06-satellite communications.ppt - Satellite Communications outline Categorization of satellites Frequency bands their applications Satellite Link

06-satellite communications.ppt - Satellite Communications...

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Satellite Communications
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outline Categorization of satellites Frequency bands & their applications Satellite Link Performance Factors Satellite communication configuration Capacity Allocation Strategies
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Satellite-Related Terms Earth Stations – antenna systems on or near earth Uplink – transmission from an earth station to a satellite Downlink – transmission from a satellite to an earth station Transponder – electronics in the satellite that convert uplink signals to downlink signals
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Satellite-Related Terms Satellite radio is a microwave transmission system utilizing a non-terrestrial (non-land-based) relay station positioned in space; i.e. a communications satellite can be thought of as a big microwave repeater in the sky. The figure below illustrates how a communication satellite in orbit around the earth can provide a network connection across an ocean. The satellite contains a transponder that consists of a radio- wave receiver and transmitter. The transponder accepts an incoming signal, amplifies it, and transmits the amplified signal back toward the ground at a slightly different angle than it received it. A ground station on one side of the ocean transmits a signal to the satellite, which then sends the signal to a ground station on the other side .
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How the Satellite Operates
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How Satellites Operate A single satellite usually contains multiple transponders that operate independently (typically six to twelve); each transponder uses a different radio frequency (i.e., channel), making it possible for multiple communications to proceed simultaneously. Communication satellites can be grouped into categories. A Geo-stationary Earth Orbit (GEO) is an orbit such that, when viewed from the ground, a satellite in the orbit appears to be at the same point in the sky at all times. It has been determined that such an orbit is about 35,785 kilometers from the earth. A satellite orbiting in such an orbit is sometimes known as a Geo-synchronous Satellite.
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VSAT A new development in the communication satellite world is the development of low-cost micro-stations – known as Very Small Aperture Terminals (VSAT). These tiny terminals have 1-meter or small antennas (versus 10 meters for a standard geostationary earth orbit (GEO) satellite antenna). These terminals can put out about 1 watt of power; the uplink speed is 19.2 kbps while the downlink speed is 512 kbps or more In many VSAT systems, the micro-stations do not have enough power to communicate directly with one another (via the satellite). Instead, a special ground station (called the Hub) with a large, high-gain antenna is needed to relay traffic between VSATs as shown below .
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VSAT
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  • Summer '16
  • macharia
  • communications satellite, Geosynchronous orbit, Geostationary orbit

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