Mumbai University > Computer Engineering > Sem6 > Mobile Communication and Computing

Marks: 5M

Year: Dec 2015

• A satellite is an object that orbits or revolves around another subject.

• Man-made satellites are highly specialized wireless receiver transmitters that are launched by a rocket and placed in orbit around the earth.

• Unlike conventional terrestrial systems, the satellite systems have its transmitter based in sky and not on ground.

• The transmitter consists of a

  • Ground based part called Uplink

  • Satellite based part called transponder that reflects signals towards the receiver.

• These satellites have wide applications in many fields including weather forecasting, TV broadcast, Navigation (GPS) etc.

Orbits:

An orbit is the path that a satellite follows as it revolves around the earth. Basically there are three main orbits as shown in figure below:

1) Geosynchronous Earth Orbit (GEO):

• GEO satellites have a distance of almost 36,000 km to the earth.

• It travels in the same direction and at the same speed as the earth’s rotation.

2) Medium Earth Orbit (MEO):

• MEO satellites operate at a distance of about 5,000-12,000 km from the earth’s surface.

1) Low Earth Orbit (LEO):

• LEO satellites operate at an altitude of 500-1500 km.

• The LEO satellites require traveling at high speed so that it does not get pulled out of its orbit by earth’s gravity.

2) Highly Elliptical Orbit (HEO): Satellites in HEO have orbits that are close to the Earth at one point of their orbit, but are much farther away from the Earth at other times.

Architecture:

1) Satellite: A satellite orbits around earth in the outer-space. Communication is send from earth to satellite using antenna or Earth stations. The satellite receives and retransmits it (downlink) to other antennas or earth stations.

2) Ground stations: Ground stations basically perform the network control activities like housekeeping data, command data, and tracking of satellites.

3) Users: A satellite network user may use a satellite telephone (sat-phone) or a communication unit that connects to orbiting satellites instead of terrestrial cell sites.