SATELLITE COMMUNICATION

SATELLITE COMMUNICATION
A communications satellite (sometimes abbreviated to SATCOM) is an artificial satellite stationed in space for the purposes of telecommunication.
In telecommunication, the use of artificial satellites to provide communications links between various points on Earth. Communications satellites relay voice, video, and data signals between widely separated fixed locations (e.g., between the switching offices of two different national telephone networks), between a fixed location and numerous small fixed or mobile receivers in a designated area (e.g., direct satellite broadcasting of television programming), and between individual mobile users (e.g., aircraft, ships, motor vehicles, and personal handheld units). The technique involves transmitting signals from an Earth station to a satellite. Equipment onboard the satellite receives the signals, amplifies them, and retransmits them to a region of Earth. Receiving stations within this region pick up the signals, thus completing the link.
Satellites provide communications links via microwave radio, most commonly in the superhigh-frequency band of 3 to 30 gigahertz (3 billion to 30 billion hertz, or cycles per second). These frequencies correspond to wavelengths ranging from 10 cm to 1 cm (4 inches to 0.4 inch). On land this can be achieved by using towers or hilltop locations, but microwave communication across oceans is impossible without the use of satellites.
FREQUENCY BANDS
The specific frequency bands open to civilian satellite communication are assigned by the International Telecommunication Union, based in Geneva. Each band consists of an uplink (Earth-to-satellite) frequency and a downlink (satellite-to-Earth) frequency .The two bands that have been in use longest, and still carry the most traffic, are the C band, with uplink frequencies centred on 6 gigahertz and downlink frequencies centred on 4 gigahertz, and the Ku band, with uplink/downlink frequencies centred on 14/11 gigahertz.


TYPES
There are three different types of satellite systems.
1. International satellite communication system INTELSAT.
2. Domestic satellite system DOMSAT.
3. Search and rescue system SARSAT.

INTELSAT
The INTELSAT Organization was established in 1964 to handle the myriad of technical and administrative problems associated with a world wide telecommunication system. The international regions served by INTELSAT are divided in to the Atlantic Ocean region (AOR), the Pacific Ocean Region (POR) and the Indian Ocean region (IOR). For each region , satellites are positioned in geo-stationary orbit above the particular Ocean, where they provide a transoceanic telecommunication route. In addition to providing trans oceanic routes, the INTELSAT satellites are used for domestic services within any given country and regional services between countries. Two such services are vista for telephony and Intelnet for data exchange.
DOMSAT
Domestic satellites are used to provide various telecommunication services, such as voice, data, and video transmission (T.V channels), with in a country.
SARSAT
SARSAT is one type of Polar orbiting satellites.
Polar-orbiting satellites orbit the earth in such a way as to cover the north and south polar-regions. Infinite number of polar polar satellite orbits are possible
Polar satellites are used to provide environmental data , and to help locate ships and aircrafts in distress .This service known as SARSAT, for search and rescue satellite.
ADVANTAGES
o HIGH CAPACITY
o LONG RANGE
o GOOD QUALITY
o COVERAGE
o REALIABLITY
APPLICATIONS
AIR TRAFFIC CONTROL(ATC)
Satellites can provide two types of communication services to support air traffic control functions. Air traffic control satellites collect navigation data from ground monitoring systems and broadcasts it to aircraft aloft, greatly increasing the navigational accuracy and reliability of the global positioning system (GPS) for aircraft location and safe take-offs and landings. These satellites also provide a highly reliable digital communications path for air traffic controllers and pilots to share vital flight information.
BROAD BAND DIGITAL COMMUNICATIONS
Broadband satellites transmit high-speed data and video directly to consumers and businesses. Markets for broadband services also include interactive TV, wholesale telecommunications, telephony, and point-of-sale communications, such as credit card transactions and inventory control.
DIRECT BROADCAST SATELLITES
Direct-broadcast satellites (DBS) transmit signals for direct reception by the general public, such as satellite television and radio. Satellite signals are sent directly to users through their own receiving antennas or satellite dishes, in contrast to satellite/cable systems in which signals are received by a ground station, and re-broadcast to users by cable.
ENVIRONMENTAL MONITORING
Environmental monitoring satellites carry highly sensitive imagers and sounders to monitor the Earth's environment, including the vertical thermal structure of the atmosphere; the movement and formation of clouds; ocean temperatures; snow levels; glacial movement; and volcanic activity. Large-scale computers use this data to model the entire earth's atmosphere and create weather forecasts such as those provided by national weather services in the U.S. and abroad
FIXED SATELLITES SERVICES
Satellites providing Fixed-Satellite Services (FSS) transmit radio communications between ground Earth stations at fixed locations. Satellite-transmitted information is carried in the form of radio-frequency signals. Any number of satellites may be used to link these stations. Earth stations that are part of fixed-satellite services networks also use satellite news gathering vehicles to broadcast from media events, such as sporting events or news conferences. In addition, FSS satellites provide a wide variety of services including paging networks and point-of-sale support, such as credit card transactions and inventory control.
MILTARY APPLICATIONS
RADAR(Radio Detection And Ranging) is used to detect the targets such as submarines and air craft along with its distance.
CONCLUSION
Thus satellite communication provides the basis of the different types of communication in today’s world.