Satellite Communication 1p1a2m

Presented By A.Bhanu Swetha 09/455.

•Satellite: A celestial body that orbits a planet

Why satellite communication? Microwave band of frequency is used High frequency waves travel in straight line Earth is curved Solution: satellite An earth station transmits the signal up to the

satellite-called the up-link and is transmitted on one frequency.  The satellite receives the signal and retransmits it on the down link which is on another frequency.

Overview What is satellite comm. Types of Satellite comm. Advantages Disadvantages Applications

Satellite Communication Communication is the transfer of message or

signals from transmitter at one point to another point i.e. receiver. If the above comm. is done with the help of satellite, it is said to be satellite comm. From the transmitter the signal which is basically a modulated microwaves is sent to the satellite. Then the satellite amplifies the signals and sent it back to the receiver’s antenna on the earth.

Block Diagram Of Satellite Communication

satellite transponders

Earth Transmitte r

Earth Receiver

Types of Satellite orbits Satellite Orbits  GEO  LEO  MEO  Molniya Orbit

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.

GEO (contd.) 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.

GEO (contd...) Disadvantages  A

GEO satellite’s distance also cause it to have a weak and time delay in the signal.  GEO satellites, centered above the equator, cannot broadcast signals to 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 . A network of LEO satellites is necessary for LEO satellites to be useful

LEO (contd…) Advantages  A

LEO satellite’s compared to GEO gives a better signal strength and less time delay.  A LEO satellite’s smaller area of coverage is less of a waste of bandwidth.

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 (Contd…) MEO

satellites are visible for much longer period than LEO satellites usually 2 to 8 hours. MEO satellites have a larger coverage area than LEO satellites.

Other Orbits Molniya Orbit Satellite  Molniya

Orbit is an elliptical orbit. The satellite remains in a nearly fixed position relative to earth for eight hours.  Useful in near polar regions.

Advantages of Satellite Communication 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.

Disadvantages of Satellite Communication 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.

Applications Service Types  Point to Point Communication  Satellite Television/Radio  Mobile service - Satellite Phones  Video Conference  National Defense  Direct PC