Topic:- Satellite communication system

AN INTRODUCTION TO SATELLITE COMMUNICATION SYSTEMS

What exactly is a satellite?

• The word satellite originated from the Latin word “Satellite”- meaning an attendant, one who is constantly hovering around & attending to a “master” or big man.

• For our own purposes however a satellite is simply any body that moves around another (usually much larger) one in a mathematically predictable path called an orbit.

• A communication satellite is a microwave repeater station in space that is used for telecommunication , radio and television signals.

• The first man made satellite with radio transmitter was in 1957.

. There are about 750 satellite in the space, most of them are used for communication.

How 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 transmits the signals to the satellite. Up link frequency is the frequency at which Ground Station is communicating with Satellite.

* The satellite Transponder converts the signal and sends it down to the second earth station. This frequency is called a Downlink.

Consider the light bulb example:

The period T of a satellite is given as:

T2= 4 П2 .a3 (period depends only on semi major axis,a)

μ For a satellite in circular orbit around earth-

T2= 4 П2 .(R+h)3

μ Where , R= radius of earth, h= satellite altitude

Satellite period

Components of a satellite

How does a satellite stay in it’s orbit?

Sir. Johannes Keppler

Origin of planetary laws

Derived 3 laws based

upon his observations

of planetary motion.

Sir.Tycho Brahe

• Introduced precision into astronomical measurements.

• Mentor to Johannes Keppler

Kepler’s laws only describe the planetary motion without attempting to suggest any explanation as to why the motion takes place in that manner.

Newton’s Laws

Sir .Issac Newton

• Derived three laws of motion.

• Derived the Law of Universal Gravitation.

• Explained why Kepler’s laws worked.

Advantages of satellite over terrestrial communication :

* 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 satellites:

* 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.

How do we escape gravity & place an object in orbit?

• If an object is fired fast enough it should escape the earths pull.

• This is done through the use of Rocket Launchers

Applications

Positioning in orbit

Stability

Power

Communications

Harsh environment

Major problems for satellites

2. COMMUNICATIONSStormy space weather can damage Earth-

orbiting satellites such as those carrying TV and mobile phone signals.

During high levels of solar activity, satellites are bombarded with high energy particles. If the deeply penetrating electrons build up faster than the charges are able to dissipate out of the satellite material, a discharge can result that is capable of damaging the satellite electronics.

These processes can result loss of control and even satellite failure.

3. NAVIGATIONA Global Positioning System (GPS) receiver uses

radio signals from several orbiting satellites to determine the range, or distance, from each satellite, and determines from these ranges the actual position of the receiver.

The radio signals must pass through the ionosphere, the uppermost part of the Earth’s atmosphere, and in doing so are subjected to variations in the electron density structure of the ionosphere.

Changes in the electron density due to space weather activity can change the speed at which the radio waves travel introducing a “propagation delay” in the GPS signal. Changing propagation delays cause errors in the determination of the range.

An increase in space weather activity may cause widespread disruption to aircraft and ship navigation and emergency location systems that rely heavily on satellite navigation data.

http://en.wikipedia.org/wiki/Satellitehttp://www.isro.org/satellites/satelliteshome.aspx

http://www.isro.org/satellites/geostationary.aspx

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