Mumbai University > Information Technology > Sem 7 > Wireless Technology

Marks: 5M

Year: May 2016

1. A satellite is an object that orbits or revolves around another subject.
2. Man-made satellites are highly specialized wireless receiver transmitters that are launched by a rocket and placed in orbit around the earth.
3. Unlike conventional terrestrial systems, the satellite systems have its transmitter based in sky and not on ground.
4. The transmitter consists of a
5. Ground based part called Uplink
6. Satellite based part called transponder that reflects signals towards the receiver.
7. 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.

3) 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.

4) 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.