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WHAT IS GEOSYNCHRONOUS COMMUNICATION SATELLITE

By Admin on

GEOSYNCHRONOUS COMMUNICATION SATELLITE

 

Geosynchronous Satellites have now become almost synonymous for communications satellites, because of its wide use in telecommunications due to the advantages over non-geosynchronous satellites.  Because of the availability of a number of communication satellites over the geosynchronous arc, the communications between different parts of the world have become possible and affordable.  The communication satellites have played a significant role in converting the world into a global village.

Salient features of Geosynchronous Communications Satellite



 

Salient features of Geosynchronous Satellite are:

Wide Coverage

Stationary Position

Multiple Access

Suitability for transcontinental telecommunications, broadcasting, mobile and thin route communications.

Frequency reuse capability

Very low Doppler Shift

Reliability.

Cost effectiveness.

Brief description  of each of these features are given below:

Wide Coverage: From the geosynchronous orbit the satellite can cover an area equal to about 42% of the area of the earth (38% if angles of elevation below 5º are not used).  Thus three satellites placed 120º apart can cover almost the whole world for the purpose of communications.  INTELSAT Satellites strategically placed over Atlantic Ocean Region (AOR), Indian Ocean Region (IOR) and Pacific Ocean Region (POR) covers the whole world for International Telecommunications.  With worldwide satellite TV coverage, any incidence happening in any part of the world can now be viewed live in the TV throughout the world.

Stationary Position: The orbital velocity of the geosynchronous satellite being equal to the rotational velocity of the earth on its own axis, the satellite in the geosynchronous orbit appears to be stationary with respect to any location from the earth.  Thus the satellite is always visible from any earth station situated in its coverage region and the tracking of the satellite is simple and there is no hand over problem of transferring signal from one satellite to another as in the case of satellites in NGSO.  The constant visibility of the satellite also enables both the satellite and the earth station to use highly directive antennas.  High gain of the antennas on-board the satellite and the earth station, enhances the  transmit and receive capabilities.

Multiple Access: Multiple Access is the ability of a large number of users to simultaneously interconnect their respective voice, data and television links through a satellite.  The wide geographic coverage and broadcast nature of satellite channel are exploited by means of multiple access. Multiple access also helps in optimum use of satellite capacity, satellite power, spectrum utilization and interconnectivity among different users at reduced cost.

A satellite in geosynchronous orbit can link multiple earth stations within its coverage area and separated by great circle distances up to 17,000 Km. Multiple access is the unique feature of satellite communications not possible to get by any other means.  For m earth stations visible from a Satellite, the number of potential available communication circuits is given by

n = m (m-1)/2

Attitude
35,786 km.
Period
23 Hr. 56 min. 4.091 sec. (One sidereal day)
Orbit inclination.
00
Velocity
3.075 km per sec.
Coverage
42.5% of earth’s surface.
Sub satellite point
On equator.
Area of no coverage
Beyond 810 North and South latitude.
(77º if angle of elevation below 5º are eliminated )
Advantages
- Simple ground station tracking.
- No hand over problem
- Nearly constant range
- Very small doppler shift
Disadvantages
- Transmission delay of the order of 250 msec.
- Large free space loss
- No polar coverage


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