDIUM EARTH ORBIT (MEO)
• Altitude : 5000-12,000 km
• Revolution time : 6 hours
• Diameter coverage : 10,000 – 15,000 km
• Round Trip signal propagation delay about 50 ms
• These orbits are reserved for communication satellites that covers north and south poles.
• Generally inclined orbit
• MEO are placed in Elliptical Orbit.
• EX : Global positioning system (GPS)

19. GEOSTATIONARY EARTH ORBIT (GEO)
• Altitude : 36,000 km
• Life time : 10 – 15 years
• Fixed antenna positions, no adjusting necessary
• Easy for earth stations to track satellite
• Large footprint
• Good for broadcast coverage
• Bad for point-to-point coverage: waste of
spectrum
• High transmit power needed
• High latency due to long distance (approx. 275 ms)